Postcompression and Superimposed Trusses for Bridge Rehabilitation

Abstract

The need for upgrading a large number of understrength and functionally obsolete bridges in the United States has been well documented. The purpose of this project was to investigate two schemes for strengthening the negative‐moment regions of continuous composite bridges: (1) Postcompression of stringers; and (2) superimposed trusses attached to stringers. Both strengthening schemes were designed to resist negative moments and the resulting stresses from service loads. A series of tests was conducted on a full‐scale mockup with each strengthening scheme in place. The postcompression strengthening scheme was effective in reducing the bottom‐flange stresses (36%); however, top‐flange stresses were slightly increased (18%), because of the tension applied to the section. The superimposed truss‐strengthening scheme was effective in reducing both the top (46%) and bottom (48%) flange stresses because it applied only reverse moment to the section. In addition to reducing stresses, since the superimposed trusses provide additional support to the bridge beams, the trusses also reduce live‐load bridge deflections. The superimposed trusses system is a very practical strengthening system that with appropriate connection modifications can be used to strengthen the negative‐moment regions of essentially any type of bridge.