In this work, aspects concerning the behaviour of steel joints under combined actions are investigated. Adopting the philosophy of the component method the attention focused on the analysis of a basic component of the connection: the T-stub. Research works carried out in the recent past extensively investigated the T-stub response under tension, while no data are available for the T-stub's response under combined tension (N) and shear force (V). In the thesis experimental, numerical and theoretical studies on this topic are presented. The starting point is the experimental activity carried out at University of Trento on column T-stubs under different combinations of axial and shear force. The experimental outcomes strongly highlighted the influence of the loading conditions on the strength and deformation capacity of the T-stub. In a second phase 3D numerical models were developed and calibrated to reproduce the actual behaviour of the T-stubs. The numerical simulations were then extended to different specimen geometries to investigate the main geometrical parameters which could affect the T-stub response. On the basis of experimental and numerical data a theoretical model based on limit analysis was then developed. It allows predicting a simplified load-displacement curve of the T-stub under a generic combination of N and V. The results obtained from the analytical model seem to reproduce with sufficient accuracy the complex behaviour of the T-stub, allowing to appraise the elastic stiffness and the yield load.

The research activity is focused on the study of both the linear and nonlinear behaviour of light timber-frame shear-walls buildings (called Platform Frame); in the first part the analysis of the linear-elastic behaviour is presented, whereas in the second part the non-linear behaviour is considered. After a short introduction on the state of the art of timber buildings both from the constructive and from the legislative point of view, the linear-elastic behaviour of single timber shear-wall is presented. The analysis of a single timber shear-wall allows to develop an analytical equation and simplified numerical macro-model (called UniTn-Model) which are able to represent the behaviour of a wall both in terms of displacement capacity and, much more important, in terms of stiffness. In fact, the evaluation of the correct walls stiffness constitutes a fundamental step in the seismic analysis of the timber buildings. The later section is based on what stated about the single-wall and it deals firstly with the elastic behaviour of systems composed by single-storey coupled walls and then it analyses systems of multi-storey single-walls. Theses analyses highlighted the influence of the vertical loads on the external force distribution within the shear walls, as well as the changing of the system stiffness caused by the hold-downs state variation. Both these aspects allow to develop some analytical formulations through which the stiffness matrix of full-scale buildings can be determined. Three iterative methods for the application of the Modal Response Spectrum Analysis are also presented; the differences between the methods, from the computational point of view as well as from the analytical one, are emphasized by means of a case study. The second part illustrates the non-linear analysis of a single shear-wall in order to identify the influence of the base components features on the wall ductility, both from the qualitative and the quantitative point of view; the UniTn-Model is hence extended to the non-linear field. It is also determined that the contribution of the nail deformation is not dependent on the nails spacing but it is only dependent on the geometry ratio of the sheathing-panels themselves. This property, analytically determined, is demonstrated on the basis of numerical and experimental analyses, by means of some non-linear F.E.M. analysis and some ad-hoc laboratory tests respectively. In the following section, using what developed for the single shear-wall, the non-linear analysis of single and multi-storey full-scale buildings is performed. The analyses are performed in order to assess the ductility level achievable by the buildings varying the ductility of the base components as well as the failure mechanism. In order to get generalized results and provide reliable values of ductility for the constructive system analysed, a large set of non-linear analysis has been performed through the use of a Matlab code specifically developed. This allowed to determine the ductility level that light timber-frame buildings can reach and to propose a new set of values for the behaviour factor q to be used in the seismic design. In the last section the study of the applicability of the capacity design to the light timber-frame buildings is presented. This study assesses the conditions that make the capacity design physically feasible and economically viable in comparison to the elastic design. The analyses have been conducted by varying both the geometry of the buildings that the seismic force level.

