How to evaluate the cost-effectiveness of repair/retrofit intervention vs. demolition/replacement and what level of shaking intensity can the chosen repairing/retrofit technique sustain are open questions affecting either the pre-earthquake prevention, the post-earthquake emergency and the reconstruction phases. The (mis)conception that the cost of retrofit interventions would increase linearly with the achieved seismic performance (%NBS) often discourages stakeholders to consider repair/retrofit options in a post-earthquake damage situation. Similarly, in a pre-earthquake phase, the minimum (by-law) level of %NBS might be targeted, leading in some cases to no-action. Furthermore, the performance measure enforcing owners to take action, the %NBS, is generally evaluated deterministically. Not directly reflecting epistemic and aleatory uncertainties, the assessment can result in misleading confidence on the expected performance. The present study aims at contributing to the delicate decision-making process of repair/retrofit vs. demolition/replacement, by developing a framework to assist stakeholders with the evaluation of the effects in terms of long-term losses and benefits of an increment in their initial investment (targeted retrofit level) and highlighting the uncertainties hidden behind a deterministic approach. For a pre-1970 case study building, different retrofit solutions are considered, targeting different levels of %NBS, and the actual probability of reaching Collapse when considering a suite of ground-motions is evaluated, providing a correlation between %NBS and Risk. Both a simplified and a probabilistic loss modelling are then undertaken to study the relationship between %NBS and expected direct and indirect losses.

This thesis focuses on minor-destructive testing (MDT) techniques for the mechanical characterisation of historical mortars, as it is a fundamental task for the assessment of existing masonries. In the first part, a novel in-situ MDT technique is investigated, based on the field vane shear test for soils. The instrumentation consists in a four-winged pin (X-Drill) and a torque wrench. This research presents the results of an experimental campaign based on the comparison between standard tests and X-Drill measurements on different types of mortars. The interpretation of the test provides a possible correlation between the measured torque and the compressive strength of the material. In the second part, the thesis focuses on the extraction of samples to be tested in the laboratory. Brazilian tests can be carried out on cores including a diametral mortar joint with a defined inclination with respect to its original horizontal position. A new integrated methodology is developed for the comprehensive mechanical characterization of historical mortar based on different types of experimental tests results. This task is carried out by means of a large set of experiments performed ex-novo on lime mortar masonry walls built in the laboratory. The processing of the results from Brazilian tests on cores with inclined diametral joint is complemented with the application of the double punch tests on mortar joints that may be also extracted through core drilling. The proposed experimental methodology is then compared with the results obtained from standard tests performed on the same materials, such as compression tests, flexural tests and shear tests on triplets. Finally, the parameters obtained are used as input parameters for 2D and 3D numerical analyses based on the Continuum Damage Mechanics constitutive model. The comparison between the experimental results and the numerical analyses confirms the good prediction capacity of the proposed techniques.

L’obiettivo della ricerca è stato quello di sviluppare un metodo di calcolo semplificato per l’analisi non lineare di strutture in muratura soggette ad azione sismica, attraverso l’implementazione di un codice caratterizzato da un’elevata versatilità e semplicità di utilizzo, in grado di conseguire un bilanciato compromesso tra validità teorico-sperimentale e praticità applicativa. Il codice, sviluppato in ambiente Microsoft Excel tramite il linguaggio di programmazione Microsoft Visual Basic 6.3, punta a guidare il progettista, attraverso un’interfaccia semplice ed intuitiva, nel delicato compito di svolgere un’analisi non lineare di pareti murarie caricate nel proprio piano, fornendo, in corrispondenza di ogni singolo step di carico, una rappresentazione puntuale e intuitiva degli elementi costituenti la parete, individuandone immediatamente le possibili criticità. Attraverso un’interfaccia user-friendly l’utente ha la possibilità di inserire le caratteristiche geometriche e meccaniche della parete, giungendo agevolmente alla definizione del modello a telaio equivalente e alla definizione della curva di capacità della struttura. Attraverso il calcolo della domanda sismica e la valutazione del punto di funzionamento, il codice indirizza l’utente all’individuazione mirata degli interventi di miglioramento necessari, a seconda che si voglia diminuire la domanda o aumentare la capacità di spostamento della parete. Essendo il sottoscritto un Ufficiale del Corpo degli Ingegneri dell’Esercito Italiano, un codice di questo tipo si presterebbe ad essere utilizzato dall’Amministrazione Difesa nell’ambito delle verifiche di vulnerabilità sismica degli edifici strategici: con tale applicativo, infatti, i Reparti del Genio Militare potrebbero effettuare una prima verifica (caratterizzata da un accettabile compromesso tra la speditezza e l’accuratezza dei risultati forniti) di tali strutture, individuando le maggiori criticità relative agli immobili del demanio militare e progettando, ove necessario, i conseguenti interventi di consolidamento, per poi programmare in modo maggiormente oculato l’affidamento delle verifiche di vulnerabilità previste dalla normativa attualmente in vigore. / The aim of this thesis work is to develop a simplified method for non linear analysis of masonry structures subjected to seismic action, throughout the implementation of an high versatility and simple-use code, in order to have a balanced compromise between theoretical and experimental efficiency and practical applicability. The code, written for Microsoft Excel using Microsoft Visual Basic 6.3 programming language, aims for guiding the structural designer, through a simple and intuitive interface, in the delicate task of a non linear analysis of masonry wall loaded in its own plane, giving, in correspondence of each load step, a punctual and intuitive representation of its elements, instantly defining the critical masonry panels and their failure mode. Thanks to a user-friendly interface, the user can insert geometrical and mechanical features of masonry wall, easily arriving to define the equivalent frame model and the capacity curve. Through the calculus of the seismic request and the evaluation of performance point, the code guides the user to the focused identification of proper improvement interventions, either decreasing seismic demand or increasing seismic capacity. Since I am an Officer of Italian Army Corps of Engineers, a code like the one developed could be efficiently used by military engineers for seismic vulnerability verifications of so called strategic buildings: with this application, each military unit could carry out a first approach (characterized by an acceptable compromise between rapidity and accuracy of the supplied results) for that kind of structures, identifying the main critical issues related to military buildings and designing, if necessary, the adequate improvement interventions, in order to carefully program the externalization of seismic vulnerability analysis services provided for by actual law.

