Structural characterization of multi-storey CLT buildings braced with cores and additional shear walls

In last twenty years the CLT panels have become quite widely employed to build multi-storey residential and mercantile buildings. These buildings are often characterised by the presence of many internal and perimeter shear walls. Such structures have been widely studied through experimental tests and numerical simulations. One of the most comprehensive experimental research on seismic behaviour of CLT buildings was carried out by CNR–IVALSA, Italy, under the SOFIE Project [1-2]. Other important activities have been conducted at University of Trento, Italy [3]. European seismic performance related tests have been conducted at the University of Ljubljana, Slovenia where the behaviour of 2-D CLT shear walls having various load and boundary conditions was assessed [4]. FPInnovations in Canada has undertaken tests to determine the structural properties and seismic resistance of CLT shear walls and small-scale 3-D structures [5-6]. Recently innovative connection solutions have been studied in order to create panel to panel, or panel to other material joints [7]. The innovative jointing method results in point-to-point mechanical connections designed to only connect corners of individual CLT panels in ways that fulfil both hold-down and the lateral shear function; and is an alternative to traditional connections made using shear and hold-down anchors [8]. Different connectors have been tested in order to define the best way to joint CLT panels to steel structures [9]. Failure mechanism in large shear wall systems have been characterised in multiple studies [10]. For examples, multi-storey buildings having beam-and-column frameworks resisting effects of gravity loads, and cross-bracing or core substructures and exterior CLT shear walls to resist effects of lateral earthquake or wind loads have been studied [11]. Advantages of such systems can include creation of large open interior spaces, high structural efficiency, and material economies. From a structural design and analysis perspective point-to-point interconnection between CLT panels or point-to point connections at their boundaries leads to less ambiguity in load paths than exists for other approaches. It also lessens the chances that structural systems will not fail in unintended ways if overloaded by force flows thought superstructure elements of from superstructures to foundations. Although buildings of the new typology have already been built there has not been full study of the structural behaviour. The most crucial structural performance aspects that have not been fully studied are those related to construction of CLT building cores as replacements for one constructed from materials like reinforced concrete or masonry. Pertinent issues relate to vertical continuity between storeys, connections between building core elements and elevated floors, and core to foundation connections. The in-plane deformability of floor diaphragms is also a factor known to greatly influence global responses of completed building superstructures subjected to lateral loads and therefore requires close attention [12]. 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 [13] 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 [14] 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. In particular, it is to be noted that available seismic codes do not provide guidance on most crucial aspects of how to design such structural systems. The analyses mid-rise CLT buildings demonstrates importance of representing their seismic force resisting systems in proper ways, including paying close attention to the schematization of base and inter-storey connections. Obtained results permit creation of appropriate guidelines and rules for design of the aforementioned types of hybrid buildings incorporating CLT wall panels. This takes into considering the large variation that can exist in the elastic lateral vibration periods due to differences between code and experimentally calibrated estimates of connection stiffness.