Crack Propagation In Concrete Research Articles

콘크리트의 연속적인 균열성장에 대한 수정 특이-파괴진행대 이론

In this paper, the modified singular fracture process zone (S-FPZ) model is proposed to consider variation of a fracture criterion for continuous crack propagation in concrete. The fracture properties of the proposed fracture model are strain energy release rate at a micro-crack tip and crack closure stress (CCS) versus crack opening displacement (COD) relationship in the FPZ. The proposed model can simulate the estimated fracture energy of experimental results. The analysis results of the experimental data shows that specimen geometry and loading condition did not affect the CCS-COD relation. But the strain energy release rate is a function of not only specimen geometry but also crack extension. Until 25 mm crack extension, the strain energy release rate is a constant minimum value, and then it increased linearly to the maximum value. The maximum fracture criterion occurred at the peak load for an large size specimen. The fracture criterion remains the maximum value after the peak load. The variation of the fracture criterion is caused by micro-cracking and micro-crack localizing. The fracture criterion of strain energy release rate can simply be the size effect of concrete fracture, and it can be used to quantify the micro-tracking and micro-crack localizing behaviors of concrete.

Structural performances of short steel-fiber reinforced concrete beams with externally bonded FRP sheets

The application of externally bonding FRP sheets to concrete structures has become a popular strengthening procedure. However, such FRP strengthening effect sometimes could not be well achieved due to the premature interfacial debonding along FRP–concrete bond interface. In FRP-reinforced plain concrete members, the rapid propagation of localized flexural cracks in concrete is one of the primary reasons that cause the concentration of interfacial shear stress around where concrete crack happens, thus resulting in the debonding initiation. Therefore, an effective control of crack localization and propagation in concrete might be a solution to avoid or delay the debonding. This article presents an approach to improve the FRP strengthening performance to concrete beams by mixing short steel-fibers into the concrete matrix. To investigate the enhancement of FRP strengthening effect, a series of experiments are carried out, which include a standard JIS test of short four-point bending beams without FRP strengthening and a test of three-point bending FRP-strengthened concrete beams with different volume fractions of mixed short steel-fibers. The control of crack propagation and the increase of concrete toughness through mixing short steel-fibers are achieved. In the experiment of three-point bending, FRP-strengthened concrete beams increasing steel-fiber volume fraction, leads to a smeared crack distribution in the concrete. The ultimate failure mode also changes from peeling-induced debonding to FRP rupture so that the FRP sheet can exert its strengthening effect sufficiently. In addition, a finite element analysis is performed to compare the experimental results, in which the increase of concrete toughness is described by fracture energy. The simulation basically reproduces the experiments. The validity of the proposed approach is demonstrated.

Analytical Model for Fatigue Crack Propagation in Concrete

Abstract A new approximate analytical model is presented for the fatigue crack propagation rate in concrete. The model considers fatigue cracking at all stress levels up to the modulus of rupture. As the bending stress increases, the size of the inelastic zone compared to the crack length increases, and the stress intensity factor no longer controls the stresses in the vicinity of the crack tip, necessitating the use of the path-independent J-integral. At high stress levels fatigue crack propagation becomes nonlinear, and fracture may occur by ultimate strength collapse. Recently Kharlab postulated a hypothesis that enables the prediction of fracture of concrete by a single criterion that considers failure at any stress level for any size beam. An approximate analytical method for fatigue crack propagation in concrete at any stress level is presented. It incorporates the size effect and uses the crack tip opening displacement as the primary criterion upon which the rate of crack propagation is dependent. The model is validated by the published experimental data on concrete fatigue.

Element-free Galerkin methods for dynamic fracture in concrete

Mixed-mode dynamic crack propagation in concrete is studied using the element-free Galerkin (EFG) method. The EFG methodology allows for arbitrary crack growth in terms of direction and speed. A fracture process zone (FPZ) model is used for fracture in concrete. Comparisons are made to mode I and mixed-mode experiments on concrete three-point-bend specimens. Good agreement is acheived with the experimental results.

Element-free galerkin methods for dynamic fracture in concrete

Mixed-mode dynamic crack propagation in concrete is studied using the element-free Galerkin (EFG) method. The EFG methodology allows for arbitrary crack growth in terms of direction and speed. A fracture process zone (FPZ) model is used for fracture in concrete. Comparisons are made to mode I and mixed-mode experiments on concrete three-point-bend specimens. Good agreement is acheived with the experimental results.

