ANALYTICAL MODELS FOR COLUMN BASE CONNECTIONS AND THEIR EFFECT IN SEISMIC PERFORMANCE OF STEEL MOMENT FRAMES
Analytical models for the characterization of the response of column base connections (i.e. exposed and embedded base plates) are developed and implemented in the Open System for Earthquake Engineering Simulation (OpenSees) software framework. These analytical models are validated against large-scale experimental programs conducted in different research institutions. The suggested analytical models are utilized to assess the performance of Steel Special Moment Resisting Frames (SMRFs) in the Performance Base Assessment/Design Framework. Specifically, this dissertation presents four studies:
1) A new hysteretic model formulation to capture the peculiar flag-shaped cyclic moment-rotation response of exposed base plates is proposed. This model is developed based on the physical processes involved in the hysteresis response. Five tests from a large scale experimental program at UC-Davis are used to calibrate the parameters of the proposed model.
2) A method is detailed to characterize the rotational stiffness of embedded column base connections. The method considers deformations of the components within the connection. The results are assessed against 9 tests from two experimental programs (ay UC-Davis and Brigham Young University).
3) The seismic demands on column base connections are investigated through a series of nonlinear time history simulations on 2-, 4-, 8-, and 12-story SMRFs. The 2- and 4- story frames feature exposed base plate type connections, whereas the 8-, and 12- story frames feature embedded connections. Results indicate that for exposed base plate connections, failure is likely to be controlled by the minimum axial compression accompanied by high moment. When embedded base connections are specified, the response is largely controlled by moment.
4) An approach to simulate the hysteretic and dissipative response of embedded base connections is described. This approach simulates embedded connections as an arrangement of two springs in parallel to reflect moment contributions due to horizontal and vertical bearing stresses. The resultant model is fit to five large-scale tests to calibrate its parameters.
The intention of these four studies is to contribute to a deeper understanding and more accurate characterization of the response of column base connections of Steel Moment Frames subjected to seismic loads.