This document presents a part of the wide research carried out on modern timber buildings by the timber research group of the University of Trento. In the last five years several experimental and numerical analysis have been performed on crucial structural topics about multistorey timber construction. The efforts have been focused on the traditional light timber framed system (LTF) and on the log-house system (LH). Concerning the LTF, different aspects of the structural behaviour to the lateral load bearing structure such as walls and connection devices were investigated through experimental tests from the single component up to the full-scale building tested on shake table. The goals of these capstone tests, carried out on three-storey buildings, were the investigation of peculiar aspects which especially for the European constructive tradition were not sufficiently discussed. The same layout was follow for the traditional log-house system. In a first step of the research campaign the behaviour of single components (joints, reinforce elements) was tested and analysed in order to form the basis of the second part that was dedicated to the full scale shear walls tests and analysis. The thesis is organized in two main parts. In the opening chapters, after a brief introduction to the constructive system, the seismic behaviour of light timber framed constructions is analysed. The validation of the predictive models and the mechanical characterization of the gypsum fibreboard sheathing material are presented. Different steps of the S.E.R.I.E.S. project are summarized (tests on connection and real scale walls - shake table tests). The aim of the discussion is the deeper understanding of the boundary condition and the reliability of the tests on the single component on the real scale model. In the second part, the mechanical characterization of modern timber log-house building through experimental tests is presented. The strong cooperation among Rubner Haus Company and the timber research group of the University of Trento made possible a detailed experimental campaign organized on two steps. The first is focused on the evaluation of the corner joints proprieties by means of analysis of small portion of walls. The second part deals with the behaviour of full-scale walls with vertical loads in different geometries (corner joints types, length and presence of openings). The two innovative test setup were designed to reproduce the boundary condition of the structural elements of the building, and to minimize the effects of the test pparatus on the results. The outcomes of the tests show a complex interaction between contributions provided by different mechanisms. In the last chapters, a simplified model suitable to predict the overall load displacement curves of the wall is introduced.

The use of pre-fabricated concrete components and their related coupling systems in seismic engineering constitutes a subject of wide and deep interest among researchers, practitioners and manufacturers all over the world, as demonstrated by a large number of studies conducted, among other Countries, especially in Japan, New Zealand and United States since the early ‘80s and, in relatively more recent times, in Italy. A key issue is given by the possibility to apply the typical benefits of the pre-fabrication not only to low rise industrial/commercial structures, but also to multi-storey frames for public and strategic buildings such as schools, hospitals and many others, as well as to high-rise residential premises built in areas characterized by a medium to high seismic intensity. On the basis of what stated above, an original structural system made by prefabricated composite steel truss-concrete beams and centrifuged high-strength concrete columns is presented in the following. Specifically designed joints are provided to couple the different structural components in order to guarantee an overall ease of construction with reduced tolerance problems and self-bearing capacity during temporary erection phases, with a consequent reduction in schedule and costs. The use of high performance concrete for columns allows for a high bearing capacity with limited overall dimensions and the consequent maximization of the commercial or saleable space. The original layout of the system proposed has led to the need to perform an intensive theoretical and experimental research activity. The finite element model of the structural system was calibrated upon both static and cyclic testing evidence carried out on full scale samples built in Italy and tested at the Tongji University-Shanghai, China. On the basis of the data collected, the tuned model was used to carry out further analyses and to deepen the specific knowledge on several further aspects, as specified in the following. Firstly, an estimation of the joint’s strength domain, suitable for everyday’s design was carried out based on a component-approach. Then, a structural optimization on the component used to guarantee hogging and sagging bending moment resistance to the joint, was carried out in order to achieve the minimization of the construction material employed. Furthermore, the estimation of the seismic performance of the joint, based on the evaluation of a purposely defined vulnerability parameter, supplied encouraging results with reference to the applicability of the investigated technology over most of the National territory. Finally an improved layout of the joint, with reference to confined concrete and the related possibility to achieve a suitable seismic response also at edge joints, is presented.

The asymptotic behavior of a linearly elastic composite material that contains a thin interphase is described and analyzed by means of two complementary methods: the asymptotic expansions method and the study of the weak form using variational methods on Sobolev spaces. We recover the solution of the system of linearized elasticity in the two dimensional vectorial case and we find limit transmission conditions. The same steps are followed for harmonic oscillations of the elasticity system, and different solutions are found for concentrated mass densities. The cases in which the elastic coefficients depend on the thickness of the small parameter, for soft as well as stiff materials are considered. An approximated solution is found for harmonic oscillations of the elasticity system and limit transmission conditions are derived. Considering a bounded rectangular composite domain, with a thin interphase, we describe the weak formulation of the linearized system of elasticity. In the case of constant elastic coefficients, we estimate the bounds of the strain tensor and so, the energetic functional in the rescaled domain. We perform a variational formulation of the system of linearized elasticity and find estimates for the energetic functional of the system.

