Cyclic behaviour of typical screwed connections for cross-laminated (CLT) structures

This paper presents the results of an extensive
experimental programme on typical cross-laminated timber
(CLT) screwed connections conducted at CNR-IVALSA research institute. In-plane monotonic and cyclic shear and
withdrawal tests were performed on screwed wall-to-wall, floor-to-floor and wall-to-floor CLT connections. Mechanical properties such as strength, stiffness, energy dissipation, ductility ratio and impairment of strength were evaluated. The experimental results showed good performance of CLT
screwed joints under cyclic loads when ductile behaviour
was achieved. Brittle response occurred only in cases where requirements for end and edge distances were not satisfied. The experimental characteristic shear strength and mean slip
modulus of the connections were compared with values
obtained using analytical design equations. The Eurocode 5 (EC5) formulas overestimated the characteristic strength
values in some cases, while the Uibel and Blaß formulas
specifically developed for CLT connections provided more
accurate and conservative predictions. In cases where brittle failures were attained, the analytical values overestimated
the experimental ones. This issue can be avoided when the
requirements for minimum edge and end distances stated by
EC5 are fulfilled. EC5 empirical formulas for the prediction of the screw connection slip modulus at serviceability limit state corresponded well with the experimental elastic values.
The overstrength factor, which is of great importance in capacity-based design, was also evaluated, and a conservative value of 1.6 can be recommended for screwed CLT
connections.