Journals >> Abstract VOLUME 16 No. 1 (April 2003)
SESOC INFORMATION
SESOC MANAGEMENT COMMITTEE – PRESIDENT’S REPORT (Dr. B. Davidson)
GUEST EDITORIAL
A PATH TOWARDS PERFORMANCE BASED SEISMIC DESIGN – Andrew King
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. The challenge now being faced is to bring this concept into place for new buildings and to provide a rational approach for both standards development, and for ‘informed clients’ to make design decisions on the consideration of ‘how long can we accept this facility being out of operation’.
The NZ Building Code sets out the minimum performance objectives which are required to be met, and the Approved Documents (which accompany the Code) prescribe a set of Acceptable Solutions and Verification Methods which, when followed, will result in buildings which satisfy those performance objectives. Regulators currently resist the inclusion of public expectations or economic loss from the mandatory building code provisions, leaving these provisions to ‘market forces’. owner/operator. As such they can appreciate that enhanced performance comes at an increased initial cost. The ‘lowest contract price’ will often not satisfy expectations of additional user comfort or loss minimisation or disruption under extreme events. A framework is suggested to enable both code minimum performance levels and higher user-defined performance levels to be stated with sufficient clarity . This should provide a means of using a design technique to attain true performance levels to ensure consistency in attaining regulated minimum values.
LETTER TO THE EDITOR (Richard Fenwick)
Draft AS/NZS 1170.4 - Earthquake Loading
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. They have not been acknowledged. Points that I have raised have been ignored, even when pointing out basic errors in equations. I am concerned about the low strength levels in several submissions to Standards, as well as in the literature. The three major points ignored are given.
LETTER FROM THE EDITOR TO FORESTY RESEARCH INSTITUTE (Esli Forrest)
UNTREATED RADIATA PINE & INDUSTRY FUNDED STANDARDS
Because of present concern about rotting timber framing, we sent a letter asking questions about the durability of timber to Mr. Doug Gaunt at the Forestry Research Institute.
We received back replies to the questions. They serve 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.
TECHNICAL PAPERS
Design of cold-formed stainless steel structures (G. Charles Clifton)
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 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 parts 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 (Deam, Fenwick and Butterworth)
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 prestressed 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. The subjects are:
1. Frictional Energy Dissipation in Sliding Flange Joints
2. Influence of Precast Flooring on Moment Resisting Perimeter Frames
3. Full Scale Test of a Segment of a Perimeter Frame Building Incorporating a Hollow Core Floor Slab
Quality Control of Structural Timber in New Zealand (Walford & Gaunt)
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. The issue is still under debate.
Holistic Behaviour Of Concrete Buildings In Fire ( Professor Colin Bailey)
This paper was originally published in the Proceedings of the Institution of Civil Engineers, Structures and Buildings 152, August 2002, Issue 3, pp. 199-212. It is republished here with kind permission of Thomas Telford Limited.
Abstract
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.
Introduction
Between July and September 2001 a unique opportunity presented itself to carry out a fire test on the full-scale, seven-storey, concrete building constructed at the Building Research Establishment (BRE) laboratories in Cardington, Bedford. The design and construction of the in situ-concrete building at Cardington was part of the European Concrete Building Project[1]. This project is an industry-led initiative, with the aim of improving efficiency of production and enhancing the performance of buildings using different forms of concrete construction.
The main aim of the fire test was to investigate the behaviour of a full-scale concrete framed building subjected to a realistic compartment fire and applied static design load. Prior to the fire test, it was envisaged that the results and observations obtained would contribute towards a wider proposed programme of research work, into the holistic behaviour of concrete buildings in fire. The ultimate aim of this research is to produce design guidance based on the realistic structural behaviour of the building as a whole, which will result in the construction of safer and possibly more economical buildings.
The main objectives of the overall proposed research were identified as follows:
- To investigate how the building in its entirety resists or accommodates the large thermal expansions from the heated parts of the structure within a given fire compartment.
- To identify both beneficial and detrimental modes of whole building behaviour, that cannot be shown from standard small-scale fire tests.
- To investigate the overall effects of any concrete spalling and to determine its significance on the behaviour of the whole building.
- To compare test results and observations from large-scale fire tests with current methods of design.
