ANALYSIS OF CABLE-STAYED BRIDGES

Abstract

Cable stayed bridges have come a long way in being recognized as indicators of the development of a country and adding to its touristic value. The safety of cable stayed bridges has been of great concern to engineers ever since the failure of the famous Tacoma Narrows Bridge in 1940. The long span bridges like cable-stayed bridges are very critical to dynamic phenomena like the loss of cables. To account for cable rupture different types of analysis has been performed till date. Dynamic analysis shows the actual real time removal of the cable, but it requires significant time and computational efforts so to deal with these problems static analysis is performed by applying proper dynamic amplification factor (DAF) that approximately accounts for dynamic responses. Two different types of cable-stayed bridges, one with short span (bridge type A) and the other with moderate span (bridge type B) with different cable geometric configuration like fan type and harp type have been analysed in this study. The modelling of both the bridges is done in commercial package MIDAS Civil. The loss of one cable, two cables and, three cables simultaneously has been accounted in this study. The results of the analysis were further compared by varying the pulse duration of the cable loss. Four different pulse durations have been taken in this study. The results are evaluated for dynamic amplification factor, bending moment and axial force. The values of dynamic amplification factor as mentioned in PTI overestimate the forces in the deck while underestimating the same for the pylon. The time history graphs are also plotted for different pulse duration and for cable losses. This study provides a comprehensive review of the different parametric studies that have been performed on cable stayed bridges and with specific focus on the dynamic amplification factor for accidental loss of cables. The details of the anticipated future of dynamic amplification factor for cable stayed bridges based on current trends along with research needs in accidental loss analysis that needs to be addressed is also presented. The development of advanced software’s and improved computational capabilities of the 21st century has greatly aided the study of these types of analysis of cable stayed bridges.