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 

Multi-level Seismic Performance Assessment of a Damage Protected Beam-column Joint with Internal Lead Dampers

Kevin Solberg, Brendon Bradley, Geoffrey Rodgers, John Mander, Rajesh Dhakal and Geoffrey Chase

A multi-level seismic performance assessment is performed on a near full scale beam-column subassembly. The physical model is taken from a 3D exterior connection of a jointed precast concrete frame structure that is designed for damage avoidance. Unbonded post-tensioned prestress is provided by high-alloy high-strength thread-bars. Draped and straight tendon profiles are used in the transverse and orthogonal directions, respectively. The joint region is armoured to avoid damage by providing steel plates at the beam-column contact points. Supplemental energy dissipation is provided by high-performance lead-damping devices cast internally in each beam. Bi-directional quasi-earthquake displacement profiles are applied meaning the input displacement profiles are taken directly from the results of inelastic dynamic analysis. Three input earthquakes are selected probabilistically to represent multiple levels of seismic demand. Results from physical testing are critically discussed.

Paper P22: [Read]

Effective Stress Analysis of Pile Foundations in Liquefiable Soil

Hayden Bowen, Misko Cubrinovski and M.E. Jacka

An advanced dynamic analysis based on the effective stress principle is used to evaluate the seismic performance of foundation piles of a bridge pier in Christchurch. The employed method permits accurate simulation of the ground response in liquefying soils including the process of excess pore pressure build-up and associated highly-nonlinear stress-strain behaviour of soils.

In the analysis, complete liquefaction developed from 11 m to 17 m depth resulting in lateral ground displacements of about 28 cm and consequent damage to the pile at the pile head where the peak bending moment exceeded the yield level. Characteristics of the ground response and behaviour of piles are discussed using computed time histories and maximum values of accelerations, displacements, excess pore water pressures and pile bending moments. Results of the effective stress analysis are further examined through comparisons with a conventional analysis based on the pseudo-static approach.

Paper P23: [Read]

An Integrated Soil-foundation-structure Model to Capture the Seismic Response of Bridge Columns in Seasonally Frozen Conditions

Liam Wotherspoon, Mick Pender and Sri Sritharan

Several significant seismic events have occurred during the winter months in areas that experience seasonal freezing. In a recent study, cyclic lateral load testing of identical full-scale column-foundation systems was conducted in summer and winter months, which revealed the dramatic differences in their responses created by 0.76 m deep frozen soil. It showed that freezing temperatures can significantly influence the soil-foundation interaction and thus the lateral load response of bridge columns supported by deep foundations. The primary cause of this phenomenon has been demonstrated to be the drastic changes in the properties of soil due to freezing.

Using the material properties from the two tests, Ruaumoko models were developed to study the monotonic and cyclic responses of these test units. The methodology used to represent the structural and soil behaviour with Ruaumoko members is summarised. Validation using a range of recorded responses showed that the models were able to satisfactorily capture the characteristics of test units at both warm and cold temperatures. Analysis results and their comparisons with experimental data showing the significant differences in the displacement, effective stiffness, maximum moment, shear demand and length of plastic region between warm and frozen conditions are presented in the paper.

Paper P24: [Read]

Insitu Free Vibration Tests on a Single Degree of Freedom Structure with Foundation Uplift

Tom Algie, Rick Henry and Quincy Ma

A series of free vibration tests were conducted on a free standing single degree of freedom structure with a range of elastic natural frequencies. The tests were conducted over a rigid concrete strong floor and on Auckland soil. A typical response was obtained when the structure was displaced from its original alignment, held still, then released and allowed to rock. The response as tested over the concrete strong floor fitted Housner’s simple rocking model, however it required an empirical manipulation of the damping factors. Interestingly, the experimental result showed that the amount of radiation damping, measured as the apparent co-efficient of restitution, is relatively constant irrespective of the structure’s geometry, which contradicts the traditional rocking models. The results showed that when the structure rocked on insitu ground, the dynamic behaviour was greatly modified. The time history response demonstrated a change of principle damping scheme from radiation to viscous. The response over the continuous medium failed to correlate with Housner’s model due to the increased viscous damping, which is attributed to the soil absorbing energy through deformation. An elongation in the rocking period for a given amplitude was observed.

Paper P25: [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