Modeling of unknown seismic responses of a partially instrumented bridge structure

Monitoring technique based on the analysis of responses recorded on the structure are becoming a widespread method to monitor structural health conditions. An effective monitoring system should be characterized by three main requirements: accuracy of the recorded data, cost-effectiveness of the sensors systems, availability of procedures to interpret the recorded data. Due to economic reasons, concerning the cost related to data acquisition and/or to the inaccessibility of some degrees of freedom, bridge structures are usually instrumented with a limited number of sensors. The economic advantage associated to the lower cost of the sensors system is counterbalanced by the lack of data in location where recording sensors are not available. In this paper a tentative solution to this problem is proposed through a method to reconstruct unknown responses from the ones recorded by a limited number of sensors. Unknown responses can be calculated by interpolation of recorded ones through an appropriate spline shape function. The method has been already applied with good results in the case of multistory buildings. In this paper bridge structures are considered and the procedures has been applied for the reconstruction of the seismic response of a symmetric multispan bridge, of a cable-stayed bridge and of an arch bridge. In the first two cases analysis have been carried out on the numerical models of the structures while for the arch bridge responses recorded during a real seismic event have been analyzed. Both the accuracy of calculated responses and the cost of data acquisition increase with the number of recording sensors. In order to characterize the cost-effectiveness of the employed set of recording sensors an “effectiveness function” defined in terms of the number of recording sensor and of the achievable accuracy is proposed.