After-earthquake assessment of buildings in terms of usability and safety is nowadays performed by in-charge technicians which are called to give their judgment basing mainly on in-field surveys and visual inspections. This necessarily implies additional inconvenience for residents and economic losses in the affected area, being often large the time required for conducting the surveys and being the judgment on the safe side in absence of objective data. A near real-time assessment based on objective data related to the seismic response of the structures is possible though the use of a monitoring systems capable of providing information on the state of the monitored structure inferring observations of its dynamic response. One of the most reliable parameter which can be correlated to the state of condition of a structure after an earthquake is the ductility demand expressed in terms of interstory drift. The use in monitoring systems of this indicator is examined in this thesis through case studies on reinforced concrete framed buildings and precast industrial buildings. In the design process of the systems I proposed a capacity-demand approach, through the prior formal definition of the requirements of accuracy and the calculation of the actual accuracy of the designed monitoring system. In particular I investigated in detail the uncertainties, both instrumental and related to model, to be combined in order to obtain the overall uncertainty of the information provided by the monitoring system, when using the method of double integration of the acceleration measurements. I have found that in general the instrumental uncertainties have less importance to the uncertainties of the model, in particular in presence of residual displacements at the end of the seismic motion. Aiming to reduce uncertainties in the presence of residual displacements and to cancel the need of high-pass filtering acceleration signals, I proposed a sensing bar prototype instrumented with accelerometers and inclinometers.

Hybrid Simulation with Dynamic Substructuring (HSDS) is a mixed numerical/- experimental simulation techniques. In detail, HSDS combines a Physical Substructure(PS) -the most critical subpart- with a Numerical Substructure (NS), and a compliant time integration process calculates the overall dynamic response of the emulated system. With the objective to circumvent three among major limitations of HSDS, the present thesis offers methodological procedures and algorithms aimed at: i) emulating a consistent degradation between PSs and NSs via model updating techniques; ii) handling PSs characterized by several internal DoFs with a reduced number of interface actuation points; iii) improving the computational efficiency in the case of complex NSs via partitioned time integrators. An old reinforced concrete bridge and a steel piping network for industrial plants are introduced as full-scale structural case studies. Part of significant results were published on referee journals and proceedings of international conferences. Part of developed tools was uploaded to the NEESHub web repository that is a United States web platform for research, collaboration and education powered by the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES).

An approach based on genetic algorithm and parallel computing has been presented and discussed for structural optimizations. Some details on its software implementation are given and explained. Numerical simulations demonstrate the applicability of the proposed approach for the optimization of large-scale real structures.

This thesis regards the study of the seismic behaviour of timber-frame buildings. Three are the main sections. Firstly, the study of the linear and non-linear behaviour of a timber-frame wall subjected to a horizontal force is presented, suggesting some analytical expression to correlate the mechanical behaviour of the entire wall to the mechanical properties of connection devices (i.e. fasteners, angle brackets and hold-down). Particular attention was paid to the ductility of each component. Secondly, a numerical modelling for the seismic linear analysis of multi-storey walls is proposed. In this section the horizontal force distribution between the walls is investigated too. Thirdly, a full-scale shake table test on a prefabricated 3-storey timber-frame building is described.

