Connection and System Ductility Relationship for Braced Timber Frames

Abstract

Braced timber frames (BTFs) are an efficient lateral load-resisting system for wind and seismic loads. This paper derived a relationship between the connection ductility and the system ductility of concentric BTFs based on engineering principles. The system ductility is a function of the connection ductility, the stiffness ratio of the connection to the diagonal brace, and the number of tiers and story. The proposed relationship was verified against the pushover analysis results of single-story and multistory BTF buildings. The verified relationship was used to investigate the influence of connection ductility, stiffness ratio, and number of tiers and stories on the system ductility of BTFs. It is recommended, if possible, that the BTFs be designed in such a way that the connections at both ends of diagonal braces can yield simultaneously, so that a higher system ductility can be achieved. It was found that for moderately ductile BTFs according to National Building Code of Canada, the minimum brace connection ductility of 11.5 is needed when only one end connection is yielding and exhibiting significant nonlinear behavior, and the other connection remains linear elastic. If both end connections of each diagonal brace yield, the minimum connection ductility needed is 6.3. In the case of limited-ductility BTFs, the minimum connection ductility needed is 5.4 when yielding in a single connection occurs and 3.2 when yielding in both end connections occurs. The derived relationship will help researchers and engineers to predict the system ductility of BTFs with different connections.