Elastic stiffness of a novel steel-grout hybrid dowel-type connector for cross-laminated timber panels: analytical model development, experimental validation and genetic algorithm optimization

Abstract

This work presents the development of an analytical model for the elastic stiffness of innovative hybrid steel-grout dowel-type connectors for CLT panels. This analytical model is based on the Beam on Elastic Foundation theory using the Wrinkler assumption. Within the model, the connector’s elastic stiffness is discretized into two components: (i) the rod-grout interaction stiffness and (ii) the grout-CLT interaction stiffness. The final stiffness is derived by combining these two components. This model accommodates the complex modulus of elasticity function for CLT through a square wave function approximated using a Fourier series. 420 monotonic static full-scale tests were conducted on hybrid connectors, varying the loading angle, the CLT grade, the rod diameter and strength class, and the grout-to-rod diameter ratio. A comparison between experimental and analytical results demonstrates the accuracy of the developed analytical model, with average errors for the elastic stiffness of 13% for connectors loaded in a direction parallel to the face layers of the CLT panel and 11% for connectors loaded in a direction perpendicular to the face layers of the CLT panels. Sensitivity analyses revealed that the modulus of elasticity of the grout has the most significant effect on the variability of elastic stiffness of connectors. Finally, a genetic algorithm optimization confirmed that an optimal grout-to-rod diameter ratio falls between 2 and 4 for 3-ply CLT panels, with a selected ideal connector having a rod diameter of 27.99 mm and a grout-to-rod diameter ratio of 2.68, yielding an elastic stiffness of 156.01 kN/mm.