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Self-tapping screws are largely used in both lightweight and massive timber constructions, being able to carry out simultaneously axial (withdrawal) and lateral (shear) loads. In Europe, the requirements of such fasteners are described in EN 14592; however, the standard used until today addresses only their applications under monotonic conditions and it lacks of prescriptions when the screws are used to withstand cyclic loads. Recently, the standard has undergone a significant revision and some specific rules for screws used in seismic areas have been introduced. Specifically, the revised version of EN 14592 defines three low cycle ductility classes, to which a fastener must be assigned based on the outcomes of monotonic and cyclic bending tests. Following the new seismic provisions included in EN 14592, this paper describes the results of an independent study aimed at assessing the low cycle ductile performance of self-tapping screws that are currently available on the market. Approximately 200 experiments are presented and critically analysed, demonstrating that screws with a diameter of 6 mm must be assigned to the lowest low cycle ductility class. Conversely, all screws with diameter greater than or equal to 8 mm have the potential to be assigned to the highest low cycle ductility class.

The seismic behaviour of multi-storey heavy-frame timber building superstructures braced by Cross-Laminated-Timber (CLT) shear-walls is investigated based on numerical linear dynamic simulations. All systems analysed have the same rectangular plan footprint dimensions, type of framework and shear-walls arrangement at each storey. For structural efficiency, the layout of lateral load-resisting systems combines a central building core with partial length perimeter shear-walls. What differs between cases is the number of storeys (3, 5, or 7), components specifications, and shear-walls anchoring methods. Special attention is paid to examining how the vertical joints between CLT shear-walls affect the seismic response. The properties of connections used in the analyses are obtained from testing of hold-down anchors and angle-bracket shear connectors. Results of the simulations demonstrate that mid-rise buildings are prone to effects of the lateral flexibility and transfer high uplift loads to the foundations during design level seismic events. By implication, special design measures may be necessary to limit the lateral drifts to the levels prescribed by the standards. Simplified representations of connection properties may yield to inappropriate predictions of lateral drifts of superstructures during seismic events, and to an improper design of connections. In future, the efficient realisation of multi-storey heavy-frame timber building superstructures braced by CLT shear-walls depends on the use of proper connection devices. Suitable devices may include metal tie-downs capable of reducing the inter-storey drift, while transferring forces to foundations in a manner that does not locally damage frameworks, shear-walls, or floor and roof diaphragms.

This paper proposes a numerical model capable of predicting the mechanical behaviour and the failure mechanism of typical wall-to-floor connections for Cross-Laminated Timber structures. Such systems are assembled with angle brackets and hold-downs, anchored to the wall and floor panels with profiled nails and bolts. The metal connector and the elements to which it is fastened are modelled using 3D solid bodies, while the steel-to-timber joints are simulated as non-linear hysteretic springs. Shear and tension tests are reproduced on two connection systems and results are compared to the test data obtained from similar configurations. Simulations lead to accurate predictions of the mechanical behaviour (i.e. elastic stiffness, maximum load-carrying capacity, and shape of the hysteresis cycles) and energy dissipation. Finally, the performance when lateral and axial loads are applied simultaneously is investigated. Analyses are carried out by varying the inclination of the load, with respect to the axis of the connector, between 0° and 90°. Results exhibit a quadratic interaction relationship between shear and tension loads, and prove that their coupled effect influences the stiffness and the maximum load-carrying capacity.

This paper presents an innovative lateral load-resisting wall system, which is an evolution of the light-timber frame (LTF) shear walls currently available on the market. In comparison to traditional LTF walls, the novelty aspect is the use of Cross-Laminated Timber (CLT) beams and studs instead of solid timber elements. Thanks to this ‘hybrid’ approach, this new system combines some peculiar aspects of LTF structures (such as the limited weight and the high dissipative behaviour) with the potentials of CLT. Moreover, the use of CLT elements limits the issues due to the compressive deformations on bottom beams and permits to employ some innovative connections with high mechanical properties. Cyclic shear tests are carried out on two configurations of interest, assembled by considering different layouts of the load-bearing elements. Test results are compared to the experimental data obtained on similar LTF systems and differences are critically discussed.

This paper presents an innovative and sustainable timber constructive system that could be used as an alternative to traditional emergency housing facilities. The system proposed in this study is composed of prefabricated modular elements that are characterized by limited weight and simple assembly procedures, which represent strategic advantages when it comes facing a strong environmental disaster (e.g. an earthquake). The complete dismantling of structural elements and foundations is granted thanks to specific details and an innovative connection system called X-Mini, capable of replacing traditional anchoring devices (i.e. hold downs and angle brackets) by resisting both shear and tension loads. This constructive system, denoted as Hybrid Timber Frame (HTF), takes advantage of the strong prefabrication, reduced weight of light-frame timber systems, and of the excellent strength properties of the Cross Laminated Timber (CLT) panels. Specifically, the solid-timber members typically used in the structural elements of light-frame systems are replaced by CLT linear elements. The results of experimental tests and numerical simulations are critically presented and discussed, giving a detailed insight into the performance of the HTF under seismic conditions.

Fire resistance of timber members can be evaluated by an analytical design model known as Effective Cross-Section Method (ECSM). In this method, the residual cross-section in fire conditions is evaluated by decreasing the original cross-section by a notional charring depth and a so-called zero-strength layer. The ECSM for timber frame assemblies (TFA) exposed to standard fire conditions has been already presented. This design model considers the fire protection provided by claddings and cavity insulations, for which design values for zero-strength layers are still missing. In this paper, zero-strength layer depths for different set-ups of TFA are determined by means of a series of thermo-mechanical simulations. Model-scale furnace experiments were performed in order to validate the simulations. The study presents an analysis of the parameters that influence zero-strength layer depths for load-bearing members of timber frame assemblies exposed to the standard time-temperature fire curve.

