In this work the behaviour of hybrid multi-storey buildings braced with Cross-Laminated-Timber (CLT) cores and shear-walls is studied based on numerical analyses. Two procedures for calibrating numerical models are adopted and compared to test data and application of provisions in current design codes. The paper presents calibration of parameters characterising connections used to interconnect adjacent CLT panels and building cores, and attach shear-walls to foundations or floors that act as eleveted diaphragms. Different case studies are analysed comparing the structural responses of buildings assembled with „standard" fastening systems (e.g. hold-downs and angle-brackets), or using a special X-RAD connection system. The aim is to characterize behaviours of connections in ways that reflect how they perform as parts of completed multi-storey superstructure systems, rather than when isolated from such systems or their substructures. Results from various analyses are presented in terms of principal elastic periods, base shear forces, and uplift forces in buildings. Discussion addresses key issues associated with engineering analysis and design of buildings having around five or more storeys.
Timber has been used for building construction for centuries, until the industrial revolution, when it was often replaced by steel and concrete or confined to low-rise housings. In the last thirty years however, thanks to the development of mass timber products and new global interest in sustainability, timber has begun to make a resurgence in the building industry. As building codes and public perception continues to change, the demand for taller and higher-performance timber buildings will only grow. Thus, a need exists for new construction technology appropriate for taller mass timber construction, as well as for fabrication and deconstruction practices that respect wood’s inherent sustainable nature. With this in mind, this research program aims to develop a new hybrid shear connection for mass timber buildings that allows for easy construction, deconstruction, and reuse of the structural elements.
This report includes results of Phase 1, which focused on connections consisting of partially threaded 20M and 24M steel rods bonded into pockets formed in CLT and surrounded by thick crowns of high-strength three-component epoxy-based grout. A total of 168 specimens were designed and fabricated, and push-out shear tests carried out with a displacement-controlled monotonic loading protocol. Strength and stiffness values were assessed and effective failure modes in specimens identified. These latter, along with the recorded load-deformation curves, indicate that it is possible to develop mechanics-based design models and design formulas akin to those already used for typical dowel-type fastener timber connections. Additionally, the specimens were easily fabricated in the lab and quickly fastened to the test jig by means of nuts and washers, suggested such connections have a strong potential for prefabrication, disassembly, and reuse.
The seismic behaviour of timber buildings is strongly related to the energy dissipation capacity of connections. According to Standard, since timber is characterized by a brittle failure when subjected to tensile or bending actions, the dissipative zones shall be located in joints and connections, whereas timber members themselves shall be regarded as behaving elastically. In order to ensure the global structural ductility, connections and joints shall be able to deform plastically at the associated ductility level without a significant reduction of their resistance under cyclic loads. The paper deals with an experimental campaign for the mechanical characterization of timber connection systems, commonly adopted in Europe, in the seismic design of timber buildings. The main objective was to find out the capacity, the stiffness and the ductility of the tested connections and to investigate their loss of capacity under cyclic loads. The obtained results were analysed in order to understand if the current provisions, reported in Standard for the different typology of traditional connectors, can be adopted in case of connection systems used for seismic purposes, such as hold-down or angle brackets. Their interaction with other structural parts was then investigated testing six fullscale timber walls, subjected to monotonic and cyclic loads. The tests were carried out at the Laboratory of Materials and Structural Testing of the Trento University (Italy).
Hybrid structural systems assembled connecting steel elements and cross-laminated timber panels (CLT) can be a valid alternative to traditional systems in the construction of residential buildings. Such systems can combine the industrialized construction technology typical of steel systems with the advantages offered by CLT panels, namely lightness and geometric stability. Moreover, CLT panels are timber-based products, and wood is recognized as an eco-friendly and eco-compatible material. In hybrid structural systems, the seismic-resistant capacity of the structure can be achieved by ensuring an adequate transmission of actions among the resistant elements, namely plain timber panels (floor and wall) and steel frame elements (beams and columns). Specifically, the interaction between the steel frame and the wood panels shall ensure both horizontal and vertical bracing to floors and walls, respectively. The work presented hereafter concerns the study of the connections to be used among the individual building components of the horizontal elements, with the aim of developing an effective collaboration among the materials, maximizing the level of prefabrication and industrialization of the final components. In particular, the preliminary results of the experimental tests carried out on full-scale steel-to-timber floor specimens, loaded by in-plane actions, will be presented.
