The Researches On Secondary Moment And Moment Redistribution Of Unbonded Prestressed Concrete Continuous Beams

Moment modulation of unbonded prestressed concrete continuous Beams(UPCCB)is one of the concerned problems for researchers and designers.There has been no adjustment method of bending moment for UPCCB in current Chinese codes.In this thesis,secondary moment and moment redistribution in UPCCB were studied,which was of significance to the engineering and the theory.A finite element analysis of 11 test beams was carried out by Opensees.Three basic problems including the object of moment modulation of prestressed concrete continuous beam(PCCB),the change law of secondary moment of UPCCB in the nonlinear stage and differences in performance of moment modulation between UPCCB and bonded prestressed concrete continuous beams(BPCCB)were analyzed.A moment modulation method of UPCCB was proposed on the basis of analysis on the factors influencing the degree of moment modulation in UPCCB.The thesis completed the following contents:(1)The status quo of research on the moment redistribution in PCCB was summarized,and the necessity of further research on redistribution of moment in UPCCB was put forward in this thesis,(2)A finite element analysis model of UPCCB and BPCCB was established in Opensees.A full-range analysis of 9 UPCCB and 2 BPCCB was carried out by Opensees and the analysis results of deflection,support reaction and stress increment of prestressing strands were in good agreement with the experimental results.(3)The object of moment modulation of PCCB and differences in performance of moment modulation between UPCCB and BPCCB were analyzed by Opensees.And a full-range analysis on UPCCB was conducted by increment method.The results indicate that the secondary moment will lose its independent meaning in the post-elastic range in UPCCB,and the same moment modulation coefficient should be used for the load moment and the secondary moment for the moment modulation of PCCB.(4)The influence factors of the degree of moment modulation in UPCCB were analyzed by Opensees and the moment modulation coefficient calculated by Opensees was compared with the recommended value in GB50010 code,ACI code,CSA code and MC10 code.It is found that the rotational capacity of the section in inner support and the ratio of section stiffness in inner support and mid-span are the main factors that affect the degree of moment modulation in UPCCB.A moment modulation formula for UPCCB was proposed and the moment value calculated by the proposed formula agreed well with the experimental results.