Guidance on typical corrosion steel rates in water and soil for design use is provided in the recently published NZS3404.1 Steel Structures Standard - Materials, Fabrication, and Construction (SNZ,2009). The design rates given are those to be used for long-term exposure, i.e. where the designer is calculating a required sacrificial thickness of steel in order to meet the specified design life. This article covers the background to the corrosion rates provided in NZS 3404.1.

The Sliding Hinge Joint (SHJ) is a new semi-rigid joint system developed for moment resisting steel frames. It has the ability to remain rigid under in-service conditions or ultimate state wind loading, and to rotate under severe earthquake loadings, returning to the rigid state when the severe earthquake stops. The joint is designed and detailed such that there is negligible damage to the frame or slabs. The joint has a similar cost to conventional construction.

This article presents a method for designing the collar joints of a moment connection between an I section beam and a circular hollow section (CHS) column. The procedure is developed principally for the semi-rigid flange bolted joint (FBJ). However the principles can be applied in general to other types of connections. The design procedure has been taken and slightly modified from (Clifton, 2005).

Standard moment end plate connections (MEP) have been developed by Steel Construction New Zealand Inc. The design procedures are presented in Structural Steelwork Connections Guide: Design Procedures, SCNZ 14- 1:2007 (Hyland et al, 2008). The connection details are given in table form in SCNZ 14-2:2007 (Hyland et al, 2008). However these publications only provide details for the beam side of the MEP connection. The column side aspects are not covered and reference is given to guidance in HERA Report R4-142:2007 (Clifton et al, 2007). This article updates the guidance and design example given in this publication and presents the design procedure consistent with the SCNZ publications. Development of software based on these procedures is being developed and this is briefly discussed.

Although buildings are often constructed using flexible materials, roof and structural expansion joints are required when plan dimensions are large. The maximum distance between expansion joints is dependent upon many variables, including ambient temperature during construction and the expected temperature range during the lifetime of the building. This article summarises North American practice with respect to spacing of thermal movement joints (AISC, 2003). This is based upon Federal Construction Council Technical Report No 65: Expansion Joints in Buildings and recommendations by (Fisher, 2005).

The refurbishment or ‘adaptive re-use’ of existing buildings currently forms a significant part of the workload for many architects and engineers. The structural engineer will be required to make an appraisal of the existing steelwork in these buildings. This article provides sources of information for identifying the properties and making an assessment of the historical structural steelwork.

One of the greatest problems faced by a steel erector on site is inaccuracy in the locations of the anchor bolts. Precision surveying equipment and techniques are required to accurately set out solidly cast-in anchor bolts in accordance with NZS 3404.1. The required setting out tolerances of these fixed holding down bolts is very tight. To provide increased tolerance and some allowance for site adjustment, sleeved anchor bolts can be used. See Figure 1. These allow some adjustment of bolt positioning after concreting. This article describes the requirements for holding down bolts sleeves.

This article provides an introduction to network arch bridges and is an excerpt from (Chan and Romanes 2008).

There are instances where high tensile anchor rods have been cast in with insufficient projection above the concrete. Extending the anchor rods by welding is generally not permitted. One method to extend the anchor rod is by the use of a threaded coupler. Checks are required to ensure that stripping of the threads and also tensile fracture of the coupler does not occur prior to the tensile fracture of the connected threaded rods. This article presents a method for these checks.

