AS4997-2005

AS 49972005

Australian Standard

Guidelines for the design of maritime structures

AS

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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

Keeping Standards up-to-date

Standards are living documents which reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued. Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments which may have been published since the Standard was purchased.

Detailed information about Standards can be found by visiting the Standards Web Shop at www.standards.com.au and looking up the relevant Standard in the on-line catalogue.

Alternatively, the printed Catalogue provides information current at 1 January each year, and the monthly magazine, The Global Standard, has a full listing of revisions and amendments published each month.

Australian StandardsTM and other products and services developed by Standards Australia are published and distributed under contract by SAI Global, which operates the Standards Web Shop.

We also welcome suggestions for improvement in our Standards, and especially encourage readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at [email protected], or write to the Chief Executive, Standards Australia, GPO Box 476, Sydney, NSW 2001.

This Standard was issued in draft form for comment as DR 02536.

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AS 49972005

Australian Standard


First published as AS 49972005.

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

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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.

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.

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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

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

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APPENDICES

A CONTAINER WHARF DECK LOADINGS............................................................. 43

B BERTHING ENERGIES AND LOADS.................................................................... 46

C MOORING LOADS .................................................................................................. 50

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www.standards.com.au Standards Australia

STANDARDS AUSTRALIA

Australian Standard


S E C T I O N 1 S C O P E A N D G E N E R A 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;

(c) berthing dolphins;

(d) floating berths;

(e) seawalls;

(f) breakwater structures, excluding rubble mound and floating types;

(g) boat ramps;

(h) laterally restrained floating structures; and

(i) building substructures over water.

This Standard is not intended to cover the design of

(A) pipelines;

(B) marinas (see AS 3962);

(C) offshore oil and gas structures;

(D) dredging and reclamation;

(E) coastal engineering structures such as rock armoured walls, groynes, etc;

(F) geometrical design of port and harbour infrastructure;

(G) 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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Standards Australia www.standards.com.au

1.2 REFERENCED AND RELATED DOCUMENTS

1.2.1 Referenced documents

The following documents are referenced in this Standard:

AS

1012 Methods of testing concrete

1012.13 Method 13: Determination of the drying shrinkage of concrete for samples

prepared in the field or in the laboratory.

1170 Minimum design loads on structures

1170.4 Part 4: Earthquake design loads on structures

1604 TimberPreservative-treatedSawn and round

1657 Fixed platforms, walkways, stairways and laddersDesign, construction and

installation

3600 Concrete structures

3962 Guidelines for design of marinas

3972 Portland and blended cement

4100 Steel structures

5100 Bridge design

5100.2 Part 2: Design loads

5604 TimberNatural durability ratings

AS/NZS

1170 Structural design actions

1170.0 General principles

1170.1 Part 1: Permanent, imposed and other actions

1170.2 Part 2: Wind actions

1554 Structural steel welding

1554.6 Part 6: Welding stainless steels for structural purposes

2312 Guide to the protection of iron and steel against exterior atmospheric corrosion

2832 Cathodic protection of metals (all parts)

4671 Steel reinforcing materials

4673 Cold formed stainless steel structures

4680 Hot-dip galvanized (zinc) coatings on fabricated ferrous articles

BS

6349 Maritime structures (all parts)

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 systems2002

1.2.2 Related documents

AS/NZS 1664 Aluminium structures

AS 5100 Bridge design (all parts)

SA HB 84 Guide to Concrete Repair and Protection

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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 m3 (100 ft3)).

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

The following symbols are used in this Standard.

db = reinforcing bar diameter

Ed = design action effect

Ed,dsb = design action effects destabilizing structure

Ed,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)

fc = characteristic compressive strength of concrete, in Megapascals (MPa)

fs = steel reinforcing stress, in Megapascals

Fb = berthing impact loads

Fb,u = berthing impact actions under abnormal conditions

FD = action in the direction of wind, in kilonewtons (kN)

Fe = earth pressure loads

Fenv = combined environmental loads

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Fgw = ground water loads

Flat = minimum lateral load (see Clause 5.3.1)

Flp = liquid pressure load

Fm = mooring loads

Fs = stream flow loads, including debris loads

Fwave.S = wave loads under serviceability conditions (1 in 1 year)

Fwave.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).

