Energy approach for static and linearized dynamic studies of elastic structures containing incompressible liquids with capillarity: a theoretical formulation

In the context of the study of structures coupled with internal liquids, we present in this article a theoretical work to treat the coupling between the structure elasticity and the surface tension phenomenon, which has not been the object of specific studies before (according to the authors knowledge). Considering an incompressible and inviscid liquid in an elastic container, an energy approach is used to obtain a variational formulation of the small amplitude vibrations of the coupled problem around the nonlinear static equilibrium position. The incompressibility of the liquid supposed inviscid and the contact condition at the fluid-structure interface are introduced by Lagrange multipliers. Gravitational forces and surface tensions are both taken into account considering their associated potential energies.     

Mechanical behaviour of ancient masonry

The aim of this research was to build a behaviour law for ancient masonry made during the nineteenth century with bricks and lime mortar bonds. This work should be of interest to researchers involved in the study of ancient masonry structures like arch bridges built in this period. To assess the masonry capacity vaults to support service loads and to determine their collapse loads, engineers need mechanical behaviour laws for their component parts. This experimental research was performed to explore the behaviour of the bricks, of the lime mortar, and of a wall until their failure in compression. In parallel the bricks / mortar interface criterion failure under shear and tensile load is characterised. After laboratory tests, numerical simulations were carried out using a finite element method (FEM) to define an homogenised behaviour law for a macro element including bricks and lime mortar bonds. In this goal, a behaviour law was firstly found for each component and then for the masonry as a whole by a FEM homogenisation process, including the non-linear behaviour domain up to the compression failure. The tension failure being reported into an interface element for which the failure criterion was adjusted on specific tests.     

Analysis of non-planar graphitic structures: from arched edge planes of graphite crystals to nanotubes

A unified approach to the analysis of the mechanisms that lead to the edge reconstruction of graphite and growth of a variety of non-planar graphitic structures, such as nanotubes, is suggested. Transmission electron microscopy (TEM) shows that nano-arches are formed on the edge planes of natural and synthetic graphite, as well as graphite polyhedral crystals, which are built of graphene sheets; this makes the edge reconstruction of graphite different from the surface reconstruction of other crystals. A theoretical study of edge zipping in graphite and formation of tubular carbon structures has been performed using an integrated approach combining molecular dynamics simulation and analytical continual energetics modeling. The suggested theoretical framework describes the formation of curved surfaces in a wide range of dimensions, which is a general feature of the growth of layered materials. Layered materials isostructural to graphite, such as hexagonal BN, demonstrate similar edge structures and also form nanotubes. Thus, the ability of materials to form arches as a result of edge reconstruction points out to their ability to form nanotubes and vice versa. TEM studies of graphite and hexagonal boron nitride provide experimental verification of our analytical model. Received: 29 October 2001 / Accepted: 5 November 2001     

Contribution to the static heat transfer to boiling liquid helium

Aluminium is now being used as a stabilizing material for superconducting materials. With regard to its use as a stabilizer, the heat transfer properties to boiling helium of 99.9999% pure aluminium are measured and compared with those of 99.999% pure aluminium and OFHC copper     

Nonlinear homogenization techniques to solve masonry structures problems

The behaviour of masonry material subjected to different in-plane loading combination is studied in this work. The masonry is considered as a periodic composite material composed by a regular distribution of brick and mortar and it is analyzed using a homogenization technique. The mechanical properties of the masonry, as an orthotropic homogeneous material, depend on the geometrical and mechanical properties of the components based on the study of the equilibrium and compatibility of a basic cell. The masonry is a frictional material and its behaviour depends on the loading direction, for these reasons, a unilateral damage model is chosen for the analysis. This model describes the behaviour of brittle materials subjected to tension-compression cyclic loads based on the introduction of two damage variables and it assumes that the damage is due to the beginning and growth of cracks only in the mortar joints. It is considered that the bricks have a linear elastic constitutive relationship. Numerical applications are performed with a nonlinear finite element code in order to test the proposed procedure by comparing the results with those available in the literature and also with experimental data.     

