Structural fire performance of wood-steel-wood bolted connections with and without perpendicular-to-wood grain reinforcement

• Published in: Journal of structural fire engineering Vol. 14; no. 4; pp. 441 - 460
• Main Authors: Adam Roman Petrycki, Osama (Sam) Salem
• Format: Journal Article
• Language: English
• Published: Brentwood Emerald Group Publishing Limited 10.11.2023
• Subjects: Assemblies; Bolted joints; Columns (structural); Connectors; Earthquakes; Failure; Fire resistance; Glulam; Guidelines; High temperature; Mechanical properties; Reinforcement; Shear strength; Steel plates; Tapping screws; Timber; Wooden structures; Canada
• ISSN: 2040-2317; 2040-2325
• DOI: 10.1108/JSFE-02-2019-0016

PurposeIn fire condition, the time to failure of a timber connection is mainly reliant on the wood charring rate, the strength of the residual wood section, and the limiting temperature of the steel connectors involved in the connection. The purpose of this study is to experimentally investigate the effects of loaded bolt end distance, number of bolt rows, and the existence of perpendicular-to-wood grain reinforcement on the structural fire behavior of semi-rigid glued-laminated timber (glulam) beam-to-column connections that used steel bolts and concealed steel plate connectors.Design/methodology/approachIn total, 16 beam-to-column connections, which were fabricated in wood-steel-wood bolted connection configurations, in eight large-scale sub-frame test assemblies were exposed to elevated temperatures that followed CAN/ULC-S101 standard time-temperature curve, while being subjected to monotonic loading. The beam-to-column connections of four of the eight test assemblies were reinforced perpendicular to the wood grain using self-tapping screws (STS). Fire tests were terminated upon achieving the failure criterion, which predominantly was dependent on the connection’s maximum allowed rotation.FindingsExperimental results revealed that increasing the number of bolt rows from two to three, each of two bolts, increased the connection’s time to failure by a greater time increment than that achieved by increasing the bolt end distance from four- to five-times the bolt diameter. Also, the use of STS reinforcement increased the connection’s time to failure by greater time increments than those achieved by increasing the number of bolt rows or the bolt end distance.Originality/valueThe invaluable experimental data obtained from this study can be effectively used to provide insight and better understanding on how mass-timber glulam bolted connections can behave in fire condition. This can also help in further improving the existing design guidelines for mass-timber structures. Currently, beam-to-column wood connections are designed mainly as axially loaded connections with no guidelines available for determining the fire resistance of timber connections exerting any degree of moment-resisting capability.