Seismic Performance of RC Beam–Column Joints Designed According to Older and Modern Codes: An Attempt to Reduce Conventional Reinforcement Using Steel Fiber Reinforced Concrete

Abstract

An analytical and experimental investigation was conducted herein to examine the cyclic load behavior of beam–column joint subassemblages, typical of both the modern reinforced concrete (RC) structures and of the pre-1960s–1970s existing ones. Seven exterior RC beam–column joint subassemblages were constructed and subjected to earthquake-type loading. Three specimens were designed according to the requirements of the Eurocode (EC) for ductility class medium (DCM), while the other three specimens possessed poor seismic details, conforming to past building codes. The hysteresis behavior of the subassemblages was evaluated. An analytical model was used to calculate the ultimate shear capacity of the beam–column joint area, while also predicting accurately the failure mode of the specimens. It was clearly demonstrated experimentally and analytically that it is possible for excessive seismic damage of the beam–column joint region to occur when designing according to the current European building codes. In addition, the proposed analytical model was found to be very satisfactory in accurately predicting seismic behavior and in preventing the premature brittle shear failure of the joints. The seventh subassemblage, constructed with steel fiber RC and significantly less transverse reinforcement than that required according to the EC, exhibited satisfactory ductile seismic performance, demonstrating the effectiveness of the proposed design solution.

Analytical Model for the Design of HSFC and UHSFC Jackets with Various Steel Fiber Volume Fraction Ratios for the Retrofitting of RC Beam-Column Joints

“…Recently, in [41,42], it was clearly demonstrated both experimentally and analytically that, even in modern RC structures designed according to the recommendations of the EC8 for ductility class medium (DCM), a mixed-type failure which includes shear damage in the beam-column joint region cannot always be effectively precluded. Contrarily, if the shear stresses developed in the joint region during an earthquake event are moderate to high (0.5γ ult < γ < γ ult ) or high (γ ≥ γ ult ), the joint shear failure is possible to occur regardless of the capacity design ratio value and the number of ties provided in the joint region.…”

“…Thus, an analytical formulation, which allows the accurate prediction of the behavior of the beam-column joints under reversed inelastic lateral displacements, would be particularly useful to secure the desirable ductile seismic performance of the joints. Under these lines, an analytical model was proposed by Tsonos [41][42][43] which precisely predicts the ultimate shear capacity of the joint region, τ ult , as well as the developed actual shear stress, τ cal . The accuracy of the analytical formulation (Tsonos model) has been checked using data acquired from more than 160 seismic tests performed in the Laboratory of Reinforced Concrete and Masonry Structures of the Aristotle University of Thessaloniki, as well as data from numerous experimental works found in the literature.…”

“…However, this cannot be achieved solely by satisfying design requirements such as the flexural strength ratio value (ΣM Rc /ΣM Rb > 1.30 according to the EC8 for ductility class medium buildings). On the contrary, the determination of the developed shear stresses during cycling, which should remain low to prevent shear failure of the joint, is necessary as well [41,42]. This is possible by implementing the analytical formulation proposed by Tsonos (Tsonos model) [41][42][43], which allows for both the precise calculation of the actual shear stresses when yielding of the beam(s) reinforcement occurs and for the accurate prediction of the ultimate joint shear capacity.…”

“…On the contrary, the determination of the developed shear stresses during cycling, which should remain low to prevent shear failure of the joint, is necessary as well [41,42]. This is possible by implementing the analytical formulation proposed by Tsonos (Tsonos model) [41][42][43], which allows for both the precise calculation of the actual shear stresses when yielding of the beam(s) reinforcement occurs and for the accurate prediction of the ultimate joint shear capacity. By comparing these values, the seismic behavior of the joints and the type of earthquake damages can be predicted for both the modern and the old existing buildings.…”

Effect of Carbon Black and Hybrid Steel-Polypropylene Fiber on the Mechanical and Self-Sensing Characteristics of Concrete Considering Different Coarse Aggregates’ Sizes

“…Based on conductive concrete mixture proportioning, various conductive materials (steel fiber, carbon fiber, carbon nanotube, carbon black, nickel powder, etc.) were added and/or used to replace coarse aggregates and compared with conventional concrete [ 17 , 18 , 19 , 20 ].…”