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.
A new numerical model able to account for the interaction between tension and shear forces on typical hold-down connections used in CLT structures is proposed and discussed, starting from results of an experimental campaign conducted at University of Bologna. A specifically developed method appropriate to evaluate the main strength and stiffness parameters from the experimental cyclic force-displacement curves is presented, and the corresponding trilinear backbone approximation is defined. Parameters obtained from tri-linear backbone curves were used to define the effect of the tension-shear interaction on the behaviour of hold-down connections, particularly as far as yielding and peak strength and stiffness parameters are concerned. In order to numerically reproduce the behaviour of connections, a coupled zero-length element is developed and presented. The model is implemented in OpenSees and adopted to model single connection element. The model is calibrated referring to experimental results of specimens loaded only in tension. Then the model is validated referring to tests with increasing level of tension-shear interaction. The proposed model is able to reproduce the actual behaviour of hold-down connection with coupled tension-shear forces under monotonic load conditions. Finally, a first proposal for accounting the hysteretic behaviour is presented, and some preliminary results are shown.
The construction of mid- and high-rise wooden buildings has attracted more attention in the last decade, particularly due to the utilization of engineered materials and related construction methods. The wood industry offers a wide range of engineered wood products, such as glue-laminated timber (GLT), cross-laminated timber (CLT) or timber concrete composites (TCC), which have improved mechanical qualities and the freedom to select shapes and sizes. As a consequence, attention has shifted to solve structural design issues to meet specific building requirements, such as their seismic, fire and serviceability performance. The objective of this work is to explore some of the technologies currently available for wooden mid-rise buildings using a 5-storeys case study building under gravity and earthquake loads. An innovative construction method, obtained by combining TCC floors, CLT shear-walls and GLT columns to ensure a fast erection on site is presented and the building response analyzed by means of static and dynamic seismic analyses. Specifically, the gravity load resisting system was designed to meet ultimate and serviceability limit state requirements according to Eurocode. Different seismic bracing technologies are compared: CLT cores (i) and hybridized cores with (ii) post-tensioned tendons and (iii) steel link-beams.
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.
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.
International Conference on Structures and Architecture
Structures and Architecture: Beyond their Limits
Proceedings of the Third International Conference on Structures and Architecture (ICSA2016), July 27-29, 2016, Guimaraes, Portugal
In the last twenty years CLT (cross-laminated timber) panels have become quite widely employed to build multi-storey buildings often characterized by the presence of many internal and perimeter shear walls. Building superstructures in which beam-and-column frameworks resits effects of gravity loads and core substructures and exterior CLT shear walls resist effects of lateral forces have been found structurally effective. Advantages of such structural arrangements can include creation of large interior spaces, high structural efficiency, and material economies. Here the behaviour of multi-storey buildings braced with CLT cores and additional CLT shear walls is examined based on numerical analyses. Two procedures for calibrating numerical analysis models are proposed and discussed here. The first approach is to use information from Eurocode 5, and the second approach is to use specifically applicable experimental data obrained through laboratory studies. Technically different ways of connecting CLT panels in order to obtain suitably stiff horizontal diaphragms are also presented.
A crucial issue in the design of a mid-rise Cross Laminated Timber (CLT) building under horizontal seismic action, is the definition of the principal elastic vibration period of an entire superstructure. Such vibration period depends on the mass distribution and on the global stiffness of the buildings. In a CLT structure the global stiffness of the buildings is highly sensitive to deformability of the connection elements. Consequently for a precise control of the vibration period of the building it is crucial to define the stiffness of each connections used to assemble a superstructure. A design procedure suitable for a reliable definition of the connection stiffness is proposed referring to code provisions and experimental tests. Discussion addresses primary issues associated with the usage of proposed procedure for numerical modeling of case study tall CLT buildings is reported.
The behaviour of multi-storey buildings braced with Cross-Laminated-Timber (CLT) cores and additional shear walls is examined based on numerical analyses of various 3-dimensional configurations. Two ways of calibrating numerical model are proposed according to codes and experimental test data respectively, including calibration of parameters that characterise connections between CLT panels in building cores and shear walls. Results of analyses of entire buildings are presented in terms of principal elastic periods, and base shear and up-lift forces. Discussion addresses primary issues associated with behaviour of such systems and modelling them.
This paper related to elimination of the deficiencies. The behaviour of multi-storey buildings braced with cores and CLT shear walls is examined based on numerical analyses. Two procedure for calibrating numerical analysis models are proposed using information from Eurocode 5  and specific experimental test data. This includes calibration of parameters that characterise connections between CLT panels and other CLT panels, building cores and shear walls. The aim is to make the characterizations of behaviours of connections that reflect how those connections perform within complete multi-storey superstructures, rather than in isolation or as parts of substructures. The earthquake action for cases studied was according to Eurocode 8  and using the appropriate behaviour factor (q factor). Results of analyses of entire buildings are presented in terms of principal elastic periods, base shear and up-lift forces. Discussion addresses key issues associated with behaviour of such systems and modelling them. Obtained results permit creation of appropriate guidelines and rules for design of the aforementioned types of hybrid buildings incorporating CLT wall panels.