In recent years, thanks to the simple and yet efficient design, Micro Electro-Mechanical Systems (MEMS) accelerometers have proven to offer a suitable solution for Structural Health Monitoring (SHM) in civil engineering applications. Such devices are typically characterised by high portability and durability, as well as limited cost, hence resulting in ideal tools for applications in buildings and infrastructure. In this paper, original self-made MEMS sensor prototypes are presented and validated on the basis of preliminary laboratory tests (shaking table experiments and noise level measurements). Based on the well promising preliminary outcomes, their possible application for the dynamic identification of existing, full-scale structural assemblies is then discussed, giving evidence of their potential via comparative calculations towards past literature results, inclusive of both on-site, Experimental Modal Analysis (EMA) and Finite Element Analytical estimations (FEA). The full-scale experimental validation of MEMS accelerometers, in particular, is performed using, as a case study, the cable-stayed bridge in Pietratagliata (Italy). Dynamic results summarised in the paper demonstrate the high capability of MEMS accelerometers, with evidence of rather stable and reliable predictions, and suggest their feasibility and potential for SHM purposes.

Summary Free vibrations of a taut cable with an attached passive Targeted-Energy-Transfer (TET) device are investigated using an analytical formulation of the complex generalized eigenvalue problem. This problem is of considerable practical interest in the context of stay-cable vibration suppression in bridges, induced by wind, rain–wind and parametric excitation. The TET device is a nonlinear apparatus, which has been investigated and successfully applied to the vibration suppression in several structural or mechanical systems. This study proposes, for the first time, the use of the TET device as a simple passive apparatus for stay-cable vibration mitigation. In this application, the device was modelled as a dashpot with a viscous damper in parallel with a power-law nonlinear elastic spring element and a lumped mass restrained to one end. The ‘flexibility of the support’ (imperfect anchorage to the deck) was also simulated by placing an elastic support (linear elastic spring) in series between the dashpot and the deck. The study derives a new family of ‘universal design curves’ for the TET device, by accounting for the effects of nonlinear elastic stiffness, lumped mass and flexibility of the support. To verify the adequacy of the universal curves and to evaluate the effectiveness of the TET devices, parametric numerical simulations were performed on a reference stay cable. As an application example, analytical results were employed to design the dampers of one flexible stay, installed on an existing cable-stayed bridge. In all the investigations, theoretical and numerical results were obtained and compared. Copyright © 2015 John Wiley & Sons, Ltd.

Cross-laminated timber (CLT) wall systems are composed of massive timber panels that are fastened together and to the horizontal elements (foundations or intermediate floors) with step joints and mechanical connections. Due to the high in-plane stiffness of CLT, the shear response of such systems depends strongly on the connections used. This paper proposes a numerical model capable of predicting the mechanical behavior and failure mechanisms of CLT wall systems. The wall and the element to which it is anchored are simulated using three-dimensional (3D) solid bodies, while the connections are modeled as nonlinear hysteretic springs. Typical racking tests of wall systems are reproduced by varying the assumptions used to schematize the behavior of the connections. Results are compared with test data published in the literature, and the differences are discussed. The influence of the boundary conditions (vertical load applied on top of the wall and friction at its base) and aspect ratio of the panel are investigated via a parametric numerical study. Finally, the performance of a wall system assembled with two CLT panels is analyzed, highlighting how the properties of the anchoring connections and vertical step joints affect the load-displacement response and energy dissipation.

Cross-Laminated Timber (CLT) structures exhibit satisfactory performance under seismic conditions. This is possible because of the high strength-to-weight ratio and in-plane stiffness of the CLT panels, and the capacity of connections to resist the loads with ductile deformations and limited impairment of strength. This study summarises a part of the activities conducted by the Working Group 2 of COST Action FP1402, by presenting an in-depth review of the research works that have analysed the seismic behaviour of CLT structural systems. The first part of the paper discusses the outcomes of the testing programmes carried out in the last fifteen years and describes the modelling strategies recommended in the literature. The second part of the paper introduces the q-behaviour factor of CLT structures and provides capacity-based principles for their seismic design.

This paper investigates the mechanical and the hysteretic behaviour of steel-to-timber joints with annular-ringed shank nails in Cross-Laminated Timber (CLT). These fasteners are used to anchor typical metal connectors, such as hold-downs and angle brackets, to the CLT panels. The experimental programme presented in the paper was carried out at the Institute of Timber Engineering and Wood Technology, Graz University of Technology (Graz, Austria). Average and characteristic values of the experimental strength capacities are evaluated and compared to the analytical predictions determined according to current structural design codes and literature. Furthermore, to fulfil the requirements of the capacity-based design, the overstrength factor and the strength degradation factor are evaluated and conservative values are recommended.

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.

Blockhaus structural systems are obtained by assembling multiple timber logs able to interact with each other by means of simple mechanisms (e.g. contacts, tongues and grooves, and carpentry joints, also referred to as ‘corner’ joints). Although these systems have ancient origins, the structural behaviour of Blockhaus systems under well-defined loading and boundary conditions is still complex to predict. The paper focuses on the assessment of the typical buckling behaviour and resistance of in-plane compressed timber log-walls. The effects of various mechanical and geometrical aspects such as in-plane rigid inter-storey floors, load eccentricities, different types of lateral restraints, openings (e.g. doors or windows) or additional metal stiffeners, are investigated by means of full-scale buckling experiments. Results are then critically discussed and preliminarily assessed via analytical formulations taken from classical theory of plate buckling and column buckling. Although further advanced studies are required for the development of a generalized buckling design method, it is shown that several mechanical and geometrical aspects should be properly taken into account to correctly predict the structural capacity of Blockhaus systems under in-plane compression.