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Straw bale construction is a building technique offering many advantages: it provides excellent hygro-thermal insulation; it ensures good performance against earthquakes; and it is sustainable. From a mechanical point of view, straw bales can act as a surviving cell for the building in case of calamity. For this reason, measuring the mechanical properties of straw bales is important for the comprehension of the behaviour of straw bale buildings. Despite the fact that the use of straw bales in construction has been constantly increasing since the ‘80s, the behaviour and the performance of straw bale buildings have not been fully assessed so far. Using a recently developed test methodology (Maraldi et al., 2016), an analysis of the performance of small prismatic straw bales under monotonic compressive loads has been conducted. Force-displacement curves obtained from the tests have been fitted with a two-parameter rheological model to extract bales performance indicators. Results show that bales laid flat are stiffer than bales laid on-edge. However, if the influence of bales initial geometry is disregarded by considering stress and strain instead of force and displacement, no difference in the elastic modulus between flat and on-edge orientation appears. Furthermore, bales stiffness and elastic modulus are dependent on the initial density of the bale. It has been also found that straw bales exhibit a typical deformation pattern which depends on the baling process and that the Poisson’s ratio does not remain constant along the longitudinal direction during loading, whereas it is null along the transverse direction.

From the point of view of environmental awareness, construction sustainability is a theme that is gaining considerable attention. This has brought to a re-discovery of the use of straw as a construction material, a technology that has been widely used in the past centuries. Straw is a natural material having excellent insulating capabilities, considerable mechanical properties when packed in bales and is relatively low cost (it is indeed a by-product of farming activity). Two are the techniques adopted in straw bale construction: post-and-beam, where the load is sustained by a wooden frame and straw bales are used merely as infill material; and load-bearing, where the entire load is sustained by the plastered straw bale walls. Especially regarding the latter technique, there is a need for a deeper understanding of the mechanical properties of straw bales. The characterization of the material is made difficult by the variability brought about by the variety of plants from which straw can be obtained, unpredictability of the baling process, moisture content in the bale and other parameters. Moreover, there is not a standard regulating the productive chain of straw bales to be used for construction. In this paper, a literature review on the tests performed on single unplastered straw bales is conducted and, based on this, some ideas are proposed for the development of a model describing the mechanical behavior of straw bales.

In this study we show that the key to understand why the same salt can cause damage in some conditions and not in others is the kinetics of re-crystallization. Salt contaminated porous materials are known to deteriorate with environmental fluctuations causing the weathering of rocks and buildings. Salts can be naturally present in the materials used for construction (such as mortars and bricks) or can derive from external sources (capillary rising ground water, eolian origin, sea water along rocky coasts, and atmospheric pollution). With the variation of outdoor climate such as relative humidity, temperature or rain, the entrapped salt crystals can form again a salt solution after contact with liquid water (dissolution) or with water vapor (deliquescence). The so formed salt solution is subsequently mobilized in the porous network and re-crystallizes with drying. We present both macroscopic and microscopic experiments assessing the recrystallization dynamics of NaCl in sandstone with wetting/drying and humidity cycling. Advanced techniques such as high resolution X-ray computed tomography and Scanning Electron Microscopy are used to study the recrystallization process in the porous network in parallel with the drying kinetics. Our results show that recrystallization following deliquescence and dissolution leads to very different crystallization patterns. With humidity cycling, recrystallization promotes the formation of localised bigger cubic crystals at the subsurface of the stone whereas rewetting leads to efflorescence in the form of large localised cauliflowers at the surface. The different growth dynamics have direct consequence on the drying behaviour of the sandstone and its deterioration. This work is part of the European Project KISADAMA, a JPI- Cultural Heritage : Joint Heritage European Programme.

Over the last thirty years, the use of strawbales as a construction material has re-gained a lot of popularity for several reasons: baled straw has superior thermal insulation properties; buildings made with straw-bales are less expensive; straw is a by-product, hence its usage can help reduce the costs and emissions related to its disposal; structures built with strawbales can resist earthquakes better than those built according to traditional techniques. In the context of using materials and techniques sustainable for the environment, strawbale construction appears a more than promising choice establishing a strong link with the territory as well. Indeed, straw has been extensively used as a construction material since pre-history; more recently, strawbale houses were built in Nebraska at the end of the 19th century. The use of strawbales in construction returned popular in the late 80's (King, 2003); in some countries, this has been also supported by the development of design standards. In Italy, the lack of similar codes represents an obstacle; the procedure to have a design approved is tedious and discourages builders. In spite of this, however, strawbale houses have been and are currently being built. A deep understanding of the mechanical behavior of straw and of the material typically used in the rendering of strawbale walls is crucial for the development of construction techniques employing load-bearing strawbale walls. In the literature, studies on the mechanical properties of strawbales and strawbale assemblies have appeared since the rediscovery of this construction technique (Zhang, 2000; Vardy, 2009). Such studies report results of experimental tests conducted on single bales and on stacks of multiple bales, plastered or unplastered, loaded both on-edge and flat. However, very few of them provide some modeling to substantiate the results. In this paper, a review of the relevant literature regarding the mechanical properties of single unplastered straw bales is proposed and critically analyzed in order to provide guidance for future modeling; furthermore, the procedure for a comparative LCA between the options of building with conventional materials and with straw bales is sketched out and preliminary results of such an analysis are discussed.

