Design And Study Of Medium Span Composite Truss Bridge With Concrete-filled Rectangular Hollow Section

Composite truss bridge with concrete-filled rectangular hollow section(CFRHS)is a new type of bridge structure composed of CFRHS truss and concrete slab.It has the advantages of large flexural rigidity,light weight,convenient construction and economical performance.In this paper,funding by the Program for National Nature Science Foundation of China(51378068),the standard drawings of medium span CFRHS composite truss bridge were designed,and the mechanical behavior under negative bending moment and joint bearing capacity of composite truss bridge were also studied.This paper carried out the following works and obtained revelant conclusions:(1)The design process,detailing requirements and calculation methods of medium span CFRHS composite truss bridge were summarized.The simplified mechanical model suitable for the design and calculation under negative bending moment of composite truss bridge was proposed.(2)According to the current design specifications,this paper designed and calculated the standard drawings of CFRHS continuous composite truss bridge with four spans of 50,60,70,80 m,and made statistical analysis of its technical economy.The results show that the structural checking calculation in the construction stage and service stage of the standard drawings meets the requirements of the current design specifications.Compared with traditional prestressed concrete box girder bridge,composite truss bridge has obvious technical economy advantages.(3)Segmental model test under negative bending moment of CFRHS composite truss beam was carried out,and the structural load-displacement relationships,failure mode,characteristic loads were all analyzed.And the structural characteristic loads at different loading stages were discussed according to the simplified mechanical model of composite truss beam.The results show that the structural plastic deformation increases because of the cracking of concrete slab and yielding of truss members at first,then the composite truss reaches ultimate state after the failure of welds at the joint.The structural characteristic loads calculated from the simplified mechanical model coincided well with the measured values,which can provide references for the design and calculation of CFRHS composite truss beam under negative bending moment.(4)This paper summarized the joint failure modes of composite truss bridge,analyzed and calculated the joint failure modes and bearing capacity detailed in standard drawings of composite truss bridge with ABAQUS,a non-linear finite element software.And compared with the joint bearing capacity formula in relevant design specifications.The results show that the bearing capacity of welded integral joints is improved by filling concrete and setting PBL ribs,which makes the yield of members precede the failure of joints.