AS-4997-2005

AS 4997—2005
AS 4997—2005
Australian Standard™
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Guidelines for the design of maritime
structures
This Australian Standard was prepared by Committee CE-030, Maritime Structures.
It was approved on behalf of the Council of Standards Australia on 29 March 2005.
This Standard was published on 28 September 2005.
The following are represented on Committee CE-030:
Association of Australian Ports and Marine Authorities
Association of Consulting Engineers Australia
Australian Stainless Steel Development Association
Boating Industry Association of Australia
Cement Concrete & Aggregates Australia – Cement
Civil Contractors Federation
Engineers Australia
Institute of Public Works Engineering Australia
Marina Association of Australia
Monash University
Queensland Transport
University of Wollongong
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This Standard was issued in draft form for comment as DR 02536.
AS 4997—2005
Australian Standard™
Guidelines for the design of maritime
structures
Accessed by Adani Mining Pty Ltd on 03 Nov 2011
First published as AS 4997—2005.
COPYRIGHT
© Standards Australia
All rights are reserved. No part of this work may be reproduced or copied in any form or by
any means, electronic or mechanical, including photocopying, without the written
permission of the publisher.
Published by Standards Australia, GPO Box 476, Sydney, NSW 2001, Australia
ISBN 0 7337 6858 X
AS 4997—2005
2
PREFACE
This Standard was prepared by Standards Australia Committee CE-030, Maritime
Structures.
The objective of this Standard it to provide designers and regulatory authorities of
structures located in the marine environment with a set of guidelines and recommendations
for the design, preservation and practical applications of such structures. These structures
can include fixed moorings for the berthing of vessels, piles and other parts of a
substructure, wharf and jetty decks, building substructures over waters, etc.
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This Standard has been prepared as a guideline only, to provide advice and
recommendations for maritime structures. Clauses in this document are written using
informative terminology and should not be interpreted otherwise. The requirements of a
maritime structure and its associated facilities should be determined for the individual
application. This Standard should be used in conjunction with the relevant materials and
design Standards.
3
AS 4997—2005
CONTENTS
Page
SECTION 1 SCOPE AND GENERAL
1.1 SCOPE ........................................................................................................................ 5
1.2 REFERENCED AND RELATED DOCUMENTS ...................................................... 6
1.3 NOTATION ................................................................................................................ 7
1.4 DEFINITIONS ............................................................................................................ 8
SECTION 2 SITE INVESTIGATION AND PLANNING
2.1 GENERAL ................................................................................................................ 10
2.2 SURVEY ................................................................................................................... 10
2.3 GEOTECHNICAL..................................................................................................... 11
2.4 ASSESSMENT OF LOADS...................................................................................... 11
SECTION 3 DIMENSIONAL CRITERIA
3.1 STRUCTURE HEIGHTS .......................................................................................... 12
3.2 FENDER HEIGHTS.................................................................................................. 12
3.3 LAYOUT OF BERTH STRUCTURES ..................................................................... 12
3.4 ACCESS AND SAFETY........................................................................................... 13
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SECTION 4 DESIGN REQUIREMENTS
4.1 AIM ........................................................................................................................... 14
4.2 DESIGN REQUIREMENTS ..................................................................................... 14
4.3 FLOATING STRUCTURES ..................................................................................... 15
4.4 BREAKWATERS ..................................................................................................... 15
4.5 EFFECTS OF SCOUR AND SILTATION................................................................ 16
4.6 SEA LEVEL RISE (global warming) ........................................................................ 16
SECTION 5 DESIGN ACTIONS
5.1 GENERAL ................................................................................................................ 17
5.2 PERMANENT ACTIONS (DEAD LOADS)............................................................. 17
5.3 IMPOSED ACTIONS (LIVE LOADS) ..................................................................... 17
5.4 WIND ACTIONS ...................................................................................................... 21
5.5 CURRENT ACTIONS............................................................................................... 22
5.6 DEBRIS ACTIONS ................................................................................................... 23
5.7 NEGATIVE LIFT DUE TO CURRENTS ................................................................. 23
5.8 HYDROSTATIC ACTIONS ..................................................................................... 23
5.9 WAVE ACTIONS ..................................................................................................... 24
5.10 CONSTRUCTION AND MAINTENANCE ACTIONS ............................................ 26
5.11 LATERAL EARTH ACTIONS ................................................................................. 26
5.12 COMBINATIONS OF ACTIONS ............................................................................. 26
5.13 PROPELLER WASH ................................................................................................ 28
5.14 EARTHQUAKE ACTIONS ...................................................................................... 28
SECTION 6 DURABILITY
6.1 GENERAL ................................................................................................................ 30
6.2 DESIGN LIFE ........................................................................................................... 30
6.3 CONCRETE .............................................................................................................. 33
6.4 STEEL....................................................................................................................... 38
6.5 TIMBER.................................................................................................................... 41
AS 4997—2005
4
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APPENDICES
A
CONTAINER WHARF DECK LOADINGS............................................................. 43
B
BERTHING ENERGIES AND LOADS .................................................................... 46
C
MOORING LOADS .................................................................................................. 50
5
AS 4997—2005
STANDARDS AUSTRALIA
Australian Standard
Guidelines for the design of maritime structures
SE CT ION
1
SCOPE
AND
GE NE RA L
1.1 SCOPE
This Standard sets out guidelines for the design of structures in a marine environment. It is
to be used in conjunction with the relevant Standards and provides recommendations
additional to the requirements of these Standards.
This Standard is intended to cover the design of near-shore coastal and estuarine structures,
such as—
(a)
jetties;
(b)
wharves;
(d)
floating berths;
(f)
breakwater structures, excluding rubble mound and floating types;
(c)
(e)
(g)
(h)
(i)
berthing dolphins;
seawalls;
boat ramps;
laterally restrained floating structures; and
building substructures over water.
This Standard is not intended to cover the design of—
(A)
pipelines;
(C)
offshore oil and gas structures;
(B)
(D)
dredging and reclamation;
(F)
geometrical design of port and harbour infrastructure;
(E)
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marinas (see AS 3962);
(G)
coastal engineering structures such as rock armoured walls, groynes, etc;
floating structures not permanently restrained, e.g., vessels, construction pontoons,
barges.
For buildings constructed over water, these guidelines apply to the structure up to and
including the main deck level. The superstructure above main deck level should be designed
in accordance with the relevant Australian Standards and relevant building regulations.
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AS 4997—2005
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1.2 REFERENCED AND RELATED DOCUMENTS
1.2.1 Referenced documents
The following documents are referenced in this Standard:
AS
1012
1012.13
1170
1170.4
1604
1657
3600
Minimum design loads on structures
Part 4: Earthquake design loads on structures
Timber—Preservative-treated—Sawn and round
Fixed platforms, walkways, stairways and ladders—Design, construction and
installation
Concrete structures
3962
Guidelines for design of marinas
4100
Steel structures
3972
5100
5100.2
5604
AS/NZS
1170
1170.0
1170.1
1170.2
Portland and blended cement
Bridge design
Part 2: Design loads
Timber—Natural durability ratings
Structural design actions
General principles
Part 1: Permanent, imposed and other actions
Part 2: Wind actions
1554
1554.6
Structural steel welding
Part 6: Welding stainless steels for structural purposes
2832
Cathodic protection of metals (all parts)
4673
Cold formed stainless steel structures
2312
4671
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Methods of testing concrete
Method 13: Determination of the drying shrinkage of concrete for samples
prepared in the field or in the laboratory.
Guide to the protection of iron and steel against exterior atmospheric corrosion
Steel reinforcing materials
4680
Hot-dip galvanized (zinc) coatings on fabricated ferrous articles
6349
Maritime structures (all parts)
BS
6744
Stainless steel bars for the reinforcement and use in concrete – Requirements
and test methods
Disability Standards for Accessible Transport (Australian Government)
PIANC
Design of fender systems—2002
1.2.2 Related documents
AS/NZS 1664
Aluminium structures
SA HB 84
Guide to Concrete Repair and Protection
AS 5100
 Standards Australia
Bridge design (all parts)
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AS 4997—2005
1.3 NOTATION
1.3.1 Abbreviations
The following abbreviations are used in this Standard.
AHD = Australian Height Datum
CD
= Chart Datum, used for the preparation of navigation charts, and usually about
the same level as LAT
CQC
= Container Quay Crane (Portainer crane, ship-to-shore crane)
DWT = Dead Weight Tonnage (The total mass of cargo, stores, fuels, crew and reserves
with which a vessel is laden when submerged to the summer loading line.)
NOTE: Although this represents the load carrying capacity of the vessel it is not the
exact measure of cargo load.
GRT
= Gross Registered Tonnage (The gross internal volumetric capacity of the vessel
as defined by the rules of the registering authority and measured in units of
2.83 m 3 (100 ft 3)).
HAT
= Highest Astronomical Tide (see Clause 3.2)
ISLW = Indian Spring Low Water (Obsolete estimate of Lowest Astronomical Tide
(LAT) formerly used as chart datum)
LAT
= Lowest Astronomical Tide (Now adopted as chart datum for all Australian
Hydrographic Charts (see Clause 3.2))
LOA
= Length Overall of a vessel, measured to the extremities of fittings.
MSL
= Mean Sea Level, usually about the same level as AHD
1.3.2 Symbols
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The following symbols are used in this Standard.
db
= reinforcing bar diameter
Ed
= design action effect
E d,dsb
= design action effects destabilizing structure
E d,stb
= design action effects stabilizing structure
Es
= serviceability earthquake action
Eu
= ultimate earthquake action
f
= co-efficient of wave height (see Clause 5.9.1)
f′ c
= characteristic compressive strength of concrete, in Megapascals (MPa)
fs
= steel reinforcing stress, in Megapascals
Fb
= berthing impact loads
F b,u
= berthing impact actions under abnormal conditions
FD
= action in the direction of wind, in kilonewtons (kN)
Fe
= earth pressure loads
F env
= combined environmental loads
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F gw
= ground water loads
F lat
= minimum lateral load (see Clause 5.3.1)
F lp
= liquid pressure load
Fm
= mooring loads
Fs
= stream flow loads, including debris loads
F wave.S = wave loads under serviceability conditions (1 in 1 year)
F wave.U = wave load under ultimate strength conditions
g
= acceleration due to gravity
G
= permanent action (dead load)
H1
= wave height used for design of structures (see Clause 1.4.3)
Hs
= significant wave height (see Clause 1.4.5)
P
= pressure, in kilopascals (kPa)
Q
= imposed action (live load)
Su
= loading combination (see Clause 5.12.4)
Ts
= period of significant waves
Ws
= wind load for serviceability limit state
Wu
= wind load for strength limit state
V
= design wind speed, in metres per second
v
= current velocity, in metres per second
1.4 DEFINITIONS
For the purpose of this Standard, the definitions below apply.
1.4.1 Action
Set of concentrated or distributed forces acting on a structure (direct action), or deformation
imposed on a structure or constrained within it (indirect action).
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NOTE: The term load is often used to describe direct actions.
1.4.2 Design life
The period for which a structure or a structural element remains fit for use for its intended
purpose with appropriate maintenance (see Clause 6.2).
1.4.3 Design wave (H1)
The highest 1% of waves in any given time interval. Used, for example, in the analysis of
structures.
1.4.4 Load
The value of a force appropriate to an action.
1.4.5 Significant wave height (Hs )
The average height of the highest one-third of waves in any given time interval. It
approximates the wave height for this train of waves as estimated by an expert observer.
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AS 4997—2005
1.4.6 Sponson
Rubbing strip, generally at main deck level, to strengthen and protect vessel from berthing
impacts.
1.4.7 Swell waves
Waves generated some distance from the site; no longer under the influence of generating
wind.
1.4.8 Vessel displacement
The total mass of a vessel and its contents.
