Cracking Mechanism and Simplified Design Method for Bottom Flange in Prestressed Concrete Box Girder Bridge

Abstract

Serious cracking has occurred frequently in the bottom flange of box girders during construction in recent years. This paper aims at studying the cracking mechanism and countermeasures. The stress field in the bottom flange associated with the bottom continuity tendon is presented, and the propagation of cracks during tensioning is simulated by nonlinear analysis according to the actual construction sequence. A cracking mode, which is not easy to detect in field investigation, is illustrated through numerical and theoretical study. It is caused by the deficient shear strength of the bottom flange attributed to the void in tendon ducts. Based on numerical results and field investigation, four types of cracking in the bottom flange are proposed and discussed, and a simplified design method is recommended for control of cracking.