Salt crystallization is one of the major factors of degradation of porous materials such as masonry. This paper presents a coupled multiphase model for hygrothermal analysis of masonry structures and the effective prediction of stress induced by salt crystallization. The independent variables chosen to describe all the process are: the pore humidity, the concentration of dissolved salt and the temperature. The governing equations of the model are: the moisture balance equation, expressed in function of the humidity, the conservation equation for the total stored energy, the balance equation for the dissolved salt and a kinetic expression for the salt crystallization law. The model is used to simulate the results of an extensive experimental campaign carried out on a masonry wall exposed to weather conditions for four months.

We propose a model for the thermomechanical behaviour of a shape memory alloy based on a phase-eld approach to the underlying martensitic phase transition. The model is applied at the macroscopic scale and it is formulated to capture essentially the one-dimensional mechanical behaviour; in fact, the eect of the martensitic phase transition has been included in terms of a uni-axial deformation along a xed direction. In addition to the usual momentum balance equation, a time-dependent Ginzburg-Landau equation is introduced to describe the evolution of the phase; a central constitutive relation couples the phase to the deformation. Finally, the heat equation accounts for the non isothermal effects due to the phase transformation in a thermodynamically consistent way. The model has been implemented within a nite-element framework and the mechanical response of the model under dierent conditions is investigated in a number of numerical tests; the results obtained are analysed and compared to experimental evidences available in literature.

In this paper, a discrete model for the coupled analysis of mechanical and environmental degradation of historic masonry structures is presented. The environmental action is represented by the diffusion of moisture within the masonry that can engender mechanical degradation, altering the structural response. On the other hand, mechanical degradation has influence on the diffusion process. Thanks to a multiscale computational strategy, the model can be used to simulate real-scale masonry structures. In particular, the model can be applied to evaluate the behaviour of structures made of ecologic building materials such as adobe bricks that have become of greater economic importance in recent years. Some numerical applications are presented to illustrate the capabilities of the model.

The linear and non-linear analysis of curved beams is a very classical but still very discussed topic in literature. The most commonly used approach is the displacement approach, which is affected, as it is well known by locking phenomena. A viable alternative to overcome the problem of locking encountered is represented by equilibrium formulation in static linear analysis and mixed formulations in dynamic and non-linear analysis. In particular, in non linear analysis of beams formulations based on a Hellinger-Reissner variational principle or modified Hu Washizu principle have been proposed in literature. In this paper a valid alternative is proposed for the non-linear analysis of an arbitrarily curved, extensible, shear flexible, elastic planar beam. The proposed formulation is based on a new variational principle expressed in terms of stress components. In particular, the unknowns are represented by the bending moment and by a variable from which the shear and the axial force can be expressed and by the generalized forces at the extremities of the bar. The Euler-Lagrange equations of this principle are the elasto-kinematic relations related to the curvature and the moment equilibrium equation. The effectiveness of the approach is illustrated through numerical examples. A comparison in terms of displacements and stress with the other formulations available in literature ends the paper.

A great attention is nowadays devoted to preserve cultural heritage against deterioration. The causes of this deterioration process can be generally subdivided in two main groups: mechanical and physico-chemical deterioration actions. The well-known mechanical deterioration of the masonry, in terms of the more meaningful phenomena, i.e. damage and friction toughness, it has been extensively studied numerically and experimentally in literature; Less attention has been devoted to the simulation of the chemical processes, which involve the diffusion of the aggressive species and water into the masonry structures. Decisive for the damaging process of salts in porous media is the interaction of the salt with the humidity in the masonry: under specific conditions the salt crystallization appear inducing stress into the masonry pores. The aim of this work is to look at the deterioration of masonry in a unified framework which accounts for both the mechanical and the chemical part of the problem and their coupling. Few are the contributions in this direction specifically for masonry while some contributions can be found for other materials, such as the concrete. In particular, here, a model for the analysis of masonry structures which couples the mechanical deterioration process with the environmental damage is presented. In order to deal with real masonry structure, the implementation of the model is developed by an efficient multilevel strategy that solves a simplified modeling of local interaction brick-brick through iterative nested solutions defined at different levels of mechanical definition. The local model is based on a discrete Lagrangean description where each brick is a rigid body and each joint is a nonlinear interface characterized by normal and tangential stress components. The environmental damage is modelled with the diffusion of penetrating agents inside the masonry and is described with a diffusion equation. The constitutive relations for stresses involve mechanical damage, chemical damage and friction. On the other hand, the mass flux of external agents depends on the concentration and on the mechanical damage. Numerical tests show the effectiveness of the proposed approach.

