# Fire Performance of Self-Tapping Screws in Tall Mass-Timber Buildings
## 5 Conclusions  
This study presents the fire performance of using self-tapping screws used for connections in mass timber constructions. The experimental program consisted of small-scale tests with perpendicular-to-grain withdrawal tests in an attempt to characterize the fire behavior of self-tapping screws exposed for up to two hours, as required for tall buildings in many countries. The results are also used to validate a three-dimensional transient heat transfer model using the finite element method and to develop design principles facilitating the determination of the fire-resistance of screwed connections.  
Influenced by the heating rate through the fastener shank, it was found that the temperature profiles through wood members mainly depend on the relative exposure of the wood and steel elements, as well as the fire duration, which affected the temperature distribution along the fastener shank. The combination of the insulating effect of timber and the favorable geometries when using long and slender fasteners provides longer fire-resistance for screw-type fasteners than bolt-type fasteners at elevated temperatures. Due to the insulating effect of timber, the smaller heated area of the exposed STS surface limited the thermal conduction along the cross-section area and the charred wood prevented the charring depth of the specimens. Mainly influenced by the temperature-dependent reduction of the embedment and withdrawal strengths of the timber, this study presented new design principles to predict the temperature profiles along unprotected STS with the influence of a steel-heated area to determine the residual length of penetration that will provide adequate residual load-capacity under fire conditions. When maintaining an adequate structural capacity of the surrounding wood fibers at a maximum of 100 \({}^{\circ}\)C, the capacity of the STS was not influenced with an increase of exposure duration. The design method presented herein allows calculating the residual capacity of unprotected STS exposed to fire for up to two hours. In our study, the measured temperatures are for a constant heat flux of 50 kW/m\({}^{2}\), corresponding to approximately 10 to 15 min of the standard temperature-time curve. To improve the numerical prediction of measured temperature profiles under the standard fire exposure, further studies should be conducted in the future by considering the parameters discussed in this study and by using a standard fire exposure of up to two hours.  
M.L.-G.: conceptualization, methodology, software, formal analysis, investigation, and writing--original draft. C.D.: methodology, supervision, validation, and writing--review and editing. P.B.: resources, funding, supervision, and writing--review and editing. All authors have read and agreed to the published version of the manuscript. Funding of this project was provided through the Natural Sciences and Engineering Research Council of Canada, through its IRC and CRD programs (IRCP) 461745-18 and RDCP] 524504-18) as well as through the Canada Graduate Scholarships Master's (CGS M) program. Funding was also provided by the industrial partners of the NSERC industrial chair on eco-responsible wood construction (CIRCERB).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available upon request to the corresponding author.  
**Acknowledgments:** The authors are grateful to Art Massif, FPI Innovations, and MTC Solutions for the materials used for the experiments and the technical support given.  
**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.