Ian Brown and Tam Larkin
Earth fills located on hillsides in areas of high seismicity have potential for shear failure (sliding) and seismically induced deformations at ground surface due to compression of the fill. A fill developed for residential purposes in the Wellington area has been analysed and shown to be of concern for potential instability as a result of fill geometry, properties, and proximity to the Wellington Fault. Conclusions are drawn about the performance of the fill during a 450 year return period earthquake, and a recommendation made to revisit applicable New Zealand Standards so that such fills are designed to provide a higher level of earthquake resistance.
Paper P27: [Read]
Howard Chapman, Merv Lauder and John Wood
Over recent years Transit New Zealand (Transit), has undertaken a systematic assessment of the seismic security of the approximately 2500 state highway bridges for which it is responsible. This paper outlines current progress on the assessment and retrofitting of the bridges, and discusses the results of the detailed assessment of 24 of the bridges and subsequent peer review. Inter-span linkages have been upgraded on Priority 1 routes and detailed assessments of 50 bridges have been undertaken to identify other structural vulnerabilities and risks of damage. However, the bulk of the physical retrofit of these vulnerabilities has yet to begin and much else remains to be done. The detailed assessments have shown that the many variables that influence the results of a structural analysis require input of a significant amount of judgement, both in deciding the input parameters for the analysis and in interpreting the results. The two peer reviewers found, however, that in most cases it was possible to reach a consensus on the appropriate degree of retrofit and priority ranking for the structures involved. The interaction that was possible as a result of using two peer reviewers working together was also found to be valuable in weighing the assessments and making recommendations.
Paper P28: [Read]
Kuen-Yi Ho and Alexei Murashev
The Clarence River Bridge is a balanced cantilever, post-tensioned box girder bridge located on State Highway 1, approximately 30 kilometres north of Kaikoura in the South Island. The bridge is approximately 305 m long and comprises 6 spans. Design of the bridge was completed around 1968 by the Ministry of Works. The bridge was constructed in 1969. Consequent to a nationwide seismic screening project, the bridge was assessed in detail in 2003 and 2004 to determine its seismic performance. This paper presents the findings of the assessments and the proposed seismic retrofitting solutions to protect the bridge.
Paper P29: [Read]
Donald Kirkcaldie, Jason Hobman and Greg Saul
The Shell Gully bridges, situated immediately north of the Terrace Tunnel are a vital link on the Wellington Urban Motorway providing access from the north to the CBD and beyond to the hospital and airport. Located in New Zealand’s capital and second largest city, and a highly seismic part of the country, Transit New Zealand assigned a high priority to ensuring the integrity of these critical structures against damage and loss of service from a major earthquake event. This paper presents the detailed assessment of the bridges’ earthquake resistance and seismic retrofitting undertaken. The retrofitting has encompassed: improving the security of short link spans, interconnecting the structures, from falling; modifying the heavy fascia units along the sides of the bridges to prevent their dislodgement under shaking of the structures; isolation of a pier from potential downhill movement of the underlying slope; and strengthening and modification of the restraint of the high northern abutment to improve its seismic performance.
Paper P30: [Read]
The feasibility and efficiency of two alternative seismic retrofit interventions on gravity load-designed frame systems either based on the use externally bonded FRP composites or on the implementation of a diagonal haunch metallic system at the beam-column connections are herein presented. Independent of the selected solution, a multi-level retrofit strategy is proposed to achieve the desired performance, based on hierarchy of strength considerations; the expected sequence of events can be visualized through demand-capacity curves within M-N Performance-Domains. Experimental results from quasi-static tests on 2/3 scaled beam-column subassemblies in as-built and retrofitted configuration as well as on a three storey frame system (retrofitted with the FRP solution only) are presented as a confirmation of the viability and reliability of the overall retrofit strategy as well as of the efficiency of the adopted simplified analytical models based on a plasticity concentrated approach.
Paper P31: [Read]
Improving seismic safety of adobe construction with used car-tyre strips: preliminary investigations
Andrew Charleson and Matt French
This paper outlines preliminary research into reinforcing adobe buildings with strips cut from used car tyres. The proposed approach has the potential to both reduce seismic vulnerability and help solve the ecological problem of vehicle tyre disposal. Tyre strips, spiral-cut from the tread area, have been tested both statically and dynamically to ascertain their strength and stiffness capabilities. The two layers of fine steel wires that form the steel belt greatly enhance these two engineering properties which prove to be quite adequate for the proposed use. Simple, albeit carefully detailed nailed connections that can develop most of the strength of strips, enable them to be placed horizontally within an adobe wall. Where laid so that their shape in plan approximates that of a catenary, they are able to resist significant out-of-plane loads, as well as act as shear reinforcement for in-plane loads. A full-scale face-load test on a three metre length of dry stacked masonry wall has confirmed the potential of the proposed system.
Paper P32: [Read]