Nonlinear Analysis Of Concrete Structures Research Articles

The influence of different safety formats proposed by Eurocode 2 on the deformability and design of slender structural elements

This paper provides new information about the differences between the two methodologies proposed by Eurocode 2 (EC2) for the nonlinear analysis of concrete structures. Proceeding from the evaluation of the second-order effects on a structural element, the results of a parametric study on isolated columns are compared, using a nonlinear analysis program especially developed for this kind of structure. Subsequently, the outcomes from the application of each safety format are contrasted in analysing the lateral deformability of the structure. In addition, an ultimate limit states design of the required cross-section mechanical reinforcement for each safety format leads to some comments about the influence of these procedures on structural design and assessment.

Tension Stiffening Model for Concrete Beams Reinforced with Steel and FRP Bars

Cracking is an important aspect of concrete behavior that considerably affects the overall response of concrete structures. The initiation of cracks is governed by concrete tensile properties. The propagation of cracks is a complicated phenomenon that plays a significant role in the nonlinear analysis of concrete structures. The cracking process in tension starts at a relatively low tensile strain, causing plain concrete to exhibit a gradual softening behavior. This softening is augmented by the tension stiffening of reinforcing bars. The smeared crack approach is typically combined with nonlinear finite-element analysis to generate an accurate global response. The key to such representative accurate predictions relates to material parameters, especially those of tension stiffening effects. For a complete understanding of the crack development process, tests should be performed on concrete specimens at various load histories. However, due to the difficulty of testing concrete in uniaxial tension, only limited and often conflicting results are available. The present work develops an inverse approach combining nonlinear numerical analysis and global experimental response to develop the tension stiffening model parameters needed to simulate homogenized concrete behavior in tension. The results of the study provide good model parameters to use in the case of concrete beams reinforced with steel and fiber-reinforced polymer (FRP) bars.

Hybrid-mixed stress model for the nonlinear analysis of concrete structures

This communication reports on the nonlinear analysis of 2D concrete structures using an hybrid-mixed stress formulation and continuum damage mechanics. The finite element model adopted is based on the direct and independent approximation of three fields: the stress and displacement fields in the domain of each element and the displacement field on the static boundary. The nonlinear behavior of the material is modelled using both a local and nonlocal isotropic damage model. Two numerical examples are presented to illustrate and validate the use of such numerical technique.

Size Effect Analysis for Pullout Strength under Various Boundary Conditions

One of the goals of this research is to apply nonlinear fracture mechanics to design problems encountered by the engineering society. Nonlinear fracture mechanics makes it possible to study the size effect with respect to the pullout cone failure of headed anchors embedded in concrete under various boundary conditions. This investigation shows that the fictitious crack approach can be extended with two orthogonal rod elements to become a new technique that can successfully predict the size effect on the pullout tests. In this study the numerical investigation that describes the behavior of headed anchors under tension loading has been carried out by a computer simulation using our original program ANACS (Advanced Nonlinear Analysis of Concrete Structures). To judge the validity of the results, the numerical results were compared with Eligehausen and Sawade’s empirical equation and test results of a report by the Reunion Internationale des Laboratoire d’Essais et de Recherches sur les Materiaux et les Constructions.

Numerical evaluation of the rotating crack model

The paper discusses typical fracture mechanics problems which have been analyzed in order to evaluate the performance of the rotating crack model. The outcome indicates that the model is a promising tool for nonlinear analysis of concrete structures. For model-I cracking, the model is capable of simulating the whole range of size covered by limit analysis and linear elastic fracture mechanics, but when a slant mesh is used, a mesh bias is observed. For mixed-mode cracking, the model is capable of predicting the ultimate load for small concrete structures; the results of simulations for large concrete structures show a good coincidence with linear elastic fracture mechanics solutions.

Detecting the size effect in concrete beams using nonlinear fracture mechanics

This paper shows that, the size effect in flexure and shear strength for different concrete and reinforced concrete beam sizes subjected to concentrated and uniformly distributed loads can be successfully predicted on the basis of nonlinear fracture mechanics. The analysis was carried out by a computer simulation using the program ANACS (advanced nonlinear analysis of concrete structures), which was originally developed by the authors. In this investigation, the fictitious crack model was adopted with two orthogonal rod elements which involves the nonlinear fracture mechanics through their constitutive model to simulate the discrete crack path and represent the localized crack zone. By combining the arc-length calculation technique with the fictitious crack model, the postpeak behaviour can be predicted well even for snapback instability.