This paper presents the results from the fire test on the Cardington building, which will address some of the above objectives. Unfortunately the test results are restrictive in that the fire destroyed the instrumentation cables during the test, leading to the loss of some data. However, the observations and results obtained are of interest and highlight both modes of beneficial and detrimental behaviour of the building as a whole, which are ignored in current design methods.
Before the observations and results from the test are discussed the paper briefly reviews current design methods, design assumptions and typical perceptions of the behaviour of concrete structures in fire. This review will allow the test results to be compared against current design assumptions.
Overstrength Factor For Pacific Steel Micro-Alloy Grade 500 Reinforcement: April 2002 (Des Bull and Chris Allington)
INTRODUCTION
With Grade 500 reinforcement to the market place in New Zealand, designers need to be aware that the overstrength factorof 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 max , to the nominal strength of the concrete member, M n . The nominal capacity is usually calculated using the lower 5 th percentile yield strength of the reinforcement. 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.
The results are not applicable to any other reinforcement produced by any other mill, as the overstrength factor is a function of the characteristics of the steel material produced; most influential of these being the mean yield strength of the steel and the ultimate tensile strength to yield strength ratio.
Full details of the analytical study are given in the Department of Civil Engineering Research Report and a summary of the rational of the variables investigated (section shape, longitudinal steel content, transverse steel content, concrete strength, axial load ratio) are presented elsewhere.
The author’s recommended overstrength factors are 1.4 for beams and 1.35 for columns. These may need to be amended after alterations to the chemistry of the reinforcing by Pacific Steel.
2.0 Analysis Method
A series of monotonic moment-curvature analyses were completed on the beam and column members to, provide a theoretical moment versus curvature response. From the recorded responses the overstrength factors were calculated for curvature ductilities of 10, 15, 20 and 30.
The behaviour of the concrete was modelled using the Mander stress‑strain response for confined and unconfined concrete. A full description of the Mander model is provided elsewhere.
The longitudinal reinforcement in the beams was modelled using the monotonic steel stress response derived by Mander et al., using the six key variables for each reinforcing bar obtained by Pacific Steel. It has been shown in the past that a monotonic response provides an accurate representation of the behaviour of longitudinal reinforcement in beam members where the steel is subjected to large tensile strains and small compressive strains.
The longitudinal reinforcement in the column members was modelled using the same stress-strain response as the beam members. However an additional pseudo-cyclic function was added to allow for the cyclic nature of large tensile and compressive strains imposed on the reinforcing. A full description of the pseudo-cyclic function is provided elsewhere.
Combinations of all of the variables for each cross-sectional shape and member type resulted in approximately 350,000 analyses being completed.
Issues Of Non-Compliance With The Steel Reinforcing Materials Standard - Des Bull
INTRODUCTION
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 AS/NZS 4671?
Designers come under understandable pressure by contractors and developers to permit cheaper alternatives to the conforming design solutions. Typically these alternatives are found after the contracts have been let and the developer is keen to see savings on the contract and increase profitability.
The commentary following may assist designers with respect to acceptance of reinforcing steel from overseas sources.
COMPLIANCE WITH AS/NZS 4671:2001
AS/NZS 4671:2001 is a different document contextually from its predecessor, NZS 3402:1989 [2], in a number of ways. AS/NZS 4671 deals with the statistical review of testing results leading to acceptance of a long term manufacturing run in a manner that is more transparent than was previously the case.
AS/NZS 3402 did have explicit criteria for demonstrating compliance for a specific bundle of reinforcing steel, either selected at a stockist or arriving on site, possibly outside of the original specifications, which was requiring review by the end user (owner/developer) or the design engineer. This was the "Purchaser's tests, 12.2, NZS 3402". In this situation, the "Purchaser" should be interpreted as the end owner of the steel (i.e. the building) and not simply the contractor.
AS/NZS 4671 does not give such an explicit opportunity to review a particular steel. Acceptance criteria of Appendix B [1] are targeted at mills, with and without long term records of demonstrating compliance with AS/NZS 4671. Today, this means that if a designer felt that a particular bundle or piece of steel needed to be verified as complying with AS/NZS 4671, in the course of a contract, then an appropriate clause should be added to the Specification on “Reinforcing Steel” in their contract documents. Clause 12 of AS/NZS 3402 would be a good starting point.
