Experimental study of shear retrofit of RC beam-column joints using external post-tensioned bolts

Document Type : Research Article

Authors

1 Department of Civil Engineering, Faculty of Civil Engineering, Semnan University, Semnan, Iran

2 Associate Professor, Faculty of Civil Engineering, Semnan University, Iran

3 Professor, Faculty of Civil Engineering, University of Semnan

Abstract

RC beam-column joints play a crucial role in transferring gravity and lateral loads from beam to column. By examining damaged buildings in recent earthquakes, RC beam-column joints are among the most vulnerable members of RC moment frames. Joint failure can pose a threat to the structure, ending up destroying the structure. The main type of failure of RC joints is shear failure due to the lack of transverse reinforcement and confinement in this area. The laboratory program of the current study suggests external post-tensioned bolts to retrofit RC joints. External post-tensioned bolts increase the confinement and enlargement of the joint panel zone and subsequently eliminate the deficient shear joints. Regarding the forces applied to the joint panel zone are implemented diagonally, the external post-tensioned bolts were used in two horizontal-vertical (HV) and diagonal (Di) patterns around the joint. The horizontal-vertical pattern was chosen owing to placing the resultants of the retrofit bolts forces in the direction of the applied forces. Furthermore, the diagonal pattern was adopted due to the placement of the retrofit bolts in the direction of the applied forces. The testing program includes four RC beam-column joint specimens with half-scale. One specimen was constructed as a standard criterion with all seismic requirements, and three specimens were made at the joint without implementing transverse reinforcement. One deficient specimen was used as a control specimen, and two specimens were subjected to cyclic loading after retrofitting by the proposed patterns. In order to investigate the effect of the proposed method, parameters such as; the force-displacement hysteresis response, energy absorption and damping value of the specimens were considered. The test results confirm the significant effect of the retrofit system against seismic loading. Accordingly, the failure was exited from the joint panel zone and transferred to the beam in retrofitted specimens. The final capacity of the retrofitted specimens increased by nearly 50% and their energy absorption by about 200%. In addition, the damping values and the ductility factors increased by about 100% and 32% in retrofitted specimens, respectively.

Keywords

Main Subjects

References

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Amirkabir Journal of Civil Engineering
Volume 55, Issue 3
June 2023
Pages 681-700

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