AS/NZS 4766:2020 pdf free.Rotationally moulded buried, partially buried and non-buried storage tanks for water and chemicals.
3 General considerations for structural analysis and design of rotationally moulded tanks
3.1 Structural analysis
Tank design analysis and independent verification should be performed by qualified professional engineer(s) as defined in Clause 1.4.5.
3.2 Design
The design of a tank, its fittings and accessories should consider long term fitness for purpose including service environment and decrease in physical properties of the material due to environmental effects.
Separation of the roof (lid) from the body of the tank after moulding shall be permitted for transport purposes, and, for buried tanks, single rotationally moulded parts such as the tank and riser may be welded together, provided that —
(a) the design considers this circumstance;
(b) the structural integrity of the tank is not adversely affected after the roof has been refitted or parts welded together by the manufacturer or its nominated representative in the manner prescribed by the design; and
(c) the prevention of insect and/or vermin ingress is maintained.
The structural design life of a tank shall be 20 years.
NOTE 1 Tanks should be decommissioned at the end of their service life.
NOTE 2 The service life of a tank may be less than the structural design life.
A tank shall have provision for overflow of contents where required.
The design shall ensure secure storage of contents and prevent inflow or infiltration of surface water
and soil water.
4 Structural analysis and design of non-buried tanks
4.1 General
This Section specifies the methods required to undertake limit state design of non-buried storage tanks manufactured from polymer.
All tanks in terms of their structural analysis shall be assessed using the finite element analysis (FEA) method. All analysis conducted shall be undertaken using a geometric nonlinear analysis solver (GNA).
Linear geometric analysis shall not be permitted unless it can be demonstrated that there is minimal difference between the displacement and stress results or that the results produced are conservative when using the linear geometric solver.
Given that FEA results are used to establish the structural integrity of the tank, the results shall be reported in such a way as to facilitate the verification of the tanks. Such a report shall include, but not be limited to, the following:
(a) A description of the model and the assumptions used.
(b) The software package and version used.
(c) The element topology adopted.
(d) The loads applied.
(e) The boundary conditions assumed.
(1) Description of failure criteria and limits that have been utilized.
(g) Plot(s) of the deflected shape(s) of the structure under all relevant loading conditions.
(h) von Mises stress plot(s) of the structure under all relevant loading conditions.
(i) The minimum material thicknesses derived from the analysis and design undertaken including provision of images/plots. etc. with dimensions to convey the design intent.
4.2 Design
The design of a non-buried storage tank shall be based on the following:
(a) Where the tank is supported by a reinforced concrete foundation slab designed in accordance with AS 3600 or NZS 3101.1 overlying stable foundation material, the tank can be designed on that basis.
(b) Where the tank is not supported by a reinforced concrete foundation slab designed in accordance with AS 3600 or NZS 3101.1 overlying stable foundation materials, then the design shall take into account factors such as (but not limited to) variable foundation conditions, subgrade creep, differential settlement and the like in the design.
(c) The tank shall be manufactured using a continuous rotational moulding technique as one discrete component. Separation of the roof (lid) from the body of the tank, after moulding, shall be permitted in the circumstances specified in Clause 3.2.
(d) Live loads shall not be placed on the roofs of the tanks unless the tank is designed for such loads. This includes stacked materials and/or human access. This limitation shall be clearly and permanently marked on the outside face of the tank and in relevant documentation. If it is found that roof loading is required, then additional loads shall be introduced in accordance with AS/NZS 1170.1 with additional load combinations in accordance with AS/NZS 1170.0.
(e) The basis of the tank design is for the application of long term loads resulting from hydrostatic pressure from the stored liquid as well as transient environmental loads such as wind loads (refer to AS/NZS 1170.2), snow loads (refer to AS/NZS 1170.3) and earthquake loads. Earthquake design loads in New Zealand shall be determined using ASCE/SEI 7-16 and NZS 1170.5. Earthquake design loads in Australia shall be determined using ASCE/SEI 7-16 and AS 1170.4.AS/NZS 4766 pdf download.