Influence of hydraulic pressure in fracture mechanics modelling of crack propagation in concrete

This paper presents a nonlinear fracture mechanics analysis of a part of an offshore concrete structure. The analysis focuses on the risk of cracking between the prestressing ducts in the shaft of the submerged platform. The influences of water and grout pressure in prestressing ducts have been taken into consideration.

Mixed Mode Fracture of Concrete under Proportional and Nonproportional Loading

A novel testing procedure for mixed mode crack propagation in concrete is presented: four point bend of notched beams under the action of two independent force actuators. In contrast to classical procedures, this method allows nonproportional loading and crack trajectory modifications by changing the action of one actuator. Different experimental crack trajectories, under mixed mode and nonproportional loading, are presented together with the corresponding curves of load-CMOD and load-displacement. The tests were performed for three homotetic specimen sizes and two mixed mode loading conditions. The results are useful for checking the accuracy of mixed mode fracture analytical and numerical models. The models should predict the crack trajectory and a complete group of experimental records of load and displacements on several control points in the specimen.

An Overview of the Fracture Mechanics of Concrete

Abstract For the design of concrete structures where adequate ductility is a concern, it is becoming increasingly necessary to use concepts based on crack growth and propagation to account for ductility and avoid catastrophic failure. While fracture based methods exist for steel design, no standard method currently exists to quantify the fracture properties of concrete. In light of a multitude of recent investigations to describe the complex nature of concrete fracture, it is currently accepted that two parameters are required to characterize crack propagation in concrete. This paper provides a brief background for the use of fracture mechanics in concrete and appeals for the establishment of standardized testing procedures for use in concrete. If appropriately determined, fracture parameters can provide a valuable tool for the design of new higher performance concretes and concrete structures.

A finite element analysis of non-prescribed crack propagation in concrete

In this paper a finite element model for the study of crack propagation in concrete is presented. The approach is based on Hillerborg's concepts of discrete crack formation and fracture energy dissipation. Interface elements with initial zero thickness are inserted along the interelement boundaries and no special remeshing procedures are required. Cracks open along those interface elements at which an approximate version of the usual criterion for mode I fracture is satisfied. The constitutive behaviour and the energy dissipation along the opening interface elements are corrected to take into account the difference between the mesh-dependent directions of the opening interfaces and the predicted direction of crack formation. Numerical results for a shear beam test and a pullout test are presented and comparisons between computed and experimental results are made.

Crack growth analysis in concrete using boundary element method

In this paper, the dual boundary element method is extended to include the non-linear behaviour of cracking in concrete. The fictitious crack model is used to simulate the pure mode I and mixed mode crack propagation in concrete. The fictitious crack in the fracture zone in front of the real crack tip is replaced by the closing forces acting on both crack surfaces. When the force at the fictitious crack tip exceeds the maximum tensile strength of the concrete, the crack will propagate perpendicular to the maximum principal stress. The numerical simulation is controlled through the crack length as a monotonic increasing function during the fracture process. Three-point bending and four-point shear specimens are used to check the numerical results for mode I and mixed mode, respectively. Under the crack length controlled scheme, the snapback instability is observed in the mixed mode problem.

Softening and Snap‐Through Behavior of Reinforced Elements

The writers present a fracture mechanics model for reinforced concrete collapse, which is a refinement of that proposed previously, based on compliance and stress‐intensification concepts. In this case, a crack‐opening displacement congruence condition replaces the rotational congruence condition, while the reinforcement reactions are applied directly to the crack surfaces and not as closing forces at infinity. The theoretical results confirm a transition from ductile to brittle collapse by varying a nondimensional brittleness number defined in previous contributions. In addition, with the present model, yielding or slippage of reinforcement can precede or follow crack propagation in concrete. The moment‐versus‐rotation response presents softening and snap‐through behaviors and is substantially in agreement with the experimental results. Such a theoretical approach appears to be very useful in estimating the minimum reinforcement for members in flexure.

