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.
Highlights
Catastrophic collapses of reinforced concrete (RC) structures during strong earthquakes of the last sixty years worldwide indicated that the design of beam–column connections for them to remain elastic throughout seismic excitation is the sine qua nonfactor for ensuring the preservation of structural integrity of ductile moment-resisting frames
The primary scope of the present study is to examine the weaknesses of the Eurocode requirements for the design of beam–column joints for ductility class medium (DCM) structures, as well as to propose an alternative cost-effective design solution by using innovative materials
The cyclic lateral response of the exterior RC beam-to-column joint subassemblages, i.e., DCM_1, DCM_2, DCM_3, D1, D2, and D3, is subsequently evaluated using data acquired from the experimental equipment during testing
Summary
Catastrophic collapses of RC structures during strong earthquakes of the last sixty years worldwide indicated that the design of beam–column connections for them to remain elastic throughout seismic excitation is the sine qua nonfactor for ensuring the preservation of structural integrity of ductile moment-resisting frames. In the case of existing RC structures before 1960s–1970s, the brittle and premature failure of beam–column joints was common, owing to a plethora of structural deficiencies These include, for instance, the quality of the materials, the use of plain steel reinforcement and concrete of low compression strength, poor reinforcement details, sparsely-spaced (or not existing) stirrups providing low confinement and/or shear strength, inadequate anchorages of reinforcement [1]. As a result, these structures are underperforming with respect to modern code requirements [2,3,4,5]. The excessive damage of the joints may cause the collapse of the structures due to P-∆ effects or due to the formation of soft-story mechanism [6,7,8,9,10]
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