Experimental and numerical investigations on steel-concrete-PVC SHS joints under axial compression

This paper presents the experimental and numerical investigations on steel-concrete-PVC SHS joints under axial compression, in which PVC pipes were used as the inner tube of chord member and SHS steel tubes were used as the outer tube of chord member. A total of 22 joints with different brace to chord width ratio (β), hollow ratio of chord (φ) and shapes of PVC inner tube of chord were tested, in which two traditional hollow joints and two grouted joints were tested for comparison. The effects of brace to chord width ratio (β), hollow ratio of chord (φ), grout strength and shapes of PVC inner tube of chord on the structural behavior of steel-concrete-PVC SHS joints under axial compression were evaluated. Failure load and initial stiffness of traditional joints are remarkably enhanced by grouting the chord member along its full length, but the ductility is greatly deteriorated. On the other hand, the failure load and initial stiffness of steel-concrete-PVC SHS joints are improved with the increase of the β ratio. Whereas, the failure loads of steel-concrete-PVC SHS joints are weakened with the increase of the φ ratio. Furthermore, the grout strength has insignificant influence on the failure loads of steel-concrete-PVC SHS joints under axial compression. In addition, the steel-concrete-PVC SHS joints with large φ ratio show good ductility. Chord web deflection is larger than the chord flange indentation for steel-concrete-PVC SHS joints. For steel-concrete-PVC SHS joints with small φ ratio, the root of brace yielded first, while in the ultimate limit state, chord member around the joint intersection region were in the elastic phase. For steel-concrete-PVC SHS joints with large φ ratio, chord member around the joint intersection region yielded first, while in the ultimate limit state, the root of brace were fundamentally in the elastic phase. The design equations are proposed based on parametric FE analysis results for steel-concrete-PVC SHS joints under axial compression, which are verified to be more accurate.