Seismic resiliency of new bridges has improved over the years due to improved seismic codes and design practices. However, the vulnerability of seismically deficient bridges, coupled with aging and deterioration, poses a significant threat to life safety and integrity of lifeline systems. It is economically not feasible to retrofit the entire seismically deficient bridges. Therefore, there is need for a comprehensive plan to identify critical bridges and prioritize their retrofit and upgrade requirements. A risk-based seismic evaluation technique is proposed in this paper to develop a ranking scheme for bridges. The complex interaction between seismic hazard, bridge vulnerability and consequence of failure is handled in a hierarchical manner. Some of the input risk parameters, expressed as qualitative and quantitative quantifiers, are transformed into commensurable values. A fuzzy-logic based modelling technique is used to aggregate through the hierarchy and obtain final risk index for prioritization. The efficacy of the proposed method is illustrated with bridges in the British Columbia, Canada.

Risk-Based Rapid Visual Screening of Bridges

The west coast of BC lies in Canada’s highest seismic zone under threat of three different types of large, highly destructive earthquakes. The British Columbia Ministry of Transportation (BCMoT) is responsible for 400 km of provincial Disaster Response Routes. The loss of any portion of one of these routes could significantly impact emergency response efforts and negatively affect public well being. The Ministry maintains 900 structures in the highest seismic zones, many of which are vulnerable to extensive damage in even a moderate quake and potential collapse in a major earthquake. The loss of the use of several structures would not only have immediate impact on public well being and the ability of emergency vehicles to respond effectively, but would also cripple the economic recovery of the region. The effects would be felt across the nation and for many years into the future. The better the information on which areas, structures and facilities are most vulnerable, the better planning and preparation can be done. By identifying those structures and facilities most susceptible to seismic forces, decision-makers can do effective risk management. Fast, accurate field intelligence immediately following an earthquake can ensure the most effective deployment of vital services and mitigate damage to the built environment. Preparation and mitigation will both aid economic recovery. Earthquakes hazards are very complex and each event unique. Most of the significant advances in identifying and understanding seismic hazards over the past 50 years have been aided by the availability of seismic monitoring data. The BCMoT has in the past had few bridges instrumented. Five structures have between two and six accelerometers and two structures have limited strain gauges. Only one structure uploads data to an internet site. The data from all the other structures must be collected at the site. This has proven most inefficient. The BCMoT has embarked on a program to instrument key structures to provide confirmation of seismic capacity, assist in focussing retrofit efforts, detect damage from any cause and provide rapid damage assessment of those structures following a seismic event. The data from this instrumentation will be capable of remote configuration and will automatically upload via the internet. The Ministry is working with the University of British Columbia to develop effective damage detection algorithms that will provide reliable intelligence close to real time. The purpose of this paper is to evaluate the status and effectiveness of the implementation.

Sharlie Huffman

Papers

Seismic Monitoring of British Columbia Bridges