103 research outputs found
Mechanical characterization of connections in seismic resistant Cross-Laminated Timber structures
No full textCross-Laminated Timber (CLT) structures are assembled with massive timber panels that are fastened together and to the horizontal elements (the foundations and the intermediate floors) with step joints and mechanical connections. Due to the high in-plane stiffness of CLT, the seismic behaviour of those structures markedly depends upon the connections used.
The mechanical behaviour of lateral load-resisting systems made with CLT panels and typical connection systems was the focus of a large body of research, especially in Europe and North America. Furthermore, full-scale shaking table tests were carried out on several multi-storey buildings, demonstrating a significant ductility and energy dissipation under seismic loading.
In contrast with the significant findings associated to those research projects, specific calculation methods have not yet been included either in Eurocode 5 (static design) or in Eurocode 8 (seismic design). Nowadays, the design is done using simplified calculation methods that neglect the connections stiffness and introduce some simplifications on their mechanical behaviour.
The mechanical characterization of typical connection systems for CLT structures (e.g. with angle brackets and hold-downs, nailed and bolted to the wall and floor panels) is an expensive and time-consuming process, since requires the execution of a large number of tests. Therefore, to limit the need of experimental testing to a minimum, significant effort should be devoted to develop advanced numerical models capable to predict their load-displacement response and failure mechanisms.
In the scope of this thesis, an extensive experimental programme was carried out on nailed steel-to-timber joints in CLT. The experimental results were used as input to assess the reliability of currently available calculation methods and to develop capacity-based design principles for nailed steel-to-timber joints in CLT (i.e. the overstrength factor and the strength degradation factor). In addition, analytical methods and numerical models capable to predict the mechanical properties and energy dissipation at different building levels (single fastener joint, connection, and wall system) were developed. Experimental results obtained during previous research projects served also for calibration of non-linear analyses, which were used to extend the test results to different configurations of technical interest. Outcomes of the parametric studies provided better understanding of the seismic behaviour and energy dissipation of typical connection systems for CLT buildings.
It was concluded that the numerical models presented within this thesis are a sound basis to investigate the seismic behaviour of CLT buildings. However, future research is required to further verify and improve these predictive models
Un passo avanti. Scritti e studi per Giovanni Spagnoletti
No full text43 saggi di cinema in onore dello storico del cinema Giovanni Spagnoletti in occasione del suo settantesimo compleann
Berlino, città aperta: Berlin-Ecke Schönhauser (1957)
No full textSaggio su celebre film "neorealista" della DD
Investigating the hysteretic behavior of Cross-Laminated Timber wall systems due to connections
No full textCross-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 dissipatio
Modelling the mechanical behaviour of typical wall-to-floor connection systems for cross-laminated timber structures
No full textThis paper proposes a numerical model capable of predicting the mechanical behaviour and the failure me- chanism 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
Investigating the use of Targeted-Energy-Transfer devices for stay-cable vibration mitigation
No full textFree 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 ap- plied 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 applica- tion, 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 per- formed 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
Advanced modelling of CLT wall systems for earthquake resistant timber structures
No full textCross-Laminated Timber (CLT) is gaining a significant popularity among the structural products as a sustainable alternative to steel and concrete. In comparison with those traditional building materials, CLT has a low carbon footprint and provides comfortable living conditions; moreover, the high strength-to-weight ratio, the prefabrication process and the erection speed are additional key points of its broad diffusion. Determining the load-carrying capacity of lateral load-resisting systems made of CLT panels (such as CLT wall systems, i.e. CLT walls with mechanical connections) is crucial for both the static and seismic design of CLT structures. However, a calculation method has not yet been included in Eurocode 5 (EN 1995-1-1:2004/A2 2014). Nowadays, the load-carrying capacity of CLT wall systems is determined with forcebased design procedures. However, since the analysis neglects the connections stiffness, those methods do not ensure that the wall system behaves in accordance with the design assumptions. Furthermore, simplified methods neglect some contributions that might affect the response of a CLT wall system, like the friction between the wall and the element that is restrained to and the effect of the overlaying floor. Based on the above-mentioned issues, this paper proposes a new numerical model of a CLT wall system. The model schematizes the CLT panel as an elastic orthotropic element, while the connections (i.e. hold-downs, angle brackets, and screws) are simulated as non-linear hysteretic springs. The interaction between the CLT panel and the foundation, and between the wall element and the CLT floor restrained on top of it, were specifically addressed in the development of the model.