Nowadays, infrastructures are of strategical importance for allowing communication between countries. Owing to its usefulness, the design and the maintenance of bridges, streets and tunnels, which represent the network, become a fundamental issue. In order to investigate the behaviour of infrastructures under different loads, such as gravity, seismic phenomena, thermal differences, and so on, appears essential a comprehensive experimental campaign on scaled and full-scale specimens. In particular, in order to guarantee the safety of citizens, the seismic response of infrastructures under an earthquake requires a careful evaluation of the level of damage of structural elements. In this thesis, typical case studies are considered, such as a concrete tunnel lining and a composite steel-concrete bridge. In the first part of the thesis, a typical concrete tunnel lining is analysed. In order to investigate the inelastic behaviour of a concrete circular tunnel, several tests were performed. In greater detail, the best Fiber Bragg Grating (FBG) package configuration was obtained by means of monotonic and cyclic tests on substructures. Based on these results, the resulting suitable configuration in a full-scale tunnel test was used to measure deformations with high accuracy. Cyclic test on the full-scale tunnel provided data on the damage of reinforcing concrete and the developing of plastic hinges. With the aim of providing information on the structural safety of a tunnel after an earthquake, a damage index was calculated. In this respect, a nonlinear fiber F.E. model in the OpenSEES environmental was developed. This model calculated the stress in terms of bending moment in concrete sections with the use of experimental curvatures measured by FBGs system. Finally, the damage evolution in the concrete tunnel was reported and commented. In the second part of this thesis, a composite steel-concrete short-medium span bridge is treated. The innovation was the application of the PEER Performance-Based Earthquake Engineering (PBEE) to this type of bridge. Moreover, the use of the Hot-rolled (HRS) steel to manufacture I-girder beams has become an innovation in civil infrastructures in Europe, as much as the use of transversal concrete cross-beams (CCBs) to connect spans. With reference to the hazard selected, a suitable case study was chosen. With the aim of understanding the most critical and stressed parts of the case study, preliminary elastic shell and stick models were developed. After the identification of interesting parts, half-scale subassembly specimens were designed and built. Several quasi-static tests, both monotonic and cyclic, were carried out with the objective of exploring global and local mechanisms in the section owing to low-cycle fatigue phenomena. To detect damage in the connection detail, a refined F.E. model in ABAQUS was developed. Fragility curve parameters of the damage's interest quantities were obtained by fitting experimental and numerical data by means of the Maximum Likelihood Estimation method. The results and the numerical model could be ready for the application of the Performance-Based Earthquake Engineering tool, in which decision variables, such as repair costs, downtime, human life loss and lane closures, were taken into consideration in order to increase the confidence in the design for both engineer and owner's viewpoint.

The Seismic Performance Analysis of Bridges (SPAB) constitutes one of the biggest challenges for structural and civil engineers. In fact, the handling of these design problems requires a deep knowledge of structural behavior and a huge expertise with numerical and analytical tools necessary to perform advanced Finite Element (FE) simulations including dynamic and probabilistic aspects. Within the scope of SPAB, this thesis proposes the analysis of complex bridges assisted by the profitable well-known method of Dynamic ubstructuring (DS), advanced model updating strategies, fully probabilistic approaches and innovative time integration algorithms. SPAB includes the evaluation of several nonlinear behaviors inside the structural components and the quantification of benefits generated by safety systems such as isolation devices. As a result, in order to highlight the main advantages of a well designed isolation system, most of the cases analyzed include the comparison between non isolated and isolated configurations. In greater detail, four different bridges have been analyzed and will be presented in this thesis. First, the Rio Torto highway viaduct, an existing Reinforced Concrete (RC) viaduct on the A1 Italian highway between Florence and Bologna. The structure has been investigated at the laboratory of the Joint Research Center in Ispra (VA) by means of Hybrid Simulations (HSs). The set of 1 : 2.5 scaled substructures included two RC frame piers and the isolation system. The critical issues of the structure due to the complexity of the geometry and the awfulness was the presence of poor seismic details characterized by plain steel rebars. Owing to lack in knowledge for this type of rebars, tests were needed to analyze the seismic response in the as built configuration and to evaluate the effectiveness of a seismic retrofitting designed with a traditional Concave Sliding Bearings (CSBs) system. Then, a typical RC bridge with an innovative prototype of Concave Sliding Bearing (CSB) has been tested at the EUCENTRE Tress Laboratory in Pavia (PV) through HSs. The set of Physical Substructures (PSs) included a 1 : 2 scaled RC box section pier and a full-scale CSB. The prototype was characterized by an asymptotic relation between friction coefficient and load rate. All the benefits of the DS were exhibited during the test; in fact, to exploit the actual potentiality of the isolation system, even with the low speed of the test, the restoring force coming from the CSB was numerically corrected at each time step. Furthermore, a short-medium span Steel Concrete Composite Bridge made with Hot rolled I-girders (SCCBH) has been investigated. The SCCBH is an example of structural optimization; in fact, it combines both economic and functional benefits deriving from the reduction of in site works, e.g. welding, and short construction time. In particular, The novelties were threefold: i) the testing of a novel connection between a steel I-girder and a Concrete Cross Beam (CCB); ii) the development of a novel mechanical model for this connections; iii) the application of the Performance Based Earthquake Engineering (PBEE) to SCCBH. The experimental campaign has been performed on six 1 : 2 scaled substructures, representing a deck subassembly, tested in both longitudinal and transverse loading directions. Finally, a simulation-based reliability assessment of a complex cable-stayed foot/cyclic bridge located close to the sea and equipped with dynamic viscous dampers was performed. The scope was to investigate the benefits of Circular Hollow Section (CHS) structural members for this type of structure when erected in an aggressive environment. A FE model of the structure has been validated, and then used to perform a probabilistic time dependent analysis. Therefore, two corrosion models, i.e. general and localized, capable of evaluating the reduced load bearing section were implemented; and appropriate probability distribution functions were assigned to input model parameters to evaluate the response of the facility during its service life. As a result, the time dependent probabilities of failure have been evaluated and compared with the codes prescriptions.