NOTE: This is equal to the volume of water displaced by the vessel multiplied by the density of
the water.
1.4.9 Vessel wash
Waves formed by the passage of a vessel.
1.4.10 Wind wave
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Waves formed under the influence of local generating winds, usually called seas.
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AS 4997—2005
SE CT ION
10
2
S IT E I N V E ST IG AT I ON
P L ANN I NG
AND
2.1 GENERAL
In maritime structures, the effect of the local environment and geographical configurations
(including the new configuration after completion of the proposed maritime facility) has
significant bearing on the performance of the structures. Detailed site investigations are an
essential part of the planning and design of maritime facilities. Thus, for any site on which
it is proposed to install a maritime structure, a detailed site investigation should be
undertaken to provide sufficient information for the design and construction of the
structure. Maritime structures that have the potential to obstruct currents and waves are
likely to affect the littoral processes and the effect of such structures on the adjacent natural
features must be investigated.
Hydrographic and terrestrial surveys should be undertaken. Such surveys and subsequent
investigations (e.g., geotechnical) should adopt a uniform survey grid.
The wind, wave, current, berthing and other actions that may be applicable to the structure
should be considered in the site investigation.
2.2 SURVEY
2.2.1 Survey grid
A uniform survey grid should be adopted for the project area. All terrestrial and
hydrographic surveys should use this survey grid.
Consideration should be given to incorporating the survey grid for the project area into the
regional coordinated survey grid, e.g., International Survey Grid or Map Grid of Australia
1994 (MGA94), for projects in Australia.
Where a local survey grid is adopted, this should be clearly noted on the drawings and the
correlation to GRS80 or WGS84 grid should be nominated on the drawings.
2.2.2 Survey datum
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All survey data should be reduced to a recognized datum, which may be Chart Datum (CD)
or Australian Height Datum (AHD). Chart Datum is the preferred datum for surveys and
mapping of maritime works and offshore topography, as it provides direct correlation to
navigable water depths.
The correlation between CD and AHD for the specific location should be clearly shown on
all the drawings, e.g., by a note or a diagram.
2.2.3 Hydrographic survey
The hydrographic survey should be undertaken to cover the proposed site of works and any
adjacent near-shore water up to mean high water level, including adjacent navigable
waterways where there is insufficient existing survey data to make an appropriate
assessment of design waves, currents and other pertinent analysis and design parameters.
The survey data should also contain sufficient detail to enable an assessment of the
hydraulic and seabed processes affecting the proposed structure and adjacent foreshores.
Height datum levels for hydrographic surveys should be to the relevant Chart Datum.
2.2.4 Terrestrial surveys
Terrestrial surveys should be provided over any land areas that will be incorporated or
impacted upon by the project site and should overlap with the hydrographic survey.
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AS 4997—2005
2.3 GEOTECHNICAL
The geotechnical properties and design parameters of seabed materials in the vicinity of a
maritime structure should be assessed. These parameters should be used to evaluate
foundation capacity, stability and settlement characteristics of the structures and associated
works and to determine the response to, and effect on the prevailing natural coastal and
estuarine processes. Such processes include tides, current and wave actions and effects of
propeller and boat wash.
2.4 ASSESSMENT OF LOADS
Maritime structures should be designed to resist the loads applicable to the service
performance requirements of the completed facility, the ultimate (survival) loads that the
facility may be expected to withstand, as well as loads applicable at the various stages of
construction.
Wind, wave, tide, current and storm surge and other such natural loads and conditions
(including sediment movement, flood debris) should be considered during any investigation
of loads applied to, or affecting, the performance of a maritime structure.
Wind data should be determined from AS/NZS 1170.2 and/or site-specific anemometer
records, where records of adequate duration, to determine an appropriate long-term record,
are available.
The determination of wave parameters used to derive the design wave height, wave period
and wave direction should be assessed using site-specific wave records where records of
adequate duration, to determine an appropriate long-term record, are available. If such
records are not available, wave heights and periods may be determined from available wind
data.
Tidal information, including tidal currents, for the site of the works should be determined
and appropriate design maximum and minimum tidal planes established.
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Changes in water levels due to global warming should be considered (see Clause 4.6).
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SE C T ION
3
D IM E NS I O NA L
C R IT E R I A
3.1 STRUCTURE HEIGHTS
Deck levels should generally be kept as low as practicable, in keeping with their function to
provide access to the waterway and to floating vessels.
The minimum height of deck of a wharf or jetty in tidal conditions should be determined as
the 1/100 annual exceedance of probability elevated water level, plus a suitable freeboard
depending on exposure to waves, wave heights, wind set-up, formation of bars at river
entrances and seiche.
For wharves and jetties in locations subject to local river flooding or storm surge situations,
the design may allow for periodic inundation during such events. Such structures should be
able to withstand lateral loads and uplift from elevated water levels including flood effects
from the design flood event.
Where overtopping of deck structures by waves would result in disproportionate level of
damage to the superstructure above main deck level, means to prevent water damage to the
property should be incorporated in the design.
3.2 FENDER HEIGHTS
Fender structures in tidal waters should extend to at least the height of the sponson or
rubbing strake of the highest vessel likely to use the facility, during the design elevated
water level, which should be no lower than the highest level that can be predicted to occur
under average meteorological conditions and any combination of astronomical conditions
(HAT) plus an allowance for storm surge. The fender system should also extend down to a
level no lower than the sponson of the smallest craft likely to use the facility, at the lowest
level that can be predicted to occur under average meteorological conditions and any
combination of astronomical conditions (LAT). Vessel load conditions and motion in
response to waves and any other influencing effects should also be considered.
3.3 LAYOUT OF BERTH STRUCTURES
The layout of the structures for a berth should be designed to take account of—
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(a)
restraining the vessel against environmental loads (winds, waves and currents) and
interaction effects between passing vessels;
(b)
providing safe berthing and deberthing in extreme events (storms, floods);
(d)
minimum intrusion into the navigable waterway;
(f)
safe personnel and vehicle access;
(c)
(e)
(g)
(h)
allowing safe navigation access to the berth to and from the waterway;
ease of cargo handling;
disabled access (where applicable); and
minimum impact on the hydrodynamic regime.
NOTE: The operation of some facilities may require that some vessels be removed in the event of
a major storm.
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AS 4997—2005
3.4 ACCESS AND SAFETY
3.4.1 Application
For maritime structures that may fall outside the provisions of relevant building codes or
other regulations, the guidelines in Clause 3.4.2, 3.4.3, 3.4.4 and 3.4.5 should be followed.
3.4.2 Access for operational, inspection, maintenance and servicing personnel
Where access to structures is required for operational, inspection and maintenance
personnel, the structures should comply with the requirements of AS 1657.
Ramps or sloping surfaces should not be located in the tidal zone (where marine growth can
make them slippery). Where slopes are required below high water mark, access should be
provided by way of a series of horizontally surfaced steps let into the slope, proud of the
slope, or cleats fixed to the surface at maximum 300 mm centres. Appropriate non-slip
surfacing should be provided.
3.4.3 Access to public transport facilities
Where access is required to public transport facilities, structures should comply with the
requirements of the Disability Standards for Accessible Public Transport.
Gradients of gangways (hinged ramps attached to floating structures, whose gradients varies
with the tide) should not exceed 1 in 8 when the tide is at LAT, or steeper than 1 in 12 for
more than 20% of the time.
3.4.4 Safety fencing
In general, wharf faces and the like are not provided with safety or other fencing to prevent
persons or vehicles from falling off the edge of a public access structure. Such fencing
would hinder the normal operation of the wharf or maritime facility. Edge kerbs may be
considered in areas generally used by wheeled vehicles.
Where access to the water or vessels is not required and where a person falling from the
structure is likely to fall more than 1.5 m to strike a hard surface or the seabed, a guardrail
(handrail) in accordance with AS 1657 should be provided.
3.4.5 Safety ladders
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Where persons who fall from a wharf or maritime facility would not be able to easily regain
the shore, safety ladders should be provided. Such ladders should be of durable material and
extend from deck level down to below low water level—bottom rung should be 300 mm
below LAT. Such ladders should be located at maximum 60 m intervals.
Where safety ladders are used to provide access to craft, suitable buffer rails, at least
250 mm proud of the ladder, should be provided each side to prevent vessels crushing
persons on the ladder.
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SE C T ION
4
DE S IG N
R E QU I R E ME N T S
4.1 AIM
The aim of the design of maritime structures covered by this Standard is to provide
structures that are stable, have adequate strength against ultimate conditions and remain
serviceable while being used for their intended function, and which also satisfy
requirements for robustness, economy and ease of construction, and are durable (low
maintenance and low repair costs).
4.2 DESIGN REQUIREMENTS
4.2.1 General
The design of the structure and its components should take into account, as appropriate,
stability, strength, serviceability and durability. The design should be in accordance with
the relevant Australian Standards together with any additional recommendations in these
guidelines.
4.2.2 Stability
The structure and its component members should be designed for static stability under
overturning, uplift and sliding and dynamic stability in design conditions as given in
Clause 5.12, such that stability loads and other actions exceed the destabilizing loads and
other actions. The loads and other actions will need to be combined as given in Clause 5.12.
4.2.3 Strength
The structure and its component members should be designed for strength as follows:
(a)
(b)
(c)
(d)
Determine the appropriate loads and other actions in accordance with Section 5.
Combine and factor the loads in accordance with Clause 5.12 to determine the design
loads for strength.
Determine the design action effects for the structure and its components for each load
case.
Determine the design strength in accordance with the requirements of the appropriate
Australian Standard(s).
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The effects of fatigue from wind, wave, current and other actions under both normal and
storm conditions should be considered.
4.2.4 Serviceability
The structure and its component members should be designed for serviceability by
controlling or limiting settlement, horizontal displacement and cracking.
Under the load combinations for serviceability design detailed in Clause 5.12.4, vertical
deflection should be limited in accordance with the requirements of the appropriate
materials Standards.
Horizontal deflection and acceleration limits for trafficable structures should be limited to a
maximum deflection of l/150, where l is the distance between underside of the deck
structure to the level of the support in the seabed, and a maximum acceleration of 0.1g.
Designers should exercise care at the interface between flexible maritime structures and
rigid shoreline structures. Horizontal deflection limits in commercial structures subject to
heavy vehicle loadings need to consider dynamic effects of the horizontal vehicle loads
(e.g., braking) on the structure.
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AS 4997—2005
For maritime structures, serviceability conditions are those that may be experienced under
normal conditions, and may include for example wave action, which has dynamic effects as
well as fatigue effects on those elements constructed from fatigue-prone materials.
Typically service conditions would include effects from waves with significant wave
heights that occur once or more each year.
4.2.5 Durability
The structure and its component members should be designed for durability in accordance
with Section 6.
4.2.6 Other relevant design requirements
The design should take into account the effects of vessel berthing, scour, flood, cyclic
loading, fatigue, temperature effects and any other special performance requirements.
4.3 FLOATING STRUCTURES
Floating structures dealt with in this Standard include pontoons used for floating berths
(ferry wharves and similar) that are stationary, restrained by piles or permanent moorings
and generally in enclosed waters.
Floating structures should be designed to maintain a safe freeboard under the most adverse
combination of live load and environmental loads including consideration of dynamic
effects. The design of floating structures for full live load as well as full environmental
loads (storm conditions) is not usually necessary. However live load under serviceability
environmental conditions (e.g., once in one-year storm or wave) should be considered in
analysis for stability and freeboard.
When assessing stability of floating structures under live load, the load cases of full load
intensity on the whole deck as well as the case of the full load intensity on part of the deck
(e.g., one side of the structure centre-line) should be investigated.
