Keynote Address 1 Defining Acceptable Performance Criteria Planning for Expected Performance / Improving Existing Performance I Improving Existing Performance II Keynote Address 2 Developments Within Design I Developments Within Design II Developments Within Design III / Understanding the Inputs Assessing Existing Performance Poster Papers 

AS/NZS 1170 and the New Zealand Building Code

Graeme Lawrance, Mike Stannard, David Hopkins and Ian Brewer

With the publication of NZS1170.5:2004, the Department of Building and Housing initiated its citation process for AS/NZS 1170 as a Verification Method for determining compliance with the New Zealand Building Code.

The Department’s review highlighted: the restricted range of buildings covered; the exclusion of some loading types from its scope; the benefits and costs of changes in loadings, particularly earthquake and wind; the suitability of definitions of importance levels for New Zealand; the clarity of definition of facilities that need to be functional after a major earthquake; the extent to which “engineering judgement” was relied upon in applying the provisions; and the desirability of including the definitions of importance levels in the Building Code rather than in the loadings standard.

Some of the issues raised have influenced the Department’s review of the Building Code in relation to the Building Act 2004. A particular objective of the Building Code Review is to define performance requirements more clearly. This has led to closer examination of the probabilities of exceedance implied in the various loads and load combinations specified, and consideration of overall risk and performance criteria to achieve “tolerable impacts”.

Paper P02: [Read]

Improved Hazard Model for Performance-Based Earthquake Engineering

Brendon Bradley, Rajesh Dhakal, John Mander and Greg MacRae

An improved seismic hazard model for use in performance based earthquake engineering is presented. The model is an improved approximation from the so-called 'power law' model, which is linear in log-log space. The mathematics of the model is briefly described, and various means of fitting the approximation to 'exact' hazard curves developed by seismologists are discussed. Based on these 'exact' curves for major centers in New Zealand, the parameters for the proposed model are calibrated. To illustrate the significance of the proposed model, a simplified financial loss assessment is conducted on a moment resisting concrete frame, via numerical integration. The integration tool is first validated against a closed form solution (based on the power law hazard model) of the loss assessment. The new hazard model is then incorporated to illustrate its effects on the loss estimation assessment compared to the current power law relationship.

Paper P03: [Read]

Performance Based Assessment and Design Policy Recommendations

Renee Brook, Trevor Kelly and Chris Mackenzie

Holmes Consulting Group has undertaken a series of non-linear time history analyses of existing properties, including a number of essential facilities. These have been to provide specialist advice about the seismic risk, and associated recommended strengthening schemes.

These analyses have raised a number of issues which need to be fully resolved before we, as a profession, can achieve true Performance Based Assessment and Design.

What are the appropriate levels for strengthening? Should we be strengthening to “as close as is reasonably practical to that of a new building”? Does this automatically set a de facto level of load to evaluate to? In turn, how do the FEMA performance limits (IO/LS/CP) directly apply to NZ codes and are these relevant to the 67% or 100% load level? Recommendations based on our experiences are presented.

There are also several limitations in NZS3101 that inhibit true Performance Based Design being an economical tool for the strengthening of existing buildings. There are set limits on the tie spacing in columns, regardless of the building drift and column axial load ratio. Similarly there are issues of beam column joint performance, where the existing joint steel does not comply with current codes. Recommendations for an approach to these issues are presented.

The need for clear policy and a consistent approach in developing strengthening schemes using Performance Based Design is highlighted.

This paper also offers some guidance as to where future research could be targeted to clarify some of the issues raised with respect to existing buildings.

Paper P04: [Read]

Hollow Core Floors – a Regulator’s Perspective

Mike Stannard, Richard Bialostocki, David Hopkins, Rob Jury and Dean Saunders

In October 2001, load tests on a full-scale model of a hollowcore floor assembly at the University of Canterbury indicated potentially serious gaps between assumed and actual behaviour of hollowcore floor systems in ductile frame buildings during strong earthquake shaking.

In July 2003, the Department of Building and Housing (then the Building Industry Authority) commenced a review of the use of hollowcore floor systems in New Zealand. The objective was to determine the extent and nature of usage of these systems nationally, and to advise the industry of any concerns.

Building consent drawings were surveyed in Christchurch and Wellington to obtain a profile of size, span, depth, building type and support details used. In addition, an assessment was made of the likely displacements of buildings designed in Auckland, Wellington and Christchurch.

A report was compiled, summarising the findings and implications. Recommended actions included advice to owners to have their building checked if they had concerns, and to territorial authorities (TAs) to ask for a report on the hollowcore floor performance when an existing building was significantly altered. A need for guidelines for the assessment of existing buildings and the design of new buildings was identified.

Paper P07: [Read]

Keynote Address 1 Defining Acceptable Performance Criteria Planning for Expected Performance / Improving Existing Performance I Improving Existing Performance II Keynote Address 2 Developments Within Design I Developments Within Design II Developments Within Design III / Understanding the Inputs Assessing Existing Performance Poster Papers