• Structural Engineering and Mechanics
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• v.5 no.6
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• pp.729-741
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• 1997

Cracked reinforced concrete in compression has been observed to exhibit lower strength and stiffness than uniaxially compressed concrete. The so-called compression softening effect responsible is thought to be related to the degree of transverse cracking and straining present. It significantly affects the strength, ductility and load-deformation response of a concrete element. A number of experimental investigations have been undertaken to determine the degree of softening that occurs, and the factors that affect it. At the same time, a number of diverse analytical models have been proposed by various this behavior. In this paper, the softened truss model thoery for low-rise structural shearwalls is employed using the principle of the stress and strain transformations. Using this theory the softening parameters for the concrete struts proposed by Hsu and Belarbi as well as by Vecchio and Collins are examined by 51 test shearwalls available in literature. It is found that the experimental shear strengths and ductilities of the walls under static loads are, in average, very close to the theoretical values; however, the experiment shear strengths and ductilities of the walls under dynamic loads with a low (0.2 Hz) frequency are generally less than the theoretical values.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1995.10a
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• pp.185-193
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• 1995

The softening behaviors of concrete have been the object of numerous experimental and numerical studies, because the load carrying capacity of cracked concrete structure is not zero. Numerical studies are devoted to the investigation of three-dimensional softening behaviors of concrete on the basis of a viscoplastic theory, which may be able to represent the effects of plasticity and also of rheology. In order to properly describe material behaviors corresponding to different stress levels, two surfaces in stress space are adopted; one is a yield surface, and the other is a failure or bounding surface. When a stress path reaches the failure surface, it is considered that the softening behaviors are initiated as micro-cracks coalesce and are simulated by assuming that the actual strain increments in the post-peak region are less than the equivalent viscoplastic strain increment. The experimental studies and the finite element analyses have been carried out under the displacement control. Numerically simulated results indicate that the model is able to predict the essential characteristics of concrete behaviors such as the non-linearity, stiffness degradation, different behaviors in tension and compression, and specially dilatation under uniaxial compression.

• Structural Engineering and Mechanics
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• v.67 no.3
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• pp.255-265
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• 2018

The prestress force effect on the fundamental frequency and deflection shape of Prestressed Concrete I (PCI) beams was studied in this paper. Currently, due to the conflicts among existing theories, the analytical solution for properly considering the structural behavior of these prestressed members is not clear. A series of experiments were conducted on a large-scale PCI beam of high strength concrete with an eccentric straight unbonded tendon. Specifically, the simply supported PCI beam was subjected to free vibration and three-point bending tests with different prestress forces. Subsequently, the experimental data were compared with analytical results based on the Euler-Bernoulli beam theory. It was proved that the fundamental frequency of PCI beams is unaffected by the increasing applied prestress force, if the variation of the initial elastic modulus of concrete with time is considered. Vice versa, the relationship between the deflection shape and prestress force is well described by the magnification factor formula of the compression-softening theory assuming the secant elastic modulus.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.308-313
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• 2003

High temperature deformation and softening behavior of SAF 2507 super duplex stainless steel (SDSS) has been investigated in connection with an FEM analysis of hot forging process. Flow curves at various strain rates and temperatures were determined first from compression tests, and the kinetics of dynamic recrystallization were also formulated through the analysis of load relaxation test results. Using the dynamic materials theory proposed by Prasad, the deformation behavior was effectively determined for various conditions. Constitutive relations and recrystallization kinetics formulated from the test results were then implemented in a commercial FEM code. The forming load as well as the distribution of recrystallized volume fraction after forging was successfully predicted by means of the flow stress compensation formulated upon the volume fraction of recrystallization and adiabatic heating.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.2
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• pp.101-111
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• 2021

Two different types of shear-friction tests were classified by external loadings and referred to as a push-off and a pull-off test. In a pull-off test, a tension force is applied in the transverse direction of the test specimen to produce a shear stress at the shear plane. This paper presents a method to evaluate shear transfer strengths of uncracked pull-off specimens. The method is based on the compression field theory and different constitutive laws are applied in some ways to gain accurate shear strengths considering softening effects of concrete struts based on Modified Compression Field Theory (MCFT) and Softened Truss Model (STM). The validity of the proposed method is examined by applying to some selected test specimens in literatures and results are compared with the predicted values. A general agreement is observed between predicted and measured values at ultimate loading stages in initially uncracked pull-off test specimens. A shear strength evaluation formula considering the effective compressive strength of a concrete strut was proposed, and the applicability of the proposed formula was verified by comparing with the experimental results in the literature.