The 2012 Emilia earthquakes caused significant damages to existing precast RC structures. These buildings were found being extremely vulnerable because, being designed for vertical loads only, they featured friction-based connections between structural elements, and in particular between beams and columns. Given the large diffusion of these structures as industrial buildings, and consequently the high social and economic impact of damages, their retrofit is critical. Various techniques have been proposed in the literature; in most of them friction-based connections are removed by inserting mechanical connectors that will make beam-column connections hinged. These approaches lead to a significant increase of the base shear and therefore often require strengthening of columns and foundations. The research presents dissipative devices based on carbon-wrapped steel tubes to be used as an alternative low-damage solution for the retrofit of beam-column friction connections able to minimize structural damages. Firstly, the study presents results of experimental tests on the devices and discusses their innovative energy absorption mechanism and dissipative behaviour. Then, numerical analyses carried on to investigate the effectiveness of the introduction of dissipative devices in beam-column connections of precast structures are presented. Incremental Dynamic Analyses have been performed in order to evaluate an equivalent behaviour factor for structures with dissipative devices, by comparing the seismic response of simple frame structures with dissipative connections with equivalent elastic systems. Findings of numerical investigation show how the introduction of the dissipative devices in friction-based joints provides an effective connection between structural elements and, in addition, the capability to reduce forces transmitted to the columns, improving the seismic behaviour of the entire structure. Finally, a simplified approach to evaluate an equivalent behaviour factor for a structure equipped with dissipative devices in friction-based beam-column joints is proposed.

Da oltre 20 anni vengono utilizzati i materiali compositi per il rinforzo e/o adeguamento strutturale di singoli elementi o interi fabbricati in c.a.. I materiali compositi maggiormente diffusi in edilizia sono a base di fibre di carbonio e/o fibre aramidiche e/o fibre di vetro e matrice epossidica. Come noto, la scarsa resistenza al fuoco delle resine epossidiche limita l’utilizzo dei materiali compositi. Infatti, per temperature superiori alla Tg della matrice si verifica un rapido calo del modulo elastico del composito. Solitamente per le resine epossidiche laminate in situ, il valore di Tg è inferiore a 100°C. Nel presente articolo vengono presentati i risultati di una sperimentazione condotta su travi in c.a. rinforzate con resine a base acqua del tipo IPN e nastri unidirezionali in carbonio. Queste resine IPN presentano una struttura microcristallina costituita da una fase polimerica ed una cristallina interpenetrata, tale da essere classificate come reazione al fuoco di classe 1 ai sensi dell’UNI 9177. In particolare, le travi sono state rafforzate con diverse configurazioni di rinforzo a taglio e flessione. Sono stati confrontati i risultati delle prove di carico dei rinforzi applicati con le resine IPN con quelli applicati con le resine epossidiche. Al vantaggio della resistenza al fuoco delle resine IPN, la sperimentazione condotta ha evidenziato l’eccellenti proprietà meccaniche dei rinforzi applicati con la matrice IPN con valori analoghi a quelli dei rinforzi applicati con l’epossidica / ABSTRACT For over 20 years composite materials have been used for the reinforcement and / or structural adjustment of individual elements or complete reinforced concrete buildings. The composite materials most widely used in construction are based on carbon fibers and / or aramid fibers and /or glass fibers and epoxy matrix. As known, the poor fire resistance of epoxy resins restricts the use of composite materials in building construction. Indeed, for temperatures above the Tg of the matrix occurs a rapid decrease of the composite elastic modulus. Usually for the epoxy resins laminated on site, the Tg value is less than 100 ° C. The article presents the results of an experiment conducted on RC beams reinforced with water-based IPN resins and unidirectional tapes carbon. As these IPN resins have a microcrystalline structure consisting of a polymer phase and a crystalline interpenetrated, they are material with class1 reaction to fire (according to UNI 9177). Particularly, the beams have been reinforced with different configurations of strengthening to shear stress and bending. By comparing the results of load tests applied on IPN resins and on epoxy resins, it has been proved that not only IPN resins have a better fire resistance, but also excellent mechanical properties of the reinforcements applied with the IPN matrix, showing similar values to the one obtainable with epoxy reinforcements.

