Yield and ultimate rotations of beam-to-column end-plate connections

Abstract

The deficiencies of traditional force-based design approaches and the recognition of the key-role of displacements and deformations as reliable and direct index of structural damage caused by earthquakes recently produced a shift in seismic design and assessment philosophy. In fact, new performance-based design requirements have strongly emerged internationally in seismic design and analysis. One design concept that was developed in response to these needs is currently known as “displacement-based” design (DBD). A large amount of work has already been undertaken in the field of displacement-based design especially for reinforced concrete structures. Recommendations for steel moment resisting frame (MRF) structures are few and the available proposals have not been fully confirmed. In this context, a research project – named DiSTEEL (Displacement based seismic design of STEEL moment resisting frame structures) and aiming to develop performance-based design guidelines for moment resisting steel frame structures – has been funded by the European Community. The DiSTEEL Project was the framework of the study presented in this thesis. In case of moment resisting steel frames, beam-to-column joints are essential structural components that significantly affect the overall seismic response. Therefore, a first step towards the development of DBD rules for MRFs is the analysis of response of beam-to-column joints with a focus on limit-state deformations. Within the context briefly outlined, the focus of this work is on the features of the inelastic response of beam-to-column end-plate joints. The efforts are addressed to the development of simple yet reliable design equations and tools to predict joint rotations associated with selected limit-states. After a review of some available experimental data, an assessment of existing analytical models for predicting joint rotational stiffness and strength is presented. Using these analytical models the geometrical and material parameters mostly affecting the joint yield rotations are highlighted. Analytical predictions of yield rotations of both flush and extended end-plate joints are subsequently evaluated by comparison with experimental data. Once validated by such a comparison, the analytical tools are further developed for design purposes, in the form of design charts to be obtained by an automated application of the analysis tools. Finally, discussion and preliminary evaluation of the rotation capacity of extended end-plate joints are presented.