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.

No description available.

No description available.

No description available.

No description available.

Over the years the Differential Quadrature (DQ) method has distinguished because of its high accuracy, straightforward implementation and general ap- plication to a variety of problems. There has been an increase in this topic by several researchers who experienced significant development in the last years. DQ is essentially a generalization of the popular Gaussian Quadrature (GQ) used for numerical integration functions. GQ approximates a finite in- tegral as a weighted sum of integrand values at selected points in a problem domain whereas DQ approximate the derivatives of a smooth function at a point as a weighted sum of function values at selected nodes. A direct appli- cation of this elegant methodology is to solve ordinary and partial differential equations. Furthermore in recent years the DQ formulation has been gener- alized in the weighting coefficients computations to let the approach to be more flexible and accurate. As a result it has been indicated as Generalized Differential Quadrature (GDQ) method. However the applicability of GDQ in its original form is still limited. It has been proven to fail for problems with strong material discontinuities as well as problems involving singularities and irregularities. On the other hand the very well-known Finite Element (FE) method could overcome these issues because it subdivides the computational domain into a certain number of elements in which the solution is calculated. Recently, some researchers have been studying a numerical technique which could use the advantages of the GDQ method and the advantages of FE method. This methodology has got different names among each research group, it will be indicated here as Generalized Differential Quadrature Finite Element Method (GDQFEM).

Fracture mechanics plays an important role in the material science, structure design and industrial production due to the failure of materials and structures are paid high attention in human activities. This dissertation, concentrates on some of the fractural aspects of shaft and composite which have being increasingly used in modern structures, consists four chapters within two parts. Chapters 1 to 4 are included in part 1. In the first chapter, the basic knowledge about the stress and displacement fields in the vicinity of a crack tip is introduced. A review involves the general methods of calculating stress intensity factors are presented. In Chapter 2, two simple engineering methods for a fast and close approximation of stress intensity factors of cracked or notched beams under tension, bending moment, shear force, as well as torque are presented. New formulae for calculating the stress intensity factors are proposed. One of the methods named Section Method is improved and applied to the three dimensional analysis of cracked circular section for calculating stress intensity factors. The comparisons between the present results and the solutions calculated by ABAQUS for single mode and mixed mode are studied. In chapter 3, fracture criteria for a crack subjected to mixed mode loading of two-dimension and three-dimension are reviewed. The crack extension angle for single mode and mixed mode, and the critical loading domain obtained by SEDF and MTS are compared. The effects of the crack depth and the applied force ratio on the crack propagation angle and the critical loading are investigated. Three different methods calculating the crack initiation angle for three-dimension analysis of various crack depth and crack position are compared. It should be noted that the stress intensity factors used in the criteria are calculated in section 2.1.

Il presente lavoro di tesi ha riguardato una riformulazione teorica, una modellazione numerica e una serie di applicazioni della Generalized Beam Theory per lo studio dei profili in parete sottile con particolare riguardo ai profili in acciaio formati a freddo. In particolare, in questo lavoro è proposta una riscrittura della cinematica GBT che introduce in una forma originale la deformabilità a taglio della sezione. Tale formulazione consente di conservare il formato della GBT classica e introducendo uno spostamento di warping variabile lungo lo spessore della generica parete della sezione trasversale, garantisce perfetta coerenza tra la componente flessionale e tagliante della trave. E' mostrato, come tale riscrittura consente in maniera agevole di ricondursi alle teorie classiche di trave, anche deformabili a taglio. Inoltre, in tale contesto, è stata messa a punto una procedura di ricostruzione dello sforzo tridimensionale in grado ricostruire la parte reattiva delle componenti di tensioni dovuta al vincolamento interno proprio di un modello a cinematica ridotta. Sulla base di tali strumenti, è stato quindi proposto un approccio progettuale dedicato ai profili in classe 4, definito ESA (Embedded Stability Analysis), in grado di svolgere le verifiche coerentemente con quanto prescritto dalle normative vigenti. Viene infine presentata una procedura numerica per la progettazione di sistemi di copertura formati a freddo. Tale procedura permette di effettuare in pochi semplici passi il progetto dell'arcareccio e dei dettagli costruttivi relativi alla copertura. / The present work has revolved around a theoretical formulation, a numerical model and a series of applications of the Generalized Beam Theory for the analysis of thin walled profiles with particular emphasis on cold-formed steel profiles. In particular, this work presents a revised set of GBT kinematics that introduces in an original form the shear deformability of the section. Such kinematics preserves the classic GBT format and introduces a variable warping displacement along the wall thickness, thus guaranteeing perfect coherence between bending and shear behavior. It is shown how such a formulation permits to easily recover classical beam theories, even those that are shear deformable. Additionally a stress recovery procedure has been presented which allows for tridimensional reconstruction of the reactive components of stress resulting from internal constraints in the kinematics. Based on these procedures, a design approach is proposed for class 4 profiles. This approach is called ESA (Embedded Stability Analysis) and takes into account all aspects of the current code. Finally, a numerical procedure for the design of cold formed profiles is presented. The procedure allows to calculate in few simple steps all structural aspects of a purlin interaction with a roof system.