A recent United Kingdom fire test of a post tensioned slab designed for a 2 hour fire rating achieved only a 66 minute fire resistance. Spalling began after 11 minutes and after 20 minutes spalling exposed the tensioning ducts which resulted in a significant loss of strand strength. While care must be taken in extrapolating test results from one form of construction to another without assessing differences in thermal and restraint conditions (Kelly, Purkiss, 2008), it also raises concern over the elevated temperature performance of prestressed concrete floor systems used in New Zealand. Factors which affect spalling at elevated temperatures are concrete moisture content, permeability and the presence of compressive stresses. (Kelly, Purkiss, 2008) The prestressed products in New Zealand have a higher strength of concrete than the concrete strength of the post tensioned slab in the fire test. Concrete permeability deceases with an increase in concrete strength. Therefore high strength concrete is more susceptible to spalling at elevated temperatures. Further investigation is required to allay these concerns. The fire test is presented in an article on ‘Reinforced concrete structures in fire: A review of current rules’ by Fergal Kelly from Peter Brett Associates and John Purkiss formally of Aston University and was published in The Structural Engineer magazine on 7th October 2008. This article describes the fire test carried out on the post-tensioned concrete slab, the conclusions of the test and subsequent UK discussions following the fire test.

New Format of NZS 3404 The steel structures standard is being separated into seven inter-related parts as follows. The first part, NZS3404.1 is due for release mid-2009: NZS 3404.1 Steel structures – Materials, fabrication, and construction NZS 3404.2 Steel structures – Structural analysis NZS 3404.3 Steel structures – General design of members and connections NZS 3404.4 Steel structures – Design of composite members NZS 3404.5 Steel structures – Design for fire NZS 3404.6 Steel structures – Design for fatigue NZS 3404.7 Steel structures – Design for earthquakes The commentary section is being brought into the body of the Standard and is located against each relevant clause. This will facilitate interpretation and usability, removing the isolation of the commentary from every day use of the standard.

The New Zealand Steel Structures Standard (SNZ, 1997), in keeping with many international design standards has no minimum stiffness requirement for restraints systems preventing flexural-torsional buckling of steel sections bent about their major axis. To account for restraint system flexibility, NZS3404 categorises these systems as providing full or partial restraint. In the commentary to the Steel Structures Standard guidance is provided for roof rafters for the minimum ratio of purlin depth to rafter depth to ensure a lateral restraint system fully restrains the section. No such guidance is provided to allow designers to check that the restraining system is sufficiently rigid to provide at least partial restraint. This is particularly relevant for the bottom critical flanges of deep roof rafters restrained by a flexible tension side system in conjunction with full depth stiffeners (Figure 2). In this paper guidance is provided for structural engineers to help them address this situation.

This article addresses some problems that can occur when primers are incorrectly specified, and examines some misconceptions on their expected performance. Costly remedial rework can be incurred if a shop primer is damaged or exposed to exterior weather conditions for longer periods of time, or that are more severe than were expected, prior to being closed in or subsequent finishing coats being applied on site. These thoughts and observations are based on the author’s experience in the coatings industry. A common cause for arbitration on disputes over coating failures is where a short term, single pack primer has been specified and applied over St 2 (Hand Tool Clean) or more frequently St 3 (Power Tool Clean) prepared steel and left exposed for long periods during construction. Premature breakdown of the coating often initiates from undercut mill scale, transit damage, strop, chain and handling damage if it is left exposed to the weather without repair.

This article gives recommendations for Alternative Design methods for fire engineering of common types of multi-storey steel structures. These are Alternative Designs because they do not follow 100% the Compliance Document for Fire Safety, (DBH, 2005). However, they meet or exceed the provisions of the New Zealand Building Code, (DBH, 1992), which is required under the performance based Building Control System (BCS) that was introduced in 1992. Alternative Designs require the design procedure to be approved by the Building Consent Authority. In many instances, the building control official responsible for reviewing the design is familiar with historical prescriptive designs and unfamiliar with new fire engineering methods that have been developed under the current BCS. The current Steel Structures Standard NZS3404 (SNZ, 2007) provides only a simplistic and element based approach to the design for fire, as this material was written for application under a prescriptive based system. These two factors are leading to significant delays in the processing of some Alternative Designs. A complete revision of NZS 3404 commenced in 2008 and the design provisions for fire are to be presented in an expanded new stand-alone part which will provide a Complying Solution directly.

This article provides an update on the corrosion performance of the State Highway 1 Mercer weathering steel off-ramp, following an inspection by Japanese expert Dr. Makoto Ohya, two and half years after construction.