Secondary Prestressing Moments in Rehabilitated Posttensioned Bridges

Abstract

Typical rehabilitation procedures for posttensioned slab bridges involve removing concrete from the top surface of the bridge, replacing corroded reinforcement, and resurfacing with new concrete. These permanently change primary and thus secondary prestressing moments. Continuous posttensioned bridges often rely on secondary prestressing moments to counteract dead and live load moments over interior supports and thus changes caused by rehabilitation impact serviceability and, particularly, ultimate limit states. An analysis procedure is derived for computing the changes in prestressing moments caused by rehabilitation. The impact of rehabilitation on a two-span continuous voided-slab bridge is evaluated considering rehabilitation schemes where both spans are rehabilitated simultaneously, or where one span is completely rehabilitated before work commences on the other. Rehabilitation creates concentrated primary prestressing moments at the exterior supports and at interfaces between solid and voided regions that reduce or even reverse the secondary moment at the interior support. The two-span scheme virtually eliminates secondary prestressing moments and, contrary to intuition, the span-by-span scheme has a markedly greater impact.