Traceability of the bar from the casting at the foundry to in-place on the building site was a requirement of NZS 3402. This traceability is now limited to the gate of the mill by AS/NZS 4671. It appears that the Technical Code Committee for AS/NZS 4671, at the time, felt that the traceability was a designer/contractor issue having little to do with manufacture.
If the steel bar or coil from a trusted source is consistently used at a site, traceability may not be such an issue. However, if different sources of steel are to be used on the same site, then traceability becomes paramount if one of the steels is not fully compliant with AS/NZS 4671. As with review of specific bundles of steel, the designer would now have to add an appropriate clause to the Specification for Reinforcing Steel to ensure it can be located if required.
ARTICLES FOR DISCUSSION
Some Site Observations And Our Non-Existant Building Control System Authors: E. J. Forrest (Editor) And Ernie Lapish
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.
A two storey brick veneer house is being built on a site where over half the area of the platform sits on about a metre depth of uncertified clay fill which sits on the original top soil. Just to fool the unsuspecting, this clay fill has another layer of top soil over it to make it appear like original ground but all is obvious on the cut exposed down one side of the site. The clay fill gets wide cracks when it dries out.
It is a coastal area where there are the odd patches of reactive clays. There is a building restriction line in place. The house, (fortunately for it) has a pod raft foundation, which requires piles to be driven down where the fill depth exceeds 400 mm. Unfortunately for it, there were no piles inserted.
NZS 3604 clause 3.1.2(e) gives a limitation for assuming 300 kPa necessary bearing as being:
“(e) Excavation for foundations does not reveal buried organic topsoil, soft peat, or soft clay (see 3.2.1).”
Here the excavation on the side cut clearly showed the lines of the original topsoil, the clay fill, and finally the added topsoil. The footing inspection on the site was observed. The building certifier arrived in his car and looked at the job for about 1 minute. He then got out of his car and went over to the builder’s truck and spoke to the foreman.
The foreman got out the approved plans (I could see the pink form). They talked and waived their hands about for approximately 3 minutes. The foreman got out his 5 metre rule and they went and measured the distance to the nearest side boundary, (this took about 1 minute). He did not check front and back where the building restriction line exists. The certifier then walked about half way over the pods and looked at the steel in a central strip footing. He never went near the back half of the building, where the clay fill is or checked any steel cover, growing from a topsoil strip under the outer footing, thinly covered with crusher dust. He then got the plans and on the edge of the front boxing signed the job off. He gave the builder back the plans and went and sat in his car. It was there that he spotted the builder’s loo. He then got out of his car and visited this essential part of the building site. He then went back to his car and drove away. Total elapsed time – about ten minutes.
It turned out that the inspection was under the control of a Territorial Authority. It appears that inspectors were under instruction to assume that the building platform is on certified soil.
Administration steps a Territorial Authority must take, to ensure that buildings founded on fill are satisfactory, is set out in the relevant clauses of NZS 3604:1999.
Site preparation requires organic matter, such as topsoil to be removed from the area of the building and filling.
Irrespective of depth of the fill, foundations are required to “bear upon firm fill for which a certificate of suitability has been issued in terms of NZS 4431 “Code of Practice for Earth Fill for Residential Development””. If the depth of fill exceeds 600 mm within 3 m of the building, then it is outside the provisions of NZS 3604 and the foundations must be specifically designed.
At the time the plans are being examined for Building Consent the depth of fill should be noted and a Construction Review certificate (PS4) required as a condition of consent prior to commencement of the floor construction. Only then can the inspector assume the building platform is on certified soil.
Where piles are placed in boreholes through fill, and driven to a predetermined set into firm ground, a PS4 certificate is not required for the fill. However most soil reports recommend construction practices to place and compact fill to prevent instability and settlement problems that can affect driveways and landscaping.
The writer has two other examples of actual building damage because site inspection was ignored. One involves a dwelling founded on a rubbish heap which settled some 80 mm. The other was a 3 m high pole retaining wall with poles inserted in weak harbour mud which failed and caused settlement of 40mm. in the brick veneer house built just 1.4m. from the wall. In both cases the Territorial Authority accepted no responsibility despite the fact that their inspectors approved the foundations.
It is the responsibility of the building owner to establish that “Good Ground” exists on a site and to confirm this when applying for the building consent. It is also the Territorial Authority’s responsibility to ensure this information is supplied for consideration before issuing the Building Consent.
Engineers need to be wary of the tendency of local authorities to pass on their legal responsibility onto Engineer’s shoulders by way of Producer Statements.
