Nonlinear Numerical Assessment of Exterior Beam-Column Connections with Low-Strength Concrete

The ductility and capacity of reinforced concrete beam-column connections depend mainly on the concrete’s strength and the provided reinforcements. This study investigates numerically the role of low-strength concrete in beam-column joints utilizing ABAQUS software. In this simulation, a newly developed stress-inelastic strain relationship for both confined and unconfined low-strength concrete is used. This study recommended a specific value of the concrete dilation angle for both substandard and standard joints. Also, stirrups’ yield strength value was found to play an insignificant role in improving the shear resistance of such joints with low-strength. In addition, the joint shear strength prediction using empirical models that implicitly consider the stirrups contribution in improving joint resistance was found to be better than the prediction of other models that explicitly consider the stirrups’ presence. The numerical results also showed that the use of a diagonal steel haunch as a joint retrofitting technique significantly increases the joint shear capacity and changes its brittle shear failure into a ductile beam flexural failure.

Investigating Optimal Confinement Behaviour of Low-Strength Concrete through Quantitative and Analytical Approaches

Reinforced concrete is used worldwide in the construction industry. In past eras, extensive research has been conducted and has clearly shown the performance of stress–strain behaviour and ductility design for high-, standard-, and normal-strength concrete (NSC) in axial compression. Limited research has been conducted on the experimental and analytical investigation of low-strength concrete (LSC) confinement behaviour under axial compression and relative ductility. Meanwhile, analytical equations are not investigated experimentally for the confinement behaviour of LSC by transverse reinforcement. The current study experimentally investigates the concrete confinement behaviour under axial compression and relative ductility of NSC and LSC using volumetric transverse reinforcement (VTR), and comparison with several analytical models such as Mender, Kent, and Park, and Saatcioglu. In this study, a total of 44 reinforced-column specimens at a length of 18 in with a cross-section of 7 in × 7 in were used for uniaxial monotonic loading of NSC and LSC. Three columns of each set were confined with 2 in, 4 in, 6 in, and 8 in c/c lateral ties spacing. The experimental results show that the central concrete stresses are significantly affected by decreasing the spacing between the transverse steel. In the case of the LSC, the core stresses are double the central stress of NSC. However, increasing the VTR, the capacity and the ductility of NSC and LSC increases. Reducing the spacing between the ties from 8 in to 2 in center to center can affect the concrete column’s strength by 60% in LSC, but 25% in the NSC. The VTR and the spacing between the ties greatly affected the LSC compared to NSC. It was found that the relative ductility of the confined column samples was almost twice that of the unrestrained column samples. Regarding different models, the Menders model best represents the performance before the ultimate strength, whereas Kent and Park represents post-peak behaviour.

EFFECT OF STRENGTH OF FILLED-CONCRETE ON STRUCTURAL PERFORMANCE OF CONTINUOUS BEAM-TYPE SQUARE CFST BEAM-TO-COLUMN CONNECTION

Continuous beam-type concrete-filled steel tube (CFST) column connections are simple to fabricate and exhibit effective seismic performance. Fujinaga and Clifton have previously studied the performance of continuous beam-type square CFST beam-to-column connections using concrete of relatively high strength (85 MPa) and demonstrated their effective performance and high energy-absorbing capacity. However, in their study, it was found that the local deformation of the steel beam under bending-induced beam tension had a large effect on the steel tube flange near the connection. Further, it was observed that filled concrete may not contribute substantially to the transmission of compressive load at the connection panel if low-strength concrete is used. In this study, the square CFST beam-to-column connection was investigated, and the connection performance and load transfer mechanisms were examined when the strength of the concrete was relatively low (40 MPa). The specimens demonstrated effective seismic performance, exhibiting sufficient strength and stable hysteretic behavior with high energy absorption even when low-strength concrete was used. Irrespective of the strength of the concrete used, the strain developed in the steel tube flanges was low on the compression side, and the filled concrete contributed to the transmission of the compressive load at the connection panel. The compressive strain in the steel tube was slightly higher when the strength of the concrete was low.