The masonry still one of the widespread construction system for low-rise residential buildings even for countries prone to seismic risk. Seismic design methods yet in use are based on idea that controlling forces is better way to control earthquake induced damages. In recent decades, however, was highlighted as the differences in strength between two levels of damage is low, and therefore as the damage is better correlated to the displacement. Also, in recent years, has arose a widespread expectation for being able to control the damage based on the probability of occurrence of an earthquake or being able to base the design on different performance levels ("performance-based design"). In this context, the design of masonry buildings needs to develop these design methods. The results of experimental tests performed at the University of Padua in the recent years on different masonry systems both reinforced and unreinforced with different horizontal and vertical joints typologies, which were aimed to characterization under combined in-plane vertical and horizontal cyclic loading, were used to make different strategies of finite element modeling that reproduce and extend the experimental results using parametric analyses. These analyses allow a comparison and a validation of an analytical model which was then developed. This model is able to reproduce the envelope curves of the cyclic shear-compression tests and it is able to interpret the performances of panels linking them with limit states resulting from integration of cross-section equilibrium equations. Finally, it was applied a model able to reproduce the hysteretic behavior of masonry and were carried out dynamic analyses using the input data derived from the envelope curves. The data thus collected can be used as database and as input for displacement-based design methods.

The ability of plant roots to penetrate soils is affected by several stimuli from the surrounding medium such as mechanical stresses and chemical changes. Therefore, roots have developed multiple responses to the several outer stimuli. Since plant roots have to face very complex problems to grow deeply into the ground, they are remarkable examples of problem-solving behaviour and adaptation to the outer constraints. The adaptation strategies of a natural root are not yet completely known and understood with exhaustive explanations. For this reason, mathematical models and experimental techniques applied to biological phenomena can perform a key role in translating the Nature adaptive solutions into engineering applications. The aim of this thesis is to provide further insights in understanding biological phenomena for the development of new technologies inspired by the adaptive ability of plant roots. Accordingly, both theoretical and experimental explanations to the adaptive behaviour of plant roots are proposed. The mathematical modelling is based on a modified version of the extended West, Brown and Enquist universal law, considering the root growth as an inclusion problem. The proposed equation has as a particular case a growth equation exploiting an approach similar to Lockhart taking into account the soil impedance. The influence of mechanical stresses and nutrient availability on the root growth are studied. The solutions of the analytical models are compared with experimental data collected in real and artificial soils. In addition, the theories and hypotheses of the root ability to grow in the apical region through nanoindentation, wettability, and photoelasticity are investigated. The first technique provided insights for the possible role and function at both different tissues levels and distances from the tip in the root movement and penetration during the growth. The investigation of root tissue properties revealed that the penetration and adaptation strategies adopted by plant roots could be enhanced by a combination of soft and stiff tissues. The second technique aimed to highlight the wettability of the apical zone and root hairs for the acquisition of water and nutrients. Finally, photoelastic experiments provided a non-invasive and in situ observation of plant roots growth and, by exploiting the fringe multiplication, a set up for the study of plant roots growing in edible gelatine is proposed.

Motivated by the potential vulnerability of their road infrastructure, many national authorities and local Departments of Transportation are incorporating seismic risk assessment in their management systems. This Dissertation aims to develop methods and tools for seismic risk analysis that can be used in a Bridge Management System (BMS); helping bridge owners to assess the costs of repair, retrofit and replacement of the bridges under their responsibility. More specifically, these tools are designed to offer estimates of: (1) the seismic risk to single components of bridges and their expected performance after an earthquake. (2) the impact a priori (i.e. before an earthquake) of a given earthquake on the operation of a road network, in terms of connectivity between different locations. (3) the damage a posteriori (i.e. after an earthquake) to road network operation, based on prior knowledge of network vulnerability and on the observed damage to a small number of single bridges. The effectiveness of these methods is tested and validated in a specific case study, the bridge stock of the Autonomous Province of Trento (APT) in Italy. To address the first point, I will first introduce the fragility curve method for risk assessment of individual bridges. The Hazus model is chosen as the most appropriate and is applied to the bridges of the APT stock. Once the fragility curves for all the bridges have been generated, a risk analysis is performed for three earthquake scenarios (with return periods of 72, 475 and 2475 years) and four condition states (operational, damage, life safety and collapse limit state). Next, I will extend the results of the component level analysis to the network level: the APT road network is modeled in the form of a graph and the problem of connectivity between two locations is analyzed. A shortest path algorithm is introduced and implemented to identify the best path between any two given places. Correlation in capacity and demand among bridges is not considered at this stage. After reiterating the fundamentals of probability theory, the theory of Bayesian Networks is introduced. The Bayesian Network approach is used to incorporate mutual correlation in capacity and demand, in risk assessment of a bridge stock. The concept is first formulated and illustrated on a simple case (the ‘twin bridge problem’), then extended to the general case of a full stock. I will show how the same framework can be used in post-earthquake assessment problems, where the evidence of the state of one or more bridges affects the prediction of the performance of another bridge. The outcomes and the limits of this work are discussed at the end of the Thesis.