PROJECT CORNER
Britomart Underground Railway Station ( Melvyn Maylin and Sulo Shanmuganayhan)
Of Opus International Consultants, Auckland
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.
Background
A key component of Auckland Regional Land Transport Strategy, is to improve passenger transport services in the region. The current railway station is located on Beach road approximately 1.5 km from the city centre and is quite inconvenient for commuters.
In a bid to improve the public transport facilities and usage, Auckland City is creating a downtown hub called Britomart Interchange. This $NZ 204 million scheme involves a number of key elements: construction of a new underground station, restoration and seismic retrofit of the old Chief Post Office (CPO) building which becomes the main entrance to the underground station, a new concourse passing under the CPO and across Queen Elizabeth Square, a bus interchange in Queen Elizabeth Square and surrounding streets, and revitalisation of the Britomart Place with new public spaces and canopies.
This paper only deals with the design and construction of the underground railway station.
The Britomart project returns the railway station to a site that it occupied 65 years ago but this time places the station underground to maximise the use of the land above and to minimise conflict with ground level circulation.
Project stages and programme
The design of the underground station was commissioned in November 2000 and separated design into preliminary and developed stages. During the preliminary design stage, the multi disciplinary team presented feasible, conceptual designs for costing. This stage ended in February 2001 and was followed by the developed stage that focussed on detailing the concepts, and producing tender drawings and documents. The tenders for construction were invited in August 2001. The construction of the station commenced in November 2001 and will to be completed by June 2003. The first trains are scheduled to arrive in the new underground station in late July 2003.
Station Description
The underground station is approximately 300 m long, 45 m wide, and 12 m deep from the ground level. It has five platforms capable of moving 10,500 people during peak hour as targeted in the Auckland Regional Council’s Passenger Transport Action Plan. The station can accommodate up to 20 trains per hour.
Access to the station is via escalators, stairs, and lifts from both the Eastern and Western ends of the site. The main entrance is through the old CPO building, which is currently undergoing restoration and seismic retrofit.
An additional complication for the Britomart Station is the requirement that it be capable of accommodating diesel locomotives for the foreseeable future until electric engines are introduced. Running diesel engines underground presents significant challenges in terms of air quality and due consideration was given to the ventilation of the whole station and extraction of fumes. Twin, 30 m high ventilation towers at the Eastern end extract the fumes while two, 6.5m high ventilation structures at the Western end ensure that the station gets adequate fresh air.
The station structure is at two levels, with base slab and plenum (an intermediate level) at 12 m and 5 m below ground respectively.
JOINT SESOC/IPENZ/I.STRUCT.E COMMITTEE NEWSLETTER
(Richard Aitken)
Readers will be interested to know that The Institution of Structural Engineers Council unanimously agreed that the New Zealand Division should receive the Award for Branch and Division issues of “The Structural Engineer” for the New Zealand issue dated 15 January 2002. An antique level with the appropriate details will be displayed in the Institution’s Library. In addition a Diploma will be prepared for the Division.
In addition, one of the papers published in that New Zealand edition of the “The Structural Engineer” was awarded the Diploma of the Institution’s Husband Prize. The paper was “The Otira Viaduct Design and Construction” and written by Ian Billings and Richard Holyoake. Husband Prizes are awarded for papers of merit related to bridges and published in “The Structural Engineer”.
The importance of these awards is that they have been won by “ New Zealand” and it helps structural engineering and New Zealand structural engineers gain further reputation and credibility throughout the world. With issues like the John Scarry report and the many comments in the media, it is important that people know the abilities of New Zealand structural engineers.
PART 3 EXAMINATION
The Part 3 Examination, which is 7 hours long, was held at the Beca offices on 11 April 2003. There was one candidate and we wish him the best of luck for a positive result. The invigilator was Graeme Whitmore and we thank him for his services.
How many of us would pass this exam today? The older you get the more certain you are that you probably wouldn’t, and this question is now becoming more relevant as we look at CPEng in the New Zealand environment.
I started on a positive note and I apologise for ending on a slightly negative note, but it is time that IPENZ, SESOC and IStructE complete the discussions on the future of the IPENZ/IStructE agreement. In my view this agreement should be taken over by SESOC for the benefit of New Zealand structural engineering as a whole, and I have made this comment to IPENZ. I hope that we can resolve this issue in the next few months.