The minimum freeboard, ignoring other operation constraints, under the most adverse
design loading is 5% of the moulded depth (minimum 50 mm), measured from the top of
the flotation unit for rectilinear flotation systems. For horizontal cylindrical flotation
systems, freeboard should be at least 25% of the diameter of the cylindrical float, measured
from the top of the flotation system.
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Floating structures should be designed to have watertight sealed compartments to prevent
sinking or overturning in the event of a leak in the outer skin. The structure should be
capable of maintaining adequate freeboard (under dead load only) in the event of the
external skin of any compartment being punctured and filling with water up to the external
water level.
For large flotation structures (e.g., ferry landings) consideration should be given to
allowing access from hatches in the deck.
4.4 BREAKWATERS
The function of a breakwater is to reduce wave action either by attenuating the wave as it is
transmitted or by reflecting part of the wave energy. Design considerations for breakwaters
are that the structure should attenuate wave action without creating adverse conditions and
be fit for purpose over their design life.
NOTE: This Standard does not cover the design of rubble mound and floating breakwaters (see
Clause 1.1).
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4.5 EFFECTS OF SCOUR AND SILTATION
Maritime structures and their component members should be designed to remain stable and
of sufficient strength and not be overloaded in the event of temporary or permanent changes
in the level of the seabed due to scour or silting.
Wharves and jetties in river estuaries should be analysed with appropriate allowance for
velocity-induced scour, which may be exacerbated at the peak of a flood event.
Structures in coastal areas subject to littoral drift should be analysed with allowances for
erosion of the seabed in down-drift areas, and build-up of sediment in up-drift areas.
Wharves used by vessels should be designed to allow for this additional scour effect to the
materials beneath the wharf from propeller wash or bow or stern thrusters.
4.6 SEA LEVEL RISE (global warming)
Maritime facilities should be designed to cater for increase in water level due to
promulgated sea level rises caused by global warming.
The amount of sea level rise to be considered depends on the design life of the structure.
The allowance for sea level rise does not necessarily include the construction of the deck of
the facility at a higher level, although in some cases this may be prudent. Allowance for sea
level rise may include options to raise the heights of restraining piles on floating structures
at a later time, or installing substructure of adequate strength to permit future topping slabs
etc.
The allowance for future sea level rise is provided in Table 4.1.
TABLE 4.1
ALLOWANCE FOR SEA LEVEL RISE
Design life
25 years
50 years
100 years
Sea level rise
m
0.1
0.2
0.4
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NOTE: Based on the mid-scenario from the International Panel on Climate
Control (2001). These values are updated by IPCC from time to time.
 Standards Australia
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17
SE CT ION
5
DE S IG N
AS 4997—2005
A CT IO NS
5.1 GENERAL
The design for ultimate strength, serviceability, stability and other relevant limit states
should take into account the appropriate design actions arising from those given in
AS/NZS 1170, and other actions applicable to maritime structures, as follows:
(a)
Permanent actions (dead loads) (see Clause 5.2).
(b)
Imposed actions (live loads) (see Clause 5.3).
(d)
Current and debris actions.
(f)
Wave actions.
(c)
(e)
Wind actions (see Clause 5.4).
Hydrostatic actions.
(g)
Thermal, shrinkage and other movement induced actions.
(i)
Lateral earth actions on waterfront structures (seawalls).
(h)
(j)
(k)
Construction and maintenance actions.
Propeller wash.
Earthquake actions.
5.2 PERMANENT ACTIONS (DEAD LOADS)
Dead loads include the self-weight of all structures, all deck wearing surfaces, long-term
loads such as cargo storage facilities, superstructures, and mooring fittings (bollards, quickrelease hooks, etc.). Piles and other elements immersed in the sea should include the
influence of marine growth.
5.3 IMPOSED ACTIONS (LIVE LOADS)
5.3.1 Wharf deck loads
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Wharf surfaces should have a specified loading classification that will govern the design of
all elements of the structure, including deck, beams, headstocks and piles.
Distributed loads should be applied over the whole of the deck between kerbs, or inside
handrails, etc. Loads should be applied to a single span, or all spans, or alternate spans to
produce the worst design effect. Concentrated loads should be applied at a critical location
in one span in lieu of a distributed load.
The design loads and classifications shown in Table 5.1 should apply as appropriate for the
facility, or as specified by the owner of the facility particularly for large port projects.
For wharf decks that handle containers, the design of the wharf structure should be checked
for the loads applicable for the particular arrangement of containers and container handling
equipment as indicated in Appendix A, in addition to the loads given in Table 5.1.
The loads indicated in Table 5.1 and Appendix A are service loads. These loads need to be
factored to obtain ultimate limit state (strength) design loadings.
Structures should be designed for directly related horizontal live load actions such as
braking loads from vehicles, slewing/luffing loads from cranes.
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 Standards Australia
AS 4997—2005
18
Any freestanding maritime structure (jetty, dolphin, etc.) should be capable of withstanding
a minimum horizontal load (F lat), applied at deck level, of at least 2.5% of the maximum
permanent and imposed vertical actions. This horizontal action should be applied in the
lateral and longitudinal directions (not simultaneously) and should not be superimposed on
any other applied horizontal actions.
TABLE 5.1
MARITIME STRUCTURES —DECK LOAD CLASSIFICATIONS
Class
Uniformly
distributed
load (Q)
(see Note 1)
5
10
5 kPa
10 kPa
Concentrated
load
(area, mm)
s = spacing, m
(see Note 2)
Anticipated load conditions
20 kN
(150 × 150)
Pedestrian crowd load.
Light motor vehicles up to 3 t
tare
Private and public boardwalks.
Passenger jetties
45 kN
(300 × 150)
Small emergency vehicles
Public boardwalks and
promenades with access for
emergency vehicle and service
vehicles
200 kN
(400 × 700)
Bridge design code (W7, W8,
A160, T44 loading)
Small mobile crane up to 20 t
SWL
Light-duty wharf and jetty for
fishing industry, charter boat
industry, ferry wharves, light
commercial activities
1000 kN
(1000 × 1000)
Container forklift and other
machinery for 40 ft containers
Mobile crane 100 t SWL
1500 kN
(1000 × 1000)
Container forklift, reach
stacker and other machinery for
largest containers
Mobile crane 150 t SWL
General cargo wharf or
container wharf (For containers
stacked 2 high ship-side, see
Note 3 & Appendix A)
2000 kN
(1000 × 1000)
Mobile crane to 200 t SWL
s = 1.8
s = 1.8
15
15 kPa
s = 4.0
25
25 kPa
500 kN
(700 × 700)
s = 5.0
40
40 kPa
s = 7.0
50
50 kPa
s = 8.0
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60
60 kPa
Application
Bridge design code (SM1600
heavy platform loading)
Mobile crane 50 t SWL
Secondary port general cargo
wharf
Primary port, international
gateway container terminal
(For containers stacked 2 high
ship-side, see Note 3 &
Appendix A)
Heavy-duty maintenance wharf
s = 9.0
NOTES:
1
2
3
The above loads do not include any component for dynamic effect (rolling ‘impact’, or heavy landings of
cargo loads). The impact and dynamic load factors should be applied as appropriate.
s = spacing (metres) in any direction between concentrated loads, or between concentrated loads and the
edge of uniformly distributed loads. Concentrated loads and uniformly distributed loads identified in the
above table should not be superimposed.
The storage of containers on the wharf deck at ship-side is for temporary storage of containers while
accessing containers within the vessel. Loadings in container yards are not covered by these guidelines, as
such loads are terminal specific.
5.3.2 Vessel berthing and other imposed loads
5.3.2.1 General
The structure should be designed to withstand loads associated with the berthing of vessels
within the design vessel range appropriate for its use.
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19
AS 4997—2005
The energy of berthing vessels may be absorbed in one or a combination of the following
ways:
(a)
(b)
(c)
(d)
In deflection of the vessel hull (usually only for small vessels <500 t).
In deflection of the berthing structure, where it is specifically designed to flex under
loading.
Through an energy-absorbing berthing fender system mounted on a wharf or dolphin
structure.
Through the action of a vessel forcing water between the vessel and the shore.
5.3.2.2 Energy absorption through vessel hull
In the case of small vessels up to 500 t displacement, the berthing energy may be
considered to be absorbed through deflection of the hull of a vessel as well as deflection of
the berthing structure or berthing fender system. For such vessels, hull deflections of up to
75 mm for quarter-point to mid-point berthing may be considered. (For end-impacts, no
deflection should be considered.)
5.3.2.3 Energy absorbed through deflection of a berthing structure
Some berthing structures may be designed to absorb berthing energy by deflection of the
structure itself.
The energy absorbed by the flexible structure is the integral of the reaction load from the
structure over the displacement of the structure (at the point of contact with the vessel), to
bring the vessel to a standstill.
The loading in a flexible berthing structure may be reduced by providing an energy
absorbing ‘soft’ fender system on the structure (see Clause 5.3.2.5), in which case the
berthing energy imparted to the structure will be reduced by the capacity of this fender
system.
Design of flexible berthing structures, such as flexible dolphins and berthing beams, should
allow for absorption of the maximum (abnormal) berthing energy in elastic deflection of the
structure and foundations, to provide full restitution after loading. (Accidental overload
beyond abnormal berthing may result in permanent displacement of the structure).
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5.3.2.4 Energy absorbing fender systems
An energy absorbing fender system will usually comprise an elastomeric energy absorbing
unit, and associated contact faces, mounted on the front of a rigid (or semi-rigid) wharf or
dolphin structure, such that the whole of the berthing energy is absorbed by the fender
system. The structure should sustain the reaction loads from the fender system mountings,
in three axes of translation and in rotation.
5.3.2.5 Determination of berthing energy and loads
Where more accurate data is not available, berthing energy should be determined in
accordance with Appendix B.
The berthing energy is dissipated and results in loads on the berthing structure that are
either reaction loads induced during deflection of a flexible structure itself, or reactions
from the ‘soft’ fender system. Reactions on a berthing fender system may be from any or all
of—
(a)
(b)
(c)
elastomeric (‘soft’) fender unit;
fender system restraint and reaction chains;
fender piles; and/or
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 Standards Australia
AS 4997—2005
(d)
20
loads may be normal to wharf (direct impact), as well as friction loads that are
longitudinal and vertical.
The fender system should be designed for the full range of design vessels for the facility, to
accommodate the characteristics of all vessels from smallest to largest. Where possible,
particularly with passenger vessels, care should be exercised to provide a soft fendering
system for small craft, while still providing adequate capacity to absorb energy from the
largest design vessel.
The berthing energy calculated in accordance with Appendix B is the energy of the vessel
approaching perpendicular to the wharf face. This energy is based on normal operations,
and thus represents the serviceability condition.
An abnormal berthing condition should also be considered in the fender design, arising
through mishandling, malfunction or exceptionally adverse wind or current or a
combination of these. In abnormal berthing conditions, the energy capacity of a fender
system should be capable of absorbing 1.25–2 times (or greater) the calculated normal
berthing energy (refer to PIANC Guidelines).
Thus a fender unit that is to be selected should be able to accommodate—
(i)
(ii)
normal berthing energy for serviceability condition up to the rated capacity of the
fender unit; and
abnormal berthing energy up to the maximum capacity of the fender unit.
The corresponding fender unit reaction load should be applied as a lateral load into the
berthing structure. The ultimate strength design of the fender support structures should then
consider the greater load of—
(A)
(B)
the rated fender reaction load, with appropriate Limit State load factors applied; and /
or
the abnormal berthing case reaction (maximum fender reaction), considered as an
ultimate Limit State load condition.
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Shear and tension loads during fender impacts should be calculated for a range of possible
berthing events, which should be applied to the fender support structure. Shear loads are
due to longitudinal and/or vertical friction on the face of the fender during vessel impacts.
These are transferred into the berthing structure through the body of the fender unit and/or
restraint or reaction chains. Where these loads are substantial, they may be reduced with the
use of low friction facing material on the fender frontal panel.
