Guest Editorial_A Path towards Performance Based Seismic Design
Abstract
Last month I was invited to attend a workshop as part of the Applied Technology Council project 58 team who are working towards preparing Performance Based Seismic Design guidelines for the USA. The concept of multiple performance levels with regards to earthquake design and retrofit (i.e. Operational Continuity, Immediate Occupancy, Damage Control, Life Safety, Structural Stability) has been working in California since the late 1990s through the National Earthquake Risk Reduction Program (NEHRP) recommendations. Although these provisions are non-mandatory they have established the working framework which can be used to assess the performance of existing buildings.
Letter to Editor_ Draft Loadings Standard Pt4 Earthquake Loading
Abstract
Recently I read the first two thirds of draft 8 of this standard. It was released as a “calibration test version”, so that a number of structural designers could assess the proposed code requirements against those in the existing code by considering recent structures that they had designed. This draft standard is intended to be close to the final version. On the basis of this reading I sent in a number of comments to Standards. Some of these were minor but a few were of major importance. Similar comments on several of the previous drafts have also been sent. Firstly I note that my comments, along with all the other individuals who have submitted comments, have not once been acknowledged. Secondly I note that many of the points that I have raised have been ignored, even when pointing out basic errors in equations. The process of producing a standard lacks transparency, and I believe it needs to be revised.
Letter To D Gaunt Fri Re Timber Treatment Research and use of Untreated Radiata Pine in NZ Construction
Abstract
Because of concern about how untreated timber has come to be used in domestic construction in New Zealand with the resultant rotting timber framing, we sent the following letter asking these questions of the Forestry Research Institute. We received back an email from Mr. M. Hedley which gave the replies to the questions inserted in italics below. It serves to highlight the fact that industry funded standards are not working. The previous Minister of Internal Affairs was well warned by SESOC of the effects of removing government funding from Standards New Zealand, but chose to ignore what we predicted. Whoever funds a standard will get the standard that they want regardless of whether it is the public interest. Commercial control of standards is now all too apparent, as is the result.
Design Of Cold-Formed Stainless Steel Structures
Abstract
New Zealand is one of the largest users of stainless steel in the world (in terms of tonnage used for the size of the economy). With the introduction in 2001 of the Cold-Formed Stainless Steel Structures standard, AS/NZS 4673:2001, we now have a state of the art standard for design of cold-formed stainless steel structures.
The standard was introduced to New Zealand users in early 2002 through a HERA seminar series.
The notes from that series, HERA Report R4-111, provide a useful companion to the standard.
This paper provides a brief summary and overview of the key factors involved in the design of cold formed
stainless steel structures. This coverage includes addressing important practical aspects such as the material properties of stainless steels, the differences between stainless steel and carbon steel and important considerations in the design of thin-walled sections and connections. It also briefly covers considerations in the design for earthquake and fire. The paper provides an overview of these aspects only and references readers onto the relevant pans of the standard and the seminar notes for more information. It ends with coverage of some of the typical applications for stainless steel as taken from the seminar notes.
Recent Structural Research In New Zealand
Abstract
Recently, a brief research report on structural research at Auckland and Canterbury Universities was published in the “Structural Engineer”. An updated version of this is given below.
Most of the structural research at Auckland and Canterbury Universities is related to the seismic behaviour of structures. Currently there are research projects looking at the seismic behaviour of reinforced and pre-stressed masonry, structural steel, reinforced concrete and timber structures, together with a number of analytical topics that are material independent. In this report three projects, which are expected to have a major influence on the way in which structures are designed and detailed for seismic resistance, are briefly reviewed. In all cases the first phase of the research projects is nearing completion, though additional work is planned in all cases.
Quality Control Of Structural Timber In New Zealand
Abstract
The change in New Zealand’s pine forest management towards faster growth has caused an increase in the proportion of juvenile wood with its problems of low stiffness and distortion. While juvenile wood has always been present, the increased likelihood of its occurrence means that it is now more important for producers to verify that structural timber has the properties expected of it. While machine grading is more efficient at sorting sawn timber for stiffness than is visual grading, both methods need to be backed up with a third party-audited quality control system. Without such a back-up an amendment to NZS 3603 was proposed whereby a capacity reduction factor would be applied to Modulus of Elasticity, as well as to strength design values. This issue is still under debate.
Design Of Opening Corners Between Reinforced Concrete Walls and Slabs
Abstract
Some commonly used detailing for opening comers between walls or walls and slabs results in strengths which are less than the theoretical strengths of the members meeting at the comer. This paper shows how these comers can be designed and detailed, using diagonal bars, to achieve satisfactory performance. Some details, which do not perform satisfactorily, are described and a method of assessing the ultimate strength of comers reinforced with U bars that overlap in the comer is given. The paper may also be of interest to designers who use the strut and tie method as it outlines actions that should be considered in such an analysis.
Holistic Behaviour Of Concrete Buildings In Fire
Abstract
(Originally Published in The Proceedings of The Institution Of Civil Engineers, Structures and Buildings 152, August 2002. It is republished here with kind permission of Thomas
Telford Limited).
