Strengthening of a Twin Arch Bridge in Goa, India for Stability

A recently constructed bridge comprising parallel twin tied arches were observed tilted on one side soon after the cast-in-place concrete deck was poured. A three dimensional (3D) analysis of the as-built structure including both the material non-linearity and the initial imperfections demonstrated that the stiffness and strength of the existing Vierendeel lateral bracing between the arches were inadequate for developing the design capacity of the structure subjected to dead, live and wind loads. A retrofit of the structure by replacing the Vierendeel-bracing with X-bracing was proposed, which increased the limit load of the structure many folds. A step-by-step retrofit scheme for replacing bracing system was developed through virtual simulation. The study enabled developing a cost-effective retrofit measure for the bridge, and identified the need for stability bracing design guidelines for steel arches within the existing design specifications.