Nonlinear Modeling of RC Substandard Beam–Column Joints for Building Response Analysis in Support of Seismic Risk Assessment and Loss Estimation

Abstract

The paper discusses how joint damage and deterioration affect the seismic response of existing reinforced concrete frames with sub-standard beam–column joints. The available simplified modeling techniques are critically reviewed to propose a robust, yet computationally efficient, technique for simulating the nonlinear behavior of substandard beam–column joints. Improvements over the existing models include the simulation of the cyclic deterioration of joint stiffness and strength, as well as pinching in the hysteretic response, implemented considering a deteriorating hysteretic rule. A fiber-section forced-based inelastic beam–column element is developed, considering improved material models and fixed-end rotation due to bond failure, rebars-slip, and inelastic extension, to simulate the deteriorating cyclic behavior of existing pre-cracked beam–column members. For the assessment of frames with substandard exterior beam–column joints, a nonlinear model for the exterior joint is developed and validated through a full-scale quasi-static cyclic test performed on a substandard T-joint connection. The proposed model allows considering structural performance in risk assessment while accounting for true inelastic mechanisms at the joints. An assessment of a five-story RC frame revealed that the activation of the joint shear mechanism increases the chord rotation demand on the connecting beam members by up to 85%, with increases of up to 62% (mean drift) and 89% (mean + 1.std.) on the lower floors when determining the inter-story drift demand, and the collapse probability of structures subjected to design base ground motions increased from 4.20% to 29.20%.

Shaking Table Testing of a Low-Rise Reinforced Concrete Intermediate Moment Resisting Frame

“…Because the design ensured a beam-sway mechanism under the design level input motions, a caution for numerical modeling technique [33] is to consider material/section overstrength for beam/column members, as the beam provided enough hardening to cause significant damage to the joint panel at large deformation demand. The development of severe damage in the joint core confirms hardening in the joint force-deformation behavior, which is critical for joint nonlinear modeling [34].…”

Seismic Impact on Building Structures: Assessment, Design, and Strengthening

“…Beam-column joints were noted as one of the most critical components of RC buildings. Owing to the severity and widespread concern, Ahmad et al [9] proposed a computationally efficient approach to model the nonlinear behavior of beam-column joints in a substandard RC construction. They further reinforce the numerical modeling proposal with a full-scale quasistatic cyclic test.…”

In-Plane Quasi-Static Cyclic Testing of Rc Frames Retrofitted With Rigid/Dissipating Steel Haunches

“…[19] & [20] studied the effectiveness of retrofitting RC beam-column-slab joints after standard fire with steel haunches and Self-Compacting-Geopolymer-Concrete (SCGC) Retrofitted Haunches respectively. In order to investigate how damage or deterioration of RC deficient B-C joints affects the seismic response of existing RC frames with such joints, Ahmad N. et al (2022) [21] conducted nonlinear modelling of the joints. Tariq H. et al (2022) [22] constructed and utilized spring-hinge models to archetypal frame structures in order to comprehend the influence of ductile concrete materials at the potential plastic hinge area of beams and its effect at structural level seismic performance.…”