This paper discusses various modes of structural behaviour of a concrete building when subjected to a fire, based on observations from a full-scale test. Although some data were lost during the test, the available results and observations presented provide a valuable insight into the holistic behaviour of concrete buildings, when subjected to fire. The tested building was constructed using elements formed from normal and high-strength concrete and was designed for 60 minutes fire resistance, using the UK design Code. High-strength concrete was used for the columns within the fire compartment and since it has previously been shown that this type of concrete is susceptible to spalling, polypropylene fibres were added to the concrete mix during construction to alleviate the problem. Both the UK and European codified design methods suggest that concrete spalling within the fire compartment should have been nominal and could effectively be ignored during the design. However the test showed that spalling of the floor slab was extensive and exposed the bottom steel reinforcement. Although concrete spalling considerably reduced the flexural strength of the slab, collapse did not occur. This could be attributed to the slab behaving in compressive membrane action, which is currently not considered in codified design methods. The test also showed significant lateral displacement of external columns due to thermal expansion of the heated slab. The main observations from the test show that designers will need to understand the behaviour of entire structures in fire, to ensure that premature collapse will not occur.
Overstrength Factor For Pacific Steel Micro-Alloy Grade 500 Reinforcement_April 2002
Abstract
With Grade 500 reinforcement in to the market place in New Zealand, designers need to be aware that the overstrength factor of 1.25 for members constructed with Grade 430 steel cannot be applied to those members constructed with Grade 500 steel. The overstrength factor is defined as the ratio of the maximum strength of a concrete member, M, to the nominal strength of the concrete member, Mn. The nominal capacity is usually calculated using the lower 5″ percentile yield strength of the reinforcement [I, 21. The ability to accurately determine the maximum overstrength capacity of an inelastic member is the fundamental principal in “capacity design”. This paper presents the summary of results from a study aimed at determining the overstrength factor for plastic hinge zones of reinforced concrete beam and column members constructed using Pacific Steel Micro-Alloy Grade 500 longitudinal reinforcement, with the chemistry of current production.
Issues of Non-Compliance with the Steel Reinforcing Materials Standard
Abstract
For a number of years, alternative sources of supply of steel reinforcement have been available in New Zealand, other than those provided by Pacific Steel, Otahuhu. Supplies have been obtained from a number of countries including South Africa, Korea, Singapore and India. Some of the issues with this imported reinforcement are: Is the range of reinforcing steel appearing on sites “fit for
purpose”? Does the reinforcement comply with the minimum requirements of the Standard AS/NZS 4671:2001: “Steel Reinforcing Materials”? Are design engineers applying due diligence in ensuring that this reinforcement meets the requirements of AS/NZS 4671?
Can “elastic design” be considered as an excuse to not seek compliance with ASNZS 4671?
Articles For Discussion Some Site Observations and our Non-Existent Building Control System
Abstract
In the light of recent concerns about domestic construction standards I have done some observations to see what happens during site inspections. A particular site was chosen because there were known problems with the founding material.
Project Corner Britomart Underground Railway Station
Abstract
This paper describes the design and construction of the Britomart underground railway station in Auckland, New Zealand. This is the first underground station built in New Zealand. The station was constructed by cut and cover techniques using both top-down and bottom-up methods to suit the site geology. The station is approximately 300 m long, 45 m wide, and 12 m deep from the ground level. It connects to an existing tunnel at Britomart Place. The site is on a reclaimed land and the sea is within 100 metres. Close proximity to the sea and ground movement restrictions due to adjacent heritage buildings posed considerable challenges to the design team. This paper focuses on solutions adopted to overcome the site and design constraints.
The Feasibility of Round Pole Timber and Lime Concrete Composite Flooring
Abstract
An Undergraduate At Bath University, writes about his Young Researcher Grant-Funded Project
(Reproduced from the Structural Engineer); Examples of timber and concrete composite structures can be found across Europe, commonly used to construct floors and walls. The technique has also been used for bridge decks in America and France. Such systems are comprised of a layer of timber either sawn or in the round, working as the tension element, with a layer of concrete on the top forming the compression element. Mechanical fasteners provide the shear connection between the two layers and allow composite structural action.
Letter to the Editor re The Case for Tied-Back Retaining Walls
Abstract
Cantilever pole retaining walls proliferate. There are good reasons. Bobcats with earth augers are
readily available, H5 treated poles have a proven record of durability, the design is simple – especially
using the SESOC software. For non-engineered works there are numerous contractors. Nevertheless, cantilever walls are not very efficient.
Fibre Reinforced Polymer Composite Materials For Civil And Building Structures - A Review Of The State Of The Art
Abstract
This paper is a review of the development and use of fibre reinforced polymer composites in civil and building structures. It draws from information and knowledge gained by the author through the study tour conducted between 7 July and 25 August 2001. The study tour involved a 7-week around the world trip meeting up with designers, manufacturers, contractors, academia, and government agencies, who have expertise in this emerging field. Countries visited were Japan, UK, Switzerland, Denmark, Canada, and US where research and development in fibre reinforced polymer composites excel. The review is purely the author’s views and reflects upon what she learnt from the study tour.
Fibre Reinforced Polymer Composite Materials For Civil And Building Structures - A Review Of The State Of The Art
Hardened Properties Of Concrete Containing New Zealand Aggregates
Abstract
Concrete is increasingly being considered as a generic material with predictable hardened properties regardless of its aggregate constituents. This assumption is not strictly true for New Zealand concrete, being made with a wide range of aggregate types of varying quality. A study of the hardened properties of concrete made with fine and coarse aggregates from Kaitaia to Invercargill is reported. Findings suggest that while strength properties are
controlled largely by the quality of the cement phase, dimensional stability is more influenced by the quality and quantity of the aggregate component. Recommendations are made to help designers use more accurate values for material properties such as coefficient of thermal expansion, elastic modulus and drying shrinkage values. An improved understanding of concrete as a material should reduce the risk of unexpected performance and help increase the efficiency of concrete as a construction material.