The study presented herein is carried out considering the experimental tests results obtained by Gavric et al. (2015a-2015b-2015c). At first, experimental and numerical results are compared. A parametric study is carried out afterwards, (a) by varying the vertical load applied on top of the CLT wall, (b) by modifying the aspect ratio of the timber panel, and (c) by simulating a CLT floor screwed on top of the wall. Results are collected in diagrams and compared with a simplified design procedure commonly adopted by practicing engineers and discussed by Pozza et al. (2016b), highlighting how those contributions influence the elastic stiffness and the load-carrying capacity of a CLT wall system
A Hysteresis model for timber joints with dowel-type fasteners
No full textPredicting the mechanical behaviour and the failure mechanism of timber joints with dowel-type fasteners requires consideration of several factors, including the geometrical and mechanical properties of the metal fastener, the physical properties of timber and the interaction between such elements. This paper proposes a numerical model where a joint is schematized as an elasto-plastic beam in a non-linear medium with a compression-only behaviour. Unlike the differential approach adopted by most of the hysteresis models published in literature, this model predicts the load-displacement response using simple mechanical relationships and basic input parameters. Furthermore, the model is capable of reproducing the effect of the cavity formed around the fastener by timber crushing, and simulates the hysteretic behaviour and the energy dissipation under cyclic conditions. Shear tests are reproduced on nailed steel-to-timber joints in Cross-Laminated Timber and results are compared to the experimental test data obtained on similar single fastener joints. Simulations lead to accurate predictions of both the mechanical behaviour (initial stiffness, maximum load-carrying capacity, global shape of the loading curve and of the hysteresis cycles) and the total energy dissipation observed in the tests
STAY-CABLE VIBRATION MITIGATION USING NONLINEAR TARGETED-ENERGY- TRANSFER DEVICES: A PARAMETRIC STUDY
No full textLarge-amplitude oscillation of inclined stays are often associated with rain-wind induced phenomena, vortex shedding and parametric excitation. To suppress the problematic vibrations and to minimize the potential high cost of maintenance or repair, passive damping system have been widely employed. In most investigations the damper was modelled as a pure linear viscous device or as a linear viscous damper with internal stiffness perfectly anchored to the deck. Other authors evaluated the effectiveness of the damping system introducing the effects of the flexibility in the damper support. The aim of this paper is to investigate the use of Targeted-Energy-Transfer (TET) devices for cable vibration suppression; a new family of devices is proposed in which a nonlinear elastic stiffness force mechanism and device, modelled as a power-law elastic spring element, is placed in parallel with a linear viscous damper. The imperfect anchorage to the deck is also taken into account by an elastic support. The free vibration of a taut-cable with an attached passive TET device is investigated using an analytical formulation of the complex generalized eigenvalue problem in the presence of two cable segments. The concept of “universal design curve” was examined. A parametric study was performed on a reference cable to verify the adequacy of the “universal design curve” and to evaluate the effectiveness of TET device; the study was subsequently extended to two real stays, taken from the Fred Hartman Bridge (Houston, Texas, USA) and from the Stonecutters Bridge (Hong Kong, China). In all the investigations, theoretical and numerical results were obtained and compared
Prototyping and Validation of MEMS Accelerometers for Structural Health Monitoring—The Case Study of the Pietratagliata Cable-Stayed Bridge
No full textIn 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
- …
