Conference Paper

Brittle failures of connections with self- tapping screws on CLT plates

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Abstract

For general safety reasons, the occurrence of a ductile failure mechanism in the global scale of the building is desirable. Recent works have proposed analytical models to predict the brittle capacity of dowel-type timber connections, some of them discussed in previous INTER meetings [1-5]. It is planned to include brittle failure models in the future version of Eurocode 5 and the design provisions for self-tapping screws in the Canadian timber design standard (CSA O86), both currently under development. However, most of the previous works were related to the brittle failure of solid and glued-laminated timber. It is usually assumed that connections with dowel-type fastener inserted into the CLT side face and loaded laterally typically behave in a quite ductile manner. Even the current CSA O86 explicitly states that ‘for CLT, the row shear failure and group tear-out failure need not be considered’ [2]. However, as shown in previous works [1-2], brittle failures may also occur in CLT. Zarnani and Quenneville [1] adapted their brittle failure model for plug shear for its application on CLT connections. Connections in CLT are typically produced with self-tapping screws (STS), which partially penetrate into the timber element. The corresponding brittle failure is plug-shear, in which bottom, lateral and head failure planes are observed. Zarnani and Quenneville described different types of failures related to the different fastener penetration depth. This work presents two recent experimental campaigns on brittle failures of CLT connections with self-tapping screws, done in Europe and Canada. The connections were tested in tension parallel to the grain of the outer CLT layer. The tests provide a preliminary insight into the brittle failures of connections in CLT panels, a matter which has been barely studied. However, it is of importance, due to the current prevalence of this type of timber product and its increased use.

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