Strength Of Shear Stud Connections Between Steel Beams And Profiled Concrete Slabs
Abstract
An experimental investigation was conducted at the University of Auckland to quantify the performance of shear stud 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 lightweight polystyrene concrete performed comparably with studs in normal weight concrete. Comparison with strengths predicted by NZS 3404:1997 suggested that some of the equations in the Standard would benefit from a review.
Stability Of Precast Concrete Tile Panels In Fire
Abstract
This paper describes a study into the fire behaviour of industrial buildings which incorporate steel roof framing
and slender precast tilt-up reinforced concrete wall panels. Recently, industrial buildings in New Zealand have
been built with tall and slender tilt-up precast concrete wall panels. Some of these walls panels are cantilevered from the ground and directly support the roof steelwork. The stability of these wall panels in fire conditions is of concern as they may collapse outwards on to fire-fighters or onto the neighbouring property. The walls that were studied and presented in this paper were free-standing cantilever walls, propped cantilevers, or attached to a simple frame of steel beams and columns. Analysis was conducted with the non-linear finite element program, SAFIR. The results showed that, when subjected to the design fires used in these analyses, tall and slender walls are likely to buckle or collapse outwards if they are not well connected to the steel frame or if the building has inadequate resistance to transverse forces. Good performance can be obtained by providing fire-resisting connections between the panels and the steel frame, together with lateral resistance provided by a roof diaphragm or frame action. Two design fires were used and the results are sensitive to the design fire used.
Structural Engineering in NZ _ an Educator’s Perspective
Abstract
During the last fifteen years there have been a number of significant changes in the attitude of Governments and Universities to teaching. Tuition fees and the rising cost of accommodation have placed pressure on students and made it more difficult for some groups of intending students to take an engineering degree. This pressure has had an adverse effect on student learning. In addition the attitude of universities has changed, at least partly in response to pressure from government. Research and publication in international journals has become of much more importance than it was in the past, and consequently teaching receives less emphasis than it did previously.
Associated with this is a change in the type of person who is employed as an academic. Practical experience, once considered important for an academic, is now given much less weight than was previously the case. This is resulting in a change in the character of design courses.
Intending structural engineers at both Auckland and Canterbury Universities take core papers in civil engineering together with a number of electives. If a student elects to take the maximum number of electives related to structural work the total time spent on structural related papers is approximately equivalent to 40 weeks of full time work. Of this close to 40percent is in the electives. Total study time for the degree is of the order of 112 weeks. The same figures apply to both Canterbury and Auckland Universities. The university degree teaching is aimed at giving a student an insight into structural behaviour rather than turning out graduates fully conversant with code clauses and current design practice.
The Design of Farm Buildings and the use of NZS 1900 in the Building Code
Abstract
The NZ Building Code B1VM1 (BIA, 2001) clause 13 calls up the archaic Division 11.2 of NZSS 1900 from 1965 ( S m , 1965) as the current design code for farm buildings. This paper reviews the design provisions of that ancient document and suggests modern equivalent design approaches within the framework of current codes.
Improved Details for Floor/Wall Ties and Plywood overlay diaphragms to strengthen URM buildings
Abstract
This paper presents novel methods of strengthening unreinforced masonry buildings. Commonly used details for floor/hall connections and overlay plywood diaphragms can be expensive and may not always have effective load paths. The improved details offer several advantages over the existing details including reliable engineered load paths and cost efficiency. Loads, stresses, seismic, coefficients, ductility factors and Ø factors have not generally been stated in the paper: It is up to designers to assess those values for each project.
The author has trialled these improved details on three projects in Christchurch with positive feedback from the building contractors.
Editorial: Letter From The Hon. Margaret Wilson Minister Of Commerce
Abstract
The engineering community has an important part to play in shaping the future of the New Zealand building sector. The central role of engineers from the start to finish of any construction project makes you ideally placed to give specialist advice in this time of change.
Editorial Letter: No Compromise Ever
Abstract
This is the slogan of a popular brand of honey. It could well be taken up by structural engineers. Those whom structural engineers serve take for granted that a structural engineer qualified to practice in New Zealand will not compromise safety when designing, carrying out or monitoring construction of structures. How well are structural engineers earning the similar level of trust placed in them, albeit not so immediately or directly as
surgeons? Not very well according to John Scany whose Open Letter has caused widespread concern and debate in the community and amongst structural engineers.
The Bracing Performance Of Vertically Discontinuous Bracing Walls
Abstract
The Timber Framed Buildings standard, NZS 3604 [I], 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 limber 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.
Diaphragms For Timber Framed Buildings
Abstract
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 W/m. Most applied cornice details (taped and stopped, and plasterboard coving – but not nailed timber Scotia’s) enhanced this value.
Using this value of 1.6 kN/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.
Properties & Handling Procedures For 500 Mpa Reinforcing Steel
Abstract
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.
Grade 500 Reinforcement And The Concrete Design Standard Nzs 3101
Abstract
The adoption of the new reinforcing material standard ASNZS 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 3 101 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 3 101.
Welding Of Reinforcing Steel
Abstract
Controversial opinions about welding of reinforcing steel have been published during the last 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.
Performance-Based Building Regulatory Systems: Structure, Hierarchy And Linkages
Abstract
Performance-based building regulatory systems are in use or under development in numerous counties 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
Abstract
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
Abstract
The new edition of the Structural Steelwork Connections Guide, Part 1: Design Procedures, HERA Report R4-100.1: 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
Abstract
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.
Articles For Discussion_Performance Of One-Sided Welded I Section Steel Beams Under Inelastic Cyclic Loading
Abstract
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 [I]. 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 slendemesses 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 Stadia
Abstract
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 premier sports stadia developments.
