| Composite beams with external prestressing technique many attractive merits such as simple construction,convenient maintenance and economy.External tendons have been widely employed to strengthen or in the new construction of large civil engineering structures.Because of the unbonded nature of external tendons,the increase in tendon strain is dependent on the deforration of the whole member and,therefore,the tendon stress cannot be determined by a single section analysis.Many experimental studies on the behavior of externally prestressed members have been conducted,whereas few numerical analyses of these structures have been undertaken so far.Analysis of beams prestressed with external tendons is much more complicated than that of bonded concrete beams,complicated than that of bonded concrete beams.It is assumed that the reinforcement has a good bond with surrounding concrete for simplifing the simulation of concrete beam.The finite element analysis is based on the plane section assumption.On the other hand,for an external tendon system,the strain compatibility between the tendons and the surrounding eoncrete is no longer valid,and therefore analysis should be based on the deformation of the whole member.The incremental stress due to the structure deformation is also of great importance in the analysis of external tendons.The most available methods in the literature are only suitable for certain structures with specific types or neglecting the relative slip between the tendons with deviators.In this study,a numerical model based on the external tendons are members for the normally elastic strain caused by the free sliding between external tendons and deviators incorporating the existing line-elastic analysis programs is established.The analysis is capable of calculating long-span prestressed bridge with external tendons by iterative algorithm.The accuracy of the model is verified with the existing calculation method.Based on a long-span continuous rigid frame bridge,the deflection,support force and internal tendons axial force along the length of the beam are compared by two models(considering or unconsidering the free sliding).The axial force of external tendons are calculated when the slip effect is considered.The research work and main conclusions of this paper are as follows:(1)In this paper,the research status of external prestressed tendon is summarized,and a summary and review about the analysis methods of external prestressed concrete beam are given;(2)An external prestressed beam element model with free slip is developed and compared with the existing element model,The results obtained by the analysis method in this paper are in good agreement with the results calculated by the existing analysis method with different loading forms and arrangement ways of reinforcement,indicating that the method in this paper has a certain degree of precision;(3)The finite element model of long-span concrete continuous girder bridge with mixed arrangement of internal and external tendons was established and the influence of relevant parameters on the mechanical performance of the bridge was studied,the slippage effect has little influence on the deflection of the main girder,the bending moment,the supporting reaction force and the axial force of the internal tendons,but it has a bigger influence on the axial force of the main girder;(4)The effect of internal and external prestressing ratio on the deflection of the structure was analyzed.The research results of this paper provide some reference value for the construction and reinforcement design of external prestressed concrete bridge,and a further knowledge and understanding of external prestressed concrete structure can be gained. |
PDF Full Text Request