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.

The thesis aims to investigate the dynamical criticality of a pedestrian footbridge and the use of a semi-active tuned mass damper. In this respect, the work appears threefold since the first and third part regard identification of a realistic model for the damping device and semi-active control of the magneto-rheological damper. In this respect, input identification techniques are a useful tool and an aid for the control law design. As a consequence, the second part involves both input identification strategies for a dynamic system and analysis of issues related to the inherent delay. In this respect, the so called “collocation” of measurement devices with respect to the application points of the input is critical, together with the concept of kernel.

Accidental events, such as impact loading and explosions, are rare events with a very low probability of occurrence, but their effects often lead to very high human losses and economical consequences. Vulnerability of structures to the effects of local damages and its mitigation are issues widely discussed inside the scientific community. The structural property associated with such a vulnerability is named robustness. Depending on the type of the structural system and on the importance of consequences, specific design strategies can be adopted in order to ensure a robust structural response. Among them, the system redundancy, the joints and members ductility and the alternate load paths are the ones commonly adopted in case of multi-storey framed buildings. The present work focuses on the study of the behaviour of steel-concrete composite structures subjected to a column loss, and proposes a global overview to quantify the robustness of such systems subjected to this hazard scenario. The description of validated finite element models and of a new analytical tool to predict the response of flat concrete slabs subjected to large displacement are reported in this dissertation. Furthermore, important design hints for composite buildings are proposed. The starting point of the research is an experimental campaign conducted at the University of Trento. Two tests on 3D full-scale one storey composite steel-concrete frames, extracted from five storeys frames designed in accordance to the Eurocodes, were performed simulating the central column removal. The role of the beam-to-column connections and of the concrete slab for the force redistribution was investigated. The experimental data have been then taken as reference for the calibration of finite element models that allowed to conduct further numerical analyses on different structural configurations and design scenarios. In particular, it was studied the influence of the location of the removed column on the structural behaviour. The collapse of central, lateral and corner columns were investigated in order to understand the load transfer mechanism, the requirement of joint ductility and the influence of the concrete slab on the development of alternate load paths. Both experimental and numerical results showed that the concrete slab plays a key role on the load transfer mechanism within the structure: it can hence contribute significantly to the robustness of the system preventing progressive collapse. The knowledge of the response of reinforced concrete slabs subjected to large displacements, as in the case of a column loss, allows quantifying the contribution to the resistance of the building to collapse associated with activation of membrane forces. Regarding this aspect, a new analytical simplified method, based on the principle of virtual works, was developed to predict the load-deflection response of simply supported reinforced concrete slabs with planar edge restraints subjected to large displacement. In conclusion, the present work provides a significant contribution to the knowledge of composite steel-concrete structures subjected to extreme loading conditions and open the way to extend results to different structural configurations and loading scenarious.

This doctoral thesis focuses on the seismic risk mitigation of â special riskâ industrial facilities, like chemical, petrochemical and process industries. It is known that the impact of natural hazards, such as earthquakes, on this type of structures may cause significant accidents leading to severe consequences to both the environment and human lives; see, among others, Lanzano et al., (2015) and Krausmann et. al (2010). In particular, the most critical components in a petrochemical plant are fluid-filled storage tanks; they can experience severe damages and trigger cascading effects in neighbouring tanks due to large vibrations induced by strong earthquakes, indeed. In order to reduce these tank vibrations, an innovative type of foundation based on metamaterial concepts is investigated. Metamaterials are generally regarded as manmade structures that exhibit unusual responses not readily observed in natural materials. Due to their exceptional properties and advancements in recent years, metamaterials have entered the field of seismic engineering, and therefore, offer a novel approach to design seismic shields. As a result, an encouraging and practicable strategy for the seismic protection of liquid storage tanks is presented and validated. On the other hand, the outcomes of this research study also aim to improve seismic risk assessment of â special riskâ facilities mainly through experimental dynamic analysis. In view of performing a dynamic analysis of these complex components, necessary for the global seismic risk assessment procedure, online hybrid (numerical/physical) dynamic substructuring simulations have shown their potential in enabling realistic dynamic analysis of almost any type of nonlinear structural system. At the same time, owing to faster and more accurate testing equipment, a number of different offline experimental substructuring methods, operating both in time and frequency domains, have been employed in mechanical engineering to examine dynamic substructure coupling. The scope of the study is the exploitation of different Experimental Dynamic Substructuring (EDS) methods in a complementary way to expedite a hybrid experiment/numerical simulation and, consequently, the comprehensive dynamic analysis. From this perspective, after a comparative uncertainty propagation analysis of three EDS algorithms, a new Composite-EDS (C-EDS) method is proposed and numerically validated. To the best of the authorâ s knowledge, this research study presents the first algorithm used to fuse both online and offline algorithms into a unique simulator with significant advantages in terms of dynamic analysis and seismic risk assessment of industrial plants. Finally, the research activity is supported by the results from different experimental testing campaigns with the main purpose to investigate the complex behaviour of critical industrial components, such as Tee joints and Bolted Flanged Joints (BFJs), with particular regard to the leakage phenomena resistance. In this respect, a reliable an innovative model capable of predicting the leakage force for a generic BFJ, including the interaction between axial and shear load, is proposed and validated.