The main aim of this research work was to deepen the understanding of the mechanical behaviour of timber-to-timber composite (TTC) floors with incomplete interaction in order to develop, design and test high performance solutions. Several types and arrangements of connections and different timber products, made from both softwood and hardwood species, were considered for the realisation of diaphragms suitable for a wide range of structural applications. An original assembly procedure, developed at the University of Trento, was adopted in the optimization process of these technical solutions. Such innovative procedure allows the designers to pre-stress and camber composite timber elements by simply relying on screw type connectors. The experimental tests presented in this thesis positively contributed to the calibration and validation of this assembly technique, confirming the method applicability. The test results were consistent with the numerical and analytical models, in terms of uplifts, stress levels and overall mechanical performance. The benefits from adopting the above-mentioned procedure appeared to be persistent over time, as the result of an experimental test where four composite specimens, 5.4 m long, were loaded out-of-plane and subjected to continuous monitoring under controlled environmental conditions for a period of two years. The research program was organized into two phases. The first phase was dedicated to the study of alternative strategies for retrofit interventions on timber diaphragms in historical heritage buildings. An extensive experimental campaign on the out-of-plane behaviour of the retrofitted diaphragms was performed in order to evaluate the effectiveness of the different techniques analysed. Specifically, hybrid solutions that coupled the reduced weight of softwood elements with the strength of hardwood components by means of different types of fasteners, were compared with “more common†timber-to-timber strengthening techniques. A large number of tests, covering fourteen configurations obtained by changing fasteners type, fastener arrangement and timber products, were performed to maximize the performance (cost/effectiveness) of the retrofit techniques. Test outcomes included characterization of stiffness, strength, static ductility and residual strength of the connection systems as well. The second phase of the program was devoted to the development of solutions for newly constructed diaphragms, either for new building applications or replacement of damaged/inadequate existing floors. The second phase research work included the design and testing of prefabricated timber-to-timber composite floor modules to be assembled by using laminated veneer lumber (LVL) made of beech wood. Full scale tests were performed on 6 m long and 10 m long modules, respectively designed for residential areas and offices. In addition to the full-scale testing of the modules, the connection system optimization was performed by referring to different types of test protocols, including both push-out and pull-out testing.

