An Analytical Study of Improving Beam-Column Joints Behavior Under Earthquakes

Abstract

Many existing worldwide Reinforced Concrete (RC) structures, such as non-ductile RC frames, were designed for gravity loads only during the 1950s through 1970s or earlier. Due to variations in the identification of seismic active zones by national codes, such structures may not satisfy the current design requirements, especially when lying in a recently identified seismic active zone. This is because such structures, as a result of poorer reinforcement detailing, may generally do not possess the adequate ductility and strength needed to withstand an expected earthquake. Consequently, older RC frames may undergo substantial damage during earthquakes. One of the main damage aspects in such case is clear cracks around and within the beam-column connections. This is the case where the failure of beam-column joints is governed by bond and shear failure mechanisms which are usually brittle. This may be attributed to inadequate shear reinforcement in the beam-column joints region. Accordingly, several techniques of repairing and strengthening beam-column joints in older RC frames have been reported especially in earthquake prone countries. In this paper, a finite element model for an exterior beam-column joint is presented to simulate the behaviour of such joints in older gravity load designed RC frame structures. Several specimens are studied, one for the unstrengthened case, and others represent strengthened cases with different techniques. Studied strengthening techniques include using banded joints with CFRP sheets as a proposed technique, or joints reinforced with steel jackets as observed from older research in literature. Each case is modelled then analysed when loaded incrementally till failure. The stress and deformation results are evaluated then compared for each case. Numerical results show that the beam-column joint strengthened with CFRP can increase their structural stiffness, strength and energy dissipation capacity in contrast to other techniques. The proposed strengthening technique is even advantageous for practical requirements.