On Bending Resistance Of Pestressed Concrete-Filled Steel Tubular Truss Girder

Prestressed concrete-filled steel tubular (CFST) truss girder is a new type of bending truss structure, which is made of CFST chords connected with circular hollow steel section (CHSS) braces by directly welded joints and prestressed by longitudinal external prestressing. Due to its light weight, high stiffness, high load bearing capacity, convenience in construction, and higher fatigue strength compared to those of CHSS truss, prestressed CFST truss girder is prevalent among construction of long span or high rise structures and for engineering application with strict limitation on structural weight and construction conditions. Although a lot of researches about CFST truss structure have been focused on its overall structural behaviour under compression, joint strength and fatigue performance by far, the overall bending behaviours and structural design method have rarely been explored.Thanks to the funding from National Natural Science Foundation of China, the experimental investigation and finite element simulation of prestressed CFST truss girder’s structural behaviours were carried out, and the research results about its working mechanism, failure mode, ultimate bending moment resistance, as well as discussion about structural design method, were summarized in this paper. The outline of the research is given as below:a. A series of experimental tests of prestressed CFST Warren-vert truss girder under loading at midspan, with ratios of span-to-height equal to 9.6,11.5 and 14.4 and prestress degrees equal to 0,0.4 and 0.6 respectively, were carried out. Failure modes, load vs. deformation relationships, neutral axis changing characteristics, strain states of concrete filled in steel tube and prestress effect were investigated by the tests.b. Internal forces distribution modes, stress and strain states of critical section, neutral axis distribution modes, and prestress working conditions of prestressed CFST truss girder were simulated by general purpose structure software ANSYS, for which the finite element (FE) modeling method was also validated by test results of CFST truss girders subject to shear failure and to bending failure.c. FE parameter studies were carried out to investigate bending resistances and balanced failures of prestressed CFST truss girder through varying diameter ratio of brace-to-chord, wall thickness ratio of brace-to-chord, prestress degree and concrete strength grade.d. In the light of current enforcing China codes for CFST building and bridge structures, the formula of bending resistance to chord squashing failure of prestressed CFST truss girder was summarized, on the basis of research results from experimental study and FE analysis. Safety degrees of bending failure against shear failure of a scaled-down model of two-span continuous CFST truss girder, and of a completed three-span continuous CFST truss girder bridge, were compared.