Journals >> Abstract VOLUME 19 No. 1 (April 2006)
SESOC MANAGEMENT COMMITTEE
President's Report (Mr. Ashley Smith)
Note from the New Editor (Mr. Tyson Giles)LETTER TO THE EDITOR: Quenched and Tempered Reinforcing Steel (Debate continued from Vol. 18 No.1, p.30, by John Hare)
TECHNICAL PAPERS
ASI Eccentrically Loaded Cleat Compression Design Model 1996 – DO NOT USE (Charles Clifton)
In 1996 the Australian Steel Institute published the Design of Structural Steel Hollow Connections, by Syam and Chapman, commonly referred to as the “Blue Book”. This publication filled a significant gap in design coverage for hollow section connections for both Australia and New Zealand. One of the connection types covered in the Blue Book is slotted end plates into the end of SHS members. Section 9.3 includes a design model for an eccentrically connected cleat connection carrying compression load.
From HERA analyses it is apparent that the Blue Book calculated capacity with respect to eccentrically loaded cleats in compression is significantly un-conservative; that peak axial load capacity is reached at relatively low axial deformation after which sidesway occurs and this is sensitive to erection tolerances and fit-up.
A recommended design procedure has been developed by HERA, which will be in HERA’s Steel Design and Construction Bulletin Issue No. 80, due out in the third quarter of 2006.
The Concrete Design Standard 2006 (Dene Cook)
The Concrete Design Standard has been significantly modified and this article provides an overview of the changes. It is now published in a ring binder to allow easier amendments in future, and has section markers to allow easier navigation around the Standard. Layout has been modified so that all the information required to design various elements are gathered into separate chapters.
The changes can be broadly subdivided into 3 categories: Editorial; to incorporate the seismic design philosophy of NZS1170.5; and many technological advancements.Composite Metal-Deck Slabs Subject to Concentrated Loading (Alistair Fussell, Kevin Cowie and Xiao Huntian)
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. In addition, the limit state approach of BS 5950.4 [1] is compared to local design standards along with a presentation of a spreadsheet-based design aid prepared by Steel Construction New Zealand. To illustrate the ultimate limit state design checks required for composite slabs, examples have been prepared for point loading.
Shear Design of Concrete Masonry using NZS4230:2004 (K.C. Voon and J.M. Ingham)
The shear provisions in the updated masonry design standard NZS4230:2004 were significantly revised to incorporate a model that accounts for the reduction in masonry shear strength when the flexural ductility increases.
This model allows consideration of the beneficial influences on masonry shear strength of the dowel action of the tension longitudinal reinforcement and of wall aspect-ratio. The revised masonry shear provisions also treat the shear 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 the University of Karlsruhe (John Chapman)
The writer visited the timber research centre at this University. One of the projects in hand was concerned with timber joints for industrial and commercial structures. It these, coach screws are organized so that they work in tension, and not in the usual way of shear and bending. It was found that a considerably smaller number of fixings were needed.
Coach screws with drilling tips and countersunk heads have been developed which are therefore self-drilling and can mobilise the screw shanks’ tension capacity, so they can be placed in one operation.
These can be used in portal frame knees.Design and Testing of a Composite Timber and Concrete Floor System (R. Persaud and Dr. D. Symons) (Reprinted from The Structural Engineer Volume 84 No.4)
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 in the U.K. 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 the slab. The connectors have been tested in “push-out” shear tests and a three-point bend test on 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 show good correlation.
PROJECT CORNER
Arch Bridge Strengthening – Tainui Bridge Over The Waikato River, N.Z. (P.T. Sheasby and I.D. Sloane)
The 327m long Tainui Bridge over the Waikato River 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 required 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 super-structure 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 were to be replaced while the bridge remains open to traffic. The strengthened structure was to have a more aesthetic appeal, be more robust and durable, giving it an extended life, aspects which will benefit all users. The project team developed an innovative solution for erection of the new arch components.
Piers 1-1/2, 3 and 5 Strengthening and Restoration, San Francisco. (Zander Sivyer, John Hare and Trevor Kelly)
The Port of San Francisco desired the redevelopment of these 1910 piers to a combination of office and retail space. A major part of the project would be the rehabilitation of the existing concrete deck structure, which was supported on concrete piles of varying lengths and embedments.
With the existing pier substructure severely deteriorated due to the aggressive marine environment, it did not have the lateral load capacity to meet the requirements of the San Francisco Building Code, even when strengthened to support the required design loading.
A finite element model was developed to evaluate the as-is structure and assess options to increase strength and/or reduce demand by energy dissipation. Hysteretic damping combined with ductility enhancement of the strengthened existing structure was chosen as the most cost-effective method of seismic upgrade. Ductility enhancement was provided with carbon fibre reinforced polymer wraps, and hysteretic damping by yielding link beams connected to the existing structure restrained by a pair of opposing raking piles.
NEWS FROM THE REGIONAL STRUCTURAL GROUPS
Auckland Structural Group – Paul Campbell
Canterbury Structural Group – Dene Cook
Waikato Structural Group – John Dale
Wellington Structural Group – Graeme BeattieThese consist of reports of past meetings, and planned future meetings.