For fender impacts exceeding the ultimate strength condition, the designer should consider
the ramifications of failure of the berthing structure. For strategic installations, such as
major single use facilities and oil or gas loading/unloading facilities, etc., consideration
should be given to separation of the berthing structure from the wharf facility so that
accidental impact damage to the berthing structure does not necessarily prevent the
continued use of the facility.
5.3.3 Mooring loads
Mooring loads are loads generally applied to structures by mooring lines or ropes. Such
loads include wind and current loads on moored vessels, transferred to the wharf, jetty or
dolphin structures by the mooring lines. Mooring loads may also include loads resulting
from vessels manoeuvring to or from the berth using engines and rudders while moored to
bollards.
Loads applied to mooring bollards or similar fittings may be calculated using wind and
current loads on the moored vessel. To cater for mooring loads from manoeuvring vessels
bollard loads indicated in Appendix C should be considered.
 Standards Australia
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21
AS 4997—2005
There may be site-specific practices where large vessels may be directed to leave the berth
during periods of high wind speeds. These circumstances should be identified and
appropriate design wind speeds determined.
5.4 WIND ACTIONS
5.4.1 Determination of wind actions
Wind actions on wharves and wharf buildings and on stored materials or vehicles should be
designed in accordance with AS/NZS 1170.2.
Wind actions on vessels and floating structures may be designed using a wind pressure
based on a 30 s gust rather than basic wind speeds due to 3 s gusts. This is because floating
structures have a delayed response to wind loads. The 30–second wind speed may be taken
as 0.87 times the relevant basic wind speed as specified in AS/NZS 1170.2.
Terrain category 2 (in AS/NZS 1170.2) is generally appropriate for wind over exposed
fetches, due to surface roughness of the water at design wind speeds.
5.4.2 Wind actions on a vessel or structure
Wind pressure on a vessel or structure should be calculated from the following equation:
q z = 0.0006 V 2
where
qz
V
. . . 5.4.2(1)
= wind pressure, in kilopascals
= design wind speed, in metres per second
= V u for ultimate limit state
= V s for serviceability limit state
Wind loads on a vessel or structure should be calculated from the following equation:
FD = CwD Aq z
where
. . . 5.4.2(2)
F D = load in direction of wind, in kilonewtons
Cw D = coefficient of wind drag (see Table 5.2)
A
= wind pressure, determined from Equation 5.4.2(1), in kilopascals
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qz
= projected area of element, in square metres
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 Standards Australia
AS 4997—2005
22
TABLE 5.2
TYPICAL WIND DRAG COEFFICIENTS
Vessel or structure
Coefficient of drag (Cw D)
1.1 to 1.2
Vessels (up to 10 000 t)
1.2
Tubular piles
2.0
Rectangular members
NOTE: For vessels in excess of 10 000 t refer to BS 6349 for calculation of wind loads.
5.5 CURRENT ACTIONS
5.5.1 Design current
The design strength of maritime structures should allow for the combined effects of tidal
and/or river/estuarine flood currents.
5.5.2 Calculation
For structures and vessels up to 10 000 t subject to currents, the loads should be calculated
from the following equation:
. . . 5.5.2
Fs = 12 Cs D v 2 Aρ × 10 −3
where
Fs
= current load, in kilonewtons
v
= current velocity, in metres per second
CsD = stream flow drag coefficient (see Table 5.3)
A
ρ
= projected area of element, in square metres
= 1026 kg/m 3 for sea water
= 1000 kg/m 3 for freshwater
TABLE 5.3
STREAM FLOW DRAG COEFFICIENTS
Structure
Circular piles—Smooth
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Circular piles—Rough
Square piles or beams with sharp corners
Square piles or beams with corners rounded
Piles—Heavy marine growth
Debris mat
Vessels bow to current
Vessels beam to current
Drag coefficient
(CsD )
0.70
1.04
2.20
0.70–1.0
1.5–1.8
2.00 1
0.30
0.40
NOTES:
1
2
 Standards Australia
For more accurate assessment of the drag coefficient for the debris mat
refer to AS 5100.2.
For vessels in excess of 10 000 t refer to BS 6349 for stream drag loads.
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AS 4997—2005
5.6 DEBRIS ACTIONS
For structures where a debris mat could form against the structure (most river estuarine
situations), the structure should be designed for a mat of thickness not less than 1.2 m, and
not greater than 3 m.
The load exerted by the debris mat may be calculated using Equation 5.5.2, where the gross
area of the mat (A) is measured normal to the direction of the stream flow. All structures
subject to flood debris should be designed for a minimum load of 10 kN per metre of
structure. This applies to both fixed and floating structures.
5.7 NEGATIVE LIFT DUE TO CURRENTS
For floating structures in waterways subject to flood currents, a phenomenon known as
negative lift should be considered. This phenomenon occurs as a result of currents passing
under the floating structure and causing downward load on the leading edge of the structure.
The negative lift is proportional to the flow velocity squared, and can result in submersion
of the leading edge of floating structures at moderate velocities, sometimes resulting in
overturning of the structure.
Negative lift phenomena should be examined where current velocities exceed 0.5 m/s.
5.8 HYDROSTATIC ACTIONS
Hydrostatic loads on structures result in lateral pressures and uplift on walls and floor slabs
of maritime structures.
In considering hydrostatic loads, the highest design water level (flood level or storm
elevated sea level) should be used.
5.8.1 Uplift stability
Uplift stability of submerged or buried structures should be considered for the minimum
weight for the structure and should be taken as the most severe of the following:
(a)
(b)
Structure empty In maritime conditions, use of pressure relief systems cannot be
relied on for preventing uplift. Ground anchors (passive or prestressed) may be
included in stability calculations.
External water level is highest of—
(i)
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(ii)
maximum design water level plus half-wave height or more, as appropriate; or
equal to top of structure, above which rising water levels will cause the
structure to either submerge or fill.
5.8.2 Tidal lag
Hydrostatic effects on seawalls and other waterfront structures should consider tidal lag.
Tidal lag occurs when the level of ground water behind the wall lags behind the water level
in front of the wall, due to the slower drainage characteristics of the wall backfill compared
to tide level fluctuations in front of the wall.
In the absence of more detailed site-specific analysis on soil and wall permeability, the
minimum water differential to be considered due to tidal fluctuations should be the larger
of—
(a)
(b)
1/3 of the spring tidal range; or
500 mm.
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24
5.8.3 Ground water
Where rainwater run-off or other significant surface or subsurface flows could drain into
the backfill of a seawall or other waterfront structures at a higher flow rate than could be
expected to drain out through the subsoil or back-wall drainage system, the design of the
seawall or maritime structure should allow for a hydrostatic pressure based on a water table
at the top of the wall or structure backfill.
5.8.4 Wave backpressure
Backpressure on seawalls or other waterfront structures may result from the effects of
waves on the wall penetrating the face of the wall through joints or cracks. Consideration
should be given to—
(a)
(b)
waves running up and overtopping the structure, resulting in a high water table behind
the structure (up to the level of the top of the seawall or structure);
waves penetrating the fabric of the seawall (through cracks, joints, etc.) which causes
a locally high water table behind the wall, which may co-exist with the passage of a
wave trough in front of the seawall, resulting in high local differential hydrostatic
pressures on the structure. (Such localized differential pressures have resulted in
failures in seawalls.)
5.9 WAVE ACTIONS
5.9.1 General
Waves can be classified as three types, with corresponding significant wave heights (Hs)
and wave periods (T s). Wave classifications are ‘swell-waves’, ‘wind-waves’ or ‘vesselwash’.
Design storm events are generally described by the ‘significant wave height’ associated
with the peak of the storm event.
5.9.2 Design wave heights
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The design strength of maritime structures should allow for the highest wave likely to occur
on the structure over the selected design life and an annual probability of exceedance based
on the function category of the facility. The annual probability of exceedance of significant
wave heights, for structures of various design lives and function categories, are shown in
Table 5.4.
 Standards Australia
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25
AS 4997—2005
TABLE 5.4
ANNUAL PROBABILITY OF EXCEEDANCE OF DESIGN WAVE EVENTS
Design working life (years)
Function
category
Category description
1
Structures presenting a low
degree of hazard to life or
property
2
Normal structures
High property value or high
risk to people
3
5 or less
25
50
100 or more
(temporary
works)
(small craft
facilities)
(normal
maritime
structures)
(special
structures/
residential
developments)
1/20
1/50
1/200
1/500
1/50
1/200
1/500
1/1000
1/100
1/500
1/1000
1/2000
NOTE: The design water levels used in combination with waves determined from Table 5.4 should be taken as
not below mean high water springs.
The design wave for structures should be equivalent to H 1, taken to be the average of the
highest 1% of all waves in the design storm event. The design wave conditions may be
determined by more specific modelling or, for structures where the wave loads are a small
part of the design loads, the following simplifications may be used: H 1 should be
determined by applying a factor to the significant wave height for the design storm, as
follows:
H 1 = fHs
. . . 5.9.2
For fully enclosed waters with maximum fetch lengths less than 10 km, f may be taken as
1.50 (short narrow fetch) to 1.70 (longer wider fetch).
For open waters, where storm waves are likely to be superimposed on swells, f should be
taken as 1.70 (e.g., normally calm waters—tropical Australian coastlines) to 2.0 (e.g., high
energy waters—southern Australian coastlines).
Where the structures are close to reflective seawalls, account should be taken of higher
waves resulting from reflected waves interacting with incident waves.
5.9.3 Design lateral wave loads
The design of elements of structures should include design for the lateral loads of the waves
impacting the structure, using recognized wave load formulae, or from hydraulic modelling.
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5.9.4 Wave uplift loads
Structures where waves can travel under the soffit of the structure (jetty deck slabs under
extreme wave conditions, low level landings, drainage out-falls, etc.) are subject to dynamic
wave uplift loads. The uplift load may be approximated as the head of water corresponding
to the wave crest as if the structure were not present, factored by 2.0. This load may act
upwards or downwards as the wave passes.
In addition to this slowly varying dynamic pressure, structures containing re-entrant corners
(e.g., where slab soffit meets down-stand beam) can experience very high wave impact
loads, with pressures several times the slowly varying pressure. The impact loads are of
very short duration, and extend over a limited area around the re-entrant corners.
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26
Structures where these loads are exerted can often accommodate such loads if other
dynamic wave loads are adequately catered for and if the deck is structurally continuous
over a larger area than the area exposed to impact pressures. Where these impact loads are
likely to occur, designs should consider the details for resisting uplift loads (holding down
bolts, reinforcement in the region of anchors, etc.) or the provision of pressure-relief
systems or vents.
Where possible, these high impact wave loads should be avoided by eliminating re-entrant
corners (e.g., use of flat plate concrete slabs on tubular piles) or by providing pressurerelief openings.
5.10 CONSTRUCTION AND MAINTENANCE ACTIONS
Construction and maintenance actions on maritime facilities should take into consideration
the probable use of cranes and other heavy loads required to construct and maintain
maritime structures. Sometimes construction and maintenance actions on over-water
structures may exceed the service loads of the structure.
5.11 LATERAL EARTH ACTIONS
Lateral earth loads on waterfront structures and seawalls should be obtained by
consideration of the soil parameters for the in situ soil and/or backfill against the structure.
Earth-retaining structures should be designed for a minimum surcharge load equal to the
uniformly distributed load used for the design of the adjacent deck. For seawalls with no
associated wharf deck, the minimum surcharge should be 5.0 kPa. Where the area behind
seawalls is subject to vehicle or other heavy loads, the surcharge should be increased in
accordance with Table 5.1. Use of relieving slabs may be required to improve the stability
of the earth-retaining structures.