Editorial_The Changing Of The Guard
Abstract
The time has come for me to lay down the editorship of the SESOC Journal. I took this work on 9 years ago after my retirement from consultant practice. It has been both interesting and stimulating and I would encourage other engineers facing retirement to consider continuing involvement in the profession which could be beneficial both to the profession and themselves
Letters To The Editor
Abstract
I was impressed by the guest editorial, by Richard Fenwick and the integrity he exhibited in stepping outside the academic cocoon, to examine the current rationale among engineering academics.
The current scenario he describes is one where practical design experience is disdained in favour of the writing of esoteric papers for export, based on a priori conjecture. Surely, if, as he describes, researchers are virginal as to practical site experience or even practical design experience, they live in a world of the abstraction, without the anchor of reality.
The Nees@UCSD Large High Performance Outdoor Shake Table
Abstract
In October 2002, through the George E. Brown, JI: Network for Earthquake Engineering Simulation (NEE9 program, the National Science Foundation (NSF) awarded the University of California, San Diego (UCSD) $5.9 Million to provide the NEESporfolio with a Large High Performance Outdoor Shake Table (LHPOST).
The LHPOST will be the first outdoor and largest (12.2 m x 7.6 mj shake table in the United States. A large soil pit funded by the California Department of Transportation (Calhansj has been strategically located adjacent to the LHPOSTfor Soil-Foundation-Structure Interaction (SFSIJ testing. The facilities will be used to conduct large- and fill-scale testing to investigate structural and geotechnical seismic performance issues that cannot readily be extrapolated from testing at smaller scale, or under quasi-static or pseudo-dynamic conditions, including performance under near-field ground motions. This paper details the main design basis, describes the specifications and possible uses of the NEES@,UCSD facility.
Hardened Properties Of New Zealand Self-Compacting Concretes
Abstract
Self-compacting concrete has a reduced coarse aggregate function and increased fjnes to produce a viscous, flowable material, which does not segregate. The material is dominated by the high paste content but must perform like normal structural concrete in the hardened state. Five commercial self-compacting concretes containing either fly ash, slag, microsilica, limestone powder or viscosity modifying agents were tested in the laboratory and compared to normal structural concretes. Findings from this research indicate that strength properties are enhanced when using self-compacting concretes but dimensional stability may be compromised, leading to slightly higher drying shrinkage, thermal expansion and cracking potential and lower elastic modulus.
Wind Tunnel Study Of Crosswind Force Spectra For Low Aspect Ratio Buildings
Abstract
The structural form of buildings in New Zealand is generally driven by earthquake life-safety design considerations. These encourage the development of light-weight, flexible, ductile structures with low natural frequencies. Such structures are less affected by damaging high frequency ground motions and develop structural damage in a predictable and reliable way. However, as designs become more structurally advanced and building forms more varied, design calculations using the Australia / New Zealand Wind Loading Standard 1′” have shown that some medium-rise buildings, even as low as 10-storeys high, may become wind sensitive under in-service weather conditions with a return period of 1 to 5 years. This may lead to wind motion discomfort for some occupants on upper floors of such buildings. While not wanting to compromise the important earthquake life-safety characteristics of building structures, a greater appreciation of the ways to analyse and design for satisfactory occupant comfort during low return period winds is now needed for a greater range of multi-storey buildings in New Zealand.
Bond Strength Of Reinforced Concrete-Beam Column Joints Incorporating 500 Mpa Reinforcement
Abstract
A database of beam-column joint test results has been assembled and analysed to determine appropriate design drift limits for the prevention of bond failure in reinforced concrete frames. In order to enhance the coverage of the database which predominantly contains units having small beam reinforcing bar sizes, further beam-column joints have been designed at the University of Auckland using 25 mm beam reinforcement. Results from the first two of these tests are reported. Despite the first unit not meeting the requirement,! of the recent amendment to NZS 3101:1995 with respect to column depth, the units did not exhibit a bond failure in the joint region.
Charts For Singly Reinforced Rectangular R.C. Beam In Flexure
Abstract
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.
Articles for Discussion_Updating the Soils Programme
Abstract
The SESOC Soils Program has proved very popular and has over 400 users, however, the program was originally written to help members in the use of document BINM4 of the Building Code and in its conception and architecture was limited to this. As development proceeded over a period of four years many requests were received to extend its use to cover a much greater range of design elements than was ever intended in the original architecture. The result was a program that was not as user friendly as we would desire.
Project Corner Design And Construction Of The New Upper Harbour Crossing
Abstract
This paper was prepared for the Austroads 5th Bridge Conference held in Hobart in May 2004. It is reproduced here with the addition of current photographs with the kind permission of Austroads and Transit New Zealand.
The New Upper Harbour Bridge consists of a 458 m long balanced cantilever bridge together with approach spans and is under construction alongside the existing crossing of the Waitemata Harbour in Auckland. The new bridge is being implemented under a Design and Construct contract.
The design employs a wide transversely post tensioned single cell box girder, elimination of joints and bearings (except at abutments), use of approach span deck units for temporary access staging, two stage pours for cantilever segments and the use of external and internal longitudinal post tensioning in the box girder. It meets or exceeds all project aesthetic, environmental, durability and operational requirements and was proved via the tender process to be particularly cost-effective.
