The design of cross-laminated solid timber (CLT) as load-bearing plates is mainly governed by serviceability criterions like maximal deflection and susceptibility to vibration. Hence, predicting the respective behavior of such plates requires accurate information about their elastic properties. According to product standards, the bending stiffness of CLT has to be assessed from 4-point bending tests of strip-shaped specimens, cut from the CLT panels. By comparing elastic properties of CLT derived by means of modal analysis of full panels with the results of bending tests on 100 mm and 300 mm wide strip-shaped specimens it is shown, that by testing single 100 mm wide strip-shaped specimens bending stiffness of full panels cannot be assessed correctly, whereas single 300 mm wide strips or averages of 5 to 6 100 mm wide strip-shaped specimens lead to acceptable results. Hence, strip-shaped specimens should only be used in the course of factory quality control or when assessing the bending stiffness of parts of CLT panels used as beam-like load-bearing elements but not to derive bending stiffness of gross CLT panels. Verification by carrying out static bending tests of gross CLT panels under different loading situations showed that alternatively to tests on strip-shaped specimens or estimations with the compound theory, the overall stiffness properties of CLT can be derived directly by a modal analysis of full-size panels.
To support the associated Sir Matthew Begbie Elementary School and Bayview Elementary School projects in pushing the boundaries forward for long-span floor and roof construction, this testing project aims to compare different connection approaches for composite connections between glulam and cross-laminated timber (CLT) – for vibration, stiffness, and strength. Working with the University of Northern British Columbia (UNBC), Fast + Epp aimed to complete a series of vibration and monotonic load tests on 30’ long full-scale double-T ribbed panels. The tests consisted of screws in withdrawal, screws in shear, and nominal screws clamping with glue. Both the strength and stiffness are of interest, including slip stiffness of each connection type. This physical testing was completed in January and February 2020, where the full composite strength of each system was reached. Initial data analysis has provided information for comparison with existing models for shear connection stiffness. Publications will follow in 2021.
The research presented in this paper is related to estimating the in-plane stiffness and strength of CLT shearwalls with different connections for platform-framed construction. Finite element analyses (FEA) for CLT shear walls with various types of connectors for wall-to-floor, wall-to-foundation, and wall-to-wall joints were conducted. The CLT panels were modelled using plane-stress shell elements with elastic material properties and the connections were modelled using nonlinear springs. The joints, consisting of traditional steel brackets, hold-downs, and screws connections, were modelled using nonlinear zero-length spring elements with "pinching4" hysteresis properties calibrated from tests. A parametric study was performed on single and coupled CLT shear walls with the variation of the number and types of connectors. The results showed that strength and stiffness increased significantly with the increase in the number of connectors. Placing hold-downs on both sides of the coupled shear walls increased performance-i.e. 43% and 25% increase in strength and stiffness compared to coupled shear walls with hold-downs located at the outer edges only.