Consideration should be given to the effects of lateral water pressure in conjunction with
lateral earth loads, in accordance with Clause 5.8.
5.12 COMBINATIONS OF ACTIONS
5.12.1 General
Unless otherwise specified, a structure and its components should be designed to resist the
loads applicable to the in-service performance requirements of the structure, ultimate loads
during storm or flood conditions, as well as loads applicable to the intermediate stages of
construction.
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Care should be exercised in defining combinations of actions to ensure the proper design
action effect for actions that—
(a)
(b)
(c)
do not act simultaneously;
act simultaneously, but not superimposed; or
act simultaneously and are superimposed.
Combinations specified in AS/NZS 1170 should be considered. In addition, combinations of
actions relating to maritime facilities should be considered.
5.12.2 Stability
The basic combinations used in checking stability should be as detailed in AS/NZS 1170.0,
and as appropriate, the following:
(a)
For combinations that produce net stabilising effects (E d,stb):
 Standards Australia
E d,stb = [0.9G]
permanent action only
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27
(b)
AS 4997—2005
For combinations that produce net destabilising effects (E d,dst):
(i)
E d,dst = [1.2G, S u , Fenv ]
(ii)
E d,dst = [1.2G, Q, S u , Fenv ]
5.12.3 Strength
permanent action and actions given in
Clause 5.12.4 and/or Clause 5.12.5
permanent and imposed actions, and actions
given in Clause 5.12.4 and/or Clause 5.12.5
The basic combinations used in checking strength should be as detailed in AS/NZS 1170.0,
plus, as appropriate, the following:
(a) E d = [1.2G, S u , Fenv ]
(b) E d = [1.2G, 0.6Q, S u , Fenv ]
(c) E d = [0.9G, S u , Fenv ]
permanent actions and actions given in Clause 5.12.4
and/or Clause 5.12.5
permanent and imposed actions and actions given in
Clause 5.12.4 and/or Clause 5.12.5
permanent actions and actions given in Clause 5.12.4
and/or Clause 5.12.5
5.12.4 Combinations for berthing and stream loads, water pressure, ground water
and earth pressure
The basic combinations should be modified for berthing and stream loads, water pressure,
ground water and earth pressures. Appropriate combinations may include one or a number
of the following factored values:
(a) S u
= 1.5Fb
for normal berthing loads
= 1.5F m
for mooring loads
(b) S u
= 1.0Fb.u
(d) S u
= 1.5F lat
(c) S u
for abnormal berthing loads
for the minimum horizontal load (see Clause 5.3.1)
(e) For submerged or partially submerged structures, where the design water height is at
the top of the structure and cannot be exceeded:
Su
= 1.2F lp
Su
= 1.5F lp
(f) S u
= 1.5Fe
(h) S u
= 1.5Fs
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(g) S u
= 1.5F gw
for static water pressure that is measured to the top of
the structure (see Clause 5.8.1(b))
where the design water level could be exceeded
for earth pressures
for ground water
for ultimate stream flood flow and debris
5.12.5 Combinations of wind and wave loads
The basic combinations should be modified for environmental loads due to wind and waves.
Appropriate combinations may include one or a number of the following ultimate values:
(a) F env = W u
(b) F env = F wave.u
(c) F env = W u ,0.7F wave.u , 1.5Fs
(d) F env = 0.7W u , F wave.u
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ultimate wind load
ultimate wave load
ultimate wind and wave
ultimate wave and wind
 Standards Australia
AS 4997—2005
28
5.12.6 Serviceability
Combinations for the serviceability limit states should be those appropriate for the
serviceability condition being considered. Appropriate combinations may include one or a
number of the following using the short-term and long-term values as appropriate:
(a)
G
(c)
Es
(b)
(d)
(e)
Q
Fb
Fm
(f)
F lp
(h)
Fe
(g)
(i)
Fs
F gw
(j)
Ws
(l)
Serviceability values of other actions, as appropriate.
(k)
F wave.s
5.12.7 Cyclic actions
Structures that are subject to continuous wave action should be designed to cater for cyclic
loadings. The magnitude of the repeated loadings when designing such structures, or
elements of structures, for fatigue performance should be determined from in-service cyclic
actions. That is, structures should be adequate to resist the ultimate wave loads as well as
substantially smaller waves that result in constant cyclic loads leading to fatigue conditions.
NOTE: Structures in a waterway where waves constantly occur, with a typical period of 2 s to 4 s,
will experience 106 cycles per annum.
5.13 PROPELLER WASH
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The submerged elements of structures that are subject to propeller wash from passing
vessels, in particular tugs, and from thrusters should be designed to cater for such loads.
Where tugs are likely to be operating routinely for assistance in manoeuvring large vessels,
the siting of small craft facilities in such areas should be planned carefully, as propeller
wash from tugs can affect the safe operation of small craft. (Propeller wash current speeds
may be up to 8 m per second, adjacent to a tug vessel.)
5.14 EARTHQUAKE ACTIONS
5.14.1 General
Design of structures for earthquake actions (E u ) have to ensure that adequate capacity exists
for overall stability and member strengths and that the detailing of the structure will be
sufficient for the expected movements of the structure.
Design actions to be resisted are defined by AS 1170.4. Nevertheless, in considering the
application of AS 1170.4 it should be recognized that the Standard is particularly directed
to the design of buildings and similar structures that are often significantly different to
maritime applications.
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AS 4997—2005
5.14.2 Maritime structures
Structures subjected to earthquake conditions often sustain less damage if the structure has
a higher degree of shape regularity, simple load paths with multiple redundancies and
simple connections. These properties should be considered at the time of definition of the
structural systems and carried through the design where at all possible. Also of significant
effect on maritime structures designed to withstand an earthquake are the following:
(a)
Structural ductility Often maritime structural design has elements with significant
variation in member ductility, e.g., limited ductility concrete deck supported on
ductile steel piles. The elements of lesser ductility need to be considered to ensure the
displacements that would be expected to occur in the elements of higher ductility do
not adversely affect the structure.
The structural ductility factor(s) selected needs to be able to be reliably achieved by
the structure.
(b)
(c)
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(d)
(e)
If suitable for the application, ductile response may be achieved by utilizing ‘fuse’
elements in the structure, designed to absorb the earthquake energy while protecting
the significant structure. If a fuse element is used, it should be easily accessible and,
if necessary, replaceable/repairable.
Soil conditions The soil conditions in the surface layers generally define the site’s
dynamic stiffness and period regardless of the depth of actual founding stratum.
Special consideration is, however, required for the possibly more adverse conditions
where raking piles or squat members are founded on a stiff stratum, regardless of the
depth.
The possibility of liquefaction, especially of sand layers, should be considered. If
liquefaction is determined to occur, then the effect of liquefaction on the structural
analysis has to be included.
Response of adjacent structures and supported structures Consideration of the
earthquake response of adjacent structures is required to ensure that conflict in
responses does not result in the adverse contact, or loss in contact, between the
structures, e.g., impact of wharf segments or loss of bridging elements to dolphins.
Adverse interactions between the structure and any supported structures (e.g., cranes,
buildings, etc.) should be considered in the analysis (e.g., crane stability).
Structural importance factors Many significant maritime structures perform a postdisaster function or could be considered economically significant structures due to
loss of function or cost of reinstatement. Elements of a structure of high importance,
which are not required for the general function of the structure, may be assigned a
lower structural importance factor, provided the elements will not compromise the
remaining structure by its possible failure under a lesser effective design event.
Stability of reclamation and revetments The maritime structure being considered
may be adversely affected by the failure of adjacent slopes due to an earthquake. This
slope stability effect may or may not occur during the peak earthquake accelerations.
Specialist advice is recommended.
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30
SE CT ION
6
DURAB I L I T Y
6.1 GENERAL
Maritime structures are generally sited in very aggressive environments for normal
structural materials, and the design of maritime structures should include consideration of
the requirements to withstand the aggressive environment while the structure remains
serviceable.
The effect of extreme events on the structure’s durability should also be considered. For
example, the effect on concrete structures, which may be heavily stressed and cracked in an
extreme event early in the life of the structure, should be considered, where such cracking
may then lead to accelerated corrosion of steel reinforcement.
6.2 DESIGN LIFE
6.2.1 General
Design life is defined as the period for which a structure or a structural element remains fit
for use for its intended purpose with appropriate maintenance. The design life of maritime
structures will depend on the type of facility and its intended function (see Table 6.1). This
design life will depend on the owner’s requirements.
As well as determining loads for a facility, it is necessary to decide on a realistic design life
for the structure. This design life should be based on consideration of capital and
maintenance expenditure. Durability is to be realized either by a maintenance program, or,
in those cases when maintenance cannot (or is not expected to) be carried out, by design
such that deterioration will not lead to failure. In the latter case the initial capital cost is
expected to be high.
The designer should determine an appropriate maintenance regime consistent with the
adopted design and materials that will achieve the design life. Particular care should be
taken when considering design life and maintenance regimes for inaccessible members.
Sections or components of the structure that have limited access or are inaccessible after
construction should have a design life (with no maintenance) equal to the design life of the
structure.
At the end of the design life, the structure should have adequate strength to resist ultimate
loads and be serviceable, but may have reached a stage where further deterioration will
result in inadequate structural capacity.
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TABLE 6.1
DESIGN LIFE OF STRUCTURES
Type of facility
1
Temporary works
5 or less
Normal commercial structure
50
2
3
4
 Standards Australia
Design life
Facility
category
Small craft facility
Special structure/residential
(years)
25
100
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AS 4997—2005
6.2.2 Material considerations
6.2.2.1 General
The choice of materials to achieve the design life of a maritime structure should reflect the
required design life and the agreed maintenance regime. Issues that should be considered
when selecting concrete, steel or timber are detailed in Clauses 6.2.2.1, 6.2.2.2 and 6.2.2.3.
Whilst this Section deals with the use of concrete, steel and timber, it does not preclude the
use of other materials.
6.2.2.2 Concrete
The following items should be considered when selecting concrete as a material in the
design of a maritime structure:
(a)
(b)
(c)
Concrete deterioration is usually a result of corrosion of reinforcing steel due to
chloride ingress.
Reinforced concrete may not be a ‘lifetime’ maintenance-free material. Reinforced
concrete structures require regular condition inspection and maintenance of
deteriorated sections. Recent history has shown some maritime concrete structures
experiencing significant premature deterioration as a result of an inappropriate
selection of materials for the required design life.
Improved performance of concrete structures will be achieved by a combination of
the following:
(i)
Limiting design stresses in reinforcing steel.
(ii)
Appropriate selection of member sizes, shapes and detail.
(iv)
Improved performance reinforcements.
(iii) Improved performance concrete.
(d)
(v)
Closely controlled construction methods.
(i)
access the member with working scaffold for inspection and repair;
Repairs may require the removal and replacement of deteriorated concrete and
reinforcement. Considerations include the ability to—
(ii)
remove and contain waste materials during repair works; and
(iii) apply and maintain an adequate curing regime to the repair works.
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6.2.2.3 Steel
The following items should be considered when selecting steel as a material in the design of
a maritime structure:
(a)
(b)
(c)
Steel deterioration (corrosion) results from the breakdown of the protective coating or
other protective system.
Paint coatings provide a
repair/recoating is necessary.
service
life
of
approximately
20 years,
before
The maintenance strategy may allow the reinstatement of a protective coating/system
before corrosion of steel begins, or for the deterioration of the steel member until
replacement of the protective coating/system and/or the member is required.
Considerations include the ability to—
(i)
(ii)
access the member with working scaffold for inspection and repair;
remove and contain waste materials during repair works; and
(iii) prepare and apply protective coatings in situ to achieve required standard.
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The preparation and recoating of steel in the marine environment is difficult and
standards reached in the manufacturing process are not usually achievable in this
environment.