Although industrial piping systems and their components have been found highly vulnerable under earthquake events, there exists an inadequacy of proper seismic analysis and design rules for these structures. Current seismic design Standards and Codes are found to be over-conservative and some components, e.g., elbows, bolted flange joints and Tee joints, do not have detailed design guidelines that take into account earthquake loading. Thus, a clear need for the development of improved seismic design rules for such systems is evident. In this respect, numerical and experimental studies on piping systems and their components subjected to earthquake loading could be useful. As a result, valuable information, such as seismic capacities and demands under different limit states, could be utilized for the amendment of relevant design Codes and Standards. This thesis undertook a numerical and experimental investigation on a typical industrial piping system and some of its components in order to assess their seismic performance. In particular, the following issues have been pursued: (i) design of two non-standard Bolted Flange Joints (BFJs) suitable for seismic applications; (ii) experimental testing of the designed BFJs under monotonic and cyclic loading in order to check their leakage, bending and axial capacities; (iii) finite element analysis of a piping system containing several critical components under seismic loading; (iv) implementation of a pseudo-dynamic and real time testing schemes to test the piping system under seismic loading; and (v) pseudo-dynamic and real time tests on the piping system under several levels of earthquake loading corresponding to both serviceability and ultimate limit states. The above-mentioned activities were attained in this thesis. In particular, two different non-standard BFJs, comparatively thinner than the Standard ones, were designed, and their performance was examined through a number of monotonic and cyclic tests. Experimental results exhibited a favourable performance of the BFJs under bending and axial loading and moderate internal pressure; a good capacity in terms of strength, ductility, energy dissipation and leakage was observed. Performance of a typical full-scale industrial piping system containing several critical components, such as elbows, a bolted flange joint and a Tee joint, under realistic seismic loading was investigated through extensive numerical and experimental activities. The techniques of pseudo-dynamic and real time testing with dynamic substructuring –hybrid testing- were adopted to carry out experimental activities on the piping system under several limit state earthquake loading suggested by performance-based earthquake Standards. Implementations of hybrid tests were challenging mainly because the piping system was endowed with distributed masses and subjected to distributed earthquake forces, for which these experimental techniques have been considered inadequate so far. A number of mode synthesis techniques, namely the Craig-Bampton and SEREP methods, were discussed and their effectiveness was analysed for the realization of these tests. A characterization of the actuators to be used in the experimental tests was performed based on a transfer function. Relevant hybrid tests were successfully executed and they displayed a favourable performance of the piping system and its components; they remained below yield limits without any leakage even for the collapse limit state.

The developments in conceptual design, material technology and efficient construction techniques enabled the creation of longer, lighter, slender and stylish Cable-Stayed Foot Bridges (CSFB). Hence, modern CSFB can be characterized by interacting phenomena like cable nonlinearities, deck dynamic instability and deck lateral oscillations due to pedestrian walking. These phenomena, if intertwined, may bring these structures out of service or to failure. In view of a better performance, additional damping can be provided by passive dampers. However, amplitude dependent behaviour of dampers and slip in connections can make them effective only above a threshold amplitude. Hence, due to high uncertainties in the complex CSFB-damper system, usually, dynamic tests are performed to investigate the performance of the overall system. In this thesis, the effectiveness of the passive vibration reduction system in a complex cablestayed footbridge characterised by two curved decks was investigated. The amplitude dependent behaviour was found both with the output-only ambient vibration and free decay tests. In order to clarify these outcomes, modal quantities were calculated instantaneously,based on time-frequency identification techniques. A thorough analysis of dynamic response signals revealed that the structure with dampers actually behaved like a threshold system: i) for low vibration levels the dampers were still, so that they performed as constraints that stiffened the structure; ii) for high vibration levels, the dampers became fully working. Moreover, a deckcable interaction between one of the longest cables and the first global mode was detected. Initially, the modal properties estimated from the dynamic tests did not match those of the numerical model. In order to have a robust FE model capable to simulate the actual behaviour of the footbridge, model updating was performed. The sensitivity-based model updating techniques and Powell's Dog-Leg method of optimisation based on the Trust-Region approach were used. The final updated model showed a considerable reduction in the percentage error of frequencies. The updated model was able to reproduce the response of the footbridge under actual wind conditions. The revealed cable-deck interaction phenomenon was a motivation to investigate in depth the dynamics of long stay cables. Therefore, efforts were made towards the identification of the nonlinear behaviour of stay cables from measured response data. In view of the fact that actual measured data contained the response of a MDoF system, the first step in this direction was to investigate the feasibility of the nonlinear identification method, i.e. a nonparametric approach applied to a SDoF cable system. The results revealed a good fitting between identified and numerical data, where only a cubic type of nonlinearity was identified. Moreover, an increase of the parameter related to damping and a decrease of the parameter relevant to linear-frequency were observed versus the loading amplitude. However, the values of the parameters stabilised at higher load amplitudes and superharmonics were present in the response. The proposed non-parametric method exhibited a good capability in the nonlinear parameter identification of cables. Approaching towards a more complete understanding of the performance of cable-stayed footbridges, it was realized that the modern footbridges are more prone to pedestrian-induced vibrations that, eventually, degrades their serviceability performance. Moreover, several researchers tried to investigate the problem of synchronous lateral excitation of footbridges, but there is no general consensus on pedestrian models. Therefore, a model of pedestrian-footbridge interaction was proposed. In detail, pedestrian was represented by a modified hybrid Van der Pol/Rayleigh (MHVR) self-sustained oscillator. Amplitude, stability and phase of the MHVR oscillator solution under a harmonic external force associated with the floor motion were analytically evaluated by the harmonic balance method and was compared with numerical results. It was shown that the phase difference tended to become constant at high excitation amplitudes. Moreover, the stability domain was found useful in predicting the percentage of pedestrians synchronized to a given oscillating floor. The numerical results of MHVR oscillator was, then, compared with the experimental result of a shake table with harmonic floor motion. A good agreement in amplitude ratio was found, however, the phase difference resulted to be underestimated by the MHVR model.

