Influence of the inclination angle of self-tapping screws on the fire performance of CLT-concrete composite floor slabs

In this study, four full-size slab-type timber-concrete composite (TCC) floor assemblies were experimentally examined under standard fire exposure. The main objectives of the study are to investigate the influence of the inclination angles of the self-tapping screws (STS) utilized as shear connectors on the fire performance of TCC floor slabs, achieve a 2-h fire resistance as a result of the composite action between a supporting cross-laminated timber (CLT) panel and a top concrete layer, and ultimately verify the residual strength of the TCC slabs after 2-h standard fire exposure. Each slab specimen comprises a 143-mm thick, 5-ply CLT panel topped with a 90-mm thick normal-strength concrete layer. The overall dimensions of each test assembly were 5300 mm long and 900 mm wide, with a 5000 mm clear span. Screws were installed following the shear flow direction at two different inclination angles (i.e., 30° and 45°), with each specimen duplicated. TCC floor assemblies were exposed to elevated temperatures following the CAN/ULC-S101 standard fire time-temperature curve while subjected to four-point flexure. The experimental results show that all test assemblies surpassed the 2-h fire resistance time with an average residual wood thickness of 48 mm. However, after 2 h of standard fire exposure, the 30° STS installation angle resulted in better performance of the TCC floor slabs with lower midspan deflections than a 45° installation angle. In addition, the residual strength tests conducted after the 2-h standard fire exposure show that a TCC floor slab with STS installed at 30° may produce an ultimate moment as much as 12 % greater than when the STS are installed at 45°. • Timber-concrete composite (TCC) slab-type floor assemblies offer advantages over beam-type assemblies due to exposure to one-dimensional charring from underneath only. • TCC floor assemblies can be designed to meet the required 2-h fire resistance rating, essential for creating tall, mass timber buildings with acceptable fire safety measures. • Appropriate design can enhance the fire resistance of CLT panels by converting a simple timber slab to an advanced TCC floor system by adding shear connectors and a top concrete layer. • After a 2-h standard fire exposure, the 30° STS installation angle resulted in better performance of the TCC floor slabs with lower midspan deflections than a 45° installation angle. • Residual strength tests showed that a TCC floor slab with STS installed at 30° may produce an ultimate moment as much as 12 % greater than when the STS are installed at 45°.