Davide Trutalli

Summary: The current trend of increasing the height limits of timber buildings makes wind‐induced vibrations a non‐negligible issue. The dynamics of high‐rise timber structures are discussed, focusing on accelerations and comfort assessment of the currently tallest timber building in the world, namely, the 18‐storey timber building in Norway. Verifications according to available standards were firstly carried out. Then, computational fluid dynamic analyses with Kratos Multiphysics were performed to simulate the wind flow around a rigid body. Afterward, the wind loads were applied to a single‐degree of freedom model and to a reduced finite element model, performing a one‐way coupling between the wind flow and the structure. Wind‐induced vibrations resulted particularly strong in the across‐wind direction, which is the most sensitive to the wind flow and the shape of the building. Provisions in international standards resulted to be not always enough to avoid discomfort in the occupants. Therefore, fluid dynamic analyses are suggested to simulate the actual response and verify the comfort criteria of tall timber buildings susceptible to wind‐induced vibrations.

Timber platform-frame shear walls are characterized by high ductility and diffuse energy dissipation but limited in-plane shear resistance. A novel lightweight constructive system composed of steel columns braced with oriented strand board (OSB) panels was conceived and tested. Preliminary laboratory tests were performed to study the OSB-to-column connections with self-drilling screws. Then, the seismic response of a shear wall was determined performing a quasi-static cyclic-loading test of a full-scale specimen. Results presented in this work in terms of force-displacement capacity show that this system confers to shear walls high in-plane strength and stiffness with good ductility and dissipative capacity. Therefore, the incorporation of steel columns within OSB bracing panels results in a strong and stiff platform-frame system with high potential for low- and medium-rise buildings in seismic-prone areas.

This paper deals with the conception and characterization of an innovative connection for cross-laminated timber (CLT) panels. The connection is designed to provide an adequate level of dissipative capacity to CLT structures also when realized with large horizontal panels and therefore prone to fragile shear sliding failure. The connector, named X-bracket, has been theorized and designed by means of numerical parametric analyses. Furthermore, its cyclic behavior has been verified with experimental tests and compared to that of traditional connectors. Numerical simulations of cyclic tests of different CLT walls anchored to the foundation with X-brackets were also performed to assess their improved seismic performances. Finally, the analysis of the response of a 6 m × 3 m squat wall demonstrates that the developed connection provides good ductility and dissipation capacities also to shear walls realized with a single CLT panel.

The proposed light-frame structure comprises steel columns for vertical loads and an innovative bracing system to efficiently resist seismic actions. This seismic force resisting system consists of a light timber frame braced with an Oriented Strand Board (OSB) sheet and an external technoprene plaster-infilled slab. Steel brackets are used as foundation and floor connections. Experimental cyclic-loading tests were conduced to study the seismic response of two shear-wall specimens. A numerical model was calibrated on experimental results and the dynamic non-linear behavior of a case-study building was assessed. Numerical results were then used to estimate the proper behavior factor value, according to European seismic codes. Obtained results demonstrate that this innovative system is suitable for the use in seismic-prone areas thanks to the high ductility and dissipative capacity achieved by the bracing system. This favorable behavior is mainly due to the fasteners and materials used and to the correct application of the capacity design approach.

Three innovative massive wooden shear-wall systems (Cross-Laminated-Glued Wall, Cross-Laminated-Stapled Wall, Layered Wall with dovetail inserts) were tested and their structural behaviour under seismic action was assessed with numerical simulations. The wall specimens differ mainly in the method used to assemble the layers of timber boards composing them. Quasi-static cyclic loading tests were carried out and then reproduced with a non-linear numerical model calibrated on the test results to estimate the most appropriate behaviour factor for each system. Non-linear dynamic simulations of 15 artificially generated seismic shocks showed that these systems have good dissipative capacity when correctly designed and that they can be assigned to the medium ductility class of Eurocode 8. This work also shows the influence of deformations in wooden panels and base connectors on the behaviour factor and dissipative capacity of the system.