The research project presented in this study aimed to study the effect of bolt numbers and patterns on protected and unprotected concealed steel-glulam hybrid connections. Fifteen full-scale concealed (wood-steel-wood) connections were experimentally examined: five ambient and ten fire resistance experiments. Four and six steel bolts in two different patterns were arranged to form four different connection configurations that were experimentally examined. Also, each connection configuration was tested with and without fire protection of the steel components using wood plugs. Ambient specimens were tested under gradually increased monotonic loads until failure; whereas the other specimens were subjected to elevated temperatures that followed CAN/ULC-S101 standard fire, while being loaded to 100% of the ultimate design load capacity of the weakest connection configuration.
The experimental results revealed that, although the protected connection configuration had slightly less moment-resisting capacity than that of the unprotected configuration at ambient temperature, it had an increased failure time of about 20 minutes at elevated temperatures. Also, increasing the bolt number from four to six, improved the connection’ moment capacity by about 66%. However, increasing the number of bolts from four to six bolt in the connections tested at elevated temperature mainly affected the connection’s failure mode. Furthermore, raising the bottom row of bolts to the mid-height of the beam section increased the maximum moment capacity of the connection by about 90% compared to that of the similar connection but with the bottom row close to the bottom side of the beam section. Similar to the bolt number, the bolt pattern mainly affected the failure mode of the connections subjected to fire.