A new trend in the mechanical design of devices for advanced technologies, such as soft robotics and micro/nano mechanics, is the exploitation of structures undergoing large deflections, in an attempt of achieving superior performances. Within this framework, non-linear modelling becomes a fundamental tool for the design of compliant structures and deformable mechanism. Two structural systems are investigated, both based on the planar elastica and subject to movable and configurational constraints. These two structures disclose unforeseen behaviours when the values of the parameters defining the models are varied. The first structural system is an elastic rod constrained by a slowly rotating clamp, while the other end is loaded with a lumped mass weight. When this weight is lower than that corresponding to buckling, the edge of the rod describes a closed curve, behaving as an elastica compass. Differently, when the load is higher than that of buckling, a release of elastic energy is observed, leading to a snapback of the structure, so that the rod realizes an elastica catapult. The clamp in the above described structure is replaced by a frictionless and fixed sliding sleeve in the second system considered in this thesis. The rod is subject to a sudden release from the underformed configuration, providing dynamic effects on the system. By means of the variational approach, the presence of a configurational force at the exit of the sliding sleeve is proven within the dynamical setting, extending previous results restricted to the quasi-static assumption. The configurational force is found to strongly affect the dynamics of the structure. In particular, two different behaviours are observed, in which the rod may either completely penetrate in ("injection") or be expelled from ("ejection") the sliding sleeve. In both the above problems, the theoretical predictions are corroborated through the experimental validation on physical models, which have been ad hoc invented and designed. A new insight is obtained in the design of flexible devices, paving the way to applications in soft robotics.

The integral abutment bridge (IAB) constituted by the superstructure and the substructure can achieve a composite action responding as a single structural unit by eliminating or reducing expansion joints and bearings. Accordingly, the construction and maintenance costs can be reduced. Therefore, the IAB concept has recently become a topic of remarkable interest among bridge engineers, not only for newly built bridges but also during refurbishment processes. The research topic concerns the retrofit of existing bridges with the IAB concept. In order to investigate the retrofitting technique with the IAB concept, the literature survey on the practical applications of this approach in worldwide was carried out firstly, including retrofitting motivations, detailed processes and structural performance after retrofitting. Besides, another literature review on the critical issues of analysis on the IAB, such as soil-structure interactions, modelling approaches and plastic hinge simulations, was conducted in order to find out the most suitable method in modelling. The case study of a simply supported prestressed concrete bridge (named Viadotto Serrone) with three spans constructed in 1972 was analyzed, which has some durability problems nowadays. The finite element model was built, involving soil-structure interactions, non-linear behaviors and retrofitting processes. The original and updated Italian design codes are compared through static analysis and seismic analysis. Another investigation was conducted to prove the necessity of considering soil-structure interactions in the IAB. Based on the appropriate finite element model, a large number of static sensitive analyses were carried out, taking thermal actions; bridge types; soil conditions and substructure heights as parameters. Through analysing the responses of girders, piers, abutment stems and piles, some important factors and the corresponding influence were found, which could be adopted to guide the retrofitting technique with the IAB concept. Then, the verification was conducted in order to check if the existing sections could be reused without any changes and point out the most critical components, which need to be repaired or replaced. Moreover, the dynamic performance of bridge before and after retrofitting was investigated preliminarily through modal analysis and response spectrum analysis.

In the last decades, powder technology has become one of the most important technological processes for the production of metallic and ceramics components; free sintering, hot isostatic pressing and hot forging are different ways to realize a key-phase in which the primary mechanical properties of the final material are obtained. A theory of sintering is necessary in order to be able to predict the final structure of a body undergoing such a kind of process. In this respect, it is crucial to be able to follow the evolution of the mechanical properties of the material (determined by this structure) during sintering and to get the final features of the compound at the end of this process. In this thesis, the influence of the pressure called “sintering stress” or “Laplace pressure” produced by the gas employed during the process and which gets trapped into the pores is analyzed. This is done for pre-compacted (micro/nano)-powdered axially-symmetric samples undergoing (i) isostatic pressing (also covering the case of free sintering), (ii) "free" forging (i.e. axial compressive load acting at the top and bottom faces of the specimens, with no lateral confinement) and (iii) constrained forging (i.e. transverse compression of the samples in a rigid die). Such cases are among the ones suggested in Olevsky, E.A., Molinari, A., “Kinetics and stability in compressive and tensile loading of porous bodies”. The role of the Laplace pressure in all of the mentioned cases is twofold. First of all, such a pressure influences the evolution of the porosity and, for instance, its residual value for a given time duration of the process. It is worth emphasizing that threshold pressures below which the sintering stress is actually not negligible are determined in this thesis; the duration of the process is indeed heavily affected by such a stress. In turn, such a duration would be underestimated otherwise. Furthermore, industrial processes often entail loading pressures lower than the thresholds mentioned above, especially of "small" grain sizes. The second aspect is based on a common feature exhibited by the two modes mentioned above: the loading parameter may be tuned in such a way that, at some stage of the sintering process, its value may equate the Laplace pressure, leading to a constant value of the porosity. Whenever this is the case, for (i) there exists a whole range of the loading parameter for which the process is actually unstable. Henceforth, in order to have stability of sintering either the loading parameter must be high enough with respect to the Laplace pressure or zero, leading to (stable) free sintering. For (ii), the stability analysis shows that the results obtained by using the different models for the shear and bulk moduli do not agree for a restricted range of external load. This is of course an intrinsic pathology of his specific loading mode. Moreover, it is worth noting that large strains occur in such a mode. Thus, both the stress and the (infinitesimal) strain employed in this analysis should be replaced by appropriate (possibly work-conjugate) choices of the stress and strain measures, although this goes beyond the aim of this work. For (iii), a stability analysis allows us to conclude that such a value represents a critical threshold, below which the sintering process cannot proceed. In the second part of the present work, the mechanical behavior of sintered specimens are investigated. Such a behavior is strongly influenced by the stress state at the end of the process, which depends on the final value of the interstitial pressure and of the loading mode used during the process. For the sake of simplicity, only the two "realistic" cases of isostatic pressing (also covering free sintering) and constrained forging are considered. For such components, isostatic pressing may induce isotropy, whereas constrained forging processes may enforce a transverse isotropic behavior in the direction of forging. Although for prestresses isotropic material the explicit constitutive law is given by Man in “Hartig's law and linear elasticity with initial stress”, the analog for the case of transversely isotropic material is deduced here, for the first time, through a method, suggested by Weiyi , “Derivation of the general form of elasticity tensor of the transverse isotropic material by tensor derivate”, based upon the partial differentiation of the strain energy with respect to both the strain tensor and the residual stress. Finally, the residual stress tensor for specimens sintered through (i) and (iii) is obtained and the correspondent stress response is deduced. Equivalent material constants (two constant in the case of isotropy, five in the case of transverse isotropy) arising in the presence of prestress may be introduced; such constants take the place of the classical material moduli characterizing the response in the absence of residual stresses. Finally, an experimental procedure to determine the values of such constants is proposed.