Many studies and post-earthquake investigations have recognized that masonry infill walls play a major role in the seismic response of structures. Although their effect may be beneficial in some situations, the walls are also susceptible to high levels of damage, including collapse that can be life-threatening because of the heavy debris. Despite the critical importance of infill walls for life safety, infill walls are often neglected in numerical models and analyses implemented by designers because they are traditionally considered to be non-structural elements. Moreover, the majority of experimental studies and numerical models include only the in-plane behaviour of the panels: indeed, until recently, only sophisticated micro-models incorporated the out-of-plane response of unreinforced masonry infill walls. Recently, however, researchers have started to advance proposals for simplified macro-models that are capable of modelling in-plane/out-of-plane interaction, paving the way for the consideration of the associated issues in design practice. However, very few studies have applied these models to the dynamic seismic response history analysis of realistic structures. In this context, this thesis focuses on the numerical modelling of unreinforced masonry (URM) infill walls, with particular attention to the combined in-plane/out-of-plane response of panels in reinforced concrete (RC) frame buildings during seismic events. In the first part of this research, existing studies for URM masonry infill walls are reviewed, with an emphasis on the out-of-plane response of the panels. Significant experimental tests, modeling strategies and post-earthquake surveys are presented, stressing the parameters that influence the behaviour of the infills. An in-depth description is dedicated to the infill wall macro-model that is adopted for the analyses performed in this work, emphasizing its capabilities and limitations. This model consists of a single diagonal formed by two beam elements representing the wall; lumped modal mass is concentrated at the midpoint node of the diagonal. In-plane axial force and out-of-plane bending of the equivalent element interact by means of two fibre sections located adjacent to the central node. User defined domains limit axial/bending strengths and in-plane/out-of-plane ultimate displacements of the wall. When the response of an element exceeds these domains, the model simulates the collapse of this infill wall by removing it from the analysis. Next, the numerical model is calibrated in the OpenSees software framework by comparing existing experimental results with numerical outputs. The laboratory tests comprise in-plane cyclic and out-of-plane quasi-static results on 1-bay and 1-storey frame specimens with two different types of clay URM infill walls that are frequently found in Italian and other Mediterranean countries. The calibrated model is then applied to the static pushover analysis of a set of planar frames, while the wall elements are simultaneously loaded in both orthogonal directions. The nucleus of present study is the application of the calibrated model to the dynamic response history analysis of planar RC frames. Frame dimensions, number of stories, design and infill configurations are selected to be representative of the Italian building stock. Acceleration time histories consist of a suite of a bidirectional ground motions that are scaled to be compatible with Eurocode 8 elastic spectra. Cracking and collapse of the infill walls are monitored during the analysis. The infill walls reach their ultimate displacement capacity by a combination of in-plane and out-of-plane displacements, with the out-of-plane component usually playing the dominant role. The intensity of seismic load that is required to fail the infill walls, as well as the patterns of failure, are shown to be consistent with observed damage to URM infill walls in similar buildings during recent earthquakes. This research suggests that simplified macro-elements are suitable for design-oriented models of URM infill walls in RC framed structures, capturing the critical interaction between in-plane and out-of-plane response of the infill walls but without making the models excessively complex.