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

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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

Waves formed under the influence of local generating winds, usually called seas.

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S E C T I O N 2 S I T E I N V E S T I G A T I O N A N D

P L A N N I N G

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

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. Acce

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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.

Changes in water levels due to global warming should be considered (see Clause 4.6).

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S E C T I O N 3 D I M E N S I O N A L C R I T 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

(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);

(c) allowing safe navigation access to the berth to and from the waterway;

(d) minimum intrusion into the navigable waterway;

(e) ease of cargo handling;

(f) safe personnel and vehicle access;

(g) disabled access (where applicable); and

(h) 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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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

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 levelbottom 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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S E C T I O N 4 D E S I G N R E Q U I R E M E 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) Determine the appropriate loads and other actions in accordance with Section 5.

(b) Combine and factor the loads in accordance with Clause 5.12 to determine the design

loads for strength.

(c) Determine the design action effects for the structure and its components for each load

case.

(d) Determine the design strength in accordance with the requirements of the appropriate

Australian Standard(s).

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

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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.

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 Sea level rise

m

25 years 0.1

50 years 0.2

100 years 0.4

NOTE: Based on the mid-scenario from the International Panel on Climate

Control (2001). These values are updated by IPCC from time to time.

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S E C T I O N 5 D E S I G N A C T I O N S

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).

(c) Wind actions (see Clause 5.4).

(d) Current and debris actions.

(e) Hydrostatic actions.

(f) Wave actions.

(g) Thermal, shrinkage and other movement induced actions.

(h) Construction and maintenance actions.

(i) Lateral earth actions on waterfront structures (seawalls).

(j) Propeller wash.

(k) 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, quick-

release 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

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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Any freestanding maritime structure (jetty, dolphin, etc.) should be capable of withstanding

a minimum horizontal load (Flat), 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)

Concentrated

load

(area, mm)

s = spacing, m

(see Note 2)

Anticipated load conditions Application

5 5 kPa 20 kN

(150 150)

s = 1.8

Pedestrian crowd load.

Light motor vehicles up to 3 t

tare

Private and public boardwalks.

Passenger jetties

10 10 kPa 45 kN

(300 150)

s = 1.8

Small emergency vehicles Public boardwalks and

promenades with access for

emergency vehicle and service

vehicles

15 15 kPa 200 kN

(400 700)

s = 4.0

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

25 25 kPa 500 kN

(700 700)

s = 5.0

Bridge design code (SM1600

heavy platform loading)

Mobile crane 50 t SWL

Secondary port general cargo

wharf

40 40 kPa 1000 kN

(1000 1000)

s = 7.0

Container forklift and other

machinery for 40 ft containers


General cargo wharf or

container wharf (For containers

stacked 2 high ship-side, see

Note 3 & Appendix A)

50 50 kPa 1500 kN

(1000 1000)

s = 8.0

Container forklift, reach

stacker and other machinery for

largest containers


Primary port, international

gateway container terminal

(For containers stacked 2 high

ship-side, see Note 3 &

Appendix A)

60 60 kPa 2000 kN

(1000 1000)

s = 9.0

Mobile crane to 200 t SWL Heavy-duty maintenance wharf

NOTES:

1 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.

2 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.

3 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

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The energy of berthing vessels may be absorbed in one or a combination of the following

ways:

(a) In deflection of the vessel hull (usually only for small vessels

AS 49972005 20


(d) 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 1.252 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) normal berthing energy for serviceability condition up to the rated capacity of the

fender unit; and

(ii) 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) the rated fender reaction load, with appropriate Limit State load factors applied; and /

or

(B) the abnormal berthing case reaction (maximum fender reaction), considered as an

ultimate Limit State load condition.

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.

