As we mentioned in last months article, the changes brought about by Amendment 16 that affect NZBC B1/VM1, 5.0 Steel will have major impacts on the whole industry.
This amendment has introduced the new Standard AS/NZS 5131: 2016, Structural Steelwork - Fabrication and Erection. The amended clauses in B1/VM1, 5.0 Steel, now modify NZS 3404.1: 1997 Steel Structures Standard, by referencing and substituting parts from AS/NZS 5131.This provides new methods of compliance for:
- Documentation & submission requirements (some)
- Modifications to existing structures
- Architecturally exposed structural steel
- Inspections of welding and bolting
- Evaluation of slip factors
- Avoidance of lamellar tearing
These items have a major effect on what and how you would specify steelwork. However it goes deeper than that. AS/NZS 5131 approaches things differently and introduces a lot of new (or nearly new) concepts and terms. It also formalises Quality Control and Management more than we have been used to in the past.
There is only a short transition period for the introduction of AS/NZS 5131 from 3 April to 30 June 2018. This seems to mean that AS/NZS 5131 must be used from 1 July 2018 to comply with NZBC B1/VM1, 5.0 Steel.
The following items are just a few key examples of what AS/NZS 5131 introduces - there are many more terms and concepts to learn over time.
Construction Category (CC)
AS/NZS 5131 (particularly Appendix B4) introduces the fundamental concept of Construction Category (CC), which is linked to the Importance Level (1 to 4 from AS/NZS 1170.0) of the structure, as well as Service Category (SC1, SC2) and Fabrication Category (FC1, FC2). It also provides the minimum levels of workmanship including welding required to ensure the design assumptions are reflected in the finished fabrication and erection work.
HERA anticipates most structures will fall into Construction Category CC2 or CC3. CC1 only applies to secondary structures for which the consequence of failure would be low such as a farm shed. CC4 applies to the likes of railway bridges with fracture critical elements.
The principle differences between CC 2 and CC3 requirements are that the material, weld procedure, welder qualifications and traceability requirements are more onerous, as is the case for the weld quality management requirement.
Architecturally Exposed Structural Steelwork (AESS)
Although not a new concept Architecturally Exposed Structural Steelwork (AESS) is now formalised into AS/NZS 5131 (Section 10) and can now be specified with a degree of consistency. It allows the definition of higher appearance requirements than that of normal structural steelwork.
There are four defined categories AESS 1 to AESS 4 and a custom category AESS C. These are detailed in AS/NZS 5131 Section 10.2. Briefly the categories are as follows;
- AESS 1 involves basic enhancement
- AESS 2 viewed from over 6m
- AESS 3 viewed from less than 6m
- AESS 4 "showcase" work.
Each category adds increased quality requirements on fabrication and erection including preparation, welds, weld finish, bolts and tolerances with the emphasis on care and appearance.
Level of traceability
In recent years the conformance of steel products has become a topical issue, AS/NZS 5131 deals with this partly under the term traceability, requiring a documented record of materials and their use.
AS/NZS 5131 (clause 4.7, New Zealand requirements) requires levels of traceability as follows:
- CC1: No specific requirement
- CC2: Basic traceability
- CC3: Partial traceability
- CC4: Partial traceability.
These are optional any of them can be downgraded or upgraded in the specification based on the assessment of risk.
There are two Tolerance Classes, 1 & 2, in AS/NZS 5131 (refer Section 12 and Appendix F). Class 1 tolerances are the default requirement in AS/NZS 5131 and should be acceptable for most steelwork construction (particularly CC1, CC2 and usually CC3).
Class 2 tolerances are tighter and might be considered for higher specification work. AS/NZS 5131 suggests Class 2 should be considered for CC3 and CC4 structures or components (particularly major bridges and similar work). AS/NZS 5131 section 3.2 also lists different types of tolerances required for different purposes.
For AESS items tolerance levels may be more stringent than Class 1 or 2.
Finishes and Corrosion Protection
AS/NZS 5131 (refer section 9) also includes preparation of steel, galvanizing, protective coatings and painting.
Masterspec 1st June 2018
In last months article we said that Masterspec's aim was to update (major re-write) and align its main structural steelwork sections with the requirements of AS/NZS 5131. This has been done and the revised sections are:
3410 STRUCTURAL STEEL
- This section has had a name change from 3410 STRUCTURAL STEELWORK - BASIC, and has been made available to Standard users. This section is intended for simpler, smaller steel structures usually found in categories CC1 or CC2, although with modification it could be adapted for some CC3 structures. This new version will be available in the Masterspec systems Basic, Standard, Structural & Civil, Services, Landscapes and Interiors.
3411 STRUCTURAL STEELWORK
- Is intended for most types of steel structures ranging from categories CC1 to CC4 and specified by Engineers. This section may need modification for structures normally subject to fluctuating loads (e.g. bridges), space frames, or suspension structures and will need to be modified for CC5 projects. This new version will be available in the Masterspec systems Structural & Civil and Services (but deleted from Standard).
3419 STRUCTURAL STEEL QUALITY CONTROL
- This section is the companion version to 3411 STRUCTURAL STEELWORK and is intended to be used when extra quality control is warranted for large, complex or critical projects. It is to be used in conjunction with section 3411 STRUCTURAL STEELWORK. This new version is available only in the Masterspec system Structural & Civil.
Masterspec 1st July 2018
By 1 July the aim is to have all other steel related sections reviewed and updated where possible. We do not anticipate any significant issues, for instance our steel finishes sections use virtually the same Standards as AS/NZS 5131 so they already align.
Masterspec also intend to create a new section specifically for Architecturally Exposed Structural Steelwork (AESS) aligning with AS/NZS 5131. This is intended to be used in conjunction with the section 3410 STRUCTURAL STEEL or 3411 STRUCTURAL STEELWORK. Essentially, where a project has higher appearance requirements than standard structural steel quality the new (AESS) section could be used to specify additional requirements. Although the revised main sections already include a limited range of AESS options, this new section will provide more options and more guidance.
The new AESS section will be able to be used by either the Architect, Designer or Engineer to define additional AESS requirements while standard structural requirements are specified in 3410 STRUCTURAL STEEL or 3411 STRUCTURAL STEELWORK. For instance the Architect/Designer could specify project AESS work in the new section while the Engineer specifies the bulk of the project structural steel requirements in 3411 STRUCTURAL STEELWORK.
If you need to refer to AS/NZS 5131: 2016, Structural Steelwork - Fabrication and Erection it is available through Masterspec for those with Standards OnLine.
NZBC B1/VM1 for the new clauses.
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