		2006 NZSEE Conference
	Abstracts

Keynote Address Learning from Hawke's Bay 1931 Earthquake Performance Assessment and Retrofit Decision Making for Risk Mitigation Behaviour of Walls and Piers Understanding Reinforced Concrete Behaviour Modelling Earthquake Performance Earthquake Performance Poster Papers Design and Development

Seismic Performance of the Terrace Tunnel Approach Walls, Wellington

Francis O'Riley, P. Brabhaharan and David Stewart

The approaches to the Terrace Tunnel on the Wellington Urban Motorway (State Highway 1) have large retaining structures that support the cuttings. The retaining structures are supported by a system of anchors tied back to anchor drive tunnels constructed in the hillside behind the walls. The retaining walls were designed in the 1970’s using a peak ground acceleration of 0.25g.

Transit New Zealand commissioned Opus International Consultants to develop a maintenance strategy for the large approach walls. The strategy identified the need for a seismic performance assessment of these structures. The seismic performance of the walls was assessed for earthquakes with return periods of 475 years (operating level, 0.38g), 1000 years (design level, 0.48g) and a maximum credible earthquake (MCE) (contingency level, 0.75g). The factor of safety against slope instability was found to be less than one for the design level and MCE events. The resulting slope displacements of up to 350 mm are likely to be accommodated by ductile behaviour of the high capacity MacAlloy anchors. The assessment therefore concluded that collapse of the structures is not likely.

The structure therefore meets its performance expectation of minimum damage in a design earthquake event and no collapse in a contingency level MCE event.

Paper P06: [Read]

Conceptual Retrofit Strategy for Existing Hollowcore Seating Connections

James Jensen, Des Bull and Stefano Pampanin

Previous research regarding the seismic performance of existing precast hollowcore floor and ductile lateral frame systems has highlighted several behavioural uncertainties. In particular poor seismic performance due to deformation incompatibilities between the floor diaphragm and frame seismic resisting system have become apparent. Significant rotation and displacement demand on the floor systems due to frame beam elongation, seating beam rotation, and longitudinal perimeter vertical displacement have been identified as the main sources of undesirable damage. As a result the structural integrity at hollowcore seating and perimeter connection interfaces can be jeopardised, potentially leading to a partial or even complete floor collapse.In this paper an overview of expected compatibility issues is given while providing suggestions for conceptual low-invasive retrofit strategies. Particular focus will be given to the experimental investigation on the vulnerability of and suggested retrofit solutions for hollow core-seating connections. The Quasi-static experimental testing procedure focusing on a series of as-built and retrofitted specimens, reproducing a hollowcore-to-seating-beam connection with traditionally adopted details will be presented. Both seating rotation due to the imposed lateral drift and beam elongation effects are simulated in the applied testing set-up. Simplified analysis and modelling aspects regarding the connection behaviour are discussed; expected damage and performance criteria associated with the alternative existing or retrofit solution are also tentatively indicated.

Paper P07: [Read]

Feasibility of Retrofitting Residential Buildings in Istanbul

David Hopkins, Richard Sharpe, Haluk Sucuoglu and Danyal Kubin

Approaches were examined to the structural retro-fitting (strengthening) of 369 apartment buildings in the municipality of Bakirkoy in Istanbul that were classified as high or very high risk in a previous, less detailed, study. Key issues included highly variable construction quality; physical, planning and legal constraints; an imperfect building controls regime; cost and benefits of retrofitting; owner attitudes; and the challenge of finding viable funding mechanisms.

The study included a review of regional seismology, geotechnical investigations, as-built condition surveys, structural analyses, earthquake performance assessment, retrofitting solutions, social impacts, and analysis of the benefits and costs of retrofitting. The integration of social and community considerations into the choice of retrofitting techniques was an important and unique aspect of the study.

The study was funded by the Government of Turkey through a World Bank loan as part of the Marmara Earthquake Emergency Reconstruction project. The overall aim is to mitigate seismic risks in the municipality of Istanbul and reduce the social, economic and financial impacts of potential future earthquakes.

By formulating technical solutions that take account of social and economic conditions, and providing detailed analyses of benefits and costs, the study provides an invaluable resource to help owners and authorities to decide on approaches for retrofitting in Turkey and elsewhere.

Paper P08: [Read]

Concept and Implementation of a Selective Weakening Approach for the Seismic Retrofit of RC Buildings

Matthew Ireland, Stefano Pampanin and Des Bull

Current seismic retrofit strategies generally focus on increasing the strength/stiffness or upgrading mechanical properties of a structure. A typical drawback with this is that the upgraded behaviour might result in an increased demand on the structural and sub-structural elements, i.e. foundation. Herein proposed is a counter-intuitive but rational seismic retrofit strategy of selectively weakening a structural system. Such a retrofit strategy is suitable for application to alternative seismic resisting systems and components including walls, beams, columns and diaphragm connections.

A selective weakening intervention is performed within an overall performance-based retrofit approach with the aim of improving the inelastic behaviour by first reducing the strength/stiffness of specific members within the structural system. This in turn results in a reduced demand on the structural member. Once weakening has been achieved the designer can use the wide range of techniques and materials available (e.g. use of fibre reinforced polymers, steel plates, jacketing or shotcrete) to ensure that adequate characteristics are achieved. Whilst performing this it has to be assured that the structure meets specific performance criteria and the principles of capacity design.

As the first phase in the development of selective weakening, the feasibility of such a retrofit strategy is discussed, with particular focus on possible applications to the seismic retrofit of existing reinforced concrete structural walls. The proposed intervention involves splitting the wall vertically and cutting it at the foundation level to change the inelastic mechanism from shear-type to a flexural/rocking-type behaviour. As part of the overall research program, a series of experimental (quasi-static cyclic) tests on 2/3 scaled reinforced concrete walls representing pre-1970 construction practice or retrofitted configurations are under preparation. A summary of the retrofit strategy design and expected behaviour will be herein given.

Paper P09: [Read]

Verification of Raker Shores using New Zealand Timber

Tony Pettigrew, Massimo Fragiacomo and Des Bull

This paper investigates the capacity of full triangle (fixed) raker shores using New Zealand Timber, through analytical analyses and experimental tests. Full triangle (fixed) raker shores, or simply raker shores, are a temporary structure used to support collapsed or damaged buildings. They are used extensively by Urban Search and Rescue (USAR) teams around the world to allow the safe location and rescue of victims of collapsed or damaged buildings following an earthquake event. The shores used by New Zealand USAR are similar to those used in the United States; however they are made from Radiata Pine which has different mechanical properties than the timber used in the U.S. Hence, the need to verify the shores constructed in New Zealand still provide the required design strength. The analytical verification suggests that raker shores are unsafe, according to the New Zealand Timber Structures Standard NZS 3603:1993. However, the experimental results on full-scale specimens indicate that the performance of the raker shores satisfies the required demands, with a safety factor of 2 with regard to the design load, and a ductile type of failure. Suggestions to increase the capacity of the shores are also included.

Paper P10: [Read]