The research hereinafter describes aims at mechanically characterize the behavior of timber framed buildings, with particular focus on their behaviour in seismic zones. An extensive experimental campaign divided into three phases has been completed in order to achieve this objective. In the first phase tests on the connection between sheating panels and timber studs were conducted. Subsequently the behavior of the connections used for anchoring the walls to the foundation were investigated. In the second stage the full scale timber framed walls were subjected to tests. The walls were realized using different materials and different type of connections to the ground. The results have allowed the study of the individual structural components which constitute an entire building, from the single connector to the entire wall. In order to understand the behavior of the components themselves in a real building, and thus their interaction with each other in case of an earthquake, in the third step a shaking table test of a three-story building has been done. All tests have permitted to collect a wealth of data with which to populate a database to be used both to understand in detail the structural behavior of the timber framed building system and in also to validate the proposed formulations. From the analytical point of view, an equation able to provide the horizontal displacement of a wall subject to a horizontal force has been developed. This equation was then successfully validated by comparing the results with those obtained from laboratory tests. For the execution of the tests have been created procedures and set-up ad hoc, that could be used also in the future to carry out similar tests. An important work has been done to achieve a configuration suitable to test full scale timber framed walls through well controlling the boundary conditions.

The importance of subsurface flow in hillslope hydrology has been widely demonstrated in the past twenty years. Neal and Rosier (1990), Sklash (1990), McGlynn (2003), McDonnell (2003), Kirchner (2003) and many others demonstrated through field monitored experiments that the most part of the hillslopes runoff production comes from the subsurface, reaching often percentages around 80% of total runoff. Furthermore they found that the subsurface flow is mainly made of old water previously stored within the catchment slopes. Torres (1998), Pierson (1980) and others evidenced that catchment subsurface runoff response time could be very fast especially for wetter ground moisture contents. Nevertheless Fiori (2006), Kumar (2004), Montanari et al. (2004), Bertoldi et al. (2006) and many others highlighted that the capability of the actual modelling techniques of predicting the temporal scales of subsurface hillslope hydrology response is very poor and in order to get good results they require the use of overestimated soil hydraulic parameters. Furthermore the uncertainties and the variability of such parameters exert indeed a crucial role and require then a deep analysis in order to highlight their effects in modelling accuracy. Nonetheless the equations for saturated and unsaturated flow modelling sometimes do not describe with great precision the physical processes that are instead highlighted in many experimental works, and this is to be imputed to all the constitutive laws employed within them (Hassanizadeh, 1993; Shultze, 1999; Germann, 1999; Torres, 2001; and many others). Therefore the modelling of subsurface processes requires great care and attention and the work done in this thesis focuses on some aspects related to this problem. The objectives of this work are to investigate some features connected to subsurface flow. First of all an extensive analysis of the most used numerical schemes on convergence and on the influence of heterogeneous hydraulic parameter fields in their behaviour in both flow and transport is achieved. We have seen that the most classical method have a more robust structure than new postprocessing schemes that are aimed at improving the classical solutions. The performed studies revealed the importance of being aware of how we are solving the equations and how they deal with the domain features, that are hydraulic parameters, in order to be conscious that the numerical solution might fail to predict correctly the processes we want to model and to give the correct weight to modelling uncertainties. The second important point regards the use of constitutive laws in the governing equations which can have a great drawback on the modelling problems exposed above. The analysis on the validity of such physical constitutive laws employed in saturated and in non saturated flow equations is done. In particular the validity of Darcy law in non stationary flow fields in both saturated and unsaturated media is done as well as the comparison with solutions achieved with the more general momentum balance equation. This is done specifically to investigate some strange soil behaviour revealed in field and laboratory based works in which the unsaturated flow showed unexpected responses Germann, 1999; Torres, 2001; Torres, 2002). On the basis of this study we could make our own speculations on what happens at the base of strange flow behaviour in unsaturated flow. In our opinion a kind of capillary barrier formation in non localized areas of the flow field might explain many of the evidences arisen experimentally. We decided then to design and realize a laboratory column experiment. The work is actually ongoing and preliminary work is reported. Then discussion on our expectations and speculations around the physical processes that are poorly described by the unsaturated flow equations are then exposed.

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.