This dissertation presents a study on the coupling effects of tension and shear force on CLT connections in mid-rise structures. Unlike the current simplified design assumption that CLT connectors only take either pure shear or pure tension force in the structures, this research first considers the significant interactions between tension and shear loads from two orthogonal directions for CLT connections through bi-axial loading experimental tests and numerical analysis.
Four sets of experimental tests were conducted: 1) AE 116 angle bracket connection tests under monotonic/cyclic tension loading with four levels of co-existent shear loads (0 kN, 20 kN, 30 kN, and 40 kN), 2) AE 116 angle bracket connection tests under monotonic/cyclic shear loading with four levels of co-existent tension loads (0 kN, 20 kN, 30 kN, and 40 kN), 3) HTT5 hold-down connection tests under monotonic/cyclic tension loading with three levels of co-existent shear loads (0 kN, 10 kN, and 20 kN), and 4) HTT5 hold-down connection tests under monotonic/cyclic shear loading with five levels of co-existent tension loads (0 kN, 20 kN, 30 kN, 40 kN and 60 kN). The specimens exhibited changes in strength and hysteresis behaviour under different configurations. Under bi-axial loading, different interactions between nails and surrounding wood embedment caused the coupling effect. Based on the mechanisms of CLT connections under bi-axial loading, a pseudo-nail model was developed using a modified protocol-independent nail connection algorithm. Two key parameters, a gap size factor ß, and an unloading stiffness degradation index , were implemented into the original algorithm to capture the unloading stiffness degradation and coupling effect of bi-axial loading.
The developed model was able to capture all the characteristics of CLT connections, including strength degradation, reloading/unloading stiffness degradation, the pinching effect, and the coupling effect. Model parameters were calibrated for all 32 configurations from the tests, and compared in terms of load carrying capacity and energy dissipation. Accurate agreements were reached. The results show that the proposed CLT connection model was able to predict the hysteresis behaviour of all nail-based connections.
This paper presents the modeling of coupling effect of tension and shear loading on Cross Laminated Timber (CLT) connections using a finite element based algorithm called HYST. The model idealizes the connections as a “Pseudo Nail” - elastoplastic beam elements (the nail) surrounded by compression-only spring elements (steel sheath and wood embedment). A gap size factor and an unloading stiffness degradation index of the spring elements under cyclic loading were integrated into the optimized HYST algorithm to consider the coupling effect. The model was calibrated to compare with 32 configurations of CLT angle bracket and hold-down connections tests: in tension with co-existent constant shear force, and in shear with co-existent tension force. The results showed that the proposed model can fully capture the coupling effect of typical CLT connections, considering strength degradation, unloading and reloading stiffness degradation, and pinching effect. The model provided a useful tool for nailbased timber connections and a mechanism-based explanation to understand the hysteretic behaviour of CLT connections under bi-axial loading.
This paper presents results of an experimental study of commonly used angle bracket and hold-down connections in Cross Laminated Timber (CLT) wall systems under bi-directional loading. Monotonic and cyclic tests of the connections were carried out in one direction, while different levels of constant force were simultaneously applied in a perpendicular direction. The experiment aims to consider the combined and coupling effect of loads for connections in a rocking CLT shear wall system. Key mechanical characteristics of those connections were calculated, evaluated and discussed. The results show that shear and tension actions for hold-downs are quite independent but strongly coupled for angle brackets. The study gives a better understanding of hysteretic behaviour of CLT connections, and provides reliable data for future numerical analysis of CLT structures.
In this paper, an innovative type of mid-rise Cross Laminated Timber shear walls with coupling beams was designed. The 5-layer CLT panels were continuous along the height. Hold-downs and angle brackets were installed at the bottom of the panels. Coupling beams with energy dissipation devices were used to decrease the deformation and internal forces of the walls, providing adequate stiffness and strength. A numerical model was developed in OpenSees for a six storey prototype to investigate its seismic behaviour with different configurations. Strength degradation, stiffness degradation, and pinching effect were considered in the connection models. The structural performance was evaluated through a series of static and transient analyses. The simulation results indicated adequate lateral resistance and deformation capacity of this structural type. This study will lead to more application of large size CLT panels in multi-storey CLT buildings as lateral resistant systems.
