Multi-axis treatment of typical light-frame wood roof-to-wall metal connectors in design

Abstract

Proper selection of metal roof-to-wall connectors is needed to provide a cost-effective load path to transfer uplift loads on a roof system down to the supporting walls and transfer lateral loads into and out of the roof diaphragm of light frame wood structures. Structural engineers, architects and builders rely upon published design values in catalogs, software, and websites provided by individual manufacturers to aid in the appropriate selection of connectors once the determination has been made for the required capacities of the connector. To date, the state-of-the-practice for dealing with multi-axis loads in these connectors is to use a linear unity equation based on uni-axis design values. However, no significant validation of this practice is to be found in the literature. This study experimentally examines three very common connector types under both bi-axis and tri-axis loads and helps to understand the behavior of such connectors under multi-axis loads. After testing over 350 connections and performing detailed analyses, the currently used design equation is found to be inefficient (has the least usable design space compared to other considered design equations) and overly conservative. Based on the criteria of efficiency, performance and safety, a design space using either the linear unity equation or by simply taking a 25% reduction on all allowable loads is proposed. The proposed design space for the three types of connectors is shown to have a high level of safety and adequate performance while providing up to 2.5 times the usable design space as compared with the current practice.