6.2.2.4 Timber
The following items should be considered when selecting timber as a material in the design
of a maritime structure:
(a)
(b)
Individual timber members are relatively small, forming an assembly of members
within a structure. Members can usually be replaced easily within a structure to
maintain the structural capacity, without significant interruption to service operations.
The service life of timber members will vary significantly depending on application,
timber quality (grade), species natural durability and preservative treatment. The
following times to first maintenance can be expected:
(i)
(ii)
(c)
(d)
(e)
Timber piles exposed to marine organisms ......................................5–10 years.
Timber piles not exposed to marine organisms ..............................10–30 years.
(iii) Timber decking exposed to weathering..........................................10–25 years.
The deterioration of timber is usually by mechanical degradation, rot or attack by
living organisms (decay fungi, termites, marine borers).
Where not in a continuously wet environment, natural shrinkage due to drying timber
will result in the need to tighten bolted connections during early years of the
structure’s life.
A maintenance strategy may allow for regular and frequent replacement of timber
members throughout the design life, as individual components deteriorate.
Considerations include—
(i)
(ii)
the availability of skilled carpenters, able to maintain the works over the
structure’s design life;
the future availability of suitable timber species and member sizes;
(iii) the commitment of resources to regular inspection and maintenance of
structures; and
(iv)
the detailing and accessibility of bolted connections for ease of replacement
during maintenance works.
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6.2.3 Maintenance
All maritime structures deteriorate over time. Early maintenance is generally recommended
to prevent more significant damage. Whilst a structure may have a prescribed design life of
25, 50 or 100 years, local marine environments, operational conditions, and other factors
will lead to maintenance requirements. Regular (annual or otherwise) inspection of the
structure will permit early detection allowing the implementation of economic maintenance
measures. Maintenance will then be determined by the inspection results.
A typical maintenance program will include—
(a)
(b)
(c)
regular inspections;
a program of routine minor maintenance; and
a program of major maintenance.
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AS 4997—2005
6.3 CONCRETE
6.3.1 General
The predominant cause of deterioration of concrete maritime structures is corrosion of
reinforcement and prestressing tendons. This is particularly evident in the splash zone.
Design of concrete maritime structures should focus on minimising the causes of premature
corrosion of steel reinforcement as the repair of this deterioration may require major
reconstruction of the affected elements and possibly pose restrictions on the use of the
facility during repair/reconstruction.
There has been a trend for designers to specify high-strength concrete, that is, concrete with
a characteristic compressive strength above 50 MPa, to reduce permeability and thus
improve the durability of maritime structures, where a lower strength would satisfy design
strength requirements. However, unless proper construction techniques are adopted,
particularly in compaction and curing, other problems including plastic shrinkage and
thermal cracking may compromise durability. In addition, economical and slender
structures, which can result from using the higher strength concretes, can lead to structures
that are more highly stressed in flexure and are susceptible to chloride penetration through
the wider crack widths.
Each concrete structure needs to be assessed individually to determine appropriate
requirements for it to be durable. Consideration should be given to the particular
environment, the type and use of the structure, the quality of the in situ concrete, the
detailing of the structure and the proposed maintenance regime. The requirements for
individual elements within a given structure will vary, as will the requirements for different
structures. The general advice given in this Standard regarding certain aspects of concrete
maritime structures is offered to facilitate this individual assessment and should not be
assumed to negate the necessity for carrying it out.
The objective of the design for durable concrete structures is to reduce the opportunity for
chlorides from sea water to cause the reinforcement to corrode. The designer should, at the
outset, review all the alternative strategies available. For example, the use of plain concrete
members, the use of stainless steel reinforcement, the encapsulation of prestressing tendons
in watertight plastic conduits, and the use of protective coatings to concrete members
should be examined.
6.3.2 Structural design
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Structural concrete should comply with
AS 3600, together with any applicable
Engineering judgement will be required
reinforcement is adopted, as AS/NZS 4671
6.3.3 Structural concrete
the design and performance requirements of
recommendations made by these guidelines.
in the use of AS 3600, where stainless steel
does not encompass this material type.
The following is recommended for structural concrete in a maritime structure:
(a)
(b)
Specifying special-class concrete. (The designer to specify particular requirements for
the concrete, e.g., binder type and proportions as well as water-binder ratio, and
normal criteria such as strength).
A minimum characteristic compressive strength (f′ c) of 40 MPa.
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34
General purpose Portland cement alone as the binder, or a blended cement in
accordance with AS 3972.
NOTES:
1
2
(d)
(e)
(f)
(g)
(h)
It has been shown that for certain concrete mixes blended cements may improve the
resistance to chloride penetration as well as slowing the rate of hydration of the binder,
reducing the potential for thermal cracking.
When using blended cements particular attention needs to be paid to placement, finishing
and curing, to achieve the required strength and performance of concrete.
Cementitious content (Portland and blended cements) should be not less than
400 kg/m 3 .
For exposure classes C1 and C2, a drying shrinkage at 56 days not greater than
600 × 10 −6 mm/mm, determined in accordance with AS 1012.13.
A maximum water to binder material ratio not more than 0.40. Super-plasticizers
should be used, to reduce water content whilst maintaining adequate workability.
Concrete should be placed in watertight forms, thoroughly compacted and protected
from excessive temperature and wind evaporation.
All maritime concrete structures should be water-cured for at least 7 days and
preferably 14 days under ambient conditions. Curing should commence immediately
after finishing horizontal surfaces. If forms are stripped within 7 days, then
supplementary water curing should take place to 7 days.
NOTE: The use of chemical curing compounds is not recommended on maritime concrete.
The use of penetrating chemicals for chloride inhibitors, such as silanes, siloxanes or other
surface coatings, precludes the use of chemical curing compounds on maritime concrete.
6.3.4 Requirements for reinforcement
Carbon steel reinforcement should comply with AS/NZS 4671 and be used and fabricated in
accordance with AS 3600 and the following:
(a)
The total surface area of carbon steel reinforcement in maritime structures should be
minimized to reduce the opportunity for corrosion by chloride-contaminated concrete.
A smaller number of large diameter bars is preferable to a larger number of small
bars, provided that the crack control provisions of AS 3600 for bar diameter and bar
spacings, as appropriate, are satisfied. Minimum size bars for reinforcement should be
in accordance with Table 6.2, and be 16 mm diameter in slabs and 20 mm (preferably
24 mm) in beams. Small bars used for ties and ligatures should be not less than
10 mm diameter.
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TABLE 6.2
MINIMUM BAR DIAMETERS IN MARITIME CONCRETE STRUCTURES
(CARBON STEEL)
Bar location
Minimum diameter
Beams, up to 500 mm deep
20 mm (24 mm preferred)
Slabs
Beams, over 500 mm deep
Ties and ligatures
(b)
16 mm
24 mm (28 mm preferred)
10 mm (12 mm preferred)
In parts of concrete structures likely to be intermittently inundated, splashed or
sprayed with sea water, the use of stainless steel reinforcement should be considered,
either throughout the exposed section of the structure, or in combination with carbon
steel reinforcement. Stainless steels equivalent to Grade 1.4436 (316) or 1.4429
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AS 4997—2005
(316LN), 1.4301 (304) and Duplex 1.4462 (2205) should be used. (Grade 1.4301
(304) is not recommended for use in areas in C2 exposure conditions).
Stainless steel, when used in combination with carbon steel reinforcement, may be
used in the more exposed locations, e.g., the corner bars in beam soffits, and for thin
reinforcing steel elements such as ties and stirrups. Stainless steel reinforcement
should comply with BS 6744.
(c)
The ductility properties of stainless steel reinforcement should be ascertained when
applying the structural design rules of AS 3600.
Galvanizing of carbon steel reinforcement may delay the onset of corrosion compared
with normal (uncoated) carbon steel in a maritime environment, provided the
measures outlined below are taken. The galvanizing provides corrosion protection to
the base steel due to its resistance to the effects of reduction in the pH of the concrete
mass (the carbonation effect) and its higher chloride tolerance compared to normal
steel.
When using galvanized reinforcement, the provision of an adequate cover of a good
quality concrete, as is necessary with normal carbon steel reinforcement, will provide
the best overall result.
Galvanizing of reinforcement should be by the hot-dip process and an average
minimum coating mass of 600 g/m2 should be provided in accordance with
AS/NZS 4680. For best performance, it is preferable for the galvanizing of
reinforcement to be undertaken after all cutting, bending and welding of
reinforcement cages is complete. In normal practice, repairs to cut ends and breaks in
the coating should be undertaken following the recommendations in AS/NZS 4680.
(d)
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(e)
If galvanized reinforcement is used, all steel within the member should be galvanized
to prevent potential sacrificial corrosion of the galvanized coating. If selective use is
made of galvanized reinforcement or other components in concrete (e.g., galvanized
bolts, fittings, attachment plates), it is important that the point of connection to
normal steel reinforcement be deeply embedded. The use of galvanized reinforcement
in conjunction with stainless steel is not recommended.
Epoxy coating or other enveloping protection system for steel reinforcement is not
recommended for concrete in a marine environment.
Cathodic protection of carbon steel reinforcement may be used to extend the design
life of a maritime structure, although this should only be used when the designer is
confident that the system will remain operational and will be routinely maintained.
(In parts of maritime structures with exposure classification C2 (see Table 6.3),
bonding of all reinforcement cages by welding every bar intersection to facilitate the
later introduction of cathodic protection of the reinforcement should be considered).
6.3.5 Prestressing steel
6.3.5.1 General
The use of prestressed concrete in a marine environment requires additional consideration
to be given to the protection of the highly stressed steel elements. While the permanent
compression in such concrete structures aids in reducing saltwater penetration through
cracks, the effect of chlorides on highly stressed strand and wire can produce unpredictable
structural performance. These effects include chloride corrosion and stress corrosion
(embrittlement), which can result in sudden tensile failures in concrete members. Often
these failures are unpredictable because the small cross-section of the high-strength steel
will undergo substantial strength losses without any evidence on the concrete surface,
(unlike the staining and spalling behaviour of conventional steel reinforcement).
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Exposed ends of prestressing steel should be cut back and protected with a suitable
impermeable mortar to prevent ingress of water.
6.3.5.2 Post-tensioned members
Post-tensioned members, with strand grouted within fully enclosed waterproof ducts of
heavy-gauge inert materials (e.g., 3 mm–5 mm thick walled PVC or HDPE) can be expected
to have substantial design life.
6.3.5.3 Pre-tensioned members
When using pre-tensioned members stressed with unprotected carbon steel wires (protected
only by concrete cover), consideration should be given to minimizing the chloride ion
content arising from aggregates and any admixtures used, and to the use of other
preventative forms of future ingress of chloride ions (concrete additives for corrosion
inhibitors, pore-blockers, surface sealants etc.).
It is recommended that in a marine environment where pre-tension wire or strand is used,
non-prestressed carbon steel be used. This non-prestressed steel should be located in the
most exposed section of the element to provide an early indication of chloride-induced
corrosion. It is suggested that such non-prestressed reinforcement provide at least 40% of
the total prestressed and non-prestressed reinforcement capacity.
6.3.6 Exposure classifications
The exposure classifications given in Table 6.3 amplify those given in Table 4.3 of
AS 3600.
Reinforcement in concrete permanently submerged in sea water suffers only limited
corrosion. However, in the splash (tidal) zone, where the concrete is alternately wet and
dry, rapid corrosion is the consequence of chloride concentration and penetration, together
with the high availability of oxygen and presence of moisture in the concrete. In this regard,
special consideration should be given to the effect of saltwater splash due to reflective
waves off rear walls and rock revetments at the landward end of maritime structures.
