Study On The Static Behavior Of Rectangular Steel Tube Truss With Concrete-Filled Compressive Chord

The content of this paper is about the western science project and application project of communications ministry. Partially concrete-filled rectangular steel tube truss is novel structure form. The static behavior of steel tube truss with concrete-filled compressive Chord is studied.Based on the analysis about the influence factors of the static behavior of steel tube truss, two trusses with directly welded K-joints are designed, including the hollow rectangular tube truss and upper chord concrete-filled truss. Making use of finite element package program ANSYS and considering both material nonlinearity and geometric nonlinearity, the integral working character and static behavior of the structure is analyzed.The theory of partially concrete filled concept is basing on the factual of bridge load-bearing state. So the load-bearing behavior of rectangular steel tube truss under the joint vertical load and the moment is analyzed which is very necessary. The full process under loading, plastic development and failure mode of the structure are traced. The main conclusion we can get as follows:1) Under the joint load, it is evident for filling concrete to improve the carrying capacity of the structure. The stress concentrating phenomenon of joints on the hollow tube is evident. It may reach the yield stress even the load is small. Both the two truss failure mode is that the deformation of the joints is too large to lose the load carrying capacity, which is the critical factor for the rectangular steel tube truss. The deformation of the tube wall which is connect to the compressing brace is large, and the typical character is that the web plane of chord convex towards external to failure or local buckling takes place, at the same time, the upper surface of the chord is compressed concave into entrails by the compression brace. According to the load-displacement curve of the two trusses, the integral stiffness of the hollow tube truss decreases quickly after entering the plastic phase, and the curve intends to flat. But the integral stiffness of the truss filled concrete in upper chord is still large and its load-displacement curve is still rising, which indicates that the ductility of the structure would be improved by filling concrete in upper chord. 2) Under the joint load and moment, the load-carrying capacity of rectangular steel tube truss is improved more evident by filling concrete in compressed chord under large moment. The stress level of the lower chord mid-span is higher if the compressed chord is filled with concrete. So the use rate of material is also improved evidently. Furthermore, the axial tensile force of chord would strengthen the joint load-capacity, while the axial compressive force of chord would decrease the joint load-capacity.Basing on this theory, a three-span and two-flour continuous steel truss bridge with rigid cable is attempted to design and analyze. The stress level of the structure decreases evidently after partially filling concrete in chords. The contribution of concrete to sharing the compression stress is larger than the own weight effect. The natural frequency of the structure increases evidently after filling concrete, which certifies that it is reasonable for the rectangular steel tube truss to be partially filled with concrete.