Journals >> Abstract VOLUME 17 No. 2 (September 2004)
SESOC INFORMATION
SESOC MANAGEMENT COMMITTEE
TECHNICAL PAPERS
The Bracing Performance of Vertically Discontinuous Bracing Walls – G.J. Beattie
The Timber Framed Buildings standard, NZS 3604, provides a method for the determination of the bracing "demand" on the structure and the calculation of the combined strength of the walls in a light timber framed building, built in accordance with that standard. The process essentially calculates the bracing demand on the structure, taking into account the building dimensions, the number of storeys, the weights of the cladding materials, and the seismic and wind zones in which the structure is located. Some elements of walls are designated as bracing walls requiring special detailing to achieve a bracing rating that has been previously determined by testing. The sum of the bracing "capacities" of these walls is compared to the calculated "demand", and provided the capacity exceeds the demand, the structure is considered to be satisfactorily designed to resist the design earthquake and wind loads.
The test procedure for determining the strength capacity (the so-called P21 test) requires the wall element to be placed on a near-rigid foundation, but in service the walls may be positioned on a rigid or a flexible foundation (such as transverse to floor joists and part way along their span). It is assumed that the stiffness of the same bracing wall element is similar when placed in both situations, but in reality this is not the case. The purpose of the project described in this paper was to determine the effect of the degree of flexibility of the supporting floor on the performance of a bracing wall positioned at the joist mid-span and, as a consequence, its contribution to the overall bracing capacity of the structure.
Diaphragms For Timber Framed Buildings – Roger Shelton
This paper describes a study carried out at BRANZ on timber diaphragms within the context of NZS 3604 Timber framed buildings".
The provisions of NZS 3604 relating to floor and ceiling diaphragms are described, and found to be somewhat confusing and inconsistent. An experimental investigation was undertaken to establish the strength and stiffness of the connection between wall and ceiling of the "weakest" of the detailing options provided for in NZS 3604. Examples of both traditional stick-framed and battened ceilings were tested under cyclic loading both parallel and perpendicular to the joint. It was found that irrespective of the type of ceiling construction. the strength of the joint (both parallel and perpendicular) could be represented by a value of 1.6 kN/m. Most applied cornice details (taped and stopped, and plasterboard coving - but not nailed timber scotias) enhanced this value.
Using this value 1.6kN/m, and the limiting dimensions permitted by NZS 3604, it is shown that the top plate provisions are a little deficient in providing the continuity required of boundary members expected to resist diaphragm chord forces.
Strength of Shear Stud Connections Between Steel Beams and Profiled Concrete Slabs - Yan Lin, Jason Ingham and John Butterworth
An experimental investigation was conducted at the University of Auckland to quantify the performance of shear studs embedded in composite profiled slabs, formed by placing in-situ concrete onto profiled steel decking. In total, 18 tests were conducted using a new type of push-off test rig, with test units composed of either normal weight concrete or lightweight polystyrene concrete. This paper reports on and discusses the main results of these tests. Results indicated that studs embedded in Iightweight polystyrene concrete performed comparably with studs in normal weight concrete. Comparison with strengths predicted by NZS 3404:J997 suggested that some of the equations in the Standard would benefit from a review.
Papers Presented at a Seminar on the Use of Grade 500E Reinforcing Steel: (1) Properties and Handling Procedures for 500 MPa Reinforcing Steel – Keith Towl
A few cases of reinforcing bar breakages in 2003 caused some consternation but acted as a catalyst for a wider discussion on the suitability and fitness for purpose of 500 MPa steel in New Zealand. Investigations by Pacific Steel revealed that the problems were related more to the lack of understanding of the properties of the material and the criticality of appropriate handling procedures rather than the material itself. The development of the new reinforcing bar standard, the significant property changes and the causes and prevention of possible failure are explained.
The history of 500 MPa reinforcing steel for New Zealand goes back almost a decade. In November 1994, as part of the move towards trans-Tasman collaboration in product standardisation, a committee was formed to investigate and establish a joint Australian-New Zealand standard for reinforcing / prestressing materials for reinforced concrete structures. After many years of development and refinement, the joint reinforcing standard AS/NZS 4671:2001 was published that included the introduction of 500 MPa or Grade 500 steel reinforcing.
