		2009 NZSEE Conference
	Abstracts

Keynote Address Session 1 Session 2 Session 3A Session 3B Session 4A Session 4B Session 5A Session 5B Session 6 Session 7 Poster Session

It’s Our Fault: Better Defining the Earthquake Risk in Wellington - Results to Date & a Look to the Future

R. Van Dissen, K. Berryman, A. King, T. Webb, H. Brackley, P. Barnes, J. Beavan, R. Benites, P. Barker, R. Carne, U. Cochran, G. Dellow, B. Fry, M. Hemphill-Haley, C. Francois-Holden, G. Lamarche, R. Langridge, N. Litchfield, T. Little, G. McVerry, D. Ninis, N. Palmer, N. Perrin, N. Pondard, S. Semmens, W. Stephenson, R. Robinson, P. Villamor, L. Wallace and K. Wilson

The goal of the It’s Our Fault programme is to see Wellington positioned to become a more resilient city through a comprehensive study of the likelihood of large Wellington earthquakes, the size of these earthquakes, their effects and their impacts on humans and the built environment. Some key results to date include better definition and increased constraints on: 1) faulting in Cook Strait, 2) timing and size of past ruptures on the Wellington, Wairarapa, Wairau, and Ohariu faults, 3) state of locking of the subduction interface, and 4) fault interactions throughout the region, in particular rupture statistics of the Wellington-Wairarapa fault-pair. Current investigations are focused on characterisation of earthquake ground shaking behaviour in Wellington City and the Hutt Valley.

Paper P48: [Poster] [Read] [Presentation]

Earthquake Resistant Design of Tied-Back Retaining Structures

Kevin McManus

A seismic design procedure for tied-back retaining walls was synthesized based on an existing, widely used, semi-empirical design procedure for gravity design of tied-back walls. The design procedure was tested by designing a range of case study walls and then subjecting them to simulated earthquakes by numerical time-history analysis using PLAXIS finite element software for soil and rock. The response of the walls to a variety of real earthquake records was measured including deformations, wall bending moments, and anchor forces.

From the results of these analyses, it was observed that all of the wall designs were robust and performed very well, including those designed only to resist gravity loads. In some cases large permanent deformations were observed (up to 400 mm) but these were for very large earthquakes (scaled peak ground acceleration of 0.6 g). In all cases the walls remained stable with anchor forces safely below ultimate tensile strength. Wall bending moments reached yield in some cases for the extreme earthquakes, but this is considered acceptable provided the wall elements are detailed for ductility.

Walls designed to resist low levels of horizontal acceleration (0.1 g and 0.2 g) showed significant improvements in performance over gravity only designs in terms of permanent displacement for relatively modest increases in cost. Walls designed to resist higher levels of horizontal acceleration (0.3 g and 0.4 g) showed additional improvements in performance but at much greater increases in cost.

Paper P49: [Read] [Presentation]

The Initial Assessment of Earthquake Prone Buildings: A Wairarapa Experience

Michelle Rafferty

This paper presents the practical application of earthquake risk assessment of buildings in the Wairarapa area. An outline of the specific seismic hazard in the Wairarapa and a brief history of the development of the definition of earthquake prone buildings, is followed by an overview of the application of the NZ Society for Earthquake Engineering document ‘Assessment and Improvement of the Structural Performance of Buildings in Earthquakes’ to buildings in the Masterton locality. Focus is given to the Initial Evaluation Procedures outlined in the document, including a review of the alternative methods available, with local examples of varying types of materials and construction.

Paper P50: [Read] [Presentation]

Performance Focussed Conceptual Design to Enhance Route Security, Transmission Gully Highway, Wellington

P. Brabhaharan

Transport access into Wellington after a major earthquake is recognised to be a major issue. The opportunity of improving the security of access, through engineering the proposed Transmission Gully project in an area of rugged terrain and straddling one of the major active faults, was a challenge taken up by the design team.

Route security was adopted as a key objective for the project. An alignment on the western slopes of Transmission Gully was chosen, and is a more secure route in earthquakes and storms than an alignment on the eastern slopes. Enhanced route security was achieved through careful selection of fault crossings, road forms robust to fault movement to enable quick restoration of access, and careful configuration of cut slopes. Configuration of major cut slopes involved integrated consideration of normal, storm and earthquake performance, as well as rock fall hazards and cost effectiveness.

Expected route performance was illustrated through consideration of resilience as damage, availability and outage states in future hazard events. Comparison with the resilience of the existing routes shows that the current Transmission Gully scheme would significantly improve security of access into Wellington. Early focus on route security performance enabled the development of a Transmission Gully scheme with improved security and at a lower cost than the previous schemes.

Paper P51: [Read] [Presentation]

Why Do We Still Tolerate Buildings That Are Unsafe in Earthquakes?

Jitendra Bothara and Richard Sharpe

Earthquakes continue to kill thousands of people and make hundreds of thousands homeless. Within a few seconds they destroy infrastructure that was developed over decades. To a degree, we have the means and knowledge to stop this happening. But, painfully, we are unable to do this because we tolerate unsafe buildings. In this paper, we explore why we are unable to stop this - from both engineering and socio-cultural/ economic perspectives. We look into both issues together, because these are related from a seismic safety point of view.

Not tolerating unsafe building means having a sound engineering definition and a sound implementation strategy. From an engineering perspective, we looked at the common concepts/ terminology we use in engineering to describe safe buildings and the procedures we use to satisfy ourselves as designers that we are doing the right thing. However, we find there are many paradoxes (i.e., conflicts with expectations) in our common procedures and explanations when we try to define safe. These are because interpretations vary between people and cultures. We authors (each coming from a very different culture) have debated over many years our appreciation of risk. It is clear that a definition of safe depends both on how we define risk, and on how much risk we are prepared to accept.

From an implementation point of view, there also seem to be many myths and fallacies in our concepts. We believe that a good seismic standard enforced with legal means could solve the problem, but when developing a strategy for implementation of safer buildings, we overlook that safety is a socio-cultural and economic issue. This is because different cultures perceive and interpret risk in very different ways, and then there are economic reasons not to implement safer buildings even though people know they are living in an unsafe one.

Paper P52: [Read] [Presentation]

Keynote Address Session 1 Session 2 Session 3A Session 3B Session 4A Session 4B Session 5A Session 5B Session 6 Session 7 Poster Session