Cyclic behavior 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.