Plain Concrete Structures Research Articles

Shaking table model tests of concrete containment vessel (CCV) for CPR1000 nuclear power plant

Containment vessel of nuclear power plant is the last barrier to prevent the leakage of radioactive materials, so the seismic performance is of high importance. In order to investigate the seismic performance of the CPR1000 prestressed concrete containment vessel (PCCV) structure under design and beyond-design basis earthquake, a 1/20 scale concrete containment vessel (CCV) model was designed and constructed on the shaking table based on the similitude requirements from the Buckingham's π-Theorem. The horizontal and vertical earthquake waves generated from RG1.60 spectrum were selected as the input earthquake waves in the shaking table model test, and the earthquake waves with peak ground acceleration (PGA) 0.2g, 0.3g, 0.4g, 0.5g, 0.7g, 0.9g and 1.2g respectively were loaded step by step until the macroscopic failure occurred in the model containment vessel. The dynamic responses of the model CCV were obtained from the acceleration sensors and resistance strain gages. The model test results showed that the maximum acceleration magnification factor of the model CCV was 1.974 with PGA of 0.2g, which indicated that the CCV had a good seismic-resistant behavior under 0.2g earthquake. Until the second last test case with the horizontal peak earthquake motion of 0.9g (corresponding to 0.9g for the prototype structure), the fundamental frequency of the model CCV only decreased slightly and the maximum tensile strains at all monitoring points were much smaller than the ultimate tensile strain. It meant that the model CCV as a whole was within the elastic range. In the last case (1.2g), the model fundamental frequency decreased steeply. At the same time, the maximum tensile strains at the heel of the cylinder wall far exceeded the ultimate tensile strain and a circle of cracks occurred at the cylinder wall heel. It meant rupture failure had occurred and the cylinder wall heel of the CCV was the weak region. It agreed well with the numerical analysis results and the visual inspection and camera record at the test site. Although a circle of concrete cracks appeared around the cylinder wall foot, the model CCV still remained integral as a whole and neither cracking parts dislocation nor collapse occurred. Because the test model was a plain concrete structure and the model test results should be conservative estimation, it can be concluded that the prototype PCCV for CPR1000 nuclear power plant had sufficient seismic safety margin.

Modelling the behaviour of steel fibre reinforced concrete using a discrete strong discontinuity approach

The use of Fibre Reinforced Concrete (FRC) is gradually wide-spreading due to the significant advantages relatively to Normal Concrete (NC). In the case of steel fibres, the quasi-brittle behaviour of plain concrete structures can be modified into an enhanced ductile behaviour as a direct result of this addition. Since the mechanical properties of both FRC and NC can be significantly different, this work aims at developing a finite element formulation to specifically address the simulation of the behaviour of FRC members up to failure. For this purpose, the Conforming Generalised Strong Discontinuity Approach (CGSDA) is adopted with steel fibres explicitly introduced in the finite element mesh. The resulting formulation has the following main characteristics: (i) variational consistency; (ii) fibre elements automatically considered regardless of the presence of cracks; and (iii) no additional degrees of freedom are required. The proposed formulation is validated using experimental results from tests conducted with different dosages of steel fibres.

Field Test Method for Residual Stress in Plain Concrete Pavements and Structures

Abstract Residual stresses form in concrete structures and rigid pavements as a result of differential shrinkage, loss of subgrade support, and physical restraint by the superstructure. These stresses diminish a concrete member's capacity to carry its design load, making the structure vulnerable to premature cracking and failure. Few methods for quantifying the residual stress in concrete exist, although several methods have been developed for measuring material stresses in metals and rocks. Here, a new field test method for concrete pavements and structures, inspired by the ASTM E837 method for measuring residual stress in steel, is presented. The test is performed by installing strain gages on the surface of a concrete pavement or structure and then saw-cutting around the gages to isolate the gages from the bulk concrete material. The difference between the strain reading before and after the saw-cuts is used to compute the stress present at the surface of the concrete material. The method was developed and validated in laboratory experiments, and finite element modeling was conducted to enhance understanding of the three-dimensional strain distribution around saw-cut notches in materials with residual stress. Full-scale testing on plain concrete pavements demonstrated the method's potential as a field test method.

