Fire Performance of Self-Tapping Screws in Tall Mass-Timber Buildings

Article de Mathieu Létourneau-Gagnon, Christian Dagenais and Pierre Blanchet

Abstract

Building elements are required to provide sufficient fire resistance based on requirements
set forth in the National Building Code of Canada (NBCC). Annex B of the Canadian standard for
wood engineering design (CSA O86-19) provides a design methodology to calculate the structural
fire-resistance of large cross-section timber elements. However, it lacks at providing design provisions
for connections. The objectives of this study are to understand the fire performance of modern mass
timber fasteners such as self-tapping screws, namely to evaluate their thermo-mechanical behavior
and to predict their structural fire-resistance for standard fire exposure up to two hours, as would
be required for tall buildings in Canada. The results present the great fire performance of using
self-tapping screws under a long time exposure on connections in mass timber construction. The
smaller heated area of the exposed surface has limited thermal conduction along the fastener’s shanks
and maintained their temperature profiles relatively low for two hours of exposure. Based on the
heat-affected area, the study presents new design principles to determine the residual length of
penetration that would provide adequate load-capacity of the fastener under fire conditions. It also
allows determining safe fire-resistance values for unprotected fasteners in mass timber construction
exposed up to two hours of standard fire exposure.

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