Fire resistance of a fully concealed, moment-resisting new timber connection utilizing mechanically-fastened steel rods

One major hindrance to more utilization of timber in the construction of tall buildings is the limited fire resistance of the connections between its structural elements. In an experimental study that aimed to investigate the structural behaviour of a new connection configuration that utilizes fully concealed, mechanically fastened steel rods, eight (8) full-size glued-laminated timber beam-end connections were tested under the CAN/ULC-S101 standard time-temperature curve. Test variables investigated in this study included rod anchorage length (200 and 250 mm) and washer size (38.1 x 38.1 and 50.8 x 50.8 mm). Results show that using the smaller washer provided more wood side cover to protect the steel components from the effects of elevated temperatures. Also, utilizing longer rod anchorage length provided larger internal surface area of the wood prism to better resist shear stresses as well as longer length for the rods to bear against the wood at high rotation values of the connection. By combining the said two aspects (longer anchorage length and smaller washer) a fully concealed glulam beam-end connection that utilizes only two mechanically-fastened steel rods can be successfully designed to achieve a 1-h fire resistance without the application of additional fire protection.