Geometric Nonlinearity Effect on Seismic Behavior of High Arch Dams

In this research, geometrically nonlinear dynamic analysis of arch concrete dam is attempted. At first, suitable models for large deformation analysis of massive plain concrete structures are investigated and by considering arch dam special features and properties, proper model for large displacement analysis is developed. A nonlinear analysis of the Dez arch dam using the engineering stress – strain model for large displacements is carried out under MCE ground motion. Fluid-Structure interaction is modeled including water compressibility and reservoir bottom absorption and the rock foundation is modeled as a mass-less flexible medium. Joint nonlinearity is also taken into consideration in the analysis. The penetration of water in opening joint during the earthquake is also considered and the significance of nonlinear geometry effects when accompanied by hydrodynamic pressure in joints is investigated. It is indicated that considering large deformation effects could be magnified when water penetration into opening joints is permitted. The obtained results showed that because the structural behavior of an arch dam does not allow large strains in a general manner, one can rule out the appearance of large displacements in the models including linear material.

Continuum large cracking in a rate‐dependent plastic–damage model for cyclic‐loaded concrete structures

SUMMARYFormulation and algorithmic treatment of a rate‐dependent plastic–damage model modified to capture large tensile cracking in cyclic‐loaded concrete structures are presented in detail for a three‐dimensional implementation. The plastic–damage model proposed by Lee and Fenves in 1998 was founded based on isotropic damaged elasticity in combination with isotropic multi‐hardening plasticity to simulate cracking and crushing of concrete under cyclic or dynamic loadings. In order that the model can capture large crack opening displacements, which are inevitable in plain concrete structures, the excessive increase in plastic strain causing unrealistic results in cyclic behaviors is prevented when the tensile plastic–damage variable controlling the evolution of tensile damage is larger than a critical value. In such a condition, the crack opening/closing mechanism becomes similar to discrete cracking. The consistent tangent operator required to accelerate convergence rate is also formulated for the large cracking state including viscoplasticity. The validation and performance of the modified algorithm implemented in a special finite element program is exemplified through several single‐element tests as well as three structural applications. The last example examines the model in the seismic fracture analysis of Koyna dam as a benchmark problem and the resulting crack profile is compared with the available experiment. The numerical experimentations well demonstrate that the developed model whose modification is necessary to properly simulate the cyclic behavior of plain concrete subjected to large tensile strains is robust and reasonably accurate. Copyright © 2012 John Wiley & Sons, Ltd.

Modeling of plain concrete structures based on an anisotropic damage formulation

In this contribution, a strain-based constitutive law for concrete within the framework of continuum damage mechanics is proposed. The model allows for the multi-axial simulation of predominantly tensile loaded plain concrete structures. A second-order integrity tensor is chosen as the internal damage variable to consider the phenomenon of load-induced anisotropy. The model is implemented in the finite element method. Hence, a fracture-energy based regularization approach is included to overcome the mesh-dependence of the computational results. The proposed model is applied to the simulation of well-known experiments with plain concrete specimens, which are often used to demonstrate the applicability of damage constitutive laws. In this context, attention is focused especially on problems regarding the accurate implementation of the complex loading and boundary conditions. Oversimplifications are discussed and proposals for a more realistic involvement of the test setups in finite element models are submitted.

DEFECT DETECTION IN CONCRETE STRUCTURES USING THERMAL IMAGING TECHNIQUES

This article has successfully detected embedded defects in concrete of size 50 mm representing voids, disbands and material inhomogeneities using the thermal imaging technique, and the results have been compared with ultrasonic technique. It is found that as compared to the conventional techniques, the thermal imaging provides an easy to interpret “visual” picture, in a single scan of the specimen in question. However, the main limitation associated with the thermal imaging technique is its inability to identify small defects located deeper than the lateral dimension due to the lateral diffusion of heat and the low temperature contrast it creates. Nevertheless, thermal imaging provides an efficient defect detection technique to identify near-surface defects in concrete. In this article, only plain concrete structures have been considered. Further studies are underway to detect defects in the presence of reinforcement.