TABLE 6.3
EXPOSURE CLASSIFICATIONS
Exposure environment
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Members permanently 500 mm below the seabed
Members permanently submerged 1 m below lowest
sea water level to 500 mm below seabed level
Spray zone, (i.e., exposed to airborne salt spray, but
not in splash zone e.g., the top side of deck slabs)
Splash zone, from 1 m below water level up to 1 m
above wave crest levels on vertical structures, and all
exposed soffits of structures over the sea
Exposure classification
Reinforced or
prestressed members
A2
B2
C1
C2
6.3.7 Cover to reinforcement
6.3.7.1 General
The cover for low carbon steel bars should be not less than those shown in Tables 6.4 and
6.5 as appropriate. These covers can vary within the deviation from specified position as
prescribed in AS 3600 (that is, within the appropriate tolerances).
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AS 4997—2005
TABLE 6.4
MINIMUM COVER TO REINFORCING STEEL—STANDARD
COMPACTION CONCRETE
Minimum cover (mm)
Exposure classification
A2
f′c = 40 MPa
f′c = 50 MPa
40
30
B2
50
40
C2
75
65
C1
70
50
TABLE 6.5
MINIMUM COVER TO REINFORCING STEEL—INTENSE
COMPACTION CONCRETE
Exposure classification
A2
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3
4
f′c = 50 MPa
35
30
40
30
C2
65
60
NOTES TO TABLES 6.4 AND 6.5:
2
f′c = 40 MPa
B2
C1
1
Minimum cover (mm)
60
45
A design life of 25 years can be expected where the above tables are
adopted for cover to reinforcement. Engineering judgement is required
where a longer design life is required. Additional measures that may be
considered include the use of low corrosion rate reinforcement (stainless
steel); galvanized reinforcement (in combination with other measures);
especially designed concrete mixes; use of additives or coatings such as
organic or inorganic pore blocker concrete admixtures; chemical
corrosion inhibitor admixtures; hydrophobic surface sealants (silanes) or
other proven systems. These may be combined in appropriate
circumstances with cathodic protection systems.
Where galvanized reinforcement is used, cover to steel should not be
reduced.
Where stainless steel AISI 1.4436 (316), or higher grade stainless steel
reinforcement is used, cover to steel may be reduced to 30 mm. Where
stainless steel and carbon steel are used together in a member, the
minimum cover given in the Tables above should apply.
For temporary structures, with a design life of less than 5 years, cover
may be reduced by 25% from the values in Table 6.4 (except that
minimum cover to steel should be 30 mm).
6.3.7.2 Crack control
Cracking in concrete maritime structures can lead to reinforcement corrosion as well as
aesthetically unattractive structures.
To enhance durability, limiting the widths of cracks under serviceability conditions can be
achieved by designing structures with low stresses in the steel reinforcement. Table 6.6
provides maximum recommended stress in carbon steel reinforcement for maritime
structures in exposure classification C1 and C2. The structures have to be also designed for
other relevant limit states including both stability and strength.
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TABLE 6.6
MAXIMUM ALLOWABLE REINFORCEMENT STEEL
STRESS AT SERVICEABILITY LIMIT STATE
db (mm)
f s (MPa)
≤12
185
16
175
20
160
≥24
150
In elements with exposure classification A2 and B2, the tensile stress in steel reinforcement
may be increased to the limits provided in AS 3600 for crack control.
Prestressed concrete structures should be designed to remain uncracked throughout the
service load range.
6.3.7.3 Embedded Items
Items that may be corroded by the saltwater environment should not be embedded in the
cover zone. No potential corrosion path should be created by any material such as conduits
or bar chairs, which if corroded, would compromise the concrete cover to the
reinforcement.
Metal items that protrude from the concrete surface should be insulated from steel
reinforcement, so that galvanic cells between the reinforcing steel and the exposed metal
cannot occur. For example, exposed stainless steel fitments or bolts, etc., should be
electrically isolated from the reinforcement cage.
Plastic or mild steel bar chairs should not be used. Bar chairs comprising stainless steel or
precast concrete blocks of high density and strength (preferably stronger than the concrete
to be placed) are an acceptable method of supporting reinforcing steel.
6.4 STEEL
6.4.1 General
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Steel is a suitable material for the construction of maritime structures; however, the
decrease in steel durability after exposure to sea water should be considered when using
carbon steel in the marine environment. During design, designers should consider methods
that protect and maintain the steel members, as well as methods of installation and
connection of steel members to prevent damage to pre-applied protective systems.
The selection of the shape of steel members may not always be based on the most efficient
system with regard to strength, but should be selected to allow the easy application and
maintenance of protective coatings to allow improved durability. For example, tubular
members are easier to coat and wrap than flanged or angle sections. Tubular members can
be protected with thick inert applied coatings in factory conditions, or may be wrapped in
purpose-designed materials applied after installation.
6.4.2 Stainless steel
Where stainless steel is used in fabricated maritime structures, consideration needs to be
given to grade selection, surface finish and proper welding procedures. Grade 1.4436 (316)
or Grade 1.4462 (2205) should be selected for additional strength and corrosion resistance
for maritime applications.
Corrosion resistance of stainless steel increases with finer surface finishes. Corrosion of
stainless steel in the form of surface discolouration (tea-staining) may be reduced by
specifying high quality surface finish.
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AS 4997—2005
Stainless steel should be used cautiously in anaerobic conditions, such as mud. If scratching
or abrasion does not damage the protective surface oxide during installation or service then
stainless steel can perform well. However, if the surface oxide is damaged then some
air/oxygen should be available to allow the protective film to repair. Stagnant conditions
may also be a source of microbiologically influenced corrosion, which can attack many
metals including stainless steels.
For further information refer to AS/NZS 1554.6, AS/NZS 2312 and AS/NZS 4673.
6.4.3 Material requirements
Steel structures should comply with AS 4100, and the relevant standards relating to
manufacture and rolling and milling of steel products as listed in AS 4100.
6.4.4 Steel protection systems
6.4.4.1 General
Steel surface protection systems have been developed for various structural steel elements
and corrosion environments. Damage caused by corrosion in the various marine
environments can be attributed to varying physical processes such as rapid oxidation in the
wet, salt, surface conditions, exacerbated by wave action and seabed abrasion, as well as
wear and tear from maritime operations (chafing, flexing). These various forms of corrosion
and damage require different protection systems.
Damage caused to steel protection systems, at the time of construction and erection, must
be repairable. Normal activities such as installing piles, cutting and welding steel members,
and site drilling and bolting can cause damage to the protection system. In addition, the
protective systems should be capable of repair/replacement during scheduled maintenance,
at the end of the specified maintenance-free period.
Elements permanently buried in the seabed or permanently immersed in sea water,
generally have low corrosion rates and an annual corrosion allowance can account for the
corrosion of the element (see Clause 6.4.4.7).
Consideration should be given to the type of coating selected; the thickness of the coating
system; the method of application; surface preparation; and the implementation of a suitable
inspection and test procedure to assess the effectiveness of the applied system.
6.4.4.2 Jacket systems
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The encapsulation of steel members inside protective jackets (e.g., HDPE pipe, concrete
jackets) is a suitable method of providing long-term protection to members such as steel
piles. The jackets must extend a safe distance below seabed level, taking into account any
future scour, which may result from propeller wash, stream flow or similar.
6.4.4.3 Applied coatings
The application of thick (1 to 5 mm thick) inert materials (e.g., urethane, polyethylene etc),
under factory conditions, is a suitable method for protecting piles or substructure members
in aggressive environments.
6.4.4.4 Wrapping systems
The use of corrosion inhibiting fabrics (e.g., petrolatum-tape) to wrap piles or substructure
members is a suitable method for protecting members exposed to an aggressive
environment (splash and spray zone).
6.4.4.5 Painting systems
The use of inert, high build paint systems, such as epoxy paints, are suitable for the
protection of steel structures in the splash zone. Paint systems should be able to be reapplied to old surfaces, to allow for repair and maintenance.
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6.4.4.6 Metallic coatings
Thin metal coatings and hot dip galvanizing are suitable methods for protecting steel in
some environments; however, due to the solubility of most metal corrosion products, such
systems are not suitable where the surfaces will be subject to immersion or driven spray.
6.4.4.7 Corrosion allowance for permanently submerged steel
Where no protection systems are to be applied, e.g., in a steel section buried below the
seabed or a section permanently submerged, protection of the steel may be provided by
providing an allowance for corrosion and subsequent loss of steel cross-sectional area.
Where a corrosion allowance is to be used to protect submerged steel members, corrosion
rates should not be less than those tabulated in Table 6.7, unless test data extending over an
acceptable duration validates a lower rate for a particular location.
TABLE 6.7
CORROSION ALLOWANCE FOR STEEL SECTIONS
(PERMANENTLY SUBMERGED IN SEA WATER)
Exposure
classification
Mild
Moderate
Strong
Condition
Permanently buried in seabed
(see Note)
Cold water (south of 30°S)
and near the mud line
Tropical/Subtropical water
(north of 30°S)
Annual corrosion rate
(mm)
0.01
0.05
0.10
NOTE: The influence of ‘microbiologically induced corrosion’ (in anaerobic
conditions below seabed) or ‘accelerated low water corrosion’ (about low water
level) should be examined. These influences may produce corrosion rates
significantly higher than those above.
6.4.5 Member sizes
Steel members should be selected to be robust and have adequate reserve of strength to
allow for corrosion and unpredicted loads for structures with a design life in excess of
5 years.
Designers should consider the following:
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(a)
(b)
(c)
(d)
Structural members exposed on both faces should not have a web or flange thickness
less than 8 mm. Sealed tubular members may have a wall thickness of 4 mm. Plate
thickness on pontoons, protected on the inside face by a suitable paint coating system
may be reduced to 4 mm, but exposed decks should have minimum thickness of
6 mm.
The minimum bolt size for structural connections should be 20 mm for carbon steel
and 12 mm for stainless steel. Tie rods should be of similar diameters.
All steelwork should be designed to be free-draining, with no pockets that may trap
water or sediment.
Hollow members (tubular piles, rolled hollow sections) should be sealed to prevent
corrosion on the inside face.
6.4.6 Cathodic protection
Cathodic protection for steel structures is only applicable for parts of the structure
permanently immersed in water. Cathodic protection should be installed in accordance with
AS/NZS 2832.
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AS 4997—2005
Where cathodic protection is used and regular maintenance of the structure is unlikely,
sacrificial anodes should be used with or without a protective paint system. Where paint
systems are used, the cathodic protection should be designed to provide protection as the
paint system deteriorates.
Impressed current cathodic protection may be used where the system is likely to be well
maintained and where stray currents do not interfere with the protection system, or where
currents from vessels will not negate the effect of the system. Caution should be exercised
to avoid stray currents from cathodic protection systems affecting moored vessels and
unprotected structures.
6.5 TIMBER
6.5.1 General
Timber has many applications in maritime structures, particularly in lighter duty
recreational facilities (waterfront boardwalks, small craft facilities, piers, jetties and
similar).
Timber may be used for the construction of the total structure including piles, headstocks,
stringers, bearers and decking, or timber can be effectively used in conjunction with other
materials to provide economic, and durable structures. To alleviate the normal problems of
fungal attack caused by rainwater or other sources of moisture on timber, concrete decks
may be used on timber resulting in durable and economic structures. Timber may be used
for fendering systems and other wearing surfaces, as well as for fender piles on structures
predominantly constructed from concrete and/or steel.
Generally timber would not be used as the principal structural medium for a facility with a
design life greater than 25 years and decks classed above Class 10 (see Table 5.1).
Timber for maritime structures should generally be hardwood timber of Natural Durability
Class 1 or 2, in accordance with AS 5604.
6.5.2 Immersed timber
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Timbers in contact with tidal saltwater should be selected for their natural resistance to
marine borer attack e.g., Syncarpia glomulifera (Turpentine) or alternatively may be treated
with preservative impregnation and/or coatings/sheathing/jacketing (impermeable), to resist
marine organisms.
