Seismic Performance of Bolted Glulam Timber Brace Connections with Internal Steel Plates

Abstract

Mass timber braced frame systems achieve their ductility through the brace connections. Canadian design standards currently lack guidance on how to detail bolted brace connections to achieve a target system-level ductility as per the National Building Code of Canada. This research aims to develop guidelines on how to detail bolted glulam timber brace connections to achieve moderate or limited ductility. To accomplish this objective, 4, 8, and 12-storey prototype buildings were designed to determine realistic brace design forces. Experimental tests were conducted on brace connections from the prototype buildings and finite element models using ABAQUS were developed to predict and compare to the experimental brace behaviour. A total of 12 brace specimens with one or two slotted-in steel plates and two different bolt sizes were studied with the aim to determine the ductility of the connections and brace assemblies. The use of self-tapping screws as perpendicular-to-grain reinforcement to prevent splitting and enhance brace ductility was also investigated. The results of the experimental study showed that both end connections in a brace can experience larger plastic deformations if the connections exhibit a post-yield hardening response. To ensure a post-yield hardening response, connections can be designed with bolt spacing greater than the minimum allowable in Canadian Wood design standards with the addition of self-tapping screws perpendicular to grain to minimize splitting. The experimental yield strengths were compared to the design yield resistance and the results showed that the design yield resistance was more accurate for connections with two slotted-in steel plates than those with only one. The results of the experimental tests were then compared to finite element models of two of the connections that were calibrated for a connection with a single dowel. The finite element models were reasonably accurate for the connection with the two slotted-in plates and less accurate for the connection with a single slotted-in plate.