The research is aimed at developing seismic methods for the design and evaluation of the seismic vulnerability of wooden structures, using a displacement-based approach. After a brief introduction on the seismic behaviour of timber structures, the general Direct Displacement-Based Design (Direct-DBD) procedure and the state-of-the-art are presented, with clear reference to the application of the Direct-DBD method to wooden buildings. The strength of the Direct-DBD method is its ability to design structures in a manner consistent with the level of damage expected, by directly relating the response and the expected performance of the structure. The research begins with a description of the procedural aspects of the Direct-DBD method and the parameters required for its application. The research presented focuses on the formulation of a displacement-based seismic design procedure, applicable to one-storey wooden structures made with a portal system. This typology is very common in Europe and particularly in Italy. A series of analytical expressions have been developed to calculate design parameters. The required analytical Direct-DBD parameters are implemented based on the mechanical behaviour of the connections, made with metal dowel-type fasteners. The calibration and subsequent validation of design parameters use a Monte Carlo numerical simulation and outcomes obtained by tests in full-scale. After the description of the Displacement-Based method for one-storey wooden structures, a series of guidelines to extend the Direct-DBD methodology to other types and categories of timber systems are proposed. The thesis presents the case of a multi-storey wood frame construction, which is a simple extension of the glulam portal frame system. Part of this work has been done within the RELUIS Project, (REte dei Laboratori Universitari di Ingegneria Sismica), Research Line IV, which in the years between 2005 and 2008 involved several Italian universities and Italian institutes of research in the development of new seismic design methods. The Project produced the first draft of model code for the seismic design of structures based on displacement (Direct-DBD). This thesis is the background to the section of the model code developed for timber structures.