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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 30second 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:

2

z0006.0 Vq = . . . 5.4.2(1)

where

qz = wind pressure, in kilopascals

V = design wind speed, in metres per second

= Vu for ultimate limit state

= Vs for serviceability limit state

Wind loads on a vessel or structure should be calculated from the following equation:

zDDAqCwF = . . . 5.4.2(2)

where

FD = load in direction of wind, in kilonewtons

CwD = coefficient of wind drag (see Table 5.2)

A = projected area of element, in square metres

qz = wind pressure, determined from Equation 5.4.2(1), in kilopascals

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TABLE 5.2

TYPICAL WIND DRAG COEFFICIENTS

Vessel or structure Coefficient of drag (CwD)

Vessels (up to 10 000 t)

Tubular piles

Rectangular members

1.1 to 1.2

1.2

2.0

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:

32

D2

1

s10

= AvCsF . . . 5.5.2

where

Fs = current load, in kilonewtons

CsD = stream flow drag coefficient (see Table 5.3)

v = current velocity, in metres per second

A = projected area of element, in square metres

=

=

1026 kg/m3 for sea water

1000 kg/m3 for freshwater

TABLE 5.3

STREAM FLOW DRAG COEFFICIENTS

Structure Drag coefficient

(CsD)

Circular pilesSmooth 0.70

Circular pilesRough 1.04

Square piles or beams with sharp corners 2.20

Square piles or beams with corners rounded 0.701.0

PilesHeavy marine growth 1.51.8

Debris mat 2.001

Vessels bow to current 0.30

Vessels beam to current 0.40

NOTES:

1 For more accurate assessment of the drag coefficient for the debris mat

refer to AS 5100.2.

2 For vessels in excess of 10 000 t refer to BS 6349 for stream drag loads.

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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) 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.

(b) External water level is highest of

(i) maximum design water level plus half-wave height or more, as appropriate; or

(ii) 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) 1/3 of the spring tidal range; or

(b) 500 mm.

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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) 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);

(b) 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 (Ts). Wave classifications are swell-waves, wind-waves or vessel-

wash.

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

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.

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TABLE 5.4

ANNUAL PROBABILITY OF EXCEEDANCE OF DESIGN WAVE EVENTS

Design working life (years)

Function

category Category description

5 or less

(temporary

works)

25

(small craft

facilities)

50

(normal

maritime

structures)

100 or more

(special

structures/

residential

developments)

1

Structures presenting a low

degree of hazard to life or

property

1/20 1/50 1/200 1/500

2 Normal structures 1/50 1/200 1/500 1/1000

3 High property value or high

risk to people 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 H1, 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: H1 should be

determined by applying a factor to the significant wave height for the design storm, as

follows:

H1 = 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 waterstropical Australian coastlines) to 2.0 (e.g., high

energy waterssouthern 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.

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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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 pressure-

relief 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.

Care should be exercised in defining combinations of actions to ensure the proper design

action effect for actions that

(a) do not act simultaneously;

(b) act simultaneously, but not superimposed; or

(c) 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 (Ed,stb):

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(b) For combinations that produce net destabilising effects (Ed,dst):

(i) Ed,dst = [1.2G, Su, Fenv] permanent action and actions given in

Clause 5.12.4 and/or Clause 5.12.5

(ii) Ed,dst = [1.2G, Q, Su, Fenv] permanent and imposed actions, and actions

given in Clause 5.12.4 and/or Clause 5.12.5

5.12.3 Strength

The basic combinations used in checking strength should be as detailed in AS/NZS 1170.0,

plus, as appropriate, the following:

(a) Ed = [1.2G, Su, Fenv] permanent actions and actions given in Clause 5.12.4

and/or Clause 5.12.5

(b) Ed = [1.2G, 0.6Q, Su, Fenv] permanent and imposed actions and actions given in

Clause 5.12.4 and/or Clause 5.12.5

(c) Ed = [0.9G, Su, Fenv] 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) Su = 1.5Fb for normal berthing loads

(b) Su = 1.0Fb.u for abnormal berthing loads

(c) Su = 1.5Fm for mooring loads

(d) Su = 1.5Flat 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 = 1.2Flp for static water pressure that is measured to the top of

the structure (see Clause 5.8.1(b))

