Revised Standard for storage of liquids published

5 August 2009

Design of concrete structures for the storage of liquids – revised Standard published

Standards New Zealand has published a revised Standard, Design of concrete structures for the storage of liquids, NZS 3106:2009, which supersedes NZS 3106:1986.  The Standard provides design requirements and guidance including design loads and seismic design criteria.

NZS 3106 is a technical document used by engineers to design concrete tank structures for facilities such as water storage reservoirs and wastewater treatment plants.

The Standard was revised in line with current practice and new technology, and to align with the loadings requirements given in the AS/NZS 1170 series of Standards (especially NZS 1170.5 Structural design actions – Earthquake actions). 

The revised Standard:

·        provides a basis for designing concrete structures for the storage of liquids so that they will require only limited periodic maintenance to remain serviceable for their design life, and will not allow an uncontrolled, rapid loss of the liquid contents in extreme events such as a major earthquake

·        includes additional useful design and analysis guidelines and data to assist the design process

·        contains a large amount of commentary, which provides examples and applications, making the clauses clearer

·        supports public safety through designs that are safe and serviceable.

The Department of Building and Housing funded the revision of NZS 3106.  The revision is based on the review of international Standards.  The development committee reviewed a number of Standards and other publications to identify ‘best practice’ and included provisions from these where appropriate. 

Significant changes

Some of the most significant changes are as follows.

·        In addition to the serviceability limit state loads, this Standard now requires users to also take into account the strength considerations required for ultimate limit state loads.  This makes NZS 3106:2009 consistent with the design procedures used for other structures.

·        A new system to classify the liquid tightness of a structure has been adopted from
BS EN 1992-3:2006 Eurocode 2 – Design of concrete structures – Liquid retaining and containing structures.  Designers can now decide what degree (if any) of leakage is acceptable from concrete cracks.  They may then choose the appropriate crack control provisions to achieve liquid tightness.

·        A new Appendix B provides procedures on how to calculate crack widths in reinforced concrete. These cracks may be caused by early-age thermal strains or from imposed loads and actions – given the critical importance of crack control in liquid retaining structures, the new procedures have been based on the worst case ‘fully restrained’ condition.

·        The earthquake provisions have been reviewed in line with the New Zealand Society for Earthquake Engineering Study Group on the Seismic Design of Storage Tanks 2009 draft recommendations.  Seismic force coefficients are based on NZS 1170.5, with allowance made for increased damping from soil-structure interaction, which is particularly significant for liquid storage tanks.

Inclusions and exclusions

Inclusions

This Standard applies to containment structures for use with water of normal temperature (approximately 17 ˚C) and pH (approximately 5.5 to 8.5) commonly found in drinking water supplies (fresh water) sewage, wastewater, and seawater.

·        The use of this Standard in the design for the following types of containment structures requires special consideration of the effects on the structure of:

-        highly aggressive waters (for example, corrosive)

-        high temperature waters (> 35 ˚C)

-        chemicals

-        oils (mineral and non-mineral) and fuels

-        slurries.

·        Tanks used for the storage of hazardous substances are required to comply with a Standard specified in Schedule 8, Clause 8 of the Hazardous Substances (Dangerous Goods and Scheduled Toxic Substances) Transfer Notice 2004 (as amended) or a code of practice approved under this clause.

Exclusions

This Standard does not apply to the design of:

·        dams

·        hydraulic tunnels

·        precast concrete pipes (pressure or non-pressure)

·        fibre-impregnated concrete that does not comply with the design requirements and procedures of NZS 3101

·        bins or silos for storage of dry bulk materials

·        pressure vessels.

The committee included representatives of the following nominating organisations: Cement and Concrete Association of New Zealand, Department of Building and Housing, GNS Science, Institute of Professional Engineers New Zealand, New Zealand Concrete Association, and New Zealand Society for Earthquake Engineering.

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