Nonlinear Dynamic Analysis of Concrete Arch Dam Using Concrete Elasto-Plastic Models

In this research, materially nonlinear dynamic analysis of concrete arch dam using Concrete Elasto-Plastic models is attempted. At first, common models for nonlinear analysis of massive plain concrete structures are investigated and finally concrete material model of Wiliam–Warnke (five parameters version) for tensional and compression failure is selected. This model is used versus other usual models such as Mohr-Coulomb and Drucker-Prager models for analysis of Morrow Point concrete arch dam under an intensive ground motion of order of 1.0g for the peak ground acceleration. A suitable algorithm for stress integration and conversion of engineering stresses to objective ones is proposed. This stress calculation is particularly desired in large deformations analysis. Fluid-structure interaction is also considered including water compressibility and reservoir bottom absorption. Staggered approach is used for coupled-fluid structure solutions. Although the foundation is considered as rigid. It is demonstrated that usual nonlinear plastic models such as Mohr-Columb and Drucker –Prager models unlike special concrete models are not capable to capture real behavior of such concrete structure. It is suggested that special concrete models such as William–Warnke must be used for the plastic nonlinear analysis of concrete arch dam.

On the dissipative zone in anisotropic damage models for concrete

This paper presents a three-dimensional model to simulate the behavior of plain concrete structures that are predominantly tensile loaded. This model, based on continuum damage mechanics, uses a symmetric second-order tensor as the damage variable, which permits the simulation of orthotropic degradation. The validity of the first and the second law of thermodynamics, as well as the validity of the principle of maximum dissipation rate, are required. That is attained by defining the loading functions in quantities that are thermodynamically conjugated to the damage variables. Furthermore, the evolution rule is derived by maximizing the energy dissipation rate. This formulation is regularized by means of the fracture energy approach by introducing a characteristic length. The basic and new idea in this paper is that the characteristic length should always coincide with the width of the dissipative zone appearing in the simulation. The integration points with increasing damage in one loading increment are the dissipative zone in this loading increment. The main objective of this paper is the convenient formulation of approaches for the characteristic length in order to attain the coincidence of the characteristic length with the width of the dissipative zone appearing in the simulation. It is shown that simulations are objective and yield good results if the requirement is fulfilled that the characteristic length in the constitutive law coincides with the width of the dissipative zone in the simulation.

銅スラグおよびＩＩ種フライアッシュを細骨材の一部に置換して用いたコンクリートの性状

In the Shikoku area, it is eager to request an alternative fine aggregate in stead of natural sand, in particular sea sand, by the reason of prohibition of borrowing sea sand in Seto Island Sea. In this study, the fundamental properties of concrete using copper slag (JIS A 5011-3) or second class fly ash (JIS A 6201) as a part of fine aggregate to apply for plain concrete structure is investigated. It is concluded that the concrete of 20 mm in coarse aggregate maximum size, 50% in water-cement ratio and 40 mm in coarse aggregate maximum size, 60% in water-cement ratio and up to 30%, except in the case of 50% in water-cement ratio of fly ash concrete is possible to 20%, at in volume percentage of sand using copper slag or second class fly ash is applicable for concrete structure.

Lattice modelling of size effect in concrete strength

This paper uses a recently improved lattice network model to study the size effect in the strength of plain concrete structures. The several improvements made to the lattice network model are: (i) tension softening of the matrix phase is included in the material modelling; (ii) the structural response is modelled by incrementing the deformation rather than the load. This eliminates the need for introducing arbitrary scaling parameters in the beam element failure criteria and; (iii) a square rather than a triangular lattice beam network is found to be adequate for modelling concrete, thus greatly reducing the computational time. The improved square lattice network has been used to simulate the complete load–deformation response of notched three-point bend beams of different sizes with a view to checking the validity of several size effect models available in the literature. Lattice simulation was found to identify microcracking, crack branching, crack tortuosity and bridging, thus allowing the fracture process to be followed until complete failure. The improved lattice model predicted smooth structural response curves in excellent agreement with test results. The simulated nominal strengths also correlated very well with the test results, apart from that for the smallest beams (depth 38.1 mm). However, even in the relatively broad range of sizes (1:8) of the test beams, there was no clear evidence that one size effect model is superior to the other. In fact, rather surprisingly the test data would appear to be equally well described by all the available size effect models. The lattice simulations however indicated a trend which is better predicted by the multifractal scaling model.