Su = 1.5Flp where the design water level could be exceeded

(f) Su = 1.5Fe for earth pressures

(g) Su = 1.5Fgw for ground water

(h) Su = 1.5Fs 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) Fenv = Wu ultimate wind load

(b) Fenv = Fwave.u ultimate wave load

(c) Fenv = Wu ,0.7Fwave.u, 1.5Fs ultimate wind and wave

(d) Fenv = 0.7Wu, Fwave.u ultimate wave and wind

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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

(b) Q

(c) Es

(d) Fb

(e) Fm

(f) Flp

(g) Fs

(h) Fe

(i) Fgw

(j) Ws

(k) Fwave.s

(l) Serviceability values of other actions, as appropriate.

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

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 (Eu) 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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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.

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.

(b) Soil conditions The soil conditions in the surface layers generally define the sites

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.

(c) 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).

(d) Structural importance factors Many significant maritime structures perform a post-

disaster 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.

(e) 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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S E C T I O N 6 D U R A B 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 structures 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 owners 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.

TABLE 6.1

DESIGN LIFE OF STRUCTURES

Facility

category Type of facility

Design life

(years)

1 Temporary works 5 or less

2 Small craft facility 25

3 Normal commercial structure 50

4 Special structure/residential 100

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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) Concrete deterioration is usually a result of corrosion of reinforcing steel due to

chloride ingress.

(b) 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.

(c) 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.

(iii) Improved performance concrete.

(iv) Improved performance reinforcements.

(v) Closely controlled construction methods.

(d) Repairs may require the removal and replacement of deteriorated concrete and

reinforcement. Considerations include the ability to

(i) access the member with working scaffold for inspection and repair;

(ii) remove and contain waste materials during repair works; and

(iii) apply and maintain an adequate curing regime to the repair works.

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) Steel deterioration (corrosion) results from the breakdown of the protective coating or

other protective system.

(b) Paint coatings provide a service life of approximately 20 years, before

repair/recoating is necessary.

(c) 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) access the member with working scaffold for inspection and repair;

(ii) remove and contain waste materials during repair works; and

(iii) prepare and apply protective coatings in situ to achieve required standard. Acc

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(d) 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) 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.

(b) 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) Timber piles exposed to marine organisms ......................................510 years.

(ii) Timber piles not exposed to marine organisms ..............................1030 years.

(iii) Timber decking exposed to weathering..........................................1025 years.

(c) The deterioration of timber is usually by mechanical degradation, rot or attack by

living organisms (decay fungi, termites, marine borers).

(d) 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

structures life.

(e) A maintenance strategy may allow for regular and frequent replacement of timber

members throughout the design life, as individual components deteriorate.

Considerations include

(i) the availability of skilled carpenters, able to maintain the works over the

structures design life;

(ii) 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.

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) regular inspections;

(b) a program of routine minor maintenance; and

(c) a program of major maintenance.

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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

Structural concrete should comply with the design and performance requirements of

AS 3600, together with any applicable recommendations made by these guidelines.

Engineering judgement will be required in the use of AS 3600, where stainless steel

reinforcement is adopted, as AS/NZS 4671 does not encompass this material type.

6.3.3 Structural concrete

The following is recommended for structural concrete in a maritime structure:

(a) 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).

(b) A minimum characteristic compressive strength (fc) of 40 MPa.

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(c) General purpose Portland cement alone as the binder, or a blended cement in

accordance with AS 3972.

NOTES:

1 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.

2 When using blended cements particular attention needs to be paid to placement, finishing

and curing, to achieve the required strength and performance of concrete.

(d) Cementitious content (Portland and blended cements) should be not less than

400 kg/m3.

(e) For exposure classes C1 and C2, a drying shrinkage at 56 days not greater than

600 106

mm/mm, determined in accordance with AS 1012.13.

(f) 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.

(g) Concrete should be placed in watertight forms, thoroughly compacted and protected

from excessive temperature and wind evaporation.

(h) 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

AS4997-2005

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