Seismic testing methodologies play a significant role in earthquake engineering due to complexities of engineering materials and ground motion. Among available testing methods, hybrid simulation is more appealing for its merits, e.g., evaluating dynamic responses of large scale structures at lower cost. As a novel member of hybrid simulation, Real-time Hybrid Simulations (RHS), since its conception in 1992, has shown its unique properties and capacity for testing complex structural components, especially rate-dependent ones. RHS often partitions the emulated structure into portions, which are then either numerically or physically simulated in real-time according to our knowledge of them. In particular, the critical nonlinear and/or rate-dependent parts are often physically modelled within a realistic real-time test, while the remainder parts are simultaneously evaluated by solving differential equations. Evidently, the challenge of these methods is to enforce the coupling at the interface between portions via real-time loading and real-time computation. Heretofore great development of RHS has been attained. This dissertation is devoted to developing RHS in two aspects, namely transfer system control and time integration algorithms. In detail, research work and findings are summarized as follows: The dissertation initially focuses on the implementation of a model-based control strategy –internal model control (IMC) and its comparison with the classic PID/PI control on the lately conceived high performance test system - the TT1 test system. The control strategy of the electromagnetic actuators consists of three loops, namely one speed loop and two displacement loops. The outer displacement loop is regulated with IMC or PID/PI whilst the inner two loops with proportional control. In order to compare different control strategies, realistic tests with swept sinusoidal waves and numerical simulations concentrating on robustness were carried out. Analysis showed that IMC is preferable for its robustness and its ease of implementation and online tuning. Both IMC and PID work similarly and well on the actuator which can be simplified into a first-order system plus dead time. In addition, RHS was performed and showed the favorable state of the system. In order to accurately compensate for a time-varying delay in RHS, online delay estimation methods were proposed and discussed based on a simplified actuator model. The model, consisting of a static gain and dead time, results in nonlinear relationships among different displacements. The estimation based on the Taylor series expansion was further developed by introducing the recursive least square algorithm with a forgetting factor. Then this scheme was investigated and assessed in pure simulations and RHS via comparison with two other methods. Finally, the proposed scheme was identified to be satisfactory in terms of its convergence speed, accuracy and repeatability and to be superior to other methods. With the insight into the weakness of available compensation schemes in mind, two polynomial delay compensation formulae considering the latest displacement and velocity targets were proposed. Assessment and comparisons of the formulae by means of frequency response functions and stability analysis were carried out. In order to facilitate delay compensation, another novel compensation scheme characterized by overcompensation and optimal feedback was conceived. Numerical simulations and realistic RHS were performed to examine the proposed schemes. The analysis revealed that the proposed polynomial formulae exhibit smaller prediction errors and the second-order scheme with the LSRT2 algorithm is endowed with a somewhat larger stability range. Moreover, the overcompensation scheme was concluded to have the ability of time-varying delay accommodation, error reduction and sometimes stability improvement. With regard to time integration algorithms, this dissertation extends the equivalent force control (EFC) method which is a method of RHS with implicit integrators to RHS on split mass systems. The EFC method for this problem was spectrally analyzed and was found more satisfactory stability than some explicit integrator. Then larger control errors due to quadartically interpolated EF commands were recognized and treated with a proposed displacement correction. In view of the inherent feature of RHS –multiple quantities coupling at the interface, the correction was extended to simultaneously update displacement and acceleration. Spectral stability analysis and numerical simulations demonstrated that: (1) the correction can remove the constraint of zero-stability to the method and reduce algorithmic dissipation; (2) it also works well for MDOF systems. Finally, an inter-field parallel algorithm for RHS, namely IPLSRT2, was developed and analyzed. This method was based on the Rosenbrock (LSRT2) method and a prior inter-field parallel integrator–PLSRT2. The LSRT2 with different stage sizes, velocity projection and modified Jacobian evaluation were introduced to the algorithm in order to avoid and/or weaken the disadvantages of the PLSRT2 method, such as inefficient computation, displacement and velocity drifts, and complicated starting procedure. Accuracy analysis, spectral stability analysis, pure numerical simulations and realistic RHS were performed to investigate the properties of the IPLSRT2 method. Compared with the PLSRT2 method, this method exhibits pros and cons. In detail, the method loses the accuracy order due to the velocity projection applied at all time steps. However, it can provide more accurate displacement and velocity results in common applications where a little larger time step is required. In some cases, the proposed method exhibits smaller phase shifts and dissipation. Moreover, computation efficiency in Subdomain A is improved and its implementation in real-time applications is simplified.

