Journals >> Abstract VOLUME 15 No. 1 (April 2002)
SESOC INFORMATION
SESOC MANAGEMENT COMMITTEE – PRESIDENT’S REPORT (Dr. B. Davidson)
GUEST EDITORIAL: Engineering Judgement, Peer Review (Barry Brown)
TECHNICAL PAPERS
Influence of Hysteretic Form on the Basic Seismic Hazard Coefficients – H.Judi, R. Fenwick, B.Davidson.
The hysteretic behaviour of different structural forms and materials varies widely. However, codes of practice generally give only one set of basic seismic hazard coefficients (response spectra) to cover all structural types. To assess the influence of different hysteretic types on seismic response a large number of time history analyses are made using a number of different earthquake records and hysteretic models. In addition the influence of changing both the level of damping and the rate of strain hardening are examined.
The analyses indicate that the form of hysteretic response has only a relatively minor influence on the maximum displacement that is sustained. Varying the viscous damping level was found to make a significant difference to elastically responding structures, but it had less effect on ductile structures. Changing the strain hardening ratio was found to have only a small influence on behaviour.
L, N and E GRADE REINFORCING STEEL – D. Bull, C.Allington
The advent of the Joint Australian New Zealand Standard AS/NZS 4671:2001, "Steel Reinforcing Materials" has resulted in the introduction of three classes of Grade 500 reinforcement into the New Zealand rnarketplace. A number of issues have been raised. This paper discusses in implications for the classes of Grade 500: L, N and E, with respect to elongation capacities of each, as well as: bond performance, stiffness of members flexural overstrength, fatigue resistance and site issues. A number of recommendations are made, including the need for more research to determine an appropriate overstrength factor for Grade 500E.
Development of Techniques to Maximise Benefits of Post-Tensioned Slabs on Grade - J. Marchant
Although PT slabs were introduced into New Zealand over 30 years ago, it is only in the last couple of years that they have been constructed in significant numbers. To illustrate this point, whereas only a dozen PT slabs were constructed prior to January 2000, at least 50 have been completed since then with many more under consideration.
The reason for this increase has been a determined effort to optimise the design process, minimise component costs and streamline construction methods to provide cost savings.
The main advantage of PT slabs is the ability to construct vast areas of floor with no joints or sawcuts. This feature is particularly desirable for applications such as large distribution warehouses with high racks serviced by solid-wheeled high-reach fork trucks which have a low tolerance to discontinuities in the floor surface.Although it is easy to design PT slabs of over 1 hectare for a single pour, the logistics of constructing such a floor are daunting and hence it is unlikely to occur, unfortunately. Hence the full advantage of PT slabs has often been forsaken in favour of the limited available concrete supply and delivery resources.
This paper outlines the recent development of design and construction techniques to overcome this challenge.
What is the Stiffness of Reinforced Concrete Walls? – Discussion on paper in V13 No.2 (R. Fenwick and D.Bull) by N. Priestley and T. Paulay.
This paper was read with interest, particularly as it raises questions about a key point adopted in several of our recent papers, namely that, for a given structural member with different amounts of reinforcement and/or axial load, strength and stiffness are essentially proportional. Since we find ourselves unable to agree with many of their conclusions we provide the following discussion of the paper:
The authors of this discussion restrict their comments to a comparatively small subset of structural elements - namely slender cantilever walls in low rise buildings - and specifically exclude discussion of the influence of shear deformation or for example additional deformation resulting from strain penetration of vertical reinforcement into foundation members. A range of axial compression loads of 0 to 0.2f’cAg, and a range of reinforcement ratios of 0.0025-0.02 are considered, though the authors state that reinforcement ratios above 0.0125 are not practical.
Although it appears that the results presented in the paper were based on analyses of specific wall details (see Fig. 4, in the original paper, relevant details therein are not provided. This makes direct checking of their results difficult. However, we feel that first we must question the range of parameters considered by the authors.
What is the Stiffness of Reinforced Concrete Walls? – Response to Discussion by N. Priestley and T. Paulay by Authors R. Fenwick and D. Bull of the original Paper.
The Authors (Fenwick and Bull) thank the discussers (Priestley and Paulay) for their comments on their paper about the stiffness of concrete walls, in the SESOC Journal Vol.13, No.2, Sept. 2000.
We hope that the comments and our response will be of interest and value to practicing structural designers.
The background to some of the analytical research that has been carried out in connection with assessing appropriate stiffness values is described. This is followed by detailed discussion of the points that the authors have raised.
The Challenge of Grade 500 Steel – C.R. O'Grady
The author explores the implications of this higher yield reinforcing, questioning the relevance of some earlier empirical tests, and suggesting the need for further early testing. Bond and shear stresses in beam column joints are discussed, in the light of the higher yield stress.