Where Turpentine timber piles are used, it is desirable to have the section of pile in the
water column free of interruptions to the bark (e.g., where branches may have been
trimmed) as these areas provide a flaw in the pile’s natural protection to marine organisms.
Similarly, timber piles below high water level should not be cut or drilled. To minimize the
risk of marine organisms attacking the exposed inner wood of cut or drilled timber, a
suitable barrier material should be applied.
Preservation of timber for use in piles or other structures below water level should be in
accordance with AS 1604. Such preserved timber should not be cut or drilled where it will
be immersed.
6.5.3 Timbers above water level
Timber members located above the level of high tide are not at risk of marine borer attack;
however, they should be of a species resistant to fungal attack due to standing fresh water
and termite attack.
Substructure timbers should be protected from standing fresh water by a layer of aluminium
sarking spiked to the top face of the timber, turned down at each side (see Figure 6.1).
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FIGURE 6.1 SARKING DETAILS
Exposed timber pile tops should have waterproof caps moulded to the top of the trimmed
pile. A steel ring should be fitted around the top of the pile to minimise splitting after
installation.
Other vertical timber sections should where possible be cut at an angle to facilitate
shedding of moisture.
6.5.4 Decking
In the design of timber decks used for pedestrian access, it is necessary to ensure that trip
hazards will not be caused by differences in plank thickness or warping due to drying.
To reduce trip hazards, decking timbers should generally be machined on the underside to
ensure uniform thickness. The topside of the timber should be rough sawn to reduce slip
hazard when wet.
Deck planks should be ‘back sawn’ sections and laid with the timber’s ‘heart’ side as the
underside of the deck.
6.5.5 Finishes
Increased protection from environmental deterioration may be achieved by the application
of coatings to timber, including paint finishes, epoxy coatings, in situ preservative
applications or by wrapping the member with protective wrapping materials.
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Interfaces of joints and drilled holes, along with timber end-grain should be protected by
application of moisture repellent and decay inhibiting preservatives. Products containing
copper naphthenate chemical, which may contain diffusing properties to penetrate below
the wood’s surface, are effective as decay inhibitors.
NOTE: Where a structure is installed adjacent to oyster leases or sensitive fishing grounds,
chemically treated piles should not be used. Piles in such situations should employ coatings,
sheathing, jacketing, etc.
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AS 4997—2005
APPENDIX A
CONTAINER WHARF DECK LOADINGS
A1 GENERAL
Container wharf deck loadings relate to the wharf-side loads from transporting and stacking
containers for loading/unloading container ships. The loads do not reflect loads from
storage of containers in container yards, which may be stacked several containers high, as
such storage is specific to each port.
In the absence of more specific equipment specifications, loads and dimensions given in
Table A1, which represent typical loads and dimensions, should be applied to design in
order to reasonably accommodate container operations. These loads do not include dynamic
effects. Adequate provision for these effects should be allowed.
A2 CONTAINER STACKING
Containers may be stacked on the apron beside a vessel while awaiting transport or loading.
Concentrated corner loads are as given in Table A1.
TABLE A1
STACKING LOADS FROM CONTAINERS ON
WHARF APRONS
Storage method
Load
(kN)
Single container
230
Block of containers
750
Line of containers
380
Dimensions
of loaded
area (mm)
150 × 150
150 × 400
400 × 400
NOTE: This is for 40 ft containers that are 12.2 m long and 2.4 m
wide, stacked 2 high, supported at each corner.
A3 CONTAINER TRANSPORT
Forklift trucks and reach-stackers to transport 40 ft containers have the following wheel
loads:
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LADEN
Maximum front wheel load
Maximum rear wheel load
UNLADEN
300 kN (4 No)
100 kN (2 No)
(Tyre pressure of 750 kPa)
Maximum front wheel load
Maximum rear wheel load
100 kN (4 No)
200 kN (2 No)
The arrangement of such loads is shown in Figure A1. Straddle carriers have a maximum
wheel load of 150 kN and an arrangement as shown in Figure A2.
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FIGURE A1 FORKLIFT TRUCK AND REACH STACKER WHEEL ARRANGEMENT
FIGURE A2 STRADDLE CARRIER WHEEL ARRANGEMENT
A4 CRANE RAILS
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Container quay cranes (CQCs) operate on crane rails set into the wharf deck, parallel to the
wharf quayline, with a rail gauge commonly ranging between 15m and 30m (see
Figure A3).
The CQC loading on the crane rail (and so to the wharf structure) varies widely with each
specific crane installation. Crane weights and corner loads vary with crane capacity, rail
gauge, operational and extreme wind conditions; these loads will have to be assessed for
each installation. Application of this load into the wharf (rail) may be regulated by the
number and spacing of the wheels at each corner.
A general design load of 750 kN/m will accommodate most CQC loadings. The length of
applied load will depend on the crane design and conditions; however, a nominal loaded
length of 8 m for one leg of the CQC will accommodate the typical corner loads shown in
Figure A3 under most conditions. Bogie arrangements with up to 12 wheels per corner, with
a maximum length of 12 m (12 wheels at 1.1 m centres) can reduce the design load to
500 kN/m. Special attention should be given to CQC loads in cyclone areas, with provision
for higher loads in tie-down zones (increased wheel loads, uplift loads, longitudinal loads
into tie-down anchors and transverse loads into the rails).
Travel stop buffer loads should also be considered.
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AS 4997—2005
DIMENSIONS IN METRES
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FIGURE A3 TYPICAL CONTAINER QUAY CRANE CONFIGURATION
FOR POST-PANAMAX VESSELS
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46
APPENDIX B
BERTHING ENERGIES AND LOADS
B1 SCOPE
This Appendix provides a commentary on methods for determining berthing energies and
corresponding reaction loads due to vessels berthing at a wharf or structure and for the
design of fender systems.
B2 GENERAL
A widely accepted guideline for design of fender systems for commercial shipping is
provided by PIANC International Navigation Association, ‘Guidelines for the Design of
Fender Systems: 2002’, Report of Working Group 33 of the Maritime Navigation
Commission. Unless more specific design practices apply for a particular port facility, it is
recommended to follow these guidelines for design of fender systems for vessels over
10 000 DWT.
The PIANC Guidelines provide a comprehensive coverage of all aspects of fender design,
including—
(a)
(b)
fender geometry: spacing; accommodation for bulbous bows;
(d)
detailed fender design;
(f)
whole of life considerations;
(h)
procedure to determine and report the performance of marine fenders;
(c)
(e)
(g)
(i)
description of fender systems;
fender selection;
special cases—vessel class, vessel to vessel, flexible dolphins and berthing beams;
procedure to determine and report the performance of pneumatic fenders;
(j)
vessel dimensions;
(l)
guidelines for specification writing.
(k)
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development of the berthing model (contact with single/multiple fenders);
selection of fender size—case studies; and
B3 APPROACH VELOCITY
The PIANC Guidelines presents two methods for determining design approach velocity, one
of which is presented in this Appendix (see Figure B1).
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AS 4997—2005
FIGURE B1 BERTHING VELOCITIES—VESSELS > 1000 t
(Source: Brolsma et al, (1977) Design berthing velocity (mean value) as a function of
navigation conditions and size of vessel)
Figure B1 distinguishes five navigation conditions, as follows:
(a)
Good berthing—sheltered.
(c)
Easy berthing—exposed.
(b)
(d)
(e)
Difficult berthing—sheltered.
Good berthing—exposed.
Difficult berthing—exposed.
The velocities assumed in Figure B1 assume that all berthings are tug-assisted.
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The impact data shows low approach values for large vessels, which may be exceeded in
adverse conditions.
Similarly, the velocity indicated for vessels below 10 000 t are high, and it is considered
that maximum velocity for berthing may be taken as 0.6 m/sec. Caution is required when
applying the velocity values at these extremes of Figure B1.
For approach velocities for vessels below 1 000 t, guidance in this range is presented in
Table B1.
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TABLE B1
BERTHING VELOCITIES—VESSELS < 1000 t
Vessel class
Tonnage range
Exposure conditions1,2,3
Mild
0.20
Severe
0.30
Private vessels
Up to 10 t
Moderate
Private vessels
Over 10 t
Moderate
Mild
0.15
0.20
0.25
0.25
Mild
Up to 1000 t
Moderate
Ferries
Up to 100 t
Moderate
Over 100 t
0.25
Severe
Commercial charter/
cruise vessel
Ferries
Vn
(m/sec)
Severe
0.20
0.30
Mild
0.30
Severe
0.40
Moderate
0.30
Mild
Severe
0.35
0.25
0.35
NOTES:
1
2
3
‘Mild’ exposure has current speeds less than 0.5 knots; fair weather prevailing wind speeds
less than 10 knots; and wave heights less than 10% of the moulded draft of the design vessel.
‘Moderate’ exposure has current speeds between 0.5 knots and 1.0 knot; or fair weather wind
speeds between 10 knots and 15 knots; or fair weather wave heights between 10% and 20% of
moulded depth of vessel.
‘Severe’ exposure is when the environmental conditions exceed any of the current wind or
wave conditions for a moderate exposure.
B4 FENDER REACTION LOADS
The reaction load from fenders should be determined from the manufacturer’s performance
charts. This load should be factored to account for—
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(a)
manufacturing tolerance (5–10%);
(b)
berthing/compression speed;
(d)
temperature.
(c)
angular compression; and
Performance figures are usually valid for fenders that have been pre-conditioned by
compression to the rated values. Fenders should be specified to be pre-conditioned before
installation to avoid higher than expected reactions on the first maximum compression by a
vessel. The PIANC Guidelines discuss all these aspects of fender reaction forces.
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AS 4997—2005
B5 LOADS ASSOCIATED WITH BERTHING IMPACTS
Associated with berthing impact loads are longitudinal and vertical loads as the vessel
slides along the face of the fender and heaves or rolls under the reaction of the impact.
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Typical friction factors, vertical and horizontal, depend on fender face material, these can
vary from 20% for UHMWPE to 40% for timber. These lateral loads are calculated as the
maximum impact reaction load (on the fender system or structure), factored by the
coefficient of friction between the sliding surfaces.
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APPENDIX C
MOORING LOADS
Vessels berthed at structures will exert loads through fenders reactions and through
mooring lines, resulting from loads acting on the vessels. These loads include wind, current
and wave forces on the vessel, as well as manoeuvring forces when vessels are berthing and
departing berths.
Refer to Section 5 for calculation of wind actions on a vessel. In determining the wind load
from a vessel on any individual structure, recognition should be given to the variability of
stiffness of the lines connecting the vessel to the several mooring points. The design lateral
load on an individual mooring point should be 20% more than the evenly distributed
component of load established from the geometry of the moored vessel. Refer also to
OCIMF papers or BS 6349 for calculation of wind and current loads on moored vessels.
Mooring forces should consider loads applied +45° and −15° to the horizontal plane, in any
direction from the forward arc from the wharf.
Mooring forces from vessel manoeuvring loads should be considered. These forces are a
result of vessels using bollards to slow vessels down or to assist in turning vessels while
using rudders and propulsion systems. The design action used in the structural design
should be equal to the rated capacity of the bollard or mooring cleat, as determined by
Table C1. Where vessels may be exposed to conditions other than mild, the bollard capacity
should by 25%.
TABLE C1
MOORING FORCES FOR
SHELTERED CONDITIONS
Vessel displacement
(tonnes)
Bollard capacity
kN
50 to 200
100
1000 to 10 000
300
Up to 50
200 to 1000
10 000 to 20 000
20 000 to 50 000
50 000 to 100 000
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100 000 to 200 000
Above 200 000
 Standards Australia
50
200
500
800
1 000
1 500
2 000
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NOTES
AS 4997—2005
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AS 4997—2005
52
NOTES
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