Letter to Editor
Abstract
Re: The Introduction Of Grade 500qt Reinforcing By Pacific Steel
Theoretical Analysis And Realworld Design
Abstract
(reprinted from The Structural Engineer Volume 83 No. 8); Jacques Heyman shows that stresses in a real structure can never be calculated uniquely – structural response to loading is governed by small unknown movements imposed by the environment
Factors To Consider In The Use Of Grade 500e Longitudinal Reinforcement In The Beams Of Ductile Moment Resisting Frames
Abstract
This paper examines a number of issues surrounding the use of Grade 500 reinforcement in moment resisting frames. These issues include the use of this reinforcement in plastic hinges and its increased bond strength demands and higher overstrength factors relative to previously Grade 430 reinforcement. In particular the effect of the recent amendment to NZS 3101:1995 on the design of interior beam-column joints is assessed. It was found that for more than 60% of joints the number of Grade 500 reinforcing bars required to resist a given force was at least twice the number of Grade 300 bars. It is also shown that it is often more expensive to use Grade 500 longitudinal reinforcement than Grade 300. It is concluded that in many cases the use of Grade 500 longitudinal reinforcement in the beams of ductile moment resisting frames is not a practical design solution, but that Grade 500 reinforcement is ideal for limited ductile columns, as transverse reinforcement or
in hybrid ductile jointed structures. It is important to note that all steel in this study referred to as Grade 500 is Grade 500E-MA not QT.
Factors To Consider In The Use Of Grade 500e Longitudinal Reinforcement In The Beams Of Ductile Moment Resisting Frames
Reinforcing Steel In New Zealand - Pacific Steel Future Product Range and Other Design Issues
Abstract
Pacific Steel are extending their product range to include Quench and Tempered (QT) product. This paper forewarns of the coming changes, as well as taking the opportunity to review and discuss
various issues pertinent to structural design engineers. The new reinforcing steel standard, AS/NZS 4671, and grade 500, are now 4 years old. However, there is still significant misunderstanding regarding the product in terms of specification and application. Some site practices which have
been anecdotally reported are causing concern in the industry.
Pacific Steel are extending their product range in late 2005 to provide both a Micro-alloyed (MA) and a Quench and Tempered (QT) Grade 500E product. This paper attempts to address the above overlapping and converging issues thereby providing the engineer with the knowledge necessary to design, specify and inspect safely and efficiently.
Quenched And Tempered Reinforcing Steel
Abstract
Pacific Steel’s decision to begin the manufacture of Quenched and Tempered (QT) Grade 500E reinforcing steel brings to the fore some issues that have been with us since before the introduction of Grade 500 steel and the joint standard, AS/NZS 4671. The following article, endorsed by the SESOC Management Committee, reviews some of the facts and opinions surrounding the use of QT steel and also other grades of reinforcing. Interim recommendations are given for structural engineers to complement those in the Department of Building & Housing Practice Advisory No. 7.
Use Of Weathering Steel In New Zealand Bridges
Abstract
HERA has published a guideline for the use of weathering steel in New Zealand bridges. This is HERA Report R4-97, and it covers aspects for designing, construction, inspection, maintenance and even rehabilitation of weathering steel bridges. Weathering steel is a product with a limited and chequered history of use in New Zealand principally in building cladding applications. This has made engineers wary of its use in bridges,
even though, in North America and Europe, there are examples of weathering steel bridges over 30 years old exhibiting excellent performance, in line with expectations. These examples clearly show that a well designed and detailed weathering steel bridge, in an appropriate environment, can provide an attractive, very low maintenance, economic solution and therefore extend the scope of cost-effective steel use in bridges.
This paper offers a summary of the important issues relating to the use of weathering steel in New Zealand bridges, starting with a brief introduction to the material and what makes it different to conventional constructional steel.
Reinforced Concrete Seating Details Of Hollowcore Floor Systems
Abstract
(reprinted by kind permission of the New Zealand Earthquake Engineering Society); Recent earthquake engineering research has raised concerns of the seismic performance of precast
prestressed concrete hollowcore floor systems. Experimental research showed that with simple detailing enhancements, significant improvement in the seismic performance of hollowcore floor systems can be expected. The present experimental research aims at validating several new detailing enhancements. Based on previous research findings, the present super-assemblage experiment included the following details:
(i) a reinforced connection that rigidly ties the floor into the supporting beam,
(ii) an articulated topping slab portion cast onto a timber infill solution that runs parallel to the hollowcore units and edge beams;
(iii) specially detailed supporting beam plastic hinge zones reducing potential damage to the hollowcore units;
(iv) Grade 500E reinforcing steel used in the main frame elements; and
(v) mild steel deformed bars in the concrete topping in lieu of the customary welded wire mesh.
The full-scale structure was cyclically tested in both the longitudinal and transverse directions to inter-storey drifts of ±5%. Observations show extremely positive results with minor damage incurred by the hollowcore flooring and the overall performance dictated by the performance of the moment resisting frame. Recommendations for the forthcoming revision of the New Zealand Concrete Standard, NZS 3101, are also made.
Structural Steel For Seismic Performance
Abstract
Structural design engineers require steels forming the primary structural lateral load resisting system of a building to be able to sustain high levels of plastic strain without suffering brittle fracture. The ability to focus plastic deformation into designated hinge zones of the structure allows kinetic energy developed, by the structure, during an earthquake to be dissipated in a way that minimises the likelihood of sudden collapse. This reliance on the plastic deformation characteristics of steel indicates the need for suitable material performance criteria that can be clearly understood and communicated between the structural design engineer and the steel producer. Most structures fabricated from structural steel do not need to sustain the potentially large cyclic plastic strain levels imposed on earthquake resisting structures. Consequently materials research and development tends to focus on the properties of steels operating well within the elastic stress range of the
material. This paper presents some interim results of research being undertaken on the effect of plastic strain and aging on the characteristics of structural steel used in New Zealand seismic resisting structures. Of particular interest is the effect of plastic strain and aging on the ability of the steel to develop ductile fracture in the presence of sharp notches and cracks, as often occur in fabricated steelwork. To investigate this characteristic, Charpy V-Notch (CVN) and Crack Tip Opening Displacement (CTOD) tests, were undertaken at the University of Auckland on steel taken from the flange of a 310UC158 Grade 300Plus section produced in Australia. The tests were made on the steel after it had been subjected to a range of plastic pre-strain levels and aging.
