Structures built with cross laminated timber (CLT) are an attractive alternative to traditional construction materials in terms of environmental performance and habitability, but its structural behavior is not well understood for each timber specie. This work provides a comprehensive study of the structural behavior of radiata pine CLT shear walls, by means of laboratory testing and numerical analysis of hold down connections. The observed test response of connections is replicated by calibrating two hysteretic models on OpenSees, and its fidelity is revised through the analysis of a full scale wall test and simulation. Main outcomes suggest that advanced modelling tools can accurately reproduce the hysteretic behaviour of the connections of timber panels. In terms of connections behaviour, it is observed that hold downs on radiata pine CLT elements reach less load capacity than hold downs on other wood specie, and no significant difference with the parallel to grain capacity of angle brackets connections is noticed. Besides, it is found that radiata pine CLT walls can achieve suitable cyclic loading performance and reach high levels of displacement ductility. Furthermore, the importance of friction on the load capacity of the wall is showed.
This paper presents a numerical study of the influence of varying story strength on the seismic performance of multi-story wood-frame shear wall buildings. In the prior FEMA P695 studies of these buildings, the non-simulated collapse limit-state was exceeded primarily in the first story . This observation raised interest in quantifying the influence of varying strength from story to story on seismic response. In this study, four different distributions of strength are used as bounding cases. The Parabolic strength distribution (1) is based upon the ELF method in ASCE 7 and assigns lateral forces to each level based on weight and story height. The Triangular strength distribution (2) is based upon the simplified procedure in ASCE 7 and distributes lateral forces based on the seismic weight at each level. The Constant strength distribution (3) assumes the same shear wall design was used on all levels. The Baseline strength distribution (4) is from actual designs provided in the FEMA P695 wood-frame example and represents the practical implementation of the ELF method for designed shear walls. The FEMA P695 methodology, which quantifies seismic performance via adjusted collapse margin ratios, is employed in this study. The analytical models include P-Delta effects and utilize the 10-parameter CASHEW hysteresis model. Based on the analysis of a subset of index models from the FEMA P695 wood-frame example, it is observed that the Parabolic strength distribution, which facilitates dissipation of energy along the entire height of the building, has larger adjusted collapse margin ratios (lower collapse risk) than other strength distributions studied and reduces occurrence of concentrated inelastic deformations in a single story from the onset of an applied lateral force.
The mechanical behaviour of steel-to-timber joints with annular-ringed shank nails is investigated using numerical modelling and a component approach. These joints are used in Cross-Laminated Timber (CLT) buildings to anchor metal connectors such as hold-downs and angle brackets to the timber panels. At first, a general hysteresis model is introduced, where a single fastener joint is schematized as an elasto-plastic beam embedded in a non-linear medium with a compression-only behaviour. A second hysteresis model is then presented, where the mechanical behaviour of the joint is simulated by a non-linear spring with three degrees of freedom. Both models are calibrated on the design rules prescribed by the reference standards. Moreover, average strength capacities are determined from the corresponding characteristic values assuming a standard normal distribution and suitable coefficients of variation. As first applicative examples of the proposed models, shear tests are simulated on single steel-to-timber joints with annular-ringed shank nails and on a connection made of an angle bracket and sixty nails. The scatter of mechanical properties in steel-to-timber joints is also taken into account in the simulations and a stochastic approach is proposed, demonstrating acceptable accuracy.