Axial Compressive Behaviour of Square Through-Beam Joints between CFST Columns and RC Beams with Multi-Layers of Steel Meshes

Abstract

The axial compressive behaviour of an innovative type of square concrete filled steel tube (CFST) column to reinforced concrete (RC) beam joint was experimentally investigated in this paper. The innovative joint was designed such that (i) the steel tubes of the CFST columns were completely interrupted in the joint region, (ii) the longitudinal reinforcements from the RC beams could easily pass through the joint area and (iii) a reinforcement cage, including a series of reinforcement meshes and radial stirrups, was arranged in the joint area to strengthen the mechanical performance of the joint. A two-stage experimental study was conducted to investigate the behaviour of the innovative joint under axial compression loads, where the first stage of the tests included three full-scale innovative joint specimens subjected to axial compression to assess the feasibility of the joint detailing and propose measures to further improve its axial compressive behaviour, and the second stage of the tests involved 14 innovative joint specimens with the improved detailing to study the effect of the geometric size of the joint, concrete strength and volume ratio of the steel meshes on the bearing strengths of the joints. It was generally found from the experiments that (i) the innovative joint is capable of achieving the design criterion of the ‘strong joint-weak member’ with appropriate designs, and (ii) by decreasing the height factor and increasing the volume ratio of the steel meshes, the axial compressive strengths of the joints significantly increased, while the increase of the length factor is advantageous but limited to the resistances of the joint specimens. Because of the lack of existing design methods for the innovative joints, new design expressions were proposed to calculate the axial compression resistances of the innovative joints subjected to bearing loads, with the local compression effect, the confinement effect provided by the multi-layers of steel meshes and the height effect of concrete considered. It was found that the proposed design methods were capable of providing accurate and safe resistance predictions for the innovative joints.

Deformation analysis of axially loaded weak PVC-fiber reinforced polymer confined concrete column-strong reinforced concrete beam joints reinforced with core steel tube

“…The existing studies have shown that the h/d of joint has obvious influence on the mechanical performances of specimens (Chen et al, 2008; Duan 2020). To simplify the analysis, considering the comprehensive influence of joint dimension on the specimens, the ultimate axial stress fcaR and axial strain εcau of weak PFCC column-strong RC beam joints strengthened with CST are determined by equations (9) and (10)where βh and ζh mean the comprehensive influence coefficient of joint dimension on ultimate axial stress and strain, respectively, which are fitted by the regression analysis of measured data in this study and test data of Zhu (2018) and Yu (2007), as shown in Figures 23–24 and equations (11), and (12)

Figure 23.Relationship between βh and h/d.

Figure 24.Relationship between ζh and

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Seismic Behavior Experimental Study on the Joint of Circular Tubed Steel‐Reinforced Concrete Columns

“…On the basis of collecting the shear failure results of steel tube-confined reinforced concrete columns with various sections, Gan et al compared and verified the existing calculation methods and formulas of shear capacity, improved the existing calculation methods, and proposed the calculation formulas of shear capacity for square steel tubes and circular steel tubes, respectively [18]. Duan et al designed a new type of square steel tubeconfined concrete column joint, carried out two-stage tests to investigate the overall axial compressive behavior of the specimen and the influence of joint geometry size, concrete strength, and mesh volume on its bearing capacity, and proposed the bearing capacity expression of this new type of joint [19]. Lin et al analyzed the shear mechanism and shear capacity of framework joints of steel-reinforced concrete-filled circular steel tube (SRCFCST), and the calculation method of composite shear capacity in the core area of joints is proposed, which can provide a reference for nonlinear analysis and engineering design of similar joints [20].…”