Damp rising and salt crystallization are important factors affecting degradation of porous materials like masonry. As the water evaporates, the salt concentration of pore solution increases until salt precipitates leading to efflorescence or sub fluorescence with possible severe damage. Here, a simple 3D model for salt diffusion and crystallization in masonry structures is proposed. The independent variables chosen to describe all the process are: the pore humidity, the concentration of dissolved salt and the temperature. These independent variables are supplemented by two internal variables: the water content and the concentration of crystallized salt. The governing equations of the model are: the moisture balance equation expressed in function of the humidity, the conservation equation for the total stored energy, the balance equation for the dissolved salt and a kinetic expression for the salt crystallization law. The model parameters have been calibrated through an extended experimental campaign conducted within the SMooHs EU project. After the calibration, the model has been employed for the long term simulation of some laboratory tests involving masonry panels subjected to various environmental conditions. A good agreement between the model predictions and the experimental evidences has been obtained, so validating the good predictive capabilities of the proposed model.

Losses from water distribution systems are reaching alarming levels in many cities throughout the world. This paper presents a simple model based on a beam with elastic constraints to evaluate the effect of pressure on the opening area of the crack and to estimate leakage in longitudinally cracked pressurized pipes. The model is calibrated on the results of a three-dimensional finite element analysis and then validated by experimental results.

The originality of Francesco di Giorgio in the field of engineering is argued by the authors. They discuss the defeat of the French army and the capture of Castel Novo by Neapolitans in November 1495. Their interpretation is based on contemporary accounts (including two unpublished documents) and two reliefs that originally decorated the facade of the Ducal Palace at Urbino. They argue that the relief no. 41 represents the first unsuccesful battle that took place on November 13, 1495, when Neapolitan forces attempted to lay siege to the castle with ladders. The castle was captured on December 8, 1495, and the battle was described by contemporary chronicles as an unforseen victory. Urbino relief no. 20 can elucidete the unexpected success, by connecting it to the first launch of an explosive mine. The authors make a convincing case by pointing out that folios 85r-86v of Francesco's codicetto, contain the development of the idea of a missile weapon which in turn, presents great similarities to the Urbino relief. In addition, the involvement of the Duke of Urbino in the capture of Castel Nuovo could justify the depiction of these battles on the palace reliefs. They celebrate the inventive powers of the architect and the resulting politico-military supremacy of his patron. -in the Introduction by Angeliki Pollali

The conservation of historical masonry structures is a problem of great importance in Europe and especially in Italy where the cultural heritage has unique dimensions. The causes of deterioration can be subdivided in two main groups: physico-chemical and mechanical ones. The mechanical behavior of the masonry has been extensively studied in literature, while less attention has been devoted to model the processes of environmental degradation of masonry. The aim of this work is to propose a simple model able to describe the diffusion and the crystallization of salt in masonry structures. The primary variables of the model are: the pore humidity, the dissolved salt concentration and the concentration of crystallized salt. Some numerical tests are shown to demonstrate the effectiveness of the model.

A Ginzburg-Landau model for the macroscopic behaviour of a shape memory alloy is proposed. The model is one-dimensional in essence, in that we consider the effect of the martensitic phase transition in terms of a uniaxial deformation along a fixed direction; a Ginzburg-Landau approach to the martensitic phase transition is applied by setting in a thermodynamical consistent framework a scalar order parameter, coupled with the balance of linear momentum equation and the heat equation. The model has been implemented within a finite-element framework and a number of numerical tests are presented which investigate the mechanical behaviour of the model under different conditions; the results obtained are analysed in relation to experimental evidences available in literature.

A diffuse interface phase field model is proposed for the unified analysis of diffusive and displacive phase transitions under non-isothermal conditions. Two order parameters are used for the description of the phenomena: one is related to the solute mass fraction and the other to the strain. The model governing equations come from the balance of linear momentum, the solute mass balance (which will lead to the Cahn-Hilliard equation) and the balance of internal energy. The model presents a very complex computational context, it is non-linear, it involves gradient terms and it is time-dependent. Some numerical tests show that the model is able to capture both the displacive and the diffusive mechanisms as well as the interplay between the two, which results - for the chosen parameters setting - in the displacive transition occurring even if the critical temperature is not reached.

The heat treatment of steels is a process of fundamental importance for manipulating the properties of the steel. We present a consistent thermodynamic framework for modelling the heat treatment process which is able to capture both displacive and diffusive mechanisms. The present formulation is applicable to the a grain size level of observation. Some salient features of the thermodynamic framework are highlighted, especially those associated with surface energies, and a number of numerical experiments are presented.

This work presents a thermodynamic model for phase transformations occurring during steel heat treating.

Steel heat treatments are very important industrial processes which involve microsctructural transformations. In the shop practice the design of these processes is conducted on empirical basis using the so called Bain curves, which cannot describe the phenomenon in its globality. Here, a model is proposed in which the first law of the thermodynamics as well as the dynamic equilibrium equation are taken into account. The internal energy allows description of the phase transformations whose evolution is followed by the Cahn-Hilliard equation.