Useful information - engineering guidelines for maritime structures
The design of maritime structures proposed on the Roads and Maritime Services land shall take into account, as appropriate, stability, strength, serviceability, durability and redundancy as set out in more detail below. The design shall also comply with appropriate Australian Standards.
In addition, it is important to note that prior to preparing any plans for a new marine structure, an investigation as to whether the structure is permissible should be undertaken. This will include reviewing clause 18 of the Sydney Regional Environmental Plan (Sydney Harbour Catchment) 2005 (SREP 2005) which sets out, in relation to each zone under SREP 2005:
- Development that may be carried out without development consent
- Development that may be carried out only with development consent
- The development that is prohibited.
Design life is the period of time for which a structure or an element of the structure remains fit for use for its intended purpose with appropriate maintenance. The design life of maritime structures will depend on the type of facility, the intended function and the applicant’s requirements.
Design life should be based on consideration of capital and maintenance expenditure. The designer, in consultation with the applicant, 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 elements of the structure. Such elements should have a design life (with no maintenance) equal to the design life of the structure.
At the end of its 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.
The effects of fatigue from wind, wave and current action under normal conditions shall also be considered.
Hydrographic surveys shall be undertaken in accordance with the Roads and Maritime Services Guidance Note GN 01 – Provision of Hydrographic and Geotechnical Data.
Materials for maritime structures shall be chosen so that the structures are capable of withstanding this environment and achieving the required design life in conjunction with an appropriate preventative maintenance programme.
Timber has many applications in maritime structures, particularly in small craft facilities such as jetties, ramps, skids and steps due to its ease of workability.
Timber can be used on its own to construct complete structures (including piles, headstocks, bearers, joists and decking) or in conjunction with other materials to provide economical, and durable structures.
The deterioration of timber is usually by rot or attack by living organisms. Timber durability is dependant predominantly upon the species chosen in the design.
Further advice regarding the use of timber is given in Standard Australia’s DR 02536 - Guidelines for Design of Maritime Structures.
It is noted the life of a timber element in a structure is governed by the environment in which it is constructed and the inspection and maintenance regime for the structure.
During the design life of a maritime structure, maintenance will need to be carried out in order to ensure that this design life is achieved.
Costs associated with such maintenance can be greatly reduced by adopting an appropriate preventative maintenance programme.
Essential features of such a programme include the following:
- Regular inspections;
- Timely repairs;
- Timely renewal of protection systems;
- Timely replacement of worn-out components; and
- Keeping records of inspections carried out and maintenance performed.
Inspections should be carried out by suitably qualified persons experienced in the design and construction of maritime structures.
Typical inspections for various structures that should be performed are given below together with suggested inspection intervals. These inspections are not an exhaustive list and will vary from structure to structure. More frequent inspections may be required where structures are located in extreme environments or subject to severe loads.
Pile inspection: The tidal zone of a pile should be inspected visually from the surface at low tide annually. Signs of excessive wear or evidence of marine borer attack or corrosion should be noted and remedial measures taken if necessary. Timber pile tops should be inspected for deterioration due to decay or dry rot annually. Inspections should be carried out at intervals of 3 years or after major storms or other severe events.
Pontoon inspection: Pontoons and their mooring systems should be visually inspected above water at 6 monthly intervals. At intervals of 3 years, a detailed inspection should be carried out. This inspection should include an underwater investigation of marine fouling and pontoon connections not normally visible above water.
Timber structure inspections: Timber components above water should be inspected annually for decay and infestation. Major structures should have a detailed inspection at 5 yearly intervals.
Steel structure inspections: Steel fittings and components should be inspected for wear and corrosion on an annual basis. Any damage to protective coatings should be noted for repair. Distortions due to overstress should be noted and remedial action taken. Attention should be paid to wear and corrosion in pile guide systems and pontoon connection hardware, where visible.
Major structures should have a detailed inspection at 5 yearly intervals.
Such inspections should consider corrosion, deterioration of protective coatings together with signs of fatigue and wear.
It is recommended that in stability calculations for concrete pontoons allowance is made for marine growth with a minimum buoyant weight on all submerged surfaces of 15 kg/m2.
Fibreglass pontoons are generally not affected by marine growth.
Design of Wharves, jetties and Boardwalks should consider:
- Wharves, jetties and boardwalks shall generally be designed in accordance with Standard Australia’s - DR 02536 - Guidelines for Design of Maritime Structures.
- Wharves, jetties and boardwalks shall be designed so as not to impose lateral loads on existing seawalls.
- Wharves, jetties and boardwalks providing for disabled access shall be designed in accordance with AS1428 and the Commonwealth Government’s - Disability Standards for Accessible Public Transport Guidelines 2001.
- Wharves, jetties and boardwalks shall have a minimum clear width of 1.8m.
Fenders should be designed to accord with PIANC document entitled “Guidelines for the Design of Fender Systems”.
To comply with the Work Health and Safety Act 2011, the risks identified and others are usually considered in the design and construction by designers and contractors.
Sea level rise
Structures shall be designed to allow for future sea level rise caused by global warming. AS4997 notes a sea level rise that must be complied with, however the recommended NSW benchmark for sea level rises suggests a +400mm to 2050 and +900 to 2100. It is suggested that these levels should be allowed for when designing domestic structures.
Geotechnical investigations are required in order to determine the properties and constituents of the seabed and underlying rock strata and the depths of the various layers comprising the seabed.
Pontoon decks shall be designed to have a positive fixing to the flotation unit. Such fixings shall be capable of supporting the deck in the event the pontoon turns over.
Although the relevant local council will be the consent authority for seawalls, if repairs or works to a seawall are ancillary to a water based structure then, where applicable, seawalls shall be designed taking into account the recommendations made in the Roads and Maritime Services – Guidelines for Waterside Works Subject to Rivercat and Harbourcat Wash.
Allowance shall be made in the design for the loss of at least 600 mm of material from the seaward face of the seawall unless the seawall is founded on rock.
Davits and winches
Proprietary davits and winches are recommended to be used. In these instances, applicants should ensure that the manufacturer is prepared to supply a certificate indicating that the davit or winch has been designed in accordance with the above requirements.
Stormwater drains shall generally be designed in accordance with the Roads and Maritime Services - Guidance Note GN 100 – Stormwater Discharge.
A minimum horizontal clearance of 600 mm over a vertically projected height of 2 m shall be provided each side of the slipway between the vessel cradle and any other object during slipway operations.
Vessel cradle track wheels shall be guarded to prevent persons becoming trapped between the leading face of the track wheel and the slipway rail.
Winch controls shall be located so that the vessel cradle remains in full view of the operator during slipway operations.
Skids shall be designed to provide a safe foothold. This can be achieved by means of spaced decking or the use of cleats. Where cleats are used they shall comply with AS1657 Clause 3.1.2.
Lifebuoys shall be provided on all public facilities.
Lifebuoys shall be located in order to cover the water area a distance of 10 m measured in plan around the perimeter of the public facility.
Lifebuoys shall generally comply with the Australian Maritime Safety Authority’s Marine Orders Part 25 Appendix 1.1.
Lifebuoys shall be fitted with a buoyant lifeline which shall comply with the Australian Maritime Safety Authority’s Marine Orders Part 25 Appendix 1.4.
Demolition (other than demolition of heritage items) may be carried out without development consent. However, although development consent is not required, it is likely that a construction licence and owner’s consent, for example, will need to be obtained from Roads and Maritime Services prior to demolition. Prior to such approvals being issued (and prior to demolition), an environmental assessment must be undertaken and endorsed by Roads and Maritime Services. Refer to Development permissible without consent for further information in this regard.