Fire Safety And Steel Construction Issues and Future Developments
Abstract
The direct and indirect costs associated with the fire protection of structural steelwork has often been seen as an impediment to the construction of structural steel buildings, As a result the steel industry worldwide has undertaken research into aspects of fire safety in an attempt to develop more cost-effective solutions for fire safety and reduce the cost of fire protection. The development of fire-safety engineering as a discipline has assisted this process and there are now many examples of fire-engineered steel-framed buildings with reduced levels of fire protection applied to structural steelwork. This paper describes some of these examples and discusses some of the approaches that have been adopted in justifying these designs. Important issues, particularly in relation to high-rise buildings,
are noted. These issues are the subject – or need to be the subject of further research and investigation. In particular, a better way of quantifying fire severity on large area floors, and the development of appropriate details and measures to avoid catastrophic building failure. There is an ongoing need for the cost-effective fire protection measures for structural steelwork to enable solutions that combine protected and unprotected steelwork.
Project Corner: Christchurch Women’s Hospital
Abstract
The new $80m Christchurch Women’s Hospital has been in the planning for some time and was opened on the 30 March 2005. This article provides the background to this project and describes aspects of the design and construction of this 9 storey base isolated hospital building.
Quenched and Tempered Reinforcing Steel
Abstract
In general, the fact remains that care must be taken to avoid any activity that may reduce the strength of the outer layer of steel that is strengthened through the quenching and self-tempering process. So welding, hot bending, re-bending or threading must also definitely be avoided.
ASI Eccentrically Loaded Cleat Compression Design Model 1996 In Need of Revision
Abstract
As a result of analyses recently undertaken by HERA, it is apparent that the calculated “blue book” (Design of
Structural Steel Hollow Connections, by Syam and Chapman) capacity with respect to eccentrically loaded cleats in compression:
1. Is significantly unconservative, with the extent of unconservatism depending on the connection geometry.
2. The peak axial load that can be carried is reached at relatively low axial deformation, after which side sway occurs, (refer Figure), resulting in the axial load capacity dropping significantly.
3. The peak axial load is particularly sensitive to erection tolerances and fit-up.
The Concrete Design Standard 2006
Abstract
The Concrete Design Standard has been reviewed and rewritten and is now available for purchase.
The Standard has been significantly modified and in this article we provide an overview of the changes.
Composite Metal-Deck Slabs Subject To Concentrated Loading
Abstract
Composite metal-deck slabs consist of a profiled steel decking and an in situ concrete topping. The decking serves the dual function of permanent formwork to the wet concrete and, when the concrete has gained sufficient strength, external reinforcement to the slab to resist applied loads.
Design aids for these floor systems have consisted of manufacturer prepared Design Manuals and recently computer based design software. This information has typically addressed uniformly distributed loading, with little guidance available to local designers for metal-deck slabs subject to concentrated loading. In lieu of appropriate local design standards reference is often made to the British limit state format Standard BS 5950.4 [1] when designing for such loading. Rather than reproducing this Code verbatim, the intention of this paper
is to focus on the modifications required to standard New Zealand reinforced concrete design practice to account for the unique features of composite metal-deck slabs in resisting concentrated loads.
Shear Design Of Concrete Masonry Structures Using NZS 4230:2004
Abstract
The shear provisions in the recently updated masonry design standard, NZS 4230_2004, were significantly revised to incorporate a model that accounts for the reduction in masonry shear strength when flexural ductility level increases. This model allows consideration of the beneficial influences on masonry shear strength of the dowel action of tension longitudinal reinforcement and of wall aspect ratio. The revised masonry shear provisions also treat the strength enhancement provided by axial compression as an independent component of shear strength, resulting from a diagonal compression strut. Design illustrations
are presented to demonstrate the intended procedure when using these new shear provisions.
Inclined Screws For More Efficient Timber Joints_Observations At University Of Karlsruhe
Abstract
Concerned with timber joints for industrial and commercial structures. In these joints, the coachscrews are organised so that they work in tension and not in the usual way of shear and bending. The researchers have found that a considerably less number of fixings is needed.
These types of coach-screw joints can be used for transferring axial load, shear, and bending moments. However, for simplicity, I shall begin by explaining how a joint with axial load works.
Design And Testing Of A Composite Timber And Concrete Floor System (Reprinted Structural Engineer
Abstract
Timber frame buildings may have low embodied energy, but have the disadvantage of low thermal mass. Steel and concrete composite construction provides good thermal mass but is becoming less economic with the increasing cost of steel. This paper presents results from testing of a composite system that allows the use of timber with improved structural efficiency and increased thermal mass. The composite system consists of a concrete slab cast on profiled steel decking acting compositely with glue-laminated timber beams. Composite action is achieved with coach screw shear connectors between the beams and slab. The connectors have been tested in “push-out” shear tests and a three-point bend test of a full-scale floor slab has been completed. The
composite system is more than three times as stiff and almost twice as strong as the same beam/slab configuration without composite action. Existing analytical and design methods are compared to finite element predictions and the experimental results and show good correlation.