The thesis investigates the seismic behaviour of moment resisting joint in timber structures. The problem is analyzed starting from the single connector to get the understanding of seismic response of a complete frame structure. The design of earthquake resistant timber structures requires a deep knowledge of the mechanical behaviour of the structure as a whole and of its single component elements, especially for what concerns ductility and energy dissipation capability. In many timber structures, the ability to absorb kinetic energy and to attenuate effects of large amplitude ground motions is strongly dependent on energy dissipation associated with plastic deformation of metal parts in mechanical connections. The first part of the thesis illustrates some recent researches on timber joints assembled with traditional and innovative dowel type connectors. Experimental results are presented in terms of force-displacement relationship for specimens tested under monotonic procedure, or in terms of hysteretic diagrams for specimens tested under cyclic procedure. The goal is to find out some quantitative values from the experimental data, in order to characterize the ductility and dissipation capability of timber joints, taking into account the definition proposed by Standards for the design of earthquake resistant structures. The last chapters of the thesis present an analytical - numerical - experimental study aimed at the characterization of beam – to – column moment resisting joint behaviour. Through theoretical analysis it is possible to define a model able to describe the mechanical behaviour of tested moment resisting joint in terms of moment – rotation curve. The primary experiments are static and cyclic deformation tests on large timber moment connections. According to the standards, and applying the analytical model it is possible to obtain a reliable prediction of the resistance mechanism of each tested joint, but also to correct values of initial stiffness, maximum slip capability, reduction of resistance under fully reversed loading cycles and energy dissipation capacity. The mechanical characterization of the joint enables the implementation of a finite element model, aimed at predicting the seismical behaviour of wood multi-storey frames. The pushover analysis, performed through the FEM model, enables to assess the behaviour factors for frames built using the different typology of joint studied within the thesis.

This doctoral thesis deals with evaluation of the mechanical performance of brick-mortar masonry after high temperature exposition, by means of a theoretical and experimental research as well as finite elements analyses. The general aims are to assess the residual mechanical properties of masonry and its components and to define a constitutive law accounting for high temperature damage. To these purposes, high temperature exposition was reproduced by means of a brick furnace; then, mechanical testing was performed on the damaged and undamaged material samples; finally, the experimental results were employed to define theoretical-experimental constitutive laws as well as to set up finite elements analyses. The reliability and applicability of the proposed model is finally discussed, with reference both to the state-of-the-art and to possible further research. / La presente tesi affronta il problema della valutazione delle prestazioni meccaniche della muratura di malta e mattoni successivamente all’esposizione ad alte temperature, attraverso uno studio sperimentale e teorico ed analisi meccaniche agli elementi finiti. Gli obiettivi posti si sostanziano nella valutazione delle proprietà meccaniche residue del materiale muratura e dei suoi componenti e nella definizione di una legge di deterioramento meccanico per la muratura danneggiata dall’esposizione alle alte temperature. Al fine di tali obiettivi, per mezzo di un forno di cottura per laterizi è stata prodotta la simulazione fisica dell’esposizione ad alte temperature; quindi, prove di caratterizzazione meccanica sono state compiute sui materiali esposti e non esposti, ed infine i dati sperimentali sono stati utilizzati sia per la costruzione di modelli teorico-sperimentali di comportamento dei materiali sia per il confronto dei modelli stessi con le risultanze di analisi agli elementi finiti che rappresentano le condizioni della muratura integra e danneggiata. Infine, è discussa la validità ed applicabilità del modello proposto in relazione sia allo stato dell’arte sia ad eventuali sviluppi futuri.

This work analyses the behaviour of in-plane timber floors which are differently refurbished. The task is to ascertain the stiffness of the different solutions and to study the influence on the global behaviour of the building. The first type analysed is a floor with simple boards to which different reinforcing techniques have been applied. These are double boards, steel plates, diagonally set FRP strips, glued plywood panels and concrete slabs. For each of these types of reinforcement experimental displacement control tests were carried out. They were monotonic and cyclic tests of specimens with dimensions 2x1 m and 5x4 m, with and without perimeter tie-beams. The same tests were numerically reproduced and a numeric model of simple implementation was created able to simulate non-linear behaviour of floor and tie-beam. On the end, the floor model was used in order to analyse a traditional building. Experimental analysis and numeric modelling confirmed the need to guarantee efficient floor-masonry connections and showed the notable contribution offered by perimeter tie-beam in terms of in-plane floor stiffness. The comparison between different techniques of reinforcement showed the inadequacy of simple boards to stand up to seismic action.

