On the behavior factor of masonry towers

A recently proposed numerical algorithm, for the pushover analysis of masonry towers, is here adopted for the evaluation of the behavior factor, entering the simplified seismic analysis of masonry towers, suggested in the Italian Directive for the assessment and reduction of the seismic risk of the cultural heritage. In order to consider, within a probabilistic context, the uncertainty of the mechanical and structural parameters involved, Monte Carlo method is adopted. The study indicated that the reduction factor of the seismic forces depends mainly on the acting stress over compressive resistance ratio. It is shown that the actual value proposed in the Italian Directive may be unsafe for high values of this ratio. Finally, an empirical formula based on the different Monte Carlo simulations is calibrated for the prediction of the behavior factor

Response of statically determined steel beams reinforced by CFRP plates in the elastic-plastic regime

The paper presents a simple approach to evaluate the response of statically determined steel beams reinforced by carbon fiber reinforced polymer (CFRP) plates in the elasticplastic regime. The formulation is applied to two cases: simply supported beams both with distributed and concentrated load. The proposed solution is validated by comparison with experimental data available in the literature

Mechanical characterization of anisotropic elasto-plastic materials by indentation curves only

Anisotropy, usually orthotropy, arises in structural materials, particularly metals, due to production processes like laminations and concerns primarily parameters which govern the plastic behavior. Identification of such parameters is investigated here by a novel approach with the following features: experimental data provided by indentation curves only (not by imprint geometry); indenter shape with elliptical cross-section derived from classical conical or spherical shape and optimized by sensitivity analyses; indentation test repeated in near places after indenter rotation; deterministic inverse analyses centered on discrepancy function minimization and made computationally economical by an ‘a priori’ model reduction procedure

An inverse analysis approach for the identification of the hygro-thermo-chemical model parameters of concrete

Hygro-thermo-chemical models provide useful representations of the mechanisms of moisture transport and temperature variations that take place in concrete structures and that can influence their durability and service behaviour. Several material parameters need to be specified when performing a hygro-thermo-chemical simulation. While some of these parameters can be evaluated based on the concrete mix specifications or from data reported in the literature, some other parameters are not readily available from the literature, partly because of their large variability and partly because they do not possess a precise physical meaning. In this context, this paper presents a robust inverse analysis procedure for the identification of this latter set of material parameters. The inverse analysis problem is formulated by using temperature and relative humidity profiles taking place within a concrete component as input. The proposed approach is applied to evaluate the minimum number of temperature and relative humidity measurements that are necessary to be performed for a successful identification of the sought material parameters. Representative results of an extensive sensitivity analysis are presented to gain insight into the most effective locations within the concrete component for the measurements and instants in time when these measurements should be collected. The inverse analysis procedure is then presented and validated against a set of pseudo-experimental results affected by different levels of noise, highlighting the robustness of the proposed methodology when applied with the arrangements suggested in terms of discrete relative humidity and temperature measurements and monitoring periods

Indentation and imprint mapping for the identification of interface properties in film substrate systems

reserved2Indentation tests are frequently employed at present for the identification of material parameters at different scales. An innovative inverse analysis technique, recently proposed by the Authors, combines the traditional indentation test with the mapping of the residual deformations (imprint), thus providing experimental data apt to be used to identify material parameters in film-substrate systems. In this paper, such methodology is enhanced to permit the identification of the fracture properties of the interface between a coating and its substrate once the bulk material parameters are known. In order to make the inverse problem well posed, a further set of experimental data, namely the horizontal displacement field measured on the film external surface, is considered as available experimental information. The sought material parameters are recovered through recursive calculations of the mechanical response of the film-substrate system, performed by a finite strain numerical simulation. The coating and a significant portion of the underlying bulk material are incorporated in the finite element models built up to this purpose, while delamination is accounted for through cohesive elements. The inverse analysis procedure rests on a batch, deterministic approach and conventional optimization algorithms are employed for the minimization of a suitably defined discrepancy norm. Extensive numerical computations have been performed in order to test the performance of the proposed methodology in terms of result accuracy and computational effort.mixedM. BOCCIARELLI; BOLZON GBocciarelli, Massimiliano; Bolzon, Gabriell