Design And Testing Of A Composite Timber And Concrete Floor System (Reprinted from Structural Engineer)
Project Corner Arch Bridge Strengthening_Tainui Bridge over Waikato River NZ (Based on paper presented at IPENZ Bridge Design Conference, October 2005
Abstract
The 327 m long Tainui Bridge over the Waikato River in New Zealand was identified as a bridge to be strengthened on the proposed route on which to haul super loads of up to 520t as part of the Huntly Power Station upgrade project. This 45 year old structure requires substantial strengthening in order to carry these loads which are some six times heavier than those for which the bridge was originally designed.
Strengthening works to the sub and superstructure required unique design solutions that took into account incorporation of existing components of the bridge, where possible, to reduce costs. While the substructure and deck components are retained and strengthened where necessary, the existing arch units will be replaced while the structure remains open to traffic. The strengthened structure will have a more aesthetic appeal, be more robust and durable giving it an extended life, aspects that will benefit all users. The project team developed an innovative solution for erection of the new arch components.
Piers 1½, 3 And 5 Strengthening and Restoration, San Francisco
Abstract
The San Francisco Waterfront is characterised by its historic Pier structures, dating back to the early part of the 20th century. Concurrent with the successful restoration of the Ferry building and the adjacent Pier 1 (now the home of the Port of San Francisco offices), the Port of San Francisco solicited proposals for the redevelopment of the adjacent Piers 1½, 3 and 5.
Holmes Consulting Group, through its San Francisco subsidiary Holmes Culley, became involved with the successful bidder, Pacific Waterfront Partners (PWP). As part of the rehabilitation, a seismic retrofit of the existing concrete Wharf and Pier substructure to meet the requirements of the San Francisco Building Code (SFBC) was required. The existing substructure was severely degraded due to prolonged exposure to the aggressive marine environment of the San Francisco Bay. A significant amount of work was required to rehabilitate the gravity load resisting system of the substructure to meet the required design loading. From our initial analysis it was obvious that the existing substructure, even when strengthened to support the required gravity loading, did not have the lateral load capacity to meet the requirements of the SFBC.
Material Strains And Relevance To Seismic Design
Abstract
With the seismic provisions in the Loadings Standard, NZS 4203:1992, being replaced by NZS 1170.5:2004 (Structural Design Actions – Earthquake Actions), a number of changes have been made to seismic design in New Zealand. The most significant of these is the requirement that the level of detailing used in potential plastic regions (nominally ductile, limited ductile or ductile) be determined on the basis of the predicted magnitudes of
deformation they are required to sustain in the ultimate limit state. Previously the level of detailing was determined principally on the basis of the structural ductility factor. However, it is shown that the structural ductility factor does not give a reliable guide to the deformation sustained in an individual plastic region. This paper outlines the background to the change in the way that the level of detailing is determined and it discusses how predicted inelastic deformation demands can be found in the design of concrete structures.
Using Disasters as a Learning Tool in Higher Education
Abstract
(Reprinted from IStructE’s – The Structural Engineer Volume 84 No. 15); This report was written by Alan Jennings DSc, CEng, FIStructE, MICE, FZMA Professor Emeritus, Queen’s University Belfast, prior to his death on 21 September 2005, and Pauline Mackinnon BSc, PhD, CEng, MICE, Senior Lecture,: QUB.
Since the first ‘Learning from Disasters’ exercises were conducted at Queen’s University Belfast in 1994 and also at the University of Glasgow in 1997, much has been learnt not only by the students but also by the organisers about disasters and how to maximise the learning experience. This report discusses how the exercises have progressed and also how awareness of disasters could improve the preparation of students for study topics and, at a later date, a life in industry.
Material Strain Limits For Seismic Design Of Concrete Structures
Abstract
The design of structures to resist seismic actions to New Zealand Standards requires the level of detailing used in potential plastic regions to be based on the predicted material strain levels that they sustain in the ultimate limit state. For potential plastic hinges in reinforced concrete sections, curvatures are used rather than strains in reinforcement or concrete. This substitution is made as it is difficult to calculate realistic reinforcement and concrete strains in plastic hinges subjected to cyclic loading. Test results from 37 beams, 25 columns and 36 walls were examined. From each of these the maximum nominal curvature sustained when the lateral force reduced to 80 percent of the theoretical strength was found. From the results of the tests, design curvature limits for plastic hinges have been developed. These limits will be submitted to Standards with the proposal that they are incorporated in an amendment to the Structural Concrete Standard NZS 3101:2006. They have a more rational basis than the existing curvature limits in the Standard and they are easier to use in design.
A Concrete Beam Design Program to be available to Members on the SESOC Website
Abstract
The Society together with the Cement and Concrete Association of New Zealand (CCANZ) has sponsored the development of a concrete beam design program to be made available to members, free of charge, on the website in the same way and under the same conditions as the Soils program.
Articles for Discussion IPENZ Structural Task Force SESOC Committee Update
Abstract
The John Scarry open letter to IPENZ in late 2002 raised concerns about the standard of structural engineering in New Zealand. Within a year of John’s letter an IPENZ Structural Engineering Taskforce recommended several changes for the industry. SESOC was represented on that Taskforce group by our then president, Dr Barry Davidson. Approximately three years have passed since the publication of the IPENZ “Report of the Structural Engineering Taskforce Enquiring into the State of Practice in Structural Engineering in New Zealand”. The SESOC Management Committee felt it would be worthwhile at this time to summarise the current status, as we see it, of the issues raised in the Taskforce report.