The concept of "integral abutment bridge" has recently become a topic of remarka-ble interest among bridge engineers, not only for newly built bridges but also during refurbishment processes. The system constituted by the substructure and the superstructure can achieve a composite action responding as a single structural unit; the elimination of expansion joint and bearings on the abutments, greatly reduce the construction and maintenance costs. To maximize the benefits from integral abutment bridges, the direct way is to achieve the super-long integral abutment bridge. However, as the environment temperature changes, the lengths of superstructure increase and decrease, pushing the abutment against the approach fill and pulling it away. The responses of bridge superstructure, the abutment, the approach system, the foundation/piles and the foundation soil are all different. And it's important to understand their interactions effective design and satisfactory performance of integral abutment bridges. In order to build longer integral abutment bridges, therefore in this research, the lit-erature survey on the applications of integral abutment bridges in worldwide, espe-cially the current development of super-long integral abutment bridges was carried out firstly. Another literature review on soil-structure interaction was conducted to find out the most suitable methods in considering this kernel issue in design of integral abutment bridge. Through proposing finite element models for integral abutment bridges that could involve the soil-structure interaction, thermal actions, non-linearity in materials and so on, structural study was performed on an existing super-long integral abutment bridge, including parametric analysis, pushover analysis, and dynamic tests. Then, the performance of integral abutment bridge was better understood, and no critical structural problem was found for integral abutment bridge. Based on that, length limit for this kind of bridge was evaluated and investigated in an analytical way. Considering capacities of abutments and piers, and under the conditions of an existing integral abutment bridge, the length limit was found to be around 540m. With this super length, the piles need to be designed with capacity of large lateral displacement. Therefore, an effective optimization approach, associating the finite element method with global optimization algorithm was presented for pile shape design. At the end, considerations accounted in the design of super-long integral abutment bridges were discussed, making construction of super-long integral abutment bridge of great possibility.

This study concerns a new probabilistic framework to evaluate road/railway bridges after an earthquake by means of analytical fragility curves and inspections on the structure. In particular, the assessment is performed on existing reinforced concrete (RC) bridges with a common structural scheme in Italy (multi-span simply supported girder bridges). The framework is set up of 6 steps and each step is investigated. Steps 1 and 2 are a sort of preliminary work before the seismic event occurs: the creation of a database to collect all information about bridges in specific road/railway networks (step 1) and the generation of fragility curves for each bridge (step 2): fragility curves are instruments describing the probability of a structure being damaged beyond a specific damage state for various levels of ground shaking. Since step 2 is a crucial step for the outcomes of the framework, a wide investigation on the generation of fragility curves is presented, considering bridges located in strategic road network points in Veneto region (North-Eastern Italy) and different numerical modellings, in order to evaluate the best seismic vulnerability assessment. Moreover, particular attention is given to retrofit interventions by means of Fiber Reinforced Polymer (FRP) and their effect on bridge seismic vulnerability reduction. The other steps concern activities to carry out after a seismic event, useful for emergency and post-emergency phases. Step 3 regards a method to decide if inspections on bridge are needed in relation to the occurred earthquake seismic intensity; if the seismic intensity measure reaches a specific threshold, step 4 suggests how to perform visual inspections on bridges, under a probabilistic point of view, and to generate the damaged bridge fragility curves. After that, the last two steps try to give useful information to Institution and owners of bridges in order to reach an optimal road/railway network management in post-earthquake phases. Step 5 concerns a quick procedure to decide whether or not allowing traffic over damaged bridges, whereas step 6 gives information about economical benefits coming from a comparison between replace costs and retrofitting costs (considering FRP retrofitting interventions) of damaged bridges. In order to clarify the framework procedure, an example for each step is developed.