Prototype Impact Test On Rockfall RetainingWalls And Its Numerical Simulation

In Japan, rockfall retaining walls as safety facilities of roads are designed as the gravity type with a plain concrete structure. In this paper, in order to investigate impact behavior of the structure, prototype impact tests are conducted by letting a steel weight with a predetermined velocity collide. Elasto-plastic impact analyses on the walls are also performed and an applicability of the proposed method is discussed comparing with the experimental results. From this study, the following results are obtained: 1) using the proposed numerical analysis method, weight impact force wave, rotation of the wall, and crack pattern can be precisely predicted; and 2) this analytical method can be used for establishment of a rational design procedure for rockfall retaining walls.

Computer Graphics for Nonlinear Strut-Tie Model Approach

This paper presents an interactive computer graphics program for implementing the nonlinear strut-tie model approach for the practical design and analysis of disturbed regions in structural concrete. The graphics program consists of three parts. The first and second parts are considered as the pre- and post-processors for a nonlinear finite-element analysis of 2D plain concrete and plane truss structures. The results of the first part provide guidance in the development of strut-tie models and in the evaluation of effective strength levels for concrete struts. The third part is a design routine for dimensioning and detailing the components of the developed strut-tie model. This graphics program implementing the nonlinear strut-tie model approach has been shown to be efficient in the development, analysis, and detailing of strut-tie models for the analysis and design of structural concrete including disturbed regions.

A REFINED STRUT-TIE MODEL APPROACH AND ITS APPLICATION TOOL.

This paper presents a refined strut–tie model approach and its application tool for the analysis and design of structural concrete. In this approach, non-linear techniques are incorporated in the development, analysis and verification processes of a strut–tie model. The additional positioning of concrete ties and steel struts at the locations of steel ties and concrete struts, respectively, is also incorporated. The proposed approach can eliminate the limitations the current strut–tie model approach has in the prediction of the behaviour and strength of structural concrete as well as in the precise design of structural concrete which experiences non-linear behaviour. The interactive computer graphics programme for the refined strut–tie model approach consists of three parts. The first and second parts are considered as the pre- and post-processors for a finite-element analysis of two-dimensional plain concrete and plane truss structures. The third part is a design routine for dimensioning and detailing the components of the developed strut–tie model. The use of the interactive computer graphics programme in the refined strut–tie model approach is illustrated with an example of the analysis of a reinforced concrete deep beam tested to failure. The refined strut–tie model approach with computer graphics capabilities can provide effective and consistent solutions to a large number of complex analysis and design problems.

A refined strut–tie model approach and its application tool

This paper presents a refined strut–tie model approach and its application tool for the analysis and design of structural concrete. In this approach, non-linear techniques are incorporated in the development, analysis and verification processes of a strut–tie model. The additional positioning of concrete ties and steel struts at the locations of steel ties and concrete struts, respectively, is also incorporated. The proposed approach can eliminate the limitations the current strut–tie model approach has in the prediction of the behaviour and strength of structural concrete as well as in the precise design of structural concrete which experiences non-linear behaviour. The interactive computer graphics programme for the refined strut–tie model approach consists of three parts. The first and second parts are considered as the pre- and post-processors for a finite-element analysis of two-dimensional plain concrete and plane truss structures. The third part is a design routine for dimensioning and detailing the components of the developed strut–tie model. The use of the interactive computer graphics programme in the refined strut–tie model approach is illustrated with an example of the analysis of a reinforced concrete deep beam tested to failure. The refined strut–tie model approach with computer graphics capabilities can provide effective and consistent solutions to a large number of complex analysis and design problems.