Damage in MMCs using the GMC: theoretical formulation

In this work the incorporation of damage in the material behavior is investigated. Damage is incorporated into the generalized cells model (GMC), and applied to metal-matrix composites (MMCs). The local incremental damage model of Voyiadjis and Park is used here in order to account for damage in each subcell separately. The resulting micromechanical analysis establishes elasto-plastic constitutive equations that govern the overall behavior of the damaged composite. The elasto-plastic constitutive model is first derived in the undamaged configuration for each constituent of the metal-matrix composite. The plasticity model used here is based on the existence of a yield surface and flow rule. The relationships are then transformed for each constituent to the damaged configuration by applying the local incremental constituent damage tensors. The overall damaged quantities are then obtained by applying the local damage concentration factors obtained by employing the rate of displacement and traction continuity conditions at the interface between subcells and between neighboring repeating cells in the generalized cells model. Examples are solved numerically in order to explore the physical interpretation of the proposed theory for a unit cell composite element.     

On the vulnerability of historical masonry structures: analysis and mitigation

This work presents a methodological approach to the study of historical structures in particularly hazardous conditions. Preliminary knowledge, diagnostic methods and assessment procedures are selected and proposed for specific structural problems, in order to define proper improvement techniques to increase safety levels according to preservation and restoration criteria. Both stone and brick masonry structures, and their performance under severe horizontal (seismic) and vertical (high-compression) actions, respectively, are examined. The use of traditional, modern and innovative materials and techniques is also discussed, in the light of experimental validation, in order to calibrate analytical and numerical models for reliable analyses and simulations. Dr Valluzzi presented a lecture of this paper at the 2005 Annual Meeting in Moscow, as she was awarded the 2005 Robert L’Hermite Medal in recognition of her work. Dr. Valluzzi’s work on masonry is closely linked to the work of RILEM Technical Committee RHM ‘Repair mortars for historic masonry’ and to the extensive work on masonry carried out by the previous TC 177-MDT ‘Masonry durability and on-site testing’. Her work is exceptional in that she is able to integrate a deep understanding of masonry structures with sophisticated analytic techniques in order to develop practical engineering solutions for their repairs.This combination of skills is, unfortunately, all too rare. Her work should lead to the more effective restoration and repair of the many historic masonry structures throughout Europe.     

An approach to the positioning of FRP provisions in vaulted masonry structures

In the paper, one starts from a theoretical formulation aimed at analysing masonry vaults by selecting, in an inverted approach, families of load shapes that may be equilibrated by sets of admissible solutions, in order to develop an operative method for the positioning of FRP reinforcements in masonry vaulted constructions. On the basis of this premise a strategy is outlined for identifying the areas of the vault to be selected for introducing the FRP provisions. As shown in the numerical investigation, higher intensities of the stress state are then allowed by the introduction of the reinforcement and the local relaxation of some of the constraints of the problem is possible.     

An adaptive multi‐scale approach to the modelling of masonry structures

We present an adaptive multi‐scale approach for predicting the mechanical behaviour of masonry structures modelled as dynamic frictional multi‐body contact problems. In this approach, the iterative splitting of the contact problem into normal contact and frictional contact is combined with a semismooth Newton/primal‐dual active‐set procedure to calculate deformations and openings in the model structures. This algorithm is then coupled with a novel adaptive multi‐scale technique involving a macroscopic scale, which is the size of the masonry structure, and a mesoscopic scale, which is the size of the constituents (bricks, stone‐blocks), to predict appearance of dislocations and stress distribution in large‐scale masonry structures. Comparisons of the numerical results with data from experimental tests and from practical observations illustrate the predictive capability of the multi‐scale algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

