Keynote Address Session 1 Session 2 Session 3 Session 4 Session 5 Session 6 Poster Session Session 8 

Ground motion records for time-history analysis of URM buildings in New Zealand – The North Island

Claudio Oyarzo-Vera, Graeme McVerry and Jason Ingham

The New Zealand Standard for Structural Design Actions, NZS 1170.5:2004, defines a criterion to select ground motion records for time-history analysis based on similarity between the seismological signature of earthquakes used for the analysis and those that are expected to be encountered at a given location. However, as most structural designers are not familiar with the specific details of the probabilistic seismic hazard model used to determine the design spectra, further information is currently required before designers can readily select appropriate earthquake records.

The objective of the study reported here was to integrate the seismologist’s and the engineer’s specialist knowledge, and to present a method to select the best set of records for different locations considering the hazard level for each location and the seismological characteristic of the expected ground motions. For this purpose has been divided into several seismological hazard zones considering the mapping of the Hazard Factor presented in NZS 1170.5:2004, and the fault mechanism. Furthermore, a suite of records is proposed for use when conducting time-history analysis of existing New Zealand unreinforced masonry (URM) buildings, satisfying the Standard requirements. Recommendations are presented for selecting the records to be used in each zone. Preliminary results are presented for the North Island of New Zealand. A similar proposal for the South Island is still under study.

Paper P25: [Read] [Presentation]

Internal forces of concrete floor diaphragms in multi-storey buildings

Debra Gardiner, Des Bull and Athol Carr

Simplistic design methods are commonly employed by design engineers to determine the approximate magnitude and distribution of inertial forces in reinforced concrete floor diaphragms of multi-storey buildings. Various researchers have identified that the commonly employed simplistic design method, the Equivalent Static Analysis method, in some cases, provides a poor representation of the true structural response. This research investigates the magnitude and trends of forces in concrete floor diaphragms, with an emphasis of transfer forces, under seismic loading. This research considers the following items: inertial forces which develop from the acceleration of the floor mass; transfer forces which develop from the interaction of lateral force resisting elements with different deformation patterns, such as wall and frame elements; and variation of transfer forces due to different strengths and stiffness of the structural elements. The magnitude and trends of forces in the floor diaphragms have been determined using 2-dimensional inelastic time history analysis. Trends have been identified which will aid the improvement of seismic floor diaphragm design methods.

Paper P21: [Read] [Presentation]

Seismic Performance of Hollow-core Flooring: the Significance of Negative Bending Moments

Lisa Woods, Richard Fenwick and Des Bull

Hollow-core flooring units, as described in the technical literature, are intended to be used as simply supported members. However, in construction continuity is often established between the units and supporting structure by the addition of insitu topping concrete and reinforcement. This change in structural form can result in negative moments and axial forces being induced in the floor by gravity loads, wind and seismic actions. Vertical seismic ground motion in particular can make a significant contribution to negative moments induced in the floor. This paper focuses on two failure mechanisms which may occur in negative moment regions of hollow-core floors, namely a flexural failure and a shear failure. It is shown that, with the detailing in common use prior to the release of the Structural Concrete Standard, NZS 3101-2006, there is a potential for brittle negative moment failure to occur under seismic conditions. Analytical work indicates that under some conditions a diagonal tension (shear) failure may also occur. As the failure of a floor may lead to progressive collapse it is important that these two aspects are considered along with a number of other potential failure modes in the retrofit or design of buildings. Guidance is given on methods of assessing the negative moment flexural strength and shear strength of hollow-core floors.

Paper P24: [Read] [Presentation]

Experimental study on the seismic performance of RC moment resisting frames with precast-prestressed floor units

Brian Peng, Richard Fenwick, Rajesh Dhakal and Des Bull

A three dimensional approximately half scale experimental sub-assemblage is currently being tested at the University of Canterbury to investigate the effect of precast-prestressed floor units, which do not span past the internal columns, on the seismic performance of reinforced concrete moment resisting frames. This paper reports the preliminary results from the test, with the focus on elongation within the plastic hinges and strength enhancement in the frames. The preliminary results have shown that elongation between the external and internal plastic hinges vary by more than two fold. With the addition of the prestressed floor units, the strength of the moment resisting frame used in the test was found to be 25% higher than the current code specified value. In other situations, particularly where there are more than 2 bays in a moment resisting frame, greater strength enhancement may be expected. Any under-estimation of beam strength is undesirable as it may result in the development of non-ductile failure modes in a major earthquake.

Paper P37: [Read] [Presentation]

Keynote Address Session 1 Session 2 Session 3 Session 4 Session 5 Session 6 Poster Session Session 8