Development and research of screwed cross-laminated timber nodal joints for multi-storey buildings

Introduction. The strength and deformability of cross-laminated timber (CLT) panels ensure the strength and stiffness of load-bearing frames. However, despite numerous studies on CLT joints, data on plastic behavior, safety coefficient, and the failure behavior of used joints are lacking in European and North American design standards.

Aim. The work addresses the load-bearing capacity, coefficients of stiffness and ductility of CLT joints, following the design features of cross-laminated timber.

Materials and methods. A series of samples were produced based on conventional solutions for CLT panels (“overlap,” “gasket-sealed,” “strapped,” “butt,” and “halved corner”), having various layers and diameters of a screw, and subjected to subsequent testing. The research procedure was developed following GOST 33082-2014 and foreign practices. The research was carried out at the Laboratory of Timber Structures of TSNIISK named after V.A. Koucherenko.

Results. Based on the experimental data, the normative and design load-bearing capacity, coefficients of stiffness and ductility for five types of CLT joints were established, depending on the number and direction of the outer layers, as well as the screw diameter. A plastic behavior rating scale was proposed to assess the performance of joints beyond elastic behavior, namely, a joint can be brittle, with low, moderate, or high plasticity.

Conclusions. The design features of CLT, such as the number of layers and their thickness, as well as the orientation of the outer layers, significantly influence the strength and deformation characteristics of screwed nodal CLT joints. The research results are intended for updating Rules and Regulations 299.13258800.2017 “Timber structures with screwed nodal joints.”

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