Alla luce degli sviluppi normativi e della crescente attenzione alla sicurezza sismica delle strutture, soprattutto dopo gli ultimi terremoti italiani, l'analisi e la verifica del patrimonio edilizio esistente è diventato uno strumento fondamentale per valutare la vulnerabilità sismica, per salvaguardare le vite umane e pianificare interventi strutturali. Il patrimonio edilizio italiano è caratterizzato da elevata complessità ed eterogeneità, sia dal punto di vista architettonico che strutturale, e consiste in strutture costruite in epoche diverse, collocate sia nel centro della città che in periferia, realizzate con diverse tecniche costruttive e caratterizzate da diversi usi. Lo scopo di questa ricerca è quello di individuare una metodologia di verifica facilmente gestibile e adattabile a molti edifici diversi, ma allo stesso tempo in grado di determinare lo stato effettivo della struttura in termini di criticità e carenze strutturali. Per fare ciò si è preso come riferimento il patrimonio dell'Università di Bologna, in particolare 59 plessi universitari quantificabili in circa 470.000 m2 di superficie utile da analizzare. Nel capitolo 1 è presentato lo "stato dell'arte" dei metodi per la valutazione della vulnerabilità sismica degli edifici esistenti. Nel capitolo 2 viene descritto il patrimonio edilizio dell'Ateneo, si analizzano le condizioni ei vincoli operativi che hanno determinato l'individuazione della metodologia utilizzata. Nel capitolo 3 è illustrata nel dettaglio la metodologia e la campagna sperimentale effettuata sui materiali nel processo di acquisizione delle informazioni. Il capitolo 4 descrive un caso studio al fine di comprendere meglio la metodologia sviluppata e le sue potenzialità. Il capitolo 5 presenta i risultati ottenuti sul patrimonio attraverso diversi indicatori di vulnerabilità e, mediante analisi probabilistica e deterministica, definisce una valutazione della vulnerabilità affidabile delle strutture analizzate. / In the light of the recent code developments and of the growing attention given to the seismic safety of structures, especially after the last Italian earthquakes, the analysis and the verification of the existing building heritage has become a fundamental tool to assess the seismic vulnerability, to safeguard human lives and to plan structural interventions. The Italian building heritage is characterized by high complexity and heterogeneity, both from architectural and structural points of view, and consists in structures built in various ages, placed both in the city center and in the outskirt, realized with different structural techniques, characterized by several intended uses. The purpose of this research is to identify a methodology of verification easily manageable and adaptable to many different buildings, but at the same time able to determine the actual state of structure in terms of critical steps and structural deficiencies. In order to develop this methodology, the building heritage of the University of Bologna has taken as a reference. In particolar this building heritage has a overall floor area of approximately 470,000 m2 and consist in 59 buildings. Chapter 1 presents the "state of the art" of the methods for seismic vulnerability assessment of existing buildings. Chapter 2 describes the building heritage of the Athenaeum, analyzes its conditions and the operational constraints that determined the selection and identification of the methodology used. Chapter 3 illustrates in detail the methodology and the experimental campaign performed on the materials in the process of acquiring information on the constructions. Chapter 4 describes a case study in order to better under stand the methodology developed and its potentiality. Chapter 5 presents the results obtained from the overall building heritage through different indicators of vulnerability and, by means of probabilistic and deterministic analysis, defines a reliable vulnerability assessment of the structures analyzed.