In the last decades the need for an effective seismic protection and vulnerability reduction of strategic structures and particularly the architectural heritage determined a growing interest in Structural Health Monitoring (SHM) as a measure of passive mitigation of earthquake effects. The object of monitoring is to identify, locate and classify type and severity of damages induced by external actions or degradation phenomena and to assess their effects on the structural performance. In this way it is possible to take appropriate measures to reduce the danger of collapse and, when necessary, perform strengthening interventions to improve the structural and seismic capacity. Motivated by the above reasons, this thesis aims at providing a contribution to the development of techniques and integrated methodologies, based on SHM, for the assessment and protection of Cultural Heritage (CH) buildings and monuments. Firstly, after a detailed state of the art review on specific topics related to SHM of civil engineering structures, a new methodology for the implementation of monitoring techniques on historic masonry structures is proposed. Selected case studies, equipped with distributed sensors and acquisition systems, allowed the definition and successive validation of SHM as a knowledge-based assessment tool, implemented to evaluate intervention needs, following an incremental approach during their execution, and to control the damage states of buildings in a post-seismic scenario. In order to maximize the benefits of SHM and optimize the entire process, dedicated software for static monitoring and automated algorithms for modal parameters identification have been developed, able to provide almost real time information on the health state of the monitored structure. Finally integrated procedures based on robust statistical and numerical models have been implemented to interpret and exploit SHM outputs to assess the structural conditions of the investigated CH buildings.

The research presented in this thesis was focused on timber floor diaphragms in unreinforced masonry (URM) buildings. The work was divided into two phases. The first phase was aimed at the investigation of the effects of the in-plane behavior of timber diaphragms on the global seismic response of URM buildings. The second phase was dedicated to the assessment and retrofit of timber floors, with particular attention to the out-of-plane behavior. A study on the equivalent frame method, which is a more and more appreciated masonry modeling technique, is presented. Both as-built and strengthened timber floors were addressed. In order to understand the influence of the masonry modeling method on the seismic response of URM structures when flexible diaphragms are concerned, a simplified elastic no tension method was proposed. Such method is able to describe the characteristic nonlinear behavior of masonry (due to extremely low tensile strength) by means of a series of linear analyses based on a Rankine failure criterion. An in-situ testing campaign on full-scale 100 year old timber diaphragms is presented. Both mechanical and dynamic in-plane properties of wood diaphragms were investigated. Cyclic and snap back tests were carried out thanks to an innovative ad hoc loading system, developed by means of wire ropes and steel pulleys. The loading system was designed to reproduce a realistic inertial load distribution and to be lightweight, versatile and easily relocatable from one diaphragm section to the next. The effect of different refurbishment techniques was also probed during the experimental campaign. The outcomes of a testing campaign regarding out-of-plane refurbishment techniques of existing timber floors by means of timber to timber composite structures are described. A numerical model based on the theory of composite beams with incomplete interaction, was calibrated to take into account the real load distribution and connector spacing. An original procedure to camber timber beams by employing the compression pressure generated by screw fasteners is presented. The camber deflection is attained by superposing a timber reinforcement element on top of a beam and then connecting the two elements by means of screws inserted at 45° to the beam axis. Such method which is currently patent pending, was validated using data obtained from experimental testing. A mathematical formulation was also developed to describe the cambering procedure. A specific experimental campaign was therefore performed to precisely evaluate the amount of pressure that each screw is capable of yielding. Many parameters supposed to affect the compression force, were explored through 170 tests.