The study of local and global instability and bifurcation phenomena is crucial for many engineering applications in the field of solid mechanics. In particular, interfaces within solid bodies are of great importance in the bifurcation analysis, as they constitute localized zones in which discontinuities or jumps in displacement, strain or stress may occur. Different instability phenomena, heavily conditioned by the presence of interfaces, were analyzed in the present thesis. The first phenomenon that has been considered is the propagation of a shear band, which is a localized shear deformation developing in a ductile material. This shear band, assumed to be already present inside of a ductile matrix material (obeying von Mises plasticity with linear hardening), is modelled as a discontinuity interface following two different approaches. In the first approach, the conditions describing the behavior of a layer of material in which localized strain develop are introduced and implemented in a finite element computer code. A shear deformation is simulated by imposing appropriate displacement conditions on the boundaries of the matrix material, in which the shear band is present and modelled through an imperfect interface, having null thickness. The second approach is based on a perturbative technique, developed for a J2-deformation theory material, in which the shear band is modeled as the emergence of a discontinuity surface for displacements at a certain stage of a uniform deformation process, restricted to plane strain conditions. Both the approaches concur in showing that shear bands (differently from cracks) propagate rectilinearly under shear loading and that a strong stress concentration is expected to be present at the tip of the shear band, two key features in the understanding of failure mechanisms of ductile materials [results of this study have been reported in (Bordignon et al. 2015)]. The second type of interface analyzed in the present thesis is a perfectly frictionless sliding interface, subject to large deformations and assumed to be present within a uniformly strained nonlinear elastic solid. This type of interface may model lubricated sliding contact between soft solids, a topic of interest in biomechanics and for the design of small-scale engineering devices. The analyzed problem is posed as follows. Two elastic nonlinear solids are considered jointed through a frictionless and bilateral surface, so that continuity of the normal component of the Cauchy traction holds across the surface, but the tangential component is null. Moreover, the displacement can develop only in a way that the bodies in contact do neither detach, nor overlap. Surprisingly, this finite strain problem has not been correctly formulated until now, so that this formulation has been developed in the thesis. The incremental equations are shown to be non-trivial and different from previously (and erroneously) employed conditions. In particular, an exclusion condition for bifurcation is derived to show that previous formulations based on frictionless contact or ‘spring-type’ interfacial conditions are not able to predict bifurcations in tension, while experiments (one of which, ad hoc designed, is reported) show that these bifurcations are a reality and can be predicted when the correct sliding interface model is used. Therefore, the presented approach introduces a methodology for the determination of bifurcations and instabilities occurring during lubricated sliding between soft bodies in contact [results of this study have been reported in (Bigoni et al. 2018)].

A shear band of finite length, formed inside a ductile material at a certain stage of a continued homogeneous strain, provides a dynamic perturbation to an incident wave field, which strongly influences the dynamics of the material and affects its path to failure. The investigation of this perturbation is presented for a ductile metal, with reference to the incremental mechanics of a material obeying the J_2-deformation theory of plasticity (a special form of prestressed, elastic, anisotropic, and incompressible solid). The treatment originates from the derivation of integral representations relating the incremental mechanical fields at every point of the medium to the incremental displacement jump across the shear band faces, generated by an impinging wave. The boundary integral equations (under the plane strain assumption) are numerically approached through a collocation technique, which takes account of the singularity at the shear band tips and permits the analysis of an incident wave impinging on a shear band. It is shown that the presence of the shear band induces a resonance, visible in the incremental displacement field and in the stress intensity factor at the shear band tips, which promotes shear band growth. Moreover, the waves scattered by the shear band are shown to generate a fine texture of vibrations, parallel to the shear band line and propagating at a long distance from it, but leaving a sort of conical shadow zone, which emanates from the tips of the shear band. Moreover, the approach is generalised to study the interaction of multiple shear bands showing that it may lead to resonance and corresponding growth of shear bands, but also to their annihilation. At the same time, multiple scattering may bring about focusing or, conversely, shielding from waves. Due to the difficulties inherent to the experimental analysis of time-harmonic dynamics of shear bands, the proposed mechanical model represents the only practical possibility of analyzing the fine micromechanisms governing material collapse and discloses the complex interplay between dynamics and shear band growth or arrest.

The deposition of waste in a landfill can be a threat to the environment and human health; in spite of their potential pollution, landfill are still of grate use for the residual municipal solid waste, thus efficient and cost effective technologies need to be studied in order to minimize aqueous and gaseous emissions. The present work focuses on the evaluation of the remediation of old landfill sites that pollutes groundwater and on the determination of a new pre-treatment of fresh waste upstream of landfilling. First the biosparging technology has been applied to remediate an aquifer polluted by leachate. The biosparging stimulates the growth of indigenous bacteria able to convert pollutants, such as ammonium nitrogen, in harmless compounds. The technology shows high efficiency in ammonium nitrogen removal via nitrification processes. The biosparging remediation technology prevents the mobilization of metals and removes the nitrates produced in the nitrification process when the organic carbon source is conveniently dosed. The application of the biosparging on site has proven to be feasible. The Solidification/Stabilization (S/S) technology is a pre-landfill waste treatment process, which has been used for different types of hazardous wastes since it has a proved efficiency on heavy metal immobilization. The S/S process uses chemically reactive formulations that, together with the water, form stable solids; it also insolubilizes, immobilizes, encapsulates, destroys, sorbs, or otherwise interacts with selected waste components. The S/S process improves the physical characteristics of the waste and reduces the mobility of the hazardous compounds, thus the waste leaches less contaminants into the environment. The result of this process is a less hazardous solid. The experimental evidences proved that this technology reduces volumes used for landfilling and inhibits the methanogenesis blocking greenhouse gases emissions. The reduced permeability and the leaching test results show that the leachate produced is of a smaller amount and less polluted. The enhanced mechanical properties and the reduced emissions both in bodies of water and atmosphere have proven the worth of this technology. Therefore an alternative waste treatment plant involving S/S pre-treatment is proposed.