• Magazine of the Korea Concrete Institute
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• v.8 no.3
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• pp.187-195
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• 1996

A finite element formulation based on the CFT(Compression Field Theory), considering the effect of compression softening in cracked concrete, and macro-scopic and rotating crack models etc., was presented for the nonlinear behaviour of structural concrete. Considering the computational efficency and the ability of modelling the post-ultimate behaviour as major concerns, the Incremental displacement solution algorithm involving initial material stiffnesses and the relaxation procedure for fast convergence was adopted and formulated in a type of 8-noded quadrilateral isoparametric elements. The analysis program NASCOM(Non1inear Analysis of Structural Concrete by FEM : Monotonic Loading) developed in this way enables the predictions of strength and deformation capacities in a full range, crack patterns and their corresponding widths, and yield extents of reinforcement. As the verification purpose of NASCOM, the predictions were made for Bhide's Panel(PB21) and Leonhardt's deep beam tests. The predicted results shows somewhat stiff behaviour for the panel test, and vice versa for deep beam tests. More refining process would be necessary hereafter in terms of more accurately simulating the effects of tension-stiffening and compression softening in concrete.

• Computers and Concrete
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• v.20 no.6
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• pp.689-704
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• 2017

The paper presents experimental and numerical investigations of prefabricated composite structural building reinforced concrete slabs with the insulating material for a residential building construction. The building slabs were composed of concrete and expanded polystyrene. In experiments, the slabs in the full-scale 1:1 were subjected to vertical concentrated loads and failed along a diagonal shear crack. The experiments were numerically evaluated using the finite element method based on two different constitutive continuum models for concrete. First, an elasto-plastic model with the Drucker-Prager criterion defined in compression and with the Rankine criterion defined in tension was used. Second, a coupled elasto-plastic-damage formulation based on the strain equivalence hypothesis was used. In order to describe strain localization in concrete, both models were enhanced in the softening regime by a characteristic length of micro-structure by means of a non-local theory. Attention was paid to the formation of critical diagonal shear crack which was a failure precursor.

• Magazine of the Korea Concrete Institute
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• v.9 no.2
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• pp.133-144
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• 1997

Concrete plasticity models fol the analysis of reinforced concrete members in plane stress are studied. The proposed plasticity model for reinforced concrete provides a unified approach combining plasticity theory and damage models. It addresses strength mhancement under rnultiaxial compression. and tensile cracking damage. The model uses multiple failure criteria for compressive crushing and tensile cracking. For tensile cracking behavior. rotating-crack and fixed-crack plasticity models are compared. As crushing failure criterion, the Drucker-Prager and the von Mises models are used for comparison. The model uses now and existing damnge models fbr tension softening, tension stiffening. and compression softening dup to tensilt. cracking. Finite element analyses using the unified method are compatxd with existing rxpcrimcntal r.esults. To vei.ify the proposcd crushing and cracking plasticity models, the experiments have load capacities govc11.nc.d either by compressive crushing of'concrete or by yi~lding of' reinforcing steel.

• Computational Structural Engineering
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• v.9 no.1
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• pp.151-159
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• 1996

A finite element formulation based on the CFT(Compression Field Theory) concept such as the effect of compression softening in cracked concrete, and macroscopic and rotating crack models etc. was presented for the nonlinear behaviour of structural concrete. In this category, tangential or secant material stiffnesses for cracked concrete were also defined and discussed in view of the iterative solution schemes for nonlinear equations. Considering the computational efficiency and the ability of modelling the post-ultimate behaviour as major concerns, the incremental displacement solution algorithm involving initial material stiffnesses and the relaxation procedure for fast convergence was adopted and formulated in a type of 8-noded quadrilateral isoparametric elements. The analysis program NASCOM(Nonlinear Analysis of structrual Concrete by FEM : Monotonic Loading) developed baed on the CFT constitutive relationships and the incremetal solution strategy described enables the predictions of strength and deformation capacities in a full range. crack patterns and their corresponding widths, and yield extents of reinforcement. As the verfication purpose of NASCOM, the prediction of Cervenka's panel test results including the load resistance and the deformation history was made. A limited number of predictions indicate a good correlation in a general sense.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.295-303
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• 2018

The semi-analytical method to study the nonlinear dynamic behavior of simply supported spiral stiffened functionally graded (FG) cylindrical shells subjected to an axial compression is presented. The FG shell is surrounded by damping and linear/nonlinear elastic foundation. The proposed linear model is based on the two-parameter elastic foundation (Winkler and Pasternak). A three-parameter elastic foundation with hardening/softening cubic nonlinearity is used for nonlinear model. The material properties of the shell and stiffeners are assumed to be FG. Based on the classical plate theory of shells and von $K{\acute{a}}rm{\acute{a}}n$ nonlinear equations, smeared stiffeners technique and Galerkin method, this paper solves the nonlinear vibration problem. The fourth order Runge-Kutta method is used to find the nonlinear dynamic responses. Results are given to consider effects of spiral stiffeners with various angles, elastic foundation and damping coefficients on the nonlinear dynamic response of spiral stiffened simply supported FG cylindrical shells.