Indentation and imprint mapping for the identification of interface properties in film-substrate systems

Available experimental information deduced from indentation, performed on the external surface of a film-substrate system, is combined with the simulation of the test and the material parameters, entering the numerical model, are estimated by minimizing the difference between experimental and their computed counterparts

Indentation and imprint mapping method for identification of residual stresses

Indentation tests are at present frequently employed for the identification of material parameters. A recently proposed technique combines the traditional indentation test with the mapping of residual deformations (imprint), thus providing experimental data which are used to identify isotropic and anisotropic material parameters in more accurate fashion and in larger number. In this paper, such new methodology is employed for the identification of bi-dimensional states of stress, in particular residual self-stresses. Axialsymmetric indenters are referred to. While the indentation curve is almost insensitive to the direction of pre-existing bi-dimensional stress states, the mapped imprint (which, generally, does not exhibit axialsymmetry because of the presence of the residual stress state) directly reflects all features of such stresses and turn out to be crucial for their identification. Three-dimensional finite element simulations are performed in finite-strain regime. Inverse analysis is carried out by a batch, deterministic approach, using conventional optimization algorithms for the minimization of a discrepancy norm between measured and computed quantities. Numerical examples are discussed apt to test the performance of the proposed methodology in terms of result accuracy and computing effort. The present method is validated also by means of applications to truly experimental data available in literature

Identification of the hygro-thermo-chemical-mechanical model parameters of concrete through inverse analysis

A wide range of parameters is required in input when applying hygro-thermo-chemical-mechanical models to concrete components with the aim of determining the variations over time of temperature, relative humidity and shrinkage induced deformations. While a sub-set of these material parameters can be evaluated on the basis of the concrete mix specifications or from literature data, this paper presents a robust inverse analysis procedure for the identification of the remaining sub-set of parameters that are characterised by a large variability and, in some cases, do not have a precise physical meaning and are not amenable to a direct measurement. The particularity of this paper is to propose different strategies for the characterisation of these material parameters that account for the presence of different exposure conditions, as these affect the outcomes and requirements of the parameter identification procedure. After introducing the adopted hygro-thermo-chemical-mechanical model, representative results of an extensive sensitivity analysis are presented in the first part of the paper to give insight into most effective number, location and duration of measurements to be used in input of the inverse analysis. The inverse analysis procedure is then presented and applied to a number of selected scenarios to highlight its robustness considering different boundary conditions in terms of external temperature and relative humidity surrounding the concrete. The ability to characterise these parameters will support a wider use of these hygro-thermo-chemical-mechanical models, especially for those applications in which humidity and temperature profiles significantly influence the structural response, for example when predicting curling in industrial pavements and non-uniform shrinkage profiles in composite steel-concrete slabs

A numerical procedure for the pushover analysis of masonry towers

In this paper, a numerical approach for the pushover analysis of masonry towers, having hollow arbitrary sections, is proposed. Masonry is considered a nonlinear softening material in compression and brittle in tension. The tower, modeled in the framework of the Euler-Bernoulli beam theory, is subjected to a predefined load distribution, but the problem is formulated as a displacement controlled analysis in order to follow the post peak descending branch of the structural response. Nonlinear geometric effects and nonlinear constraints (the latter due to surrounding buildings) are also considered. Benchmarking pushover analyses are performed with the commercial code Abaqus in relation to a real case (the Gabbia Tower in Mantua), which proved the accuracy and reliability of the results obtained with the present formulation and the noteworthy reduction of computing time

Elasto-plastic analysis of steel beams reinforced by carbon fibre reinforced polymer strips

This paper investigates the bonding between adherents in the reinforcement of steel structures by using FRP materials. The interface behaviour between the steel and the FRP strips and in particular the interaction between the plastic deformation and the debonding process is investigated. This paper first illustrates a numerical procedure to evaluate the bending moment and shear force diagram through the application of the well-known principle of virtual work. The stress migration due to plastic deformation of statically undetermined steel structures is also outlined. A method based on cross-sectional equilibrium and strain compatibility is then proposed to predict the FRP axial stress and interface shear stress of the steel beam reinforced by FRP materials. Finally, the adhesive layer shear stress concentration in critical sections and failure conditions are evaluated through numerical examples