Analysis Of Cracks Cause In Box Girder Bottom Slab And Research On Countermeasure For Continuous Rigid Frame Bridge

In recent years, the PC continuous rigid frame bridges with box-girders have been applied extensively with the development of economy and traffic construction in our country. Because of imperfect design theory, construction quality defects, and other reasons, considerable degrees of disease have appeared during most construction or operational course of PC bridges with box-girders,especially cracks in the bottom slab. The appearance of cracks exerts negative impact on the safety, endurance and normal using of the structure. It is necessary to ascertain the reason of the bottom slab cracks in box-girders not only for the preserve of the bridges but also for the designing and constructing of bridges.For the accident of bursting crack occurring in bottom slab of Xinzhaihe Bridge (continuous rigid frame bridge with box-girders) at construction stage , the research is followed as below: whole model analysis on this bridge at construction stage is carried out by using the DR.bridge software.This thesis uses ANSYS's parameterize design language (APDL),puts forward the partial models of this bridge with the considerations of two kinds of calculation load cases including ideal design condition case and local corrugated pipe with its position changed , the local stress of bottom slab in the process of extension of closure prestressed strands in middle span is simulated . The bridge reinforcement methods are checked in the selection of parabolic shapes of box-girder and the construction of cross baffle.At last, the countermeasure of box-girders bottom slab crack are discussed.On the basis of studying related literature and the results of calculation indicate that in the midspan -13.5m～13.5m prestressed line shape in the bottom slab is not recommended to take less than 1.7-th power parabola , adding cross baffle can increase the transverse stiffness significantly and come to a purpose of reducing the peak value of stress on the bottom of box girder.Smaller spacing on the layout of the transverse ribs is favorable.Aimed the different situations on the crack problems of bottom slab, pose methods of repair and compare with Xinzhaihe Bridge emerged after the bottom plate bursting crack repair construction has been applied to prove that the methods are practicable.