Low-Cycle Fatigue of Plain and Fiber-Reinforced Concrete

This paper reports on a study which is part of an investigation into the fatigue reliability of plain and fiber-reinforced concrete structures, underway at Columbia University since 1989. The ultimate purpose of this research is to develop practical tools for damage assessment and prediction of remaining life of concrete structures. The scope of the research reported herein is limited to a few key tasks. Several hundred 4-inch cube specimens were tested uniaxially under cyclic compression with constant amplitude. The variables studied were the concrete strength (r, 5, and 7 ksi cylinder strength), type of fiber (steel and polypropylene), and fiber volume (0.00, 0.25, 0.50, 0.75, and 1.00 percent). The emphasis of this study was to examine the effect of various parameters on energy absorption characteristics, fatigue life and the damage accumulation history.

Impact-Echo Condition Assessment of Structures

The impact-echo method of nondestructive testing of concrete and masonry structures is based on the use of impact-generated stress (sound) waves, propagating through the material and reflected by internal flaws and external surfaces. It can be used to locate and measure the extent of faults such as cracks, delaminations, and voids in a wide variety of plain, reinforced and post-tensioned concrete and masonry structures. These structures include slabs, pavements, walls, decks, concrete with asphalt overlays, pipes, and tunnels. The following case studies, mostly in the USA but one in Denmark, illustrate how the impact-echo method and instrument can be used as a condition-assessment tool for engineers who evaluate concrete structures: (1) detecting delaminations in a concrete bridge deck with an asphalt overlay; (2) detecting cracking in a reinforced concrete railway bridge; (3) locating voids in the grouted ducts of a post-tensioned road bridge; (4) durability of repairs in a precast segmental box-girder rail bridge; (5) detecting cracking in beams and columns of a parking garage; and (6) measuring the thickness of concrete road pavements. Each case presented includes a description of the structure and of the problems to be diagnosed, and discusses the role and summarises the results of impact-echo testing.

Is No-Tension Design of Concrete or Rock Structures Always Safe?—Fracture Analysis

Plain concrete structures such as dams or retaining walls, as well as rock structures such as tunnels, caverns, excavations, and rock slopes, have commonly been designed by elastic-perfectly plastic analysis in which the tensile yield strength of the material is taken as zero. The paper analyzes the safety of this no­ tension design in the light of the finiteness of the tensile strength of concrete or the tensile strength of rock between the joints. Through examples, it is demonstrated that: (1) the calculated length of cracks or cracking zones can correspond to an unstable state; (2) the uncracked ligament of the cross section, available for resisting horizontal shear loads, can be predicted much too large, compared to the fracture mechanics pre­ diction; (3) the calculated load-deflection diagram can lie lower than that obtained by fracture mechanics; (4) the no-tension load capacity for a combination of crack face pressure and loads remote from the crack front, calculated by elastic analysis on the basis of allowable compressive stress, can be higher than that obtained by fracture mechanics; and (5) an increase in the tensile strength of the material can cause the load capacity of the structure to decrease. Due to the size effect, these facts are true not only for zero fracture toughness (no-toughness design) but also for finite fracture toughness provided that the structure size is large enough. Several previous studies on the safety of no-tension design, including the finite-element analysis of a gravity dam, are also reviewed. It is concluded that if the no-tension limit design is used, the safety factors of concrete or rock structures cannot be guaranteed to have the specified values. Fracture mechanics is required for that.

Application of NLFM Models to Predict Cracking in Concrete Gravity Dams

Smeared crack analysis models based on a nonlinear fracture mechanics (NLFM) crack propagation criterion are considered to study the two‐dimensional static fracture behavior of plain concrete structures. A coaxial rotating crack model (CRCM) and a fixed crack model with a variable shear resistance factor (FCM‐VSRF), both using a secant stiffness formulation, are considered in studying the behaviors of a notched shear beam, a model concrete gravity dam, and a full‐scale concrete gravity dam: all have been experimentally or numerically investigated in the past. The responses obtained from smeared crack analyses are compared with those reported in the literature by other investigators. The CRCM appears to perform better than the FCM‐VSRF in alleviating the stress‐locking phenomenon generally observed in smeared crack analyses. However, the crack profiles predicted by the rotating crack model are prone to the directional bias caused by finite element meshes of the elementary beam problem and the model concret...