FEM Modeling of Fictitious Crack Propagation in Concrete

Using a mixed‐mode extension of the Hillerborg fictitious crack model, a practical interface finite element approach is used to model discrete crack propagation. The fictitious crack tip propagates perpendicular to the maximum tensile principal stress at its tip when the tensile strength is exceeded. A dynamic relaxation method is employed. Interface elements have been used before to model such cracks; however, the software technology is in a state of rapid development, making possible improvements in the modeling of discrete nonlinear crack propagation. The concept of fracture process zone is broadened to one of interface process zone, which includes the nonlinear behavior of the fracture process zone as well as the crack face interference behind the fracture process zone. A development makes the method efficient while preserving the accuracy of the fictitious crack model. The fictitious crack is represented by interface elements with linearly varying displacements; however, the traction distribution is arbitrary. As example problems demonstrate, these assumptions allow the fictitious crack to be modeled using few degrees of freedom without compromising accuracy. Modeling of the size effect is presented.

Features of mechanics of quasi-brittle crack propagation in concrete

Physical observations of crack propagation in concrete are discussed in the present paper. Based on these physical observations, different models proposed for mode I fracture of concrete are examined. In the past, verification of validity of fracture models has always been difficult. It is proposed that notch sensitivity and size effect be used as criteria to evaluate the validity of fracture models. In addition, a successful model should also satisfy a ‘portability’ condition, namely the model should be applicable to structures of an arbitrary geometry. Discussion on the effects of different loading conditions, i.e. mixed-mode loading conditions and different loading rates, on the fracture process in concrete is also presented.

Crack Propagation in Concrete under Compression

Mixedmode crack initiation and propagation starting from the aggregatematrix interface in concrete under uniaxial compression was investigated using fracture mechanics approach, finite element mode...

Fatigue crack propagation in concrete

Numerous studies have been published on portland cement concrete fracture. But no attempt has been reported to relate the crack propagation rate in concrete to stress intensity factor range. A test is being prepared to obtain such information

Acoustic emission applied to study crack propagation in concrete

This study presents a use of the acoustic emission examination technique to determine the dimensions of the microcracked zone leading a macrocrack propagating in concrete. A critical analysis of the locating method is followed by a presentation of its application to conventional concrete, steel fibre concrete, and high-strength concrete.

A holographic real time study of crack propagation in concrete

In this paper the fracture process of concrete is studied on a microscopic level during the bending of notched specimens. A holographic technique called TV-holography is used. This allows real time observation of concrete microcracking, from the first loading until final rupture. The smallest observable crackwidth size is about 0.1 μm. It was found that in this kind of loading, the onset of cracking takes place at about 80% of ultimate load, and that the main crack is not continuous. Further, coarse aggregate particles seemed to arrest propagating cracks and cause crack branching.

Interaction between tensile strength failure and mixed mode crack propagation in concrete

Crack size and structure size transitions are illustrated which connect the two limit-cases of ultimate tensile strength failure (small cracks and small structures) and mixed-mode crack propagation (large cracks and large structures). The problem of mixed-mode crack propagation in concrete is then faced. By increasing the size-scale of the element the influences of heterogeneity and cohesive crack tip forces disappear and crack branching is governed only by the linear elastic stress-singularity in the crack tip region. It is proved in this way that the fracture toughness of the material is measured by a unique parameter (GIF, GIC or KIC) even for the mixed-mode condition. The ratio of the sliding or Mode II fracture toughness (GIIF, GIIC or KIIC) to the opening or Mode I fracture toughness depends only on the crack branching criterion adopted and not on the material features. Eventually, very controversial experimental results recently obtained on the shear fracture of concrete are explained on the basis of the above-mentioned size-scale transition.

Crack propagation in concrete: Linear elastic fracture mechanics and boundary element method

Crack propagation in concrete is investigated by application of Linear Elastic Fracture Mechanics (LEFM) and the Boundary Element Method (BEM). Acoustic Emission (AE) measurement is made for detecting the load level at which unstable crack initiation occurs in a notched beam under bending. The corresponding critical stress intensity factor K Ic does not vary appreciably with notch depth. This result is in contrast to that found by the conventional procedure. The critical stress intensity factor K Ic is employed to analyze the process of crack propagation in an arbitraty direction. The BEM prediction is in good agreement with the experiments. The detection and assessment of crack initiation in concrete structures is of considerable technical interest.

Strain rate effect on crack propagation in concrete

Some aspects of cracking in concrete structural elements are discussed. The flexural behaviour of precracked beams made with materials having different mechanical properties is experimentally evaluated at different deformation rates. The crack propagation in the sample is recorded with time by means of particular electric strain gauges. An interaction between ultimate tensile strength failure and brittle crack propagation is eventually pointed out.