Most of the significant changes on the environment have resulted from individually minor but collectively significant human actions and decisions. This kind of consequences has been defined Cumulative Effects (CE) and their systematic consideration can be attributed to the scientific basis and institutional context of Environmental Assessment (EA) theory and practice. However, although Strategic Environmental Assessment (SEA) has been largely recognised as one of the most appropriate procedure to support spatial and land use plans in managing CE; the advancement in integrating the assessment of CE into SEA practice has been often stated slow to evolve, suggesting a gap between SEA theory and practice in treating cumulative effects and confirming that further investigation on this subject is required. This research aimed to propose and apply a methodological approach to improve the consideration of CE in SEA of spatial plans, by focusing on the Italian spatial planning system and urban regions. It was developed according to the main findings and shortcomings emerging from the academic literature and the exploration of SEA practice through: an international expert survey; a systematic review of SEA documents; and a couple of real-life SEA case studies following during the research period. Among the most important were: the lack of scoping of relevant resources (or Valued Ecosystem Component); the scarce exploration of future decisions and consequences; and the requirement of a more evidence-based assessment of CE. The methodological approach was then developed for SEA of regional spatial plans, consisting of four main tasks: the selection of significant valued resources; the identification of other relevant decisions (projects, plans and policies) which together with the spatial plan could contribute to CE; the generation of land use scenarios; and the prediction of CE through indicators. Then, the methodological approach was tested in a case study selected within the peri-urban region of Milan, representing one of the most urbanised and industrialised part of Italy, with significant urban pressures on existing protected areas and remaining rural patches. Firstly, the regional green infrastructure was selected as the most important regional valued resource (or VEC); then, three important ‘future policies’ were identified (i.e. highway transportation corridor, protected areas conservation plans, and rural policies). Subsequently, a set of future land use scenarios were developed and made spatially explicit, starting from a couple of regional land use maps. Then, the regional cumulative effects on the selected valued resource (e.g. habitat fragmentation, surface runoff, etc.) were assessed against a range of future conditions through a core set of indicators, mainly quantitative and spatially explicit, simulating relevant environmental processes, such as hydrological cycle, local surface temperature, ecological connectivity. They were all selected and computed starting from land cover data, allowing the combined effects to be quantified and land use scenarios to be compared. The results mainly showed that the method provided an applicable means to, firstly, transfer policies and decisions into maps, and then, predict their combined effects on selected VEC. Moreover, it can be straightforwardly included in SEA of regional spatial plans in order to support a more evidence-based CE analysis, by adding spatial thinking to decision-makers and improving the understanding and the perception of the cumulative consequences of their “minor” decisions under uncertain future policy contexts.

Bridges in service in most Western Countries were built according to codes with design loads that are now inconsistent with today’s traffic demands. Currently, transportation agencies do not know how to respond to transit applications on their bridges. This thesis focuses on the legal issues entailed by overweight/oversize load permits issued by transportation agencies. Indeed, correct decision-making should consider the legal liabilities involved in possible catastrophic events. In this thesis I illustrate how this problem is guided by the Department of Transportation of the Italian Autonomous Province of Trento (APT’s DoT), a medium-sized agency managing approximately one thousand bridges across its territory. In the basic approach, it does not authorize movement of overweight loads unless it is demonstrated that their effect is less than that of the nominal design load. When this condition is not satisfied, a formal evaluation is carried out in an attempt to assess a higher load rating for the bridge. If, after the reassessment, the rating is still insufficient, the bridge is classified as sub-standard and a formal evaluation of the operational risk is performed to define a priority ranking for future reinforcement or replacement.

This study concerns seismic vulnerability assessment of masonry arch bridges with common typologies in Europe. Bridges are, in most cases, the most vulnerable elements in the transportation network during an earthquake; therefore, their seismic vulnerability assessment is necessary for a proper planning of the emergency phase and to define a priority for retrofit interventions. Masonry arch bridges were subdivided into homogeneous classes of single span and multi-span structures, according to the result of a statistical analysis made up of a large stock of 757 railway bridges located in high seismic areas. All the different collapse mechanisms for seismic action were studied for each class of masonry arch bridges with application of limit analysis and the calibration with FEM. In particular, limit analysis methods for the seismic assessment of single and multi spans bridges were developed. A innovative limit analysis approach was proposed for the assessment of the global transverse seismic capacity of multi-span masonry bridges with slender piers. Envelope curves representing the seismic capacity expressed in terms of limit horizontal acceleration were derived by parametrical analysis by means of simplified limit analysis. These curves can be used for a simplified vulnerability assessment of masonry arch bridges and for a simple calibration of the judgment obtained by BMS through inspection visits to bridges. In the second part of the study, a new simplified approach for the fast calculation of seismic fragility curves of numerous masonry arch bridge clusters is proposed. The aim of this thesis is to propose a quickly procedure to estimate the seismic vulnerability of extended roadway and railway bridge networks in emergency conditions and to optimize the retrofit interventions.