Study On Load Bearing Capacity For PC Girders With Consideration Of Incompatible Deformation

The rapid development of prestressed concrete technology provides theoretical and technical support for the construction of Prestressed Concrete Bridges.In recent years,a large number of prestressed concrete bridges have been built in China.The incoordinated deformation influence on the load bearing capacity(LBC)for Prestressed Concrete(PC)girders can be ignored,that agrees with the design procedure of the full prestressed concrete members at serviceability limit states,where the presence of cracks is not allowed.But under the heavy load and long-term load,the existing PC bridges is often in a crack state,so it is necessary to consider incoordinated deformation caused by cracks and the corresponding bond-slip in the study of the LBC for(PC)girders.In order to learn the degree of incoordinated deformation influence on LBC for PC girders,this paper proposes an analytical method of LBC for PC girders with consideration of crack-induced and bond-slip incompatible deformation(CID and BSID).Comparisons for LBC have been carried out among the results of strain compatibility method,the proposed method and scale-reduced model tests.The effects of CID and BSID on both stress increments of prestressed tendons and the depths of compressive region have also been specified.And then the analysis of LBC for PC girders in the different degree of incompatible deformation have been raised.At last,this method is applied to a full-scale model gider with 30 m long,and the necessity and effectiveness of taking CID and BSID influence into account for LBC analysis of PC girders are verified by comparing the calculated results with the finite element solutions and the measured data.The main results of this study are the following aspects:1.This paper proposes an analytical method of LBC and deflection for PC girders with consideration of incompatible deformation based on the strain compatibility method,and gives the advice on how to get the value of CID and BSID.2.The traditional strain compatibility method is not suitable for the evaluation of existing PC gider with cracks which must consider the effect of incoordinated deformation.LBC and depth of the compressive region have also been improved more than 5% with the consideration of incoordinated deformation whose influence on ultimate deflection is about 7% compared with the strain compatibility method.3.For the scale-reduced model girder,the effect of CID and BSID on stress increments of prestress tendons reaches 18.8%(the CID and BSID accounted for 59% and 41%,respectively)and 9.83%(the CID and BSID accounted for 82% and 18%,respectively)for yielding and ultimate states,respectively.And the proportion of the two factors' influence on stress increments of prestress tendons for yielding and ultimate states coincides with its effect on the elongation ratio of prestressed tendons.The effect of CID and BSID on depth of the compressive region reaches 6.7% for ultimate states,and considering only the effect of CID,the proportion is 5.5%.4.The size of compressive pre-stress is proved to have no significant effect on the ultimate load bearing capacity of the girder while there is obvious distinctions for cracking load.5.The results of the full-scale model girder with the size of prestress being 1108 MPa reveal that the effect of incompatible deformation on stress increments of prestress tendons reaches 46% and 3.0% for yielding and ultimate states,respectively.