Reliability models of permanently monitored existing bridges
In the past it was recognized that permanent monitoring may be possibly used as compensatory measure to ensure structural stability and serviceability. The task of the monitoring system is to issue a warning if the structural condition becomes critical. Hence, failure can be prevented through timely implementation of risk-reducing measures. Consequently, the failure probability is lower in such a case compared to the case without monitoring information. However, the quantitative assessment of this failure probability was not yet possible. Aim of this work was to propose a method for quantitative assessment of the reliability of bridges equipped with permanent monitoring.
In course of this work, existing monitoring approaches were analyzed, and assessment methods were compared. This was done on a population of 100 bridges of one type, which was artificially generated and analyzed.
The proposed method for quantification of reliability of bridges equipped with permanent monitoring assumes two types of failure of the monitoring approach. First, the failure to recognize a serious damage in spite of finished measurement data analysis and subsequent structural failure; and second, lack of time to implement a risk reduction measure. A method for quantification of failure probability in both cases was proposed. Certain assumptions are made in the process, e.g. regarding the failure mechanism, as well as regarding extreme value distributions of traffic loads and measured indicators. The effect of traffic-load-induced damages on measured indicators is determined through FE-simulations.
Potential outage of the measurement system is considered through prolongation of required data acquisition duration. Data for this evaluation was acquired in course of the project through a survey among monitoring practitioners, which collected experiences with failure rates of measurement components. Measurement uncertainties are accounted for in course of determination of warning thresholds.
The method was applied on the case study of a flyover bridge, and the increase of operational reliability due to the compensatory monitoring measure was assessed.
ZumBesten was financed by the Federal Highway Research Institute (BASt).
