For predicting the shear strength and failure mechanism of the beam-column joint cores in reinforced concrete ductile frames under seismic loads, a nonlinear softened strut-and-tie model has been developed in this paper. The proposed unified model for exterior and interior joints is derived to satisfy equilibrium, strain compatibility, and the constitutive laws of cracked concrete and steel. The intended approach addresses all critical shear components within the joint, and a statically indeterminate load pattern has been chosen before and after yielding of the steel reinforcement within the joints. The macro-model of the diagonal compression strut of concrete depends on the effective joint dimensions and the level and type of column load. The horizontal and vertical ties are made-up of the joint hoops, the column intermediate bars, and the inclined joint bars. Depending on the distribution pattern and bond condition, the model accounts for the unequal participation of joint reinforcement in shear resistance. The nonlinear compression law for concrete considers the effects of the hoops-induced confinement and the cracking-related softening. For reinforced concrete in tension, the composite law accounts for the influence of concrete cracking, tension stiffening, and yielding of steel ties. The accuracy of the proposed procedure was checked by comparing the calculated shear strengths with the experimental data reported in literature, and a satisfactory correlation was found. Extensive parametric studies were performed to provide valuable insights into the strength behavior and design of the exterior and interior joints under seismic loading. |