Papers Presented at a Seminar on the Use of Grade 500E Reinforcing Steel: (2)Grade 500 Reinforcement and the Concrete Design Standard NZS 3101 – Dene Cook
The adoption of the new reinforcing material standard AS/NZS 4671 in New Zealand, necessitated a review of the formulae within the concrete design standard NZS 3101 to evaluate whether modification was required.
The review of NZS 3101 focused on four main areas:-
1 Overstrength factors;
2. The restriction that is appropriate on beam bars diameter passing through columns of ductile frames;
3. The impact on structural stiffness of using higher strength reinforcing;
4. Welding.This paper provides a brief overview and explanation to the amendment to NZS 3101.
NZS 3101 is in the process of a comprehensive review and update. A draft for public comment of the first 10 chapters was issued for public comment in March 2004, with the other chapters due for release in mid April 2004. The aim of the committee is to have a complete and reviewed document finished by December 2004.
At its first meeting the committee determined that some of the items requiring review were worthy of an amendment to the existing NZS 3101 rather than waiting for December 2004. It was considered that the levels of interest and research into Grade 500 were sufficiently developed to warrant inclusion in an amendment to the existing standard. The amendment to NZS 3101 was issued for release in March 2004.
Papers Presented at a Seminar on the Use of Grade 500E Reinforcing Steel: (3) Welding of Reinforcing Steel – Wolfram Woerner
Controversial opinions about welding of reinforcing steel have been published during recent months especially with regard to Grade 500. The technology the metallurgy and the welding requirements for this grade are in fact not different from many other steels that are successfully welded on a regular basis. It is essential to understand that high strength steels like Grade 500 require care and appropriate handling to deliver safe and reliable welded joints.
Manufacturing quality welded joints requires the balancing of the manual aspects of the welding process with the influence of the equipment, and the consequences of complex metallurgical processes. All these processes contribute to the performance of the weld. Welding is not a simple process but it can be controlled and handled safely. The procedures necessary for reliable welding have been developed since the 1920s and have reached a high standard. AS/NZS 1554.3:2002 is the current industry standard for the welding of reinforcing steel.
Performance-Based Building Regulatory Systems: Structure, Hierarchy and Linkages – Brian J. Meacham
Performance-based building regulatory systems are in use or under development in numerous countries worldwide. Within each of these regulatory systems there exists a structure, which includes enabling legislation, a regulatory instrument (regulation or code), and various types of supporting infrastructure, which combine to provide a system aimed at producing buildings that meet societal expectations in terms of safety, health and welfare. However the structure is not always explicit, and in some cases may be incomplete. This is important. as, in order for the regulatory system to function as intended, the interdependencies between the various components must be understood. Otherwise, there may exist significant gaps in the regulatory system that could inadvertently lead to an incomplete understanding of the performance of a building. This paper explores the issue of performance regulatory system structure and the linkages that are needed to assure that pertinent interdependencies are addressed.
Keywords : Performance-based; building regulation; regulatory structure; building design; performance levels; criteria; risk.
Failure Modes for Hollowcore Flooring Units – Richard Fenwick, Bruce Deam and Des Bull
Experimental work undertaken by Matthews and others at the University of Canterbury has raised serious issues on the performance of hollowcore units in diaphragms supported by ductile moment resisting frame structures. A diaphragm constructed from these units was shown to perform inadequately in simulated seismic loading. Many lessons were learnt from this and other related tests. However in an experimental study only a limited number of factors can be studied. In this paper an attempt is made to look at the different actions that can arise in hollowcore diaphragms. Where possible simple calculations are made to assess the likely magnitudes of these actions. There are two aims for the paper: Firstly to give practising structural engineers a feeling for the behaviour of these structural elements and Secondly to indicate where further analytical and experimental research is required. In addition a number
of proposals are made for detailing of these units to improve their seismic performance, though some of these require testing to verify their performance.
Many factors influence the failure modes that may occur in hollowcore units. Due to the complex interaction of these with other structural elements it is not possible to develop design criteria for hollowcore diaphragms in seismic resistant structures from experimental tests alone. However, analytical models, when calibrated against test results, could be useful in contributing to this objective.
Moment End Plate and Angle Cleat Connection Design Concepts – Clark Hyland
The new edition of the Structural Steelwork Connections Guide, Part 1: Design Procedures, HERA Report R4-l00.l: 2003, contains updated design procedures for commonly used connections. Part 2: Connection Tables, HERA Report R4-100.2: 2003, contains updated connection tables and detailing parameters for pre-engineered connections developed using the design procedures found in Part 1. This paper gives a technical overview of the general guidelines and updated design procedures for the Angle Cleat, AC, Moment End Plate, MEP and Moment End Plate Splice connections.
