Flexural Performance Of Three-main Components Concrete-filled Steel Tubular Chord-Steel Tubular Brace Truss

Concrete-filled steel tube (CFST)–steel tube truss (referred as CFST truss forshort in the below，which use CFST member as its chord and hollow tube as its brace)has been used more and more widely nowadays because of its reasonable forcetransformation mechanics, large space stiffness, good structural integrity, fine outwardappearance and so on. However relative theoretical and experimental researches aboutdesign principle of this kind of structure are seldom, and a further study is necessary.This paper studies the flexural performance of three-main components CFST trusswith and without reinforcement concrete (RC) slab. The main research work andoutcomes are summarized below:1. Theoretical and experimental researches were carried out on the axial tensionperformance of CFST. A total of18specimens were tested. The experimental resultsshowed that, the integrity of the inner concrete was good during the tensile experimentalprocess and the supporting effect of concrete tends to restrain the pinching feature of thesteel tube. A finite element model (FEM) was developed to perform mechanism andfull-range analysis for CFST under axial tension. The accuracy of FEM was verified byexperimental results. The influences of various parameters, including steel ratio,concrete strength and steel yield strength, were analyzed. Finally, a simplified formulathat could predict the tensile strength of CFST was proposed.2. A series of experiments were carried out on the CFST truss with vertical load onthe symmetrical four cent point along the span of the truss. The main parameters wereshear span ratio, RC slab and the angle between brace and chord. A hollow steel tubetruss was tested as a comparison of the CFST truss specimens. The influences of theseparameters on the flexural behavior and failure mode of CFST truss were investigated.The results showed that the inner concrete of chord can improve the mechanicalperformance of the truss notably, and the flexural bearing capacity, flexural rigidity andstructural ductility were also improved obviously.3. Full-range analysis on load versus deformation relations of CFST truss subjectedto flexural loading was performed based on an established FEM. The accuracy andrationality of the FEM were verified by the collected experimental results. Based on theFEM, the stress and strain distributions and developments at different characteristicpoints of the full-range process were analysed, and the typical flexural failure moedes of the CFST truss member were illustrated. The mechanical transmission path of CFSTtruss were also analysed. Parametric analysis was conducted on the influences offlexural performance of CFST truss. The parameters included inner concrete of chord,RC slab, shear span ratio (height to span ratio), the strength ratio of top boom and lowerboom, height to width ratio of the truss cross-section, and the angle between brace andchord.4. The flexural bearing capacities and flexural rigidities of CFST truss with orwithout RC slab were proposed herein. The strength ratio between top boom and lowerboom was defined, and the validity limit was suggested. This achievement can be usedin the project design and for the design code reference.