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In Performance-Based Earthquake Engineering (PBEE), evaluating the seismic performance (or seismic risk) of a structure at a designed site has gained major attention, especially in the past decade. One of the objectives in PBEE is to quantify the seismic reliability of a structure (due to the future random earthquakes) at a site. For that purpose, Probabilistic Seismic Demand Analysis (PSDA) is utilized as a tool to estimate the Mean Annual Frequency (MAF) of exceeding a specified value of a structural Engineering Demand Parameter (EDP). This dissertation focuses mainly on applying an average of a certain number of spectral acceleration ordinates in a certain interval of periods, Sa,avg (T1,…,Tn), as scalar ground motion Intensity Measure (IM) when assessing the seismic performance of inelastic structures. Since the interval of periods where computing Sa,avg is related to the more or less influence of higher vibration modes on the inelastic response, it is appropriate to speak about improved IMs. The results using these improved IMs are compared with a conventional elastic-based scalar IMs (e.g., pseudo spectral acceleration, Sa ( T(¹)), or peak ground acceleration, PGA) and the advanced inelastic-based scalar IM (i.e., inelastic spectral displacement, Sdi). The advantages of applying improved IMs are: (i ) "computability" of the seismic hazard according to traditional Probabilistic Seismic Hazard Analysis (PSHA), because ground motion prediction models are already available for Sa (Ti), and hence it is possibile to employ existing models to assess hazard in terms of Sa,avg, and (ii ) "efficiency" or smaller variability of structural response, which was minimized to assess the optimal range to compute Sa,avg. More work is needed to assess also "sufficiency" and "scaling robustness" desirable properties, which are disregarded in this dissertation. However, for ordinary records (i.e., with no pulse like effects), using the improved IMs is found to be more accurate than using the elastic- and inelastic-based IMs. For structural demands that are dominated by the first mode of vibration, using Sa,avg can be negligible relative to the conventionally-used Sa (T(¹)) and the advanced Sdi. For structural demands with sign.cant higher-mode contribution, an improved scalar IM that incorporates higher modes needs to be utilized. In order to fully understand the influence of the IM on the seismis risk, a simplified closed-form expression for the probability of exceeding a limit state capacity was chosen as a reliability measure under seismic excitations and implemented for Reinforced Concrete (RC) frame structures. This closed-form expression is partuclarly useful for seismic assessment and design of structures, taking into account the uncertainty in the generic variables, structural "demand" and "capacity" as well as the uncertainty in seismic excitations. The assumed framework employs nonlinear Incremental Dynamic Analysis (IDA) procedures in order to estimate variability in the response of the structure (demand) to seismic excitations, conditioned to IM. The estimation of the seismic risk using the simplified closed-form expression is affected by IM, because the final seismic risk is not constant, but with the same order of magnitude. Possible reasons concern the non-linear model assumed, or the insufficiency of the selected IM. Since it is impossibile to state what is the "real" probability of exceeding a limit state looking the total risk, the only way is represented by the optimization of the desirable properties of an IM.

Deformability is often a crucial to the conception of many civil-engineering structural elements. Also, design is all the more burdensome if both long- and short-term deformability has to be considered. In this thesis, long- and short-term deformability has been studied from the material and the structural modelling point of view. Moreover, two materials have been handled: pultruded composites and concrete. A new finite element model for thin-walled beams has been introduced. As a main assumption, cross-sections rigid are considered rigid in their plane; this hypothesis replaces that of the classical beam theory of plane cross-sections in the deformed state. That also allows reducing the total number of degrees of freedom, and therefore making analysis faster compared with twodimensional finite elements. Longitudinal direction warping is left free, allowing describing phenomena such as the shear lag. The new finite-element model has been first applied to concrete thin-walled beams (such as roof high span girders or bridge girders) subject to instantaneous service loadings. Concrete in his cracked state has been considered through a smeared crack model for beams under bending. At a second stage, the FE-model has been extended to the viscoelastic field and applied to pultruded composite beams under sustained loadings. The generalized Maxwell model has been adopted. As far as materials are concerned, long-term creep tests have been carried out on pultruded specimens. Both tension and shear tests have been executed. Some specimen has been strengthened with carbon fibre plies to reduce short- and long- term deformability. Tests have been done in a climate room and specimens kept 2 years under constant load in time. As for concrete, a model for tertiary creep has been proposed. The basic idea is to couple the UMLV linear creep model with a damage model in order to describe nonlinearity. An effective strain tensor, weighting the total and the elasto-damaged strain tensors, controls damage evolution through the damage loading function. Creep strains are related to the effective stresses (defined by damage models) and so associated to the intact material.