# Fire Performance of Self-Tapping Screws in Tall Mass-Timber Buildings
## 4 Design Proposal
### Verification and Validation from Heat Transfer Modelling  
In an attempt to verify and validate the temperature profiles of Equations (9) and (10) when exposed to the standard temperature-time curve CAN/ULC S101 [6], an extensive thermal numerical study was performed using FEM in ANSYS software. The transient heat transfer modelling gives the distribution of the temperature field on the nodes of each element constituting the assembly for each time step. Temperatures were measured at a depth of 0, 80 and 160 mm from the surface exposed to fire, i.e., at the same locations along the fastener shank used to measure the temperature during the small-scall fire tests. Figure 15 shows the comparison between the fire tests and FEM predictions for a \(\O\)10 mm full-thread STS exposed to a constant heat flux of 50 kW/m\({}^{2}\) up to two hours. The experimental and numerical results were in good agreement. Figure 14: Temperature profiles using Equation (9) compared to that of Equation (6) and test data for STS with unprotected heads and exposed to a constant heat flux. Figure 15: Numerical modelling of a \(\O\)10 mm full-thread STS exposed to a constant heat flux of 50 kW/m\({}^{2}\): **(a)** Heat transfer model at two hours of exposure; **(b)** Comparison of numerical and experiment of time–temperature curves up to two hours of exposure. Applying a constant heat flux of 50 kW/m\({}^{2}\) at the top surface of the STS head and glulam resulted in similar temperatures to that recorded from the small-scale fire tests. While the predicted curves are slightly higher at the tip of the STS, the heat transfer response was generally in agreement with the temperatures measured by the thermocouples at the same locations along the fastener shank. The FEM assumption of analyzing only one quarter of the specimen with a cylindrical shank did not seem to have affected the heat transfer response. These results suggest that the chosen thermal properties in the FEM modeling are satisfactory. In an attempt to compare the charred layer from the heat transfer model to that measured from the tests, the charred layer can be calculated numerically by considering all areas with temperatures greater than 300 \({}^{\circ}\)C, used as the temperature isotherm at which mechanical proprieties of the wood are set to zero (represented as the grey color in Figure 15a. By applying 300 \({}^{\circ}\)C isotherm of the model as shown in Figure 15a, the charred layers estimated numerically for the \(\O\Omega 10\) mm full-thread STS are 41 mm and 64 mm under one and two hours of exposures, respectively. This is consistent with the measured charred layer form the small-scale fire test in Table 3. The thermal model also showed the localized char along the STS shank, as observed in the experimental results. This is due to the presence of steel, which conducts heat faster along the fastener inside the timber. When moving away from the steel shank, the glulam cross-section shows low temperature, near to that of ambient conditions. The good insulation of timber prevents its propagation on all cross-sections by maintaining low temperature while the steel elements led to much higher temperatures inside the timber. Furthermore, the standard temperature-time curve CAN/ULC S101 [6] was also applied in the FEM model in an attempt to predict the heat transfer under standard fire exposure. Temperatures were also measured at depths of 0, 80 and 160 mm from the initial surface exposed to fire. Figure 16 illustrates the evolution of temperature for a \(\O\Omega 10\) mm full-thread STS exposed for one and two hours to the standard fire at the surface of the specimen. While the exposures are not similar, the experimental data from the small-scale fire tests are shown to compare the effect of the greater temperature from the CAN/ULC S101 standard fire. One can observe that the severity of the CAN/ULC S101 ultimately raises the shank temperature faster than when exposed to a constant heat flux of 50 kW/m\({}^{2}\).