ARTICLES FOR DISCUSSION
New Zealand Radiata Pine and Timber Grading Methods – M.L. Batchelar.
Two Questions from the SESOC Soils Seminar Series – M.J. Pender
PROJECT CORNER
PricewaterhouseCoopers Tower – A. Smith.
The PricewaterhouseCoopers (PwC) Tower, as shown in a photograph and floor plan, is the latest addition to the Auckland CBD skyline. There are 2 entry foyer and retail levels, 23 office floors, seven part-levels of carparking including two levels below ground, and three rooftop plantroom levels. A 25m. mast on top of the roof takes the building to 142 m above sea level.
The building is located in Auckland's revitalised waterfront area, with uninterrupted harbour views, the largest column free floor plates of any NZ office tower, the latest technology in building amenities and services and a high performance structure to boot.
The design approach and considerations, and the construction programme are covered by the paper.
COMPUTER CORNER
Using Computers in Engineering Calculations – from the I.Struct.E Journal “The Structural Engineer”, V80, No.3
There are growing concerns over the inappropriate use of computers in engineering design calculations. Computer use has reduced thinking downtime. A new report from the Institution of Structural Engineers provides guidance. "Guidelines for the use of computers for engineering calculations" will soon be available from the I.Struct.E. Many other valuable publications are available through their web site.
SESOC|Soils Program Available for Download from the SESOC Web Site – E.J. Forrest
The limit state soils design program that has been under development for the last four years is now available (annually to registered financial SESOC members) on the SESOC web site - www.sesoc.org.nz, in the form of a download install package. The program is based on the New Zealand Building Code document, which is a verification method, Bl/VM4. Where explicit methods are set out within the document, every effort has been made to adhere to these within the program.
The document Bl/VM4 however, like all other similar documents. has areas that lack clarity from a practitioner's point of view. Some of these are listed below:
(a.) Some equations are not capable of direct algebraic solution. Some calculation tool is necessary to solve these.
(b.) The intent and limit of the application of the 0.8 seismic strength reduction factor, Fearthquake is not clearly defined.
(c.) The length of pile shaft to be used in calculating the shaft load is not defined where lateral load is involved.
(d.) The application of stability load factors and normal dead load factors with the concrete strength reduction factor f to the calculation of footings of retaining walls is not defined.
(e.) What happens in pile design, if there is not sufficient thickness in the founding layer, to comply with the requirement for three times the base breadth for penetration and for depth below the base, is not defined.
(f.) The designer must choose on which referenced document to base the corrosion rate for steel piles.It was to clarify these questions and others, that it was decided that an educative program with worked examples would best suit the needs of practitioners to become familiar with the limit state methods. In some cases the problem is merely highlighted. and the designer still must make the choices. This paper seeks to detail where departure from the verification method is required.
The purpose for which the program was written was to assist and ease the path of members in the transition from the old elastic methods of soils analysis into the new limit-state concepts that are now required under the building code. It is not like a commercial program written as a design tool.
Prospective users need to fill the required personal details in the registration page, and get their ID Code. The computer reads the details and forms an ID Code of four, four-digit numbers. Click 'Write SoilsIni.txt File'. Open your email program and send an email to soils-reg@sesoc.org.nz – with the 'SoilsIni.txt' file attached. The registration will be attended to as expeditiously as possible – hopefully within 24 hours.
Behaviour of Simple Structures: Challenges – Part 6 - Geoff Bird
Test your analytical ability!
HERA Composite Design and Construction Seminars - Geoff Bird
These seminars covered a full range of topics associated with composite floor system design and construction. The seminar notes were HERA Report R4-113, and background papers, which are available from HERA.
The following document and design aids were also provided:-
" Guide to Practical Aspects of Composite Floor System Design and Construction, Including Concrete Placement"
HiBond Design Wizard program (available free from Dimond).
HERA Vibration Design Program (available from HERA).
STANDARDS NEW ZEALAND
Standards for Structural Engineers – Ian Brewer.
New AS/NZS Joint Loadings Standards: Public Comment Sought on Conditions of Contract, DZ3910, DZ3916, Obtaining Drafts for Comment, Closing Date: Reinforced Concrete Masonry Design.
JOINT SESOC / IPENZ / STRUCT.E COMMITTEE NEWSLETTER - R. Aitken
Joint Committee membership: Part 3 Examination (held in April)
" The Structural Engineer" magazine is available on line at www.istructe.org.uk (for members only). This web site is well worth a visit.
NEWS FROM THE REGIONAL STRUCTURAL GROUPS
News of Projects, Structural Group Meetings and Visits, from Auckland (Ashley Smith), Waikato (Gordon Hughes), Wellington (Graeme Beattie) and Canterbury (Dene Cook).
