Proposed Material Requirements for Category 3 Members in Seismic-Resisting Systems
The Steel Structures Standard material provisions for seismic applications are intended to ensure that the grade of steel chosen can meet the expected inelastic demand in both seismic and non-seismic applications (SNZ, 1997a). This includes suppressing brittle failure. The current NZS 3404 1997/2001/2007 material requirements are identical for category 1, 2, and 3 members, even though the inelastic seismic demand from category 3 members is much lower than that from category 1 and 2 members. This lack of differentiation of material requirements has created problems sourcing compliant steels for seismic-resisting systems.
The New Zealand Structural Steelwork Specification in Compliance with AS/NZS 5131: Key Elements to Managing the Compliance of Fabricated Structural Steelwork
The Structural Steelwork – Fabrication and Erection standard AS/NZS 5131 (SA/SNZ, 2016c), is cited as an acceptable standard for demonstrating compliance with the Building Code. This standard published in 2016, was developed in response to the increased compliance risk posed by global sourcing of fabricated structural steelwork. AS/NZS 5131 defines what competent structural steel contractors must do to control and demonstrate the quality of their work.
Practice Note on the Sourcing of Compliant High Strength Structural Bolts
The New Zealand Steel Structures Standard states that high strength structural bolts shall be supplied to AS/NZS 1252. This standard underwent a major revision and was published on 23rd December 2016. The major technical changes incorporated in the new edition relate to updated testing and conformity requirements, the inclusion of the nominated European standard EN 14399-3 8.8 HR bolt as a “Deemed to satisfy” alternative and an additional European EN 14399-3 high tensile grade 10.9 HR.
A significant change to AS/NZS 1252 has been the creation of a new Part 2, title “Verification testing for bolt assemblies’. This represents a restricted form of third party conformity assessment, to provide confidence in products manufactured to AS/NZS 1252.1.
Practice Note on the Sourcing of Threaded Rod Used for Foundation Bolts
Threaded bars are commonly used in the structural engineering industry. It is used as replacement for long bolts as well as for concrete anchors and foundation bolts. This product is not covered under New Zealand Standard AS/NZS 1252, ‘High strength steel bolts with associated nuts and washers for structural engineering’. This article is intended to provide information on the appropriate standard to specify for threaded rods used for foundation bolts and the recommended verification testing.
Basis for and Implications of Key Changes to 2016 Structural Steel Product Standards
In April 2016, the suite of AS/NZS structural steel product standards were republished (AS/NZS 1163, 3678, 3679.1-2) (SA/NZS, 2016). This paper provides a summary of the key changes, the basis for these changes and interim recommendations until full supply of steel products to the latest standard is available.
Checklist for Imported Structural Steelwork
The globalisation of the structural steel supply chain has sparked concern over the quality of fabricated steelwork in New Zealand building projects when sourced from low-cost countries. Demonstrating compliance of imported material with the requirements of the New Zealand structural steel and welding standards can be very challenging: there are cultural, geographical and language barriers, and often a lack of independent quality assurance associated with offshore fabricator workshops. Guidance for ensuring compliance of structural steelwork is provided in the following article:
- Fussell, A., Cowie, K., Hicks, S., Karpenko, M., Ensuring Compliance of Structural Steelwork – Regardless of Origin, Steel Advisor QLT1001, Steel Construction New Zealand, 2016 (This article was first published in SESOC Journal Volume 29 No 1 April 2016)
In response to requests from Building Control Authorities a checklist has been developed as a guide to assess compliance of imported fabricated steelwork. The checklist is to be read in conjunction with the above referenced article. The checklist provides normative references to the corresponding sections of the NZS, AS/NZS standards and defines documentation required to claim compliance. Depending on the outcome of the assessment, the fabricated steelwork may be subject to additional NDT and (destructive) testing.
Ensuring Compliance of Structural Steelwork – Regardless of Origin
This article was first published in SESOC Journal Volume 29 No 1 April 2016.
The globalisation of the structural steel supply chain has sparked concern over the quality of fabricated steelwork in New Zealand building projects when sourced from low-cost countries. Demonstrating compliance of imported material with the requirements of the New Zealand structural steel and welding standards can be very challenging: there are cultural, geographical and language barriers, and often a lack of independent quality assurance associated with offshore fabricator workshops.
This situation has placed greater onus on Construction Reviewers (typically Professional Engineers), as the technical expert relied upon by Building Control Authorities and clients to ensure steelwork for New Zealand building and infrastructure projects meets the requirements of the New Zealand Building Code.
