Redundancy analysis of existing truss bridges: 'A system reliability-based approach'

The main objective of this research is to develop a new methodology for redundancy analysis of structural systems in general and truss bridges in particular. Currently, the most serious disadvantage cited when considering a new truss bridge design is the perception that it cannot be redundant, and is thus subject to sudden collapse.; The proposed methodology depicts the required steps to build a block diagram, composed of members in series and parallel configuration, representing the structural system or the truss bridge. The proposed block diagram accounts for the system's degree of redundancy and the possible amount of redundant members' combinations, in a parallel configuration, to be laid in series with the non-redundant members in the system. Multiple failure modes, related to the system's components, are integrated in the structural system in a series system layout. General equations are then derived, for the pre-failure and post-failure phases of the system's reliability index and probability of failure. The post-failure phase is defined as the phase when a redundant member fails without causing the collapse of the system.; The proposed methodology is then applied on a truss bridge: the US bridge corporation bridge 3000. The truss bridge members are categorized as redundant members and non-redundant members based on an updated finite element analysis, which depicts the member or members responsible for the total collapse of the bridge. This will lead to identify the truss bridge redundant members and its degree of redundancy. The degree of redundancy is defined as the number of redundant members that can fail simultaneously without causing the bridge to collapse.; This methodology should eventually be a reliable tool to set new safety factors for redundant structural systems and truss bridges in future design codes, based on the calculated structural system reliability index. It can also be used in calibrating the strength of existing structural systems or truss bridges that experience a loss of a redundant member, to attain a target operational system reliability index.