SIZE EFFECT ANALYSIS FOR PULL-OUT STRENGTH BY FICTITIOUS CRACK MODEL

This paper discusses the size effect with respect to the pull-out cone failures of headed anchors embedded in concrete. In this investigation a newly developed model based on fictitious crack approach with two orthogonal rod elements has been employed. In the following the numerical investigation to describe the behavior of headed anchors under tension loading has been carried out by a computer simulation using our original program ANACS (Advanced Nonlinear Analysis of Concrete Structures). To judge the validity of the results, the behavior of the headed anchor with a cone failure, in particular the crack propagation in the concrete predicted by numerical analysis, will be explained.

SIZE EFFECT ANALYSIS FOR FLEXURE AND SHEAR STRENGTH OF CONCRETE BEAMS UNDER VARIOUS LOADING CONDITIONS BY FICTITIOUS CRACK MODEL

The behavior of concrete and reinforced concrete structures is significantly affected by their sizes. The size effect on flexure and shear strengths of concrete beams has been already confirmed experimentally. This paper presents some results of the size effect on flexure and shear failures for different concrete and reinforced concrete beam sizes subjected to concentrated and uniformly distributed loads. The analysis was carried out by a computer simulation using the program ANACS (Advanced Nonlinear Analysis of Concrete Structures). Using the arc-length method the post peak behavior can be predicted well even for snap back instability.

Constitutive modeling of concrete using a new failure criterion

A nonlinear hypoelastic constitutive relation has been proposed for the analysis of plane and axisymmetric reinforced concrete structures. Equivalent uniaxial strain concept introduced by Darwin and Pecknold, and the stress-strain curve for concrete proposed by Alexander have been used. A new ultimate strength surface for concrete is proposed. The back propagation algorithm of Rumelhart et al.[1] [D. E. Rumelhart, G. E. Hinton and R. J. Williams, Learning representations by back-propagation errors. Nature 323, 533–536 (1986)] is used to train the artificial neural network for experimental results of concrete and is used to describe the ultimate surface. Thus, a new failure criterion for concrete is proposed. The proposed constitutive model is implemented in the user friendly finite element package “FENLACS” —(Finite Element NonLinear Analysis of Concrete Structures). The capability of the model to analyze a wide variety of structural engineering problems has been observed. The user friendly features of FENLACS to study the nonlinear load deflection behavior, crack pattern and principal stress contours have also been illustrated.

Modelling of prestress in non-linear analysis of concrete structures

This paper describes a technique for modelling the structural action of prestressing tendons in finite element based models developed for the non-linear analysis and design of prestressed concrete structures. Prestressing steel is simulated by 1-D curved elements embedded in the finite elements employed to discretize the concrete structure. The contribution of bonded or unbonded prestressing tendons to the serviceability behaviour and to the ultimate strength capacity of prestressed structures is adequately quantified and accounted for. The numerical procedures adopted to model the prestressing operation and the associated prestressing losses are discussed. The formulation is developed to be incorporated with curved thick shell elements and the applicability of the computational code is appraised by the results of two numerical examples.

Engineering Approach to Nonlinear Analysis of Concrete Structures

The objective of this paper is to explore the potential of the lumped‐plasticity program STRUPL‐1C and to illustrate its use as a practical engineering tool for the nonlinear analysis of concrete structures. This result is achieved through the development of a moment‐rotation constitutive law that uses realistic material laws and is valid for any reinforced, prestressed and partially prestressed concrete planar frame at all behavioral states along the loading history. The effects of the main parameters that influence the moment‐rotation relationship are investigated and discussed. Finally, the developed constitutive law is applied to the nonlinear analysis of a few reinforced and prestressed concrete continuous beams. Comparison to both experimental tests and more‐complex nonlinear analysis techniques proves the accuracy of solutions obtained by the STRUPL‐1C computer program. The examples reported also prove that the proposed approach enables considerable simplification of the structural model required for a historical nonlinear analysis of concrete structures and demonstrate the high potential of the approach with respect to its use in engineering practice.