The aim of this paper is help Construction Reviewers better understand their role and that of the fabrication company in achieving this end. It will also discuss international and local quality initiatives that will make the Construction Reviewer’s role simpler and lower the risk of non-compliance to them. This risk is very real, in Australia there have been examples of Professional Engineers being sued for damages to cover the cost of expensive remedial work associated with non-compliant fabricated products from low cost economies (SCNZ 2014).
Welding to AS/NZS 1554.1 of Boron Containing Steel
Recent reports indicate that some imported steel may show elevated levels of boron; traditionally steel in Australia and New Zealand has been made without boron additions. The welding requirements of AS/NZS 1554 have been established without considering the effect of boron as an alloying element. This article discusses steps that should be undertaken by the fabricator to ensure the integrity of the steel fabrication work when welding structural steel with elevated boron levels.
Changes to specifying inorganic zinc silicates to AS/NZS 2312
Australian/ New Zealand Standard AS/NZS 2312 Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings provides guidelines for selection and specification of coating systems for corrosion protection of structural steelwork. The designer can choose from a selection of systems based on exposed service life to first maintenance for various environments. AS/NZS 2312 has recently undergone a major update. A short summary of the major changes to AS/NZS 2312 and use of the standard is provided in Steel Advisor GTG1008. In addition changes have been made to the designation system for Inorganic Zinc Silicates which will be highlighted in this article.
AS/NZS 5131 – Why Another Fabrication and Erection Standard?
In New Zealand we have the undesirable situation of an aged Structural Steel standard by international standards and we also have two sets of standards provisions that address the minimum requirements for the fabrication and erection of structural steelwork (NZS 3404:1997 – including amendments 1&2 and NZS 3404.1:2009) This is compounded by the fact that that the most recent provisions are not cited as a verification method document.
The introduction of a new joint Australia/ New Zealand structural steelwork fabrication and erection standard on the face of it appears to be adding to the problem. In this paper the rationale for developing this new standard is discussed along with an outline of its content and a vision of how this standard might fit within a suite of AS/NZS standards covering the design, fabrication and erection of composite and non- composite structures in New Zealand
Paint Coating Selection and Specification: Changes to AS/NZS 2312
Australian/ New Zealand Standard AS/NZS 2312 Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings provides guidelines for selection and specification of coating systems for corrosion protection of structural steelwork. The designer can choose from a selection of systems based on exposed service life to first maintenance for various environments. AS/NZS 2312 has recently undergone a major update. Galvanizing and metal spraying have now become separate standards. A short summary of the major changes to AS/NZS 2312 and use of the standard is provided.
Specifying Impact Toughness of Steel Plates for End Plate Connections in Seismic Lateral Resisting Frames
Structures designed to the Steel Structures Standard, NZS 3404, are required to be able to resist collapse under a maximum considered earthquake as directed by the Loadings Standard, NZS 1170.5. Brittle systems are not permitted. The nature of steel material is that it always contains some imperfections, albeit of very small size. When subject to tensile stress these imperfections (similar to very small cracks) tend to open. If the steel is insufficiently tough, the ‘crack’ propagates rapidly, without plastic deformation, and failure may result. This is called ‘brittle fracture’, and is of particular concern because of the sudden nature of failure. The toughness of the steel, and its ability to resist this behaviour, decreases as the temperature decreases. In addition, the toughness required, at any given temperature, increases with the thickness of the material. A convenient measure of toughness is the Charpy V-notch impact test. This test measures the impact energy (in Joules) required to break a small, notched specimen by a single impact blow from a pendulum. The tests are carried out with the specimens at specified (low) temperatures, and the steel material standards specify the required minimum impact energy values for different grades.
Bolted Column Splices with Minor Axis Bending
In multistory construction columns splices are provided for convenience of fabrication, transport and erection. If required the splices are located just above the floor level, which enables easy access to the joint.
There are two types of splice connection, full contact bearing and non-bearing. As the name suggests in bearing splices the axial load is transferred directly to the column below by full bearing contact, bolts and plates are intended to hold columns in place. In non-bearing splices the load is transferred through bolts and splice plates.
The design of bolted column splices with minor axis bending moment, ie two way moment resisting frames, is a complex process. There is not much literature available on this topic. A design guide that briefly discusses this topic is the South African Institute of Steel Construction’s Structural Steel Connections Guide or the “Green Book”. Another source of guidance is the Steel Construction Institute Publication 207, which covers the non-bearing splices with minor axis bending.
This article will cover design of bearing and non-bearing splice connections with minor axis bending based on the procedures outlined in the aforementioned guides, and relate the design equations to NZS 3404.
