The present study proposes a new connection system for Cross Laminated Timber (CLT) structures in earthquake prone areas. The system is suitable for creating wall-floor-wall and wall-foundation connections, where each connection device can transfer both shear and tension forces, thus replacing the role of traditional “hold downs” and “angle brackets”, and eliminating possible uncertainty on the load paths and on the force-transfer mechanism. For design earthquakes intensity, the proposed system is designed to remain elastic without accessing the inelastic resources, avoiding in this way permanent deformations in both structural and non-structural elements. However, in case of unforeseen events of exceptional intensity, the system exhibits a pseudo-ductile behaviour, with significant deformation capacity. Furthermore, in the proposed system the vertical forces are directly transferred through the contact between wall panels, avoiding compressions orthogonal to the grain of the floor panels. In this research, the connection system was analysed via finite element modelling based on numerical strategies with different levels of refinements. Nonlinear analyses were performed in order to investigate the response of the connection to shear, tension and a combination of such forces. The numerical responses were compared with those of full-scale experimental tests performed on the proposed connection subjected to different kind of loading configuration. The results appear as promising, suggesting that the proposed connection system could represent a viable solution to build medium-rise seismic-resistant CLT structures, that minimise damage to structural and non-structural elements and the cost of repair.
Hybrid multistory buildings are every day more common in the construction industry. However, there is little understanding of the performance of the hybrid connections. In this research, the static and dynamic response of cross-laminated timber (CLT) composites combined with reinforced concrete (RC), hollow steel profiles and laminated strand lumber (LSL) has been investigated. In addition, the effects of posttensioning stresses as well as distinct types of connectors such as nails, self-tapping screws and self-tapping dowels has been accounted for. After experimental work, numerical modelling for simulating the static and dynamic behavior for these hybrid connections was also investigated. Results indicate that such massive timber composite connections behave reasonably similar to conventional timber connections, except in that inelastic deformations may increase up to 200%. In addition, it has been found that existing hysteretic models like the modified Stewart hysteretic model (MSTEW) fit for modelling purposes except that very asymmetric hysteretic behavior can be found for timber-concrete hybrid connections.
CLT-concrete composite floor systems are a solution for timber buildings with a long-span floor. It yields a reduction of carbon footprint and even eco-friendly structure at the end of its service life. This study will evaluate the structural performance of notched connectors in the CLT-concrete composite floor, comprised of the serviceability stiffness, maximum load, and behavior at failure. The parameters of the test plan are the loaded edge length, the notch depth, the concrete thickness, and the screw length. Other secondary variables are also assessed, such as different loading sequences, speed of test, and timber moisture content. Experimental results prove that the performance of the connector depends significantly but not linearly on the notch depth and the length of the loaded edge. The connector with a deeper notch and a shorter heel will be stiffer and more robust, but it also tends to have a brittle rupture. The test results also help validate a solution for deconstructable connector systems. A nonlinear finite element model of the connector is built and validated versus the experimental results. It yields reasonably good predictions in terms of resistance and can capture the load-slip relationship.
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.
Previous studies have mainly focused on the behaviour of timber under uniformly distributed compression perpendicular to the grain (CPG) loads. However, there are many practical applications in which timber is loaded by non-uniformly distributed CPG loads. Different design and test codes like the Eurocode 5 (EC5), DIN 1052:2004, ASTM D143- 94 and EN-408:2010 only account for load configurations where timber is subjected to uniformly distributed loads. For specific uniformly distributed load (UDL) configurations the bearing capacity of timber (solid softwood timber or Glulam) in compression is adapted by using a load configuration factor (kc,90) according to EC5, the European code for design of timber structures. EC5 has no guidelines for cross-laminated timber (CLT) under UDL with the exception of the Austrian National Regulations for EC5.
In this work, an experimental and numerical study on the bearing capacity and displacement behaviour of CLT subjected to non-uniformly distributed loading (NuDL) is conducted on eight different load configurations. A steel-CLT connection in which the CLT is partially loaded is used in this study. Finite element modelling, performed using the commercial software Abaqus CAE is used as the numerical simulation of the experimental study and is validated by experimental results. Load configuration factors (kc,90) from experimental results are compared with values from the Swedish CLT handbook (KL-Trähandbok). The outcome of the study shows that load configuration factor for NuDL cases is higher than for UDL cases. Hence, for same load configurations a lower CPG strength is required in NuDL than in UDL. Moreover, numerical results feature overall good congruence with the elastic phase of the experiments and have the potential to augment experiments in further understanding other complex steel-CLT connections
Cross-laminated timber (CLT) wall systems are composed of massive timber panels that are fastened together and to the horizontal elements (foundations or intermediate floors) with step joints and mechanical connections. Due to the high in-plane stiffness of CLT, the shear response of such systems depends strongly on the connections used...