Charts for Singly Reinforced Rectangular R.C. Beam in Flexure – Doug. Mackenzie
While it is recognized that many structural engineers have computer programs that calculate the required area of reinforcing for a given bending moment, these charts are supplied to provide a quick means of doing so independently of computers.
The charts are to NZS 3101:1995, for both the 300 and 500 Mpa reinforcing yield strengths. This may be quicker for small jobs than setting up the computer program.
The charts may be copied as desired.
In the charts, values above the upper horizontal line are for under-reinforced cases, where the concrete itself can resist the bending, but would crack suddenly if the moment was increased, and before it was carried by the reinforcing. See also Cl. 8.4.3.3 of the Code for the alternative minimum area of reinforcing. No values are given below the lower horizontal line, as here there is a danger of a sudden violent compression failure. This line is drawn at 0.75 x ρ balanced
ARTICLES FOR DISCUSSION
The Performance of One-Sided Welded I-Section Steel Beams under Inelastic Cyclic Loading – Andrew Short and G. Charles Clifton
Common practice for built-up beams with single sided welds has their use in seismic design limited to seismic Category 3 and 4 of NZS 3404 [1]. While NZS 3404 does not expressly prohibit the use of I- section beams formed with single sided welds at higher ductility levels, confidence does not exist in the ability of a single weld joining the flange and web to withstand the local buckling experienced in the flange and web during severe earthquakes.
Recent large scale beam to column tests conducted by HERA at the University of Auckland were designed to simulate rigid, welded moment resisting connection performance under severe seismic demand. The specimens tested were based on traditionally used beam-to-column connections in New Zealand. A sufficiently strong column was used to ensure that during cyclic loading, the beam can develop a plastic hinge before significant deformation or damage is developed in the column. One test with a built-up beam of similar cross section flange and web element slendernesses and with a single weld joining the flange and web was used to determine the ductility capability of such a one-sided welded beam.
PROJECT CORNER
New Zealand Expertise used on International Stadiums – Trevor Robertson and David Cooke
Engineers from the New Zealand offices of Sinclair Knight Merz have provided expertise in seismic engineering and in complex analysis to some of the world's premier sports stadium developments.
Sinclair Knight Merz's first major sports stadium design was Stadium Australia used for the 2000 Olympic Games and the recent Rugby World Cup. The success of that project provided the company with a reputation for long-span roof structures which has led to engineering commissions on an enviable list of major sporting and convention facilities, ranging from the Nanjing Chinese Games stadium to Malaysia's massive Putrajaya Convention Centre. The company has developed systems that enable it to utilise its global resources to best service individual projects. Recently New Zealand engineers have enjoyed significant involvement in some of these developments.
Test Your Skill – A Structural Checking Test: The Solution to Exercise No. 1 – Richard Fenwick
This exercise was given in the September 2003 SESOC Journal.
Joint SESOC / IPENZ / I.Struct.E Committee Newsletter – Richard Aitken
STANDARDS NEW ZEALAND
Standards for Structural Engineers – Ian Brewer.
As at April 2004:
NZS 1170.5: Structural Design Actions – Earthquake Actions. Standards Australia withdrew from the development of a joint earthquake loadings standard and proceeded with an amendment to AS 1170.4-1990.NZS 3101: Concrete Structures. Under review. Comments on the first stage (Section 1 to 10) are due to close on 25 th June. The second stage (Section 11 to the end) was due for release in mid-May, 2004 but it will be further modified as a result of the about-to-be-finalised earthquake loading standard.
NZS 4230:2004 Design of Masonry Structures. A newly revised edition of this Standard is about to be released. It is intended that this Standard be used for buildings requiring structural engineering design where they fall outside the scope of NZS 4229:1999 “Concrete masonry buildings not requiring specific engineering design”.
NEWS FROM THE REGIONAL STRUCTURAL GROUPS
Auckland Structural Group – Ashley Smith
Canterbury Structural Group – Dene Cook
Waikato Structural Group – Gordon Hughes
Wellington Structural Group – Graeme BeattieThese consist of reports of past meetings, and planned future meetings.