YOUNG RESEARCHERS PROGRAM
The Institution of Structural Engineers has for some years promoted a programme for young researchers. This is a system of grants for research projects involving undergraduate students working during recess. An interesting example is given in what follows of such a project involving round timbers working compositely with lime concrete.
The project involves the use of materials that are ecologically sustainable and economic. The lime concrete falls into this category and the combining of it with roundpole timber produced from trimmings has resulted in an interesting project. The project is described on the following pages:-
THE FEASIBILITY OF ROUNDPOLE TIMBER AND LIME CONCRETE COMPOSITE FLOORING - Tobias Hodsdon, An Undergraduate At Bath University, wites About His Young Researcher Grant Funded Project.
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.
The primary benefit over a timber flooring solution is that strength and stiffness are significantly improved, thus making longer spans feasible. Other benefits include improved vibrational damping, additional thermal mass, and increased sound insulation. Benefits over a reinforced concrete floor slab include weight savings by removing redundant concrete from the tension zone, and construction cost savings by utilising the timber as permanent formwork.
Background
Previous work by TRADA, Buro Happold and Gaia Architects identified the potential of roundpole thinnings (100-150 mm diameter) for use in composite construction and established the system as feasible for spans up to 5 m. A waste by-product from woodland plantations, roundpole thinnings are considered a highly sustainable construction material.
To maximise the environmental and energy benefits of this form of construction I investigated the feasibility of using lime concrete instead of cement concrete to cast the topping. Replacement of ordinary Portland cement concrete by ‘eminently’ hydraulic lime concrete can provide around 30% savings in embodied energy, depending on mix proportions.
Hydraulic lime concrete demonstrates relatively low cube strengths of between 5 and 10 MPa at 28 days. For this application, where control of deflection is more important than strength, it was hoped that performance of the composite panels would not be adversely affected.
ASSESSING FEASIBILTY
The following key areas were identified as critical to the feasible use of lime concrete and roundpole timber in composite construction:
Generating sufficient lime concrete strength and stiffness within a reasonable time span;
Ensuring effective shear connection between the timber and lime concrete;
Establishing an optimum lime mix with sufficient water content for workability;
Demonstrating a reliable and predictable failure mode;
Maintaining ease of fabrication and practicability.
In light of the above, the investigation comprised two areas of research. These were firstly to develop a suitable lime concrete mix, and secondly to fabricate and test five prototype panels. One of these panels would be cast with a cement concrete topping, thus identifying any performance penalties resulting from the use of lime concrete.
Lime Concrete Investigation
Following the casting and testing of 24 hydraulic lime concrete cubes, an optimum mix was identified with a lime : aggregate ratio of 1:3 and a water : lime ratio of 1:2. This gave us a 28-day cube strength of 9 MPa and a sufficiently workable consistency.
Design Of The Prototype Panels
The prototype panels were built to investigate the effects of varying the number of shear connectors and altering the topping material. A control panel was designed with a lime concrete topping and 33 shear connectors, built to withstand 4.0 kPa over a 3.0 m span. To this design we varied the various parameters, as summarised in Table 1.
Fabrication
Each panel consisted of five 3.4m long Douglas Fir poles tapering from 130 to 100 mm in diameter. These were laid adjacent to each other, alternating their orientation to tessellate their tapered shape. Threaded steel bars were placed through drilled holes at each end to hold the panel together during construction and testing. 12 mm diameter mild-steel coach screws were screwed into the timber to a depth of 60 mm leaving 75 mm exposed around which the lime concrete was cast.
STANDARDS NEW ZEALAND
Standards for Structural Engineers – Ian Brewer.
As at April 2003:
NZS 3603 Timber Structures Standard - proposed amendment
As/NZS 1170.3:2003 Structural Design Actions – Snow and Ice Actions - published Jan 2003
As/NZS 1170.4 Earthquake Loadings Standard - near final draft
NZS 4230: 1990 – Design of Masonry Structures - public comment draft to be available April 2003
NZS 3101: Concrete Structures - new edition to be developed
NZS 3910 – Conditions of Contract for Building and Civil Engineering Construction - new edition nearing completion.
DZ 3916 – Conditions of Contract for Design and Construction of Building and Civil Engineering Construction - public
comment draft released at same time as draft for NZS 3910.
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.