Fracture mechanics in the characterisation of brick masonry structures

The analysis of the mechanical behaviour of masonry structures is based on the assumption that this material does not withstand tension. In this field many researchers are studying how to refine analytical and experimental procedures to obtain a more accurate correspondence between the real behaviour and the simulated one. However, this hypothesis cannot explain the masonry strength with respect to dynamic and seismic load conditions, which cause tensile stresses and dilating strains in masonry structures. The aim of this work is to give a complete set of experimental results in order to determine the mechanical properties of brick masonry. In particular, an extensive experimental programme was carried out to characterise the mechanical and structural behaviour of masonry composite in compression, along both the material directions, and in tension, along the horizontal mortar joint direction. Tensile properties in particular were estimated by means of four-point bending (FPB) tests owing to the lack of a standard tensile test and because bending tests are considered to be reliable indirect tensile ones and easy to carry out. The experimental results obtained using this testing procedure highlighted the behaviour of a bimodular material when subjected to tensile stresses, and these were then analysed by means of fracture mechanics theory to estimate the masonry toughness and stress intensity factor as further material characteristics.     

Contribution of theoretical and experimental results to powder-snow avalanche dynamics

A powder-snow avalanche can be considered as the flow of a turbulent buoyant volume of heavy fluid (air-snow suspension) in an ambient fluid, the air. In the dynamics of such a flow, two mechanisms must be taken into account: the air entrainment and the snow entrainment inside the avalanche. From fluid mechanics equations (mass conservation and momentum equations) formulae were obtained giving velocity and density of the avalanche as a function of the slope path, the growth rate of the avalanche and fresh snow-cover characteristics. On the other hand, laboratory simulations gave (among others) experimental results about the growth rates of buoyant clouds. From these theoretical and experimental studies, practical examples are proposed with given path profiles and snow-cover characteristics. Such examples can be generalised to any other cases.     

Compressive behaviour of a new reinforced masonry system

This paper presents the behaviour in compression of an innovative reinforced masonry system. The system is made of horizontally perforated units, having common steel bars or prefabricated trusses as horizontal reinforcement. At the wall edges or crossings, confining columns for vertical reinforcement are built with vertically perforated units. Experimental tests, aimed at obtaining basic mechanical characterisation of the construction system, were performed on single constitutive elements i.e., confining columns and masonry panels made of horizontally perforated units, and on completed reinforced masonry walls. Non-linear numerical models, interpreting stress and strain distributions, were developed on the basis of the results. In particular, this paper presents: (a) results of compression tests on columns, masonry panels, and complete reinforced masonry system; (b) comparison of walls built with two types of horizontal reinforcement; (c) outcome of numerical models; and (d) effectiveness of various design equations to evaluate the compressive strength of the system.     

Shear effect on seismic behaviour of masonry walls

Firstly, a finite element numerical model for nonlinear dynamic analysis of masonry walls is briefly presented. The model can simulate the main nonlinear effects of masonry and reinforced concrete. It is simple and intended to the engineering application. A macro model of masonry is adopted for simulation its behaviour in compression and for cracks modelling in tension. Two constitutive models are implemented to describe the shear resistance of the masonry wall: One that does not take the effect of the shear failure of masonry (Model 1), and second which takes into account shear failure of masonry (Model 2). By using the numerical model, the shear effect of masonry on the behaviour of two‐storey unreinforced and confined masonry walls exposed to harmonic base acceleration was investigated. The height to length ratio of the walls and the quality of masonry are varied. Analysis results for Model 1 and Model 2 are significantly different. Model 1 gives a significantly higher load bearing capacities of masonry. It was concluded that the shear effect of masonry significantly depends on the type of the masonry walls (unreinforced, confined), the quality of the masonry and height to length ratio of masonry walls.     

Application of petrographic examination techniques to the assessment of fire-damaged concrete and masonry structures

The number of building fires has doubled over the last 50 years. There has never been a greater need for structures to be assessed for fire damage to ensure safety and enable appropriate repairs to be planned. Fortunately, even after a severe fire, concrete and masonry structures are generally capable of being repaired rather than demolished.By allowing direct examination of microcracking and mineralogical changes, petrographic examination has become widely used to determine the depth of fire damage for reinforced concrete elements. Petrographic examination can also be applied to fire-damaged masonry structures built of materials such as stone, brick and mortar. Petrography can ensure accurate detection of damaged geomaterials, which provides cost savings during building repair and increased safety reassurance.This paper comprises a review of the role of petrography in fire damage assessments, drawing on a range of actual fire damage investigations.     

