Response of under-deck cable-stayed bridges to the accidental breakage of stay cables

Under-deck cable-stayed bridges with prestressed concrete decks have recently been shown to be appropriate structural types for highway overpasses. However, doubts have emerged regarding their capability to withstand the accidental breakage of stay cables, due to collisions with heavy vehicles, without collapsing. In this paper, two distinct parametric analyses are conducted on two different bridges, each of which is representative of this bridge type, in order to study their response due to the breakage of stay cables. The response is assessed through fully dynamic analyses, rather than pseudo-dynamic analysis (via the use of dynamic amplification factors), since the latter method has been shown to be un-conservative in some cases. In both parametric analyses different scenarios, i.e., different parameters, relating to the type of breakage, the time over which breakage occurs, the number of broken stay cables, the type of deviators and the amount of applied traffic live load are considered. In the present study, the capability of this bridge type to easily overcome this accidental action, with a higher degree of safety than that required by codes, is clearly demonstrated. In fact, the analysed bridges do not reach any ultimate limit-state even if 40% of their stay cables are suddenly broken when 100% of the traffic live load is applied. In addition, a set of design criteria closely related with this issue are established.