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Plane strain constitutive behaviour of von Mises and isotropic Hoffman materials is examined using single element tests. Two kinds of tests are conducted – (a) prescribed displacement tests; and (b) tests with a mixture of displacements and boundary tractions prescribed. While (a) are used to understand the manner of stress traversal on the yield surface in principal stress space, (b) are employed to study the load displacement response and the possibility of ensuing localization. Associated plasticity is assumed throughout. The tests are conducted using perfect and strain softening plasticity. It is found that for the von Mises criterion limited exact solutions can be evolved even under softening (or hardening) conditions. For isotropic Hoffman materials the nature of the stress traversal, load deflection response and the satisfaction of the localization conditions are strongly influenced by the ratio and difference of uniaxial yield strengths, in tension and compression, as well as by the softening parameters.

There are a number of different approaches for calculating creep-fatigue (CF) damage for design, such as the French nuclear code RCC-MRx, the American ASME III NH and the British R5 assessment code. To acquire estimates for the CF damage, that are not overly conservative, both the cyclic material softening/hardening and the potential changes in relaxation behavior have to be considered. The data presented here and models are an initial glimpse of the ongoing European FP7 project MATISSE effort to model the softening and relaxation behavior of Grade 91 steel under CF loading. The resulting models are used for calculating the relaxed stress at arbitrary location in the material cyclic softening curve. The initial test results show that softening of the material is not always detrimental. The initial model development and the pre-assessment of the MATISSE data show that the relaxed stress can be robustly predicted with hold time, strain range and the cyclic life fraction as the main input parameters. The paper aims to discuss these issues.

Engineering models have been developed for predicting cyclic softening and relaxation for Gr. 91 steel at 550 and 600°C.

A simple engineering model can adequately predict the low cycle fatigue (LCF) and CF softening rates of Gr. 91 steel. Also a simple relaxation model was successfully defined for predicting relaxed stress of both virgin and cyclically softened material.

The data are not yet complete and the models will be updated when the complete set of data in the MATISSE project is available.

The models described can be used for predicting P91 material softening in an arbitrary location (n/N_f0) of the LCF and CF cyclic life. Also the relaxed stress in the softened material can be estimated.

The models are simple in nature but are able to estimate both material softening and relaxation in arbitrary location of the softening curve. This is the first time the Wilshire methodology has been applied on cyclic relaxation data.

The calculation of the shear capacity of inclined section for prestressed reinforced concrete beams is an important topic in the design of concrete members. The purpose of this paper, based on the truss-arch model, is to analyze the shear mechanism in prestressed reinforced concrete beams and establish the calculation formula for shear capacity.

Considering the effect of the prestressed reinforcement axial force on the angle of the diagonal struts and regression coefficient of softening cocalculation of shear capacity is established. According to the shape of the cracks of prestressed reinforced concrete beams under shear compression failure, the tie-arch model for the calculation of shear capacity is established. Shear-failure-test beam results are collected to verify the established formula for shear bearing capacity.

Through theoretical analysis and experimental beam verification, it is confirmed in this study that the truss-arch model can be used to analyze the shear mechanism of prestressed reinforced concrete members accurately. The calculation formula for the angle of the diagonal struts chosen by considering the effect of prestress is accurate. The relationship between the softening coefficient of concrete and strength of concrete that is established is correct. Considering the effect of the destruction of beam shear plasticity of the concrete on the surface crack shape, the tie-arch model, which is established where the arch axis is parabolic, is applicable.

The formula for shear capacity of prestressed reinforced concrete beams based on this theoretical model can guarantee the effectiveness of the calculation results when the structural properties vary significantly. Engineers can calculate the parameters of prestressed reinforced concrete beams by using the shear capacity calculation formula proposed in this paper.

The main aim of this paper is to present a three‐dimensional numerical material model for concrete which combines plasticity with a classical orthotropic smeared crack formulation. A further aim is to raise a discussion leading to the creation of a comprehensive computer programme for the analyses of reinforced and prestressed concrete structures.

A new numerical material model for concrete is developed and main theoretical explanations are given to aid in understanding the algorithm. The model is based on Mohr‐Coulomb criterion for dominant compression and Rankine criterion for dominant tension influences. A multi‐surface presentation of the model is implemented which permits the rapid convergence of the mathematical procedure. The model includes associated and non‐associated flow rules, strain hardening and softening where the development of the plastic strain was described by the function of cohesion.

Provides information about developing a new numerical material model for concrete.

The model is implemented into the computer programme PRECON3D for the three‐dimensional nonlinear analysis of the reinforced and prestressed concrete structures.

In this model, the very complex behaviour of concrete is defined by elementary material parameters which can be obtained by a standard uniaxial test. The presented model enables a very detailed and precise analysis of reinforced and prestressed concrete structures until crushing with a high accuracy, so that the expensive experimental tests can be reduced. The paper could be very valuable to researchers in this field as a benchmark for their analyses.