A rotation‐free shell formulation using nodal integration for static and dynamic analyses of structures

This paper proposed a rotation‐free thin shell formulation with nodal integration for elastic–static, free vibration, and explicit dynamic analyses of structures using three‐node triangular cells and linear interpolation functions. The formulation is based on the classic Kirchhoff plate theory, in which only three translational displacements are treated as the filed variables. Based on each node, the integration domains are further formed, where the generalized gradient smoothing technique and Green divergence theorem that can relax the continuity requirement for trial function are used to construct the curvature filed. With the aid of strain smoothing operation and tensor transformation rule, the smoothed strains in the integration domain can be finally expressed by constants. The principle of virtual work is then used to establish the discretized system equations. The translational boundary conditions are imposed same as the practice of standard finite element method, while the rotational boundary conditions are constrained in the process of constructing the smoothed curvature filed. To test the performance of the present formulation, several numerical examples, including both benchmark problems and practical engineering cases, are studied. The results demonstrate that the present method possesses better accuracy and higher efficiency for both static and dynamic problems. Copyright © 2015 John Wiley & Sons, Ltd.     

Contribution of industrial composite parts to fatigue behaviour simulation

The dimensioning of composite structures presents the problem of behaviour modelling. This problem comes not only from the specific nature of the involved materials, but also from the reproducibility of the process both on the series scale as well as on the specimen characterisation level, which enables determination of the modelling parameters. In the case of static dimensioning with or without damage, the reproducibility of the mechanical parameters is satisfactory overall, regardless of the implemented experimental procedure. In fatigue dimensioning, the two aspects; process influence and procedure of identification play a major role in the application of the lifetime predictive models. This research has, as a medium-term objective, to partially answer the problems raised previously. The damage model used is based on generalised standard material thermodynamics. This model, coupled with the finite element method, allows simulation of the fatigue behaviour of composite parts.     

A non-linear masonry infill macro-model to represent the global behaviour of buildings under cyclic loading

The presence of masonry infill walls in RC buildings is very common. However, and even today, in the design of new buildings and in the assessment of existing ones, these infill walls are usually considered as non-structural elements and their influence in the structural response is generally ignored. For horizontal loading, infill panels can drastically modify the response, attracting forces to parts of the structure that have not been designed to resist them. This paper presents an improved non-linear numerical simulation model for the influence of the masonry infill walls in the seismic behavior of structure. The model is implemented in the PORANL program. After the implementation and calibration of the proposed masonry model, a series of non-linear dynamic analyses of a building representative of Modern Architecture in Europe were carried out. The main objective was to investigate the behavior of this type of building, and any weakness under seismic loading. The building geometry and the dimensions of the RC elements and infill walls were set in the original project, and confirmed in the technical visits. The building under study has nine storeys and the structure is mainly composed of 12 plane frames oriented in the transversal direction. The building was analyzed with a simplified plane model, for each direction, and the existing infill panels were looked at in accordance with their dimensions and location. The earthquake action adopted in this study was simulated through three series of artificially generated earthquakes, for a medium/high seismic risk scenario in Europe.     

Experimental tests on the shear behaviour of dowels connecting concrete slabs to stone masonry walls

An experimental investigation has been conducted on the behaviour of dowels used to connect concrete slabs to stone masonry walls in order to transfer horizontal shear forces. A technique for embedding the dowels in the stone block without injection of grouting material or resin has been developed. Special experimental equipment has been designed in order to allow the execution ofin situ load tests on representative ancient buildings. Monotonic loading tests have been carried out on eight specimens with the purpose of measuring both stone block displacement and dowel deformation