Heat Input Limits of Welding Consumables for Earthquake Resisting Structures
The Steel Structures Standard, NZS 3404, references the AS/NZS 1554 suite of standards for compliance of welding consumables. NZS 3404 includes additional requirements limiting the heat input in the deposited weld metal for welds subject to earthquake loads or effects. This article discusses the background to these requirements, identifies welding processes restricted by the heat input limits and how to qualify welding process that are restricted by the heat input limits.
Development and Research of Eccentrically Braced Frames with Replaceable Active Links
Ductile eccentrically braced frames designed in accordance with the New Zealand Steel Structures Standard, NZS 3404, provide life safety during a design level or greater earthquake; however, the eccentrically braced frame active link may sustain significant damage through repeated inelastic deformation. This may necessitate post-earthquake replacement of the active link. A bolted replaceable active link can be used to facilitate replacement after a strong earthquake, which reduces repair costs. New Zealand design guidance for the seismic design of steel eccentrically braced frames was first published in 1995 by the New Zealand Heavy Engineering Research Association within HERA Report R4-76 and has been widely used in practice. This guidance has been recently updated and now includes seismic design procedures for eccentrically braced frames with replaceable links. This article covers the development and research of eccentrically braced frames with replaceable links. This includes discussions of the comprehensive research programme recently completed in Canada investigating the performance of eccentrically braced frames with replaceable links and finite element analysis undertaken by the New Zealand Heavy Engineering Research Association, to verify the design procedure for eccentrically braced frames with replaceable links.
Welding Consumables and Design of Welds
The Steel Structures Standard, NZS 3404, references the AS/NZS 1554 suite of standards for compliance of welding consumables. New editions of the AS/NZS 1554 suite of welding Standards have recently been published and these refer to newly published editions of the AS/NZS Standards for welding consumables. Over the last few years, Australia and New Zealand have adopted the harmonized ISO welding consumable classification system. These changes in welding consumable classification system impact on structural engineers designing fillet welds and partial penetration butt welds.
Specifying Steel for Seismic Lateral Resisting Frames
There are three common seismic frame types used in New Zealand. These are the eccentrically braced frame (EBF), concentrically braced frame (CBF) and moment resisting frame (MRF). See figure 1. All steel seismic-resisting systems are required to be classified into one of four categories for seismic design in accordance with the Steel Structures Standard, NZS 3404. The category of seismic frame designed will determine the displacement demand on an individual member of that seismic frame. Members of seismic frames are classified into 4 categories in the same manner as for the seismic resisting frame. Material requirements specified in NZS 3404 become more stringent for member categories associated with higher displacement demand. The identification of the seismic member categories and the subsequent specification of appropriate steel grades in the contract documents, is the responsibility of the design engineer. This article identifies what the typical seismic member categories are for three common seismic frame types used in New Zealand and identifies complying material types for these seismic member categories.
Web Side Plate Rotation Capacity
The Steel Construction New Zealand publication Steel Connect (SCNZ 14.1 and SCNZ 14.2) provides structural engineers with a rapid and cost-effective way to specify the majority of structural steelwork connections, in accordance with accepted fabrication industry norms. Specification of these connections also facilitates the development of reliable cost estimates by designers, fabricators, consulting quantity surveyors and constructors.
Eccentrically Braced Frames Lateral Restraint of Link Bottom Flange
Eccentrically braced frames are required to be laterally restrained at both the top and bottom of the active link member ends to ensure reliable performance in a seismic event. There are occasions when direct lateral restraint to the bottom flange is not permitted. In this instance the lateral restraint of the bottom flange of the active link end can be achieved from minor axis bending of the brace. This article presents a simplified procedure for this approach by a way of a design example.
Design of the Linked Column Frame Structural System – A New Zealand Application
The Link Column Frame (LCF) system is a brace free hybrid system combining proven seismic load resisting technology; eccentrically braced frames (EBF) with removable links and moment resisting frames (MRF). It was developed to meet the requirement for continued occupancy, or at least rapid return to occupancy after a severe earthquake. This is a departure from the prevailing New Zealand seismic design approach pre the 2010/2011 Christchurch earthquake series which involves designing for controlled damage (energy dissipation) in selected elements of the seismic load resisting system which are typically not rapidly or cost effectively repaired. Engineers familiar with the design of EBF and MRF systems will readily understand and be able to apply the LCF frame structural system design concepts. The only departure from standard office practice is the requirement to undertake a nonâ€“linear push over analysis. As a result, practicing engineers will likely find the design methodology for this system easier to implement than those for some other low damage seismic load resisting solutions. Useful background information to the LCF system is found in the paper of Dusicka et. al.. It is recommended this is read in conjunction with the present paper which is intended to illustrate the application of the capacity design principles of the Steel Structures Standard (NZS 3404 ) to this new system.