Finite element nonlinear analysis of concrete structures using a “plastic-damage model”

In this paper a plastic damage model for nonlinear finite element analysis of concrete is presented. The model is based on standard plasticity theory for frictional materials. Details of the expressions of a new yield function proposed and of the evolution laws of the model parameters are given. The model allows to include elastic and plastic stiffness degradation effects. This is also discussed in the paper together with the problem of mesh objectivity, and the a posteriori determination of cracks. Finally, one example of application which shows the accuracy of the model is also given.

Nonlinear analysis of concrete structures

Solution capabilities for two- and three-dimensional nonlinear finite element analysis of concrete structures are presented. The concrete material is modeled including the triaxial nonlinear stress-strain behavior, tensile cracking, tension-stiffening, compression crushing and strain-softening. The results of various sample analyses are given to demonstrate the constitutive model and the solution strategies. These analyses include the response predictions of a test beam and of small scale models of two reactor vessels.

Nonlinear analysis system for concrete structures: STRUPL-1C

Some features and capabilities of the computer program STRUPL-1C for the nonlinear analysis of concrete structures are presented. STRUPL-1C extends the application of the general computer system for the analysis of various STRUctural PLasticity problems (STRUPL-1) to prestressed concrete. As its parent-program, STRUPL-1C uses mathematical programming algorithms for solving discretized models of structural plasticity problems. The system capabilities are illustrated by three example structures, including partially and fully prestressed continuous beams.

The Newton-Raphson method used in the non-linear analysis of concrete structures

The finite element method has been used to analyse reinforced concrete structures from zero load up to collapse. Modified Newton-Raphson method has been used as the basic solution procedure. In this paper, the performance of various accelerators are discussed and compared with each other. The numerical instabilities which have been encountered previously [1, 2 and 30when using the modified Newton-Raphson method are discussed. Techniques to avoid such instabilities are proposed and demonstrated in an example.

Nonlinear analysis of concrete structures

A computer program is developed to determine the response of reinforced and prestressed concrete structures subjected to monotonic or cycling loading. The nonlinear stress–strain relationship of concrete and steel is accounted for by applying the load in increments and performing a series of iterations. The structure is treated as an assemblage of thin plate elements subjected to in-plane forces and bending. In the calculation of the structure stiffness, each element is assumed to be composed of a number of layers and the stiffness is allowed to vary over the area of the element and from one layer to the other according to the associated stress.The program employs an efficient finite element that makes it possible to use a relatively small number of elements. The reinforcements are idealized either by smearing a mesh or bars into a steel layer or, with heavy concentrated reinforcement or a prestress tendon, each reinforcing element is accounted for separately.The efficiency of the proposed model is tested by applying the computer program to three structures employing a very small number of elements in their idealization. The finite element idealizations are shown and the results of the analyses are compared with published experimental work.

On three-dimensional nonlinear analysis of concrete structures

Solution capabilities for three-dimensional geometric and material nonlinear finite element analysis of concrete structures are presented. The concrete material is modeled including triaxial nonlinear stress-strain behavior, tensile cracking, compression crushing and strain-softening. The objective in this work was the development of a practical nonlinear concrete analysis capability. The material model can also be employed to represent some rock materials. The results of various sample analyses are given, in which the stability and accuracy of the finite element representations have been studied.

A general nonlinear analysis of concrete structures and comparison with frame tests

A computational technique is described for the general nonlinear analysis of large planar frames under static loading. The analysis accommodates both material and geometric sources of nonlinearity in a highly stable numerical procedure. For material behavior the moment-thrust-curvature relationships are reduced to polynomials made to represent common structural members. The nonlinear influence of axial shortening and P - Δ effects from displaced joints are accommodated by the analysis. Beam-column effects that magnify moments by the influence of axial force acting through deformed members can be approximated by introducing nodal points (or joints) at points of maximum deformation between the ends of members. Accuracy of the analytic procedure is demonstrated by comparing computed results with eight reinforced concrete frames tested at the University of Texas at Austin.