Project Corner Reinforcement Corrosion And Its Remediation With A Case Study Of Cathodic Protection Of Pre-stressed Beams
Abstract
(Reprinted from IStructE’s The Structural Engineer Volume 84 No. 23); The deterioration of reinforced and pre-stressed concrete structures, resulting from corrosion of steel reinforcement, is a worldwide problem. The extent of the problem is evident by the
size of the concrete repair market, which is now well established, with a multitude of materials and systems for reinstatement of the corrosion damaged structures. Equally, the attention given to this subject by international practitioner and researcher communities and the enormous number of publications on the subject demonstrates both the problem size and the desire to achieve long-term solutions.
Project Corner Reinforcement Corrosion And Its Remediation With A Case Study Of Cathodic Protection Of Pre-stressed Beams
Learning Experiences (Contributions From Members)
Abstract
Sometimes we experience learning the hard way. We build our knowledge with experiences that go as expected and well, and we also learn from some experiences that did not go so well. From these less pleasant experiences, we tell ourselves “we won’t do that again”. We need to share those experiences so we can all learn and move forward. We hope to make this section a regular feature where you can share your less pleasant experiences so that we all may learn from them.
Structural Engineering Competence in the Computer Era
Abstract
Since the introduction of computers to support design and analysis, concern has often been expressed that the use of software tends to result in a decline in basic structural engineering skills. The modern use of computer programs to carry out design processes introduces an element of risk. The risk must be assessed and managed. The use of computers has many benefits but demands a higher level of intellectual effort and competence than in the past. The paper explains why this is so and discusses how process control strategies can help to ensure that computer-aided design not only provides an acceptable level of risk but can also have potential to increase competence.
The Use of a Semi-rigid Flange Bolted Joint at Auckland International Airport – Terminal Expansion
Abstract
A semi-rigid Flange Bolted Joint system was adopted in the current expansion of the Auckland International Terminal Building. The newly developed joint offers a number of advantages, and the various design issues identified on the project were overcome. Important modifications to the design procedures are recommended for “gravity dominated” frames. Improvements to the joint were introduced and tested that significantly increase the inelastic rotation capacity.
Categorisation of Post Disaster Facilities
Abstract
The Department of Building and Housing, in conjunction with the Ministry of Civil Defence and Emergency Management, has commenced a project initiative to link structural design requirements for post-disaster facilities with overarching civil defence emergency management requirements. It is intended that this work will prompt Civil Defence Emergency Management (CDEM) Groups and Territorial Authorities to identify special facilities and set policies to help improve their post-disaster functionality. Lifeline utility organisations, government departments and local authorities have the additional requirement under section 60 of the Civil Defence Emergency Management (CDEW Act that they must ensure they are
able to function to the fullest extent possible, even though this may be at a reduced level, during and after an emergency. There is a need for informative text which provides a linkage between this requirement and Table 3.2 in AUNZS 1170.0..
Clarification of the categorisation of these facilities in A W S 1170 raises wider issues in relation to the designation of those which are critical after a disaster. Such designation should be made at a higher level than a standard for the structural design of buildings to give a wider effect. There is recognition within the Ministry of Civil Defence and Emergency Management, Ministry of Health, the Department of Building and Housing and other agencies that action should be taken. As a means of informing the decision process, the
Department of Building and Housing intends to prepare a position paper summarising the issues that need to be addressed and the reasons. This will require the involvement of all agencies directly affected by the categorisation. Through this wider involvement it is hoped to raise awareness and promote consistency in the designation of the importance of various facilities that reflect the wider community perspectives.
Ability of NZ Houses to resist Wind and Earthquake Racking Loads
Abstract
This paper summarises recent work done at BRANZ to ensure good house performance under wind and earthquake loads. Problems were identified and recommendations made for changes to the New Zealand timber framed buildings standard, NZS 3604:1999. The work comprises: Inelastic time history computer analysis of models of houses to investigate torsion in houses with horizontal irregularity. Testing walls with window openings to determine maximum opening size and location which would not prejudice the wall bracing strength. Changes of nailing pattern around the edges of windows which would simplify construction but not prejudice wall bracing strength were also investigated. Determination of the maximum racking load a bracing wall can resist which is compatible with minimum floor construction stipulated by NZS 3604.
Empirical Equations for Predicting the Fundamental Period of Eccentrically Braced Steel Buildings
Abstract
The Commentary of the Earthquake Loadings Standard NZS: II 70.5provides an empirical method for predicting the fundamental period of vibration of steel frames. The method does not use material and section properties appropriate to the limit state under consideration. Therefore the predicted period can be very different from the value obtained from more accurate analysis. The inaccuracy normally leads to significant overestimating the
design actions in the preliminary design stage. Steel Construction New Zealand has been involved with preliminary steel structural design of more than 190 steel structures in New Zealand since 1995. This paper presents an improved empirical method to estimate the fundamental period of steel framed structures according to the height and mass distribution based on the Steel Construction New Zealand, SCNZ design database.
Fibre Reinforcement – Steel vs Synthetic
Abstract
This paper looks at the two main fibre types used to reinforce concrete in slabs on grade and shotcrete (ground support). It discusses their relative performance in the different laboratory tests used to evaluate fibre reinforced concrete composites and proceeds to argue what these differences in behaviour in the laboratory will mean in real structures. It does this by particularly addressing the advantages to be gained by reinforcing slabs on grade with fibres that are tuned to improving the load carrying capacity of a product as brittle as concrete.