This thesis focuses on fatigue problem on riveted structures and the correlated experimental tests. The term “fatigue” denotes the cracking of metals under repeated loading. The technique of riveting structures is obsolete due to the low level of standardization in the construction process. Knowledge concerning riveted structure’s ability to withstand fatigue has not been investigated to the same extent as for modern structures assembled by welding. Nevertheless, many riveted structures are still in service after over 100 years. Clamping force originates when the hot rivet is placed into the hole of the plates and the rivet shorten in length due to cooling. In Europe, a large number of railway bridges are riveted. Moreover, all over the world, the rivet assembly technique has been largely used for different types of buildings. The riveted structures are subjected, evidently, to fatigue degradation as all the other steel structures. The riveted joint complexity and the non-uniform realization lead to a structure-specific consideration. In Europe, current regulations recognise only one fatigue class for riveted structures neglecting the clamping force effect. This approach is characterized by an elevated standard deviation for the assessed results. This research aims to improve the riveted structures fatigue comprehension and to propose appropriate tests. Some elements have been extracted from a dismantled railway bridge located near San Stino di Livenza (Venice). An innovative clamping test (TCT) has been conceived: applying a torsional moment to the rivets and evaluating the sliding friction, the clamping force has been estimated. Contrary to traditional clamping tests, this setup, at an affordable price, provides good precision. Moreover, the test is in-site and does not provoke damages to the examined structure. Fem models of rail bearer have been realized taking into account rivets, holes and multilayer plates section inertia. A specific laboratory set up has been designed with the intention to calibrate the fem models. Frictions and clamping force have been taken into account in the rail bearer models. There is a close correspondence between the non-linear models and the experimental tests. The clamping assumptions, derived from the TCT, have been verified. A full scale fatigue test has been prepared and the first cycles have been monitored. Full scale fatigue tests are sophisticated and involve many parameters. For this test, a specific metallic frame has been designed and realized using advanced fatigue models. An advanced analysis (hot spot method) has been carried out, for the frame, in order to evaluate the stress into the welds. This frame will be used by the DICEA laboratory to test, principally, specimens extracted from bridges.

The interaction between frames and infills in case of earthquake is a topic of great significance in structural engineering. Infills, often considered non-structural elements, in fact behave as they were. Sometimes they make low engineering buildings behave better than one would expect, other times they are responsible of rather bad seismic performances even in recently built constructions. Infills, often stiff and brittle if constructed with common fired bricks and strong mortar, are able to change to a great extent the seismic structural response, invalidating many of the basic design assumptions. Nevertheless, it is not possible to think of buildings without infills, due to the requirement of controlling energy consumption for residential climate control. To overcome this problem, the possibility of assembly ductile infills was investigated in the current thesis. The basic idea was to use weakness as the main tool, pursued both through the choice of materials and the proposal of a new, simple though effective building technique. Particular attention was devoted to adobe (earthen bricks) infills, specifically chosen in a structural perspective to take advantage of the intrinsic weakness, often unacceptable for other applications. Sustainability and thermo-hygrometric performances are considered important characteristics, even though background themes in comparison with weakness, according to the main perspective of this research work. The aim of the research was to evaluate the possibility of forcing a predefined damage pattern, consistent with reuse requirements, by means of ductile mechanisms. The modus operandi was to lay weak (horizontal) surfaces in the panels, breaking their continuity to allow a frictional, stable and ductile sliding to take place. The idea was investigated both numerically and experimentally. During a first phase, shear behavior of mud mortar joints was tested. Then, four full scale panels, confined by a steel frame, were subjected to lateral cyclic load. The four tests differed both in building technique, traditional or with internal partitions, and in material, hollow clay bricks or adobes. The experimental work was then extended numerically by means of FE analysis (through two modeling techniques) to different geometrical and mechanical situations. Attention was focused on the role of partitions in the structural response and on the possibility of capturing global behavior through a local calibration (on small assemblies) of model parameters. As a conclusion, the use of partitioned adobe infills was proposed in association with ductile timber frames because of the compatibility of materials. The solution may provide adequate stiffness and energy dissipation in case of earthquake. Moreover, this kind of buildings usually suffer for a lack of summer thermal insulation: the addition of mud infilling would improve such a performance.