In this paper, we examine the influence of the third invariant in computational plasticity. For this purpose we consider the extended Leon model, an elasto‐plastic model for concrete materials which accounts for the difference of shear strength in triaxial compression and triaxial extension. Consequently, the deviatoric trace of the loading surface is no longer circular like in von Mises and Drucker‐Prager plasticity. In the limit it approaches the triangular shape of the Rankine condition of maximum direct stress. Thereby, elliptic functions describe the out‐of‐roundness of the circular trace in terms of C¹‐continuous functions of the Lode angle. The algorithmic aspects of the third invariant considerably complicate the computational implementation since the radial return method of J₂‐plasticity does no longer maintain normality leading to loss of deviatoric associativity. The paper will focus on the computational issues near the three regions with high curvature at the compressive meridians with special attention on the lack of convergence of the plastic return algorithm and its slow rate of convergence in these regions. The algorithmic discussion at the constitutive level will be augmented by the axial plane‐strain compression test in order to illustrate the effect of the third invariant at the structural level of finite element analysis.

Some of the basic mechanical characteristics such as tensile, bending, shear, compression, and surface properties of cotton knitted fabrics after a durable flame‐retardant finishing, were studied by the objective‐evaluation method developed by Kawabata and Niva using the KES‐F system. In addition, properties such as bursting strength, drape and sewability were studied in order to further explore the influence of this treatment on the fabrics. All treated fabrics were flame‐retardant but their mechanical properties showed changes as a result of the above finishing. More specifically, a significant reduction in the bending and shear properties was recorded, which suggests that the flame‐retardant finishing primarily affects the above characteristics.

This paper aims to investigate with strain-rate controlled uniaxial cyclic compression tests the softening behavior of concrete and its elastic stiffness degradation with increasing plastic straining.

Such tests at ambient temperature show that concrete exhibits the phenomenon of elastic stiffness degradation, which can be captured by damage-plasticity models.

The experimentally derived evolutions of the elastic stiffness with plastic strain confirm the suitability of the damage-plasticity modeling concept for concrete in compression at elevated temperatures and provide novel calibration data.

Temperature-dependent concrete models implementing this modeling concept are often used presently in structural fire engineering, despite the lack of experiment-based validation data.

A nonlinear finite element (FE) beam-column model for the analysis of reinforced concrete (RC) frames with due account of shear is presented in this paper. The model is an expansion of the traditional flexural fibre beam formulations to cases where multiaxial behaviour exists, being an alternative to plane and solid FE models for the nonlinear analysis of entire frame structures. The paper aims to discuss these issues.

Shear is taken into account at different levels of the numerical model: at the material level RC is simulated through a smeared cracked approach with rotating cracks; at the fibre level, an iterative procedure guarantees equilibrium between concrete and transversal reinforcement, allowing to compute the biaxial stress-strain state of each fibre; at the section level, a uniform shear stress pattern is assumed in order to estimate the internal shear stress-strain distribution; and at the element level, the Timoshenko beam theory takes into account an average rotation due to shear.

The proposed model is validated through experimental tests available in the literature, as well as through an experimental campaign carried out by the authors. The results on the response of RC elements critical to shear include displacements, strains and crack patterns and show the capabilities of the model to efficiently deal with shear effects in beam elements.

A formulation for the nonlinear shear-bending interaction based on the fixed stress approach is implemented in a fibre beam model. Shear effects are accurately accounted during all the nonlinear path of the structure in a computationally efficient manner.

To contribute for a reliable estimation of the compressive strength of unreinforced masonry from the properties of the constituents (units and mortar).

Sophisticated non‐linear continuum models, based on damage, plasticity, cracking or other formulation, are today standard in several finite element programs. The adequacy of such models to provide reliable estimates of masonry compressive strength, from the properties of the constituents, remains unresolved. The authors have shown recently that continuum models might significantly overestimate the prediction of the compressive strength. Hence, an alternative phenomenological approach developed in a discrete framework is proposed, based on attributing to masonry components a fictitious micro‐structure composed of linear elastic particles separated by non‐linear interface elements. The model is discussed in detail and a comparison with experimental results and numerical results using a standard continuum model is provided.

Clear advantages in terms of compressive strength and peak strain prediction were found using the particle model when compared with standard continuum models. Moreover, compressive and tensile strength values provided by the model were found to be particle size‐ and particle distortion‐independent for practical purposes. It is also noted that size‐dependent responses were obtained and that shear parameters rather than tensile parameters were found to play a major role at the meso‐level of the phenomenological model.

This paper provides further insight into the compressive behaviour of quasi‐brittle materials, with an emphasis on the strength prediction of masonry composites. Reliable prediction of masonry strength is of great use in the civil engineering field, allowing one to reduce experimental testing in expensive wallets and to avoid the usage of conservative empirical formulae.

The purpose of this paper is to contribute to the solution of the fatigue damage problem of reinforced concrete frames in bending.

The problem of fatigue damage is formulated based on the rheological–dynamical analogy, including a scalar damage variable to address the reduction of stiffness in strain softening. The modal analysis is used by the finite element method for the determination of modal parameters and resonance stability of the selected frame cross-section. The objectivity of the presented method is verified by numerical examples, predicting the ductility in bending of the frame whose basic mechanical properties were obtained by non-destructive testing systems.

The modal analysis in the frame of the finite element method is suitable for the determination of modal parameters and resonance stability of the selected frame cross-section. It is recommended that the modulus of elasticity be determined by non-destructive methods, e.g. from the acoustic response.

The paper presents a novel method of solving the ductility in bending taking into account both the creep coefficient and the aging coefficient. The rheological-dynamical analogy (RDA) method uses the resonant method to find material properties. The characterization of the structural damping via the damping ratio is original and effective.