Force-Limiting Floor Diaphragm Connection for Earthquake-Resistant Buildings

The goal of this research program is to develop and evaluate a deformable connection that limits the earthquake-induced horizontal inertial forces transferred from each floor of the flexible gravity load resisting system (GLRS) to the stiff lateral force resisting system (LFRS) of earthquake-resistant buildings. The research is limited to LFRS that develop a flexural yielding mechanism at the base, such as a flexural-dominated reinforced concrete shear wall. In addition, the research considers only design basis earthquake ground motions.The research objectives are: (1) to create physical embodiments of the force-limiting deformable connection; (2) to assess experimentally the force-limiting deformable connection; (3) to develop a design procedure for the force-limiting deformable connection; (4) to validate the design procedure for the force-limiting deformable connection using numerical earthquake simulations.Numerical earthquake simulations of a 12-story reinforced concrete wall example building are used to establish a feasible design space with a broad range of force and stiffness requirements for the deformable connection. A deformable connection that consists of a limited-strength hysteretic component and bearing components is developed. A buckling restrained brace (BRB) or a friction device (FD) is used as the limited-strength hysteretic component of the connection. Low-damping rubber bearings (RB) are used as bearing components. Numerical earthquake simulations show that the use of the deformable connection reduces the LFRS force responses, the floor acceleration responses, and the dispersion of the LFRS force responses and the floor acceleration responses due to ground motion variability. The mitigation of higher mode effects in the LFRS force responses and floor acceleration responses is shown.2Full-scale experiments show that the quasi-static and dynamic force-deformation responses of the deformable connections that were developed and studied in this research are stable. Emphasis is given to the identification and assessment of the parameters that affect the experimental force-deformation response of the deformable connection components. Numerical models of the force-deformation response of the deformable connections are developed and calibrated using the experimental results.A simple design procedure for the deformable connections in an earthquake-resistant building is proposed. The seismic design forces for the deformable connections are calculated using a modified version of the ASCE7-16 method for calculating the seismic design forces for floor diaphragms.Numerical earthquake simulations of 12-story, 8-story, and 4-story buildings with reinforced concrete shear walls as the LFRS and a 9-story building with self-centering concentrically-braced frames as the LFRS show that deformable connections designed using the proposed design procedure reduce the LFRS force responses and floor acceleration responses, without excessive deformation demand in the deformable connections.