Plain Concrete Beams Research Articles

Stress Intensity Factor Based Damage Prediction Model for Plain Concrete under Cyclic Loading

Concrete highways and airfield pavements are subjected to a large number of traffic loads, which may cause failure of the pavement due to fatigue. In the present work, an experimental study has been carried out on plain concrete beam specimens to investigate the crack propagation and incremental damage characteristics of concrete under cyclic loading. A compliance test was conducted on beam specimens with different notch depths, and a relationship between notch depth and compliance was established. The fracture toughness of concrete was also estimated in a beam bending test. Fatigue tests were conducted on different sets of beam specimens under different load levels. Vertical displacement and crack mouth opening displacement were measured at each load cycle. The variation of stress intensity factor with load repetitions was observed using the crack lengths estimated from the compliance values corresponding to different load repetitions. The ratio of stress intensity factor to critical stress intensity factor (at failure), termed as toughness ratio in this work, has been found to influence the fatigue life. The fatigue life, as expected, also depended on stress ratio. A fracture mechanics–based damage prediction model was proposed for estimating the progressive damage at any intermediate load cycle. The damage prediction model was validated using the experimental results available in literature. Predicting fatigue damage at intermediate stages and due to variable sequence of loading is convenient for the design and evaluation of concrete pavements. Although the effects of frequency (in the ranges applicable for highway pavements) on the fatigue performance may not be significant, the applicability of the present model may be limited by the specific specimen size and loading waveform considered in this study.

Poly(methyl methacrylate) capsules as an alternative to the ‘’proof-of-concept’’ glass capsules used in self-healing concrete

Development of suitable capsules is essential to achieve self-healing by encapsulation. In the context of self-healing concrete, capsules that can be easily mixed into concrete and release the healing agent when cracking occurs are ideally required. The optimization of these properties would allow for a successful implementation at large scale in practical (concrete) applications. In the present work, the suitability of polymeric cylindrical capsules made of poly(methyl methacrylate) (PMMA) to carry healing agent in self-healing concrete has been evaluated. An innovative method to assess more easily the capsules survival during concrete mixing was developed. This method is based on the evaluation of the setting behavior of concrete containing capsules filled with setting accelerator. Capsules with a wall thickness of 0.7 mm were able to resist the concrete mixing process and to rupture at relatively small crack widths (116 μm) after applying a surface treatment to increase the adhesion between the capsules and the cementitious matrix. Next, the self-healing efficiency of the encapsulation materials (glass or PMMA) was evaluated on real-scale concrete beams. The results showed that cracked concrete beams with mixed-in capsules (glass or PMMA) filled with water-repellent agent showed higher resistance against chloride ingress compared to plain cracked concrete beams. PMMA capsules showed a lower self-healing efficiency (in relation to chloride ingress) compared to glass due to a less favorable distribution of the capsules in the concrete. However, concrete containing glass capsules is susceptible towards alkali-silica reaction.Although optimization of the PMMA capsules is still necessary to improve their distribution in concrete and achieve higher self-healing efficiency, the obtained results indicate that these capsules could be a promising solution towards self-healing concrete.

Analysis of concrete beams using applied element method

The Applied Element Method (AEM) is a displacement based method of structural analysis. Some of its features are similar to that of Finite Element Method (FEM). In AEM, the structure is analysed by dividing it into several elements similar to FEM. But, in AEM, elements are connected by springs instead of nodes as in the case of FEM. In this paper, background to AEM is discussed and necessary equations are derived. For illustrating the application of AEM, it has been used to analyse plain concrete beam of fixed support condition. The analysis is limited to the analysis of 2-dimensional structures. It was found that the number of springs has no much influence on the results. AEM could predict deflection and reactions with reasonable degree of accuracy.

Fatigue crack resistance characterisation of fully supported plain concrete beams

A framework for characterising the static and fatigue crack resistance of a fully supported beam on an elastic foundation is presented. The crack resistance is given as a function of the resisting cohesive stress and represented mathematically with a set of simple linear regression equations that can be easily integrated within a mechanistic–empirical design framework. The static crack resistance is derived using a weight function integral and reciprocal energy formulation that may be extended to more complex structural systems containing two-dimensional crack growth. Finally, a modified Paris law that utilises the crack resistance curves is used to develop a modified S–N diagram that can capture the fatigue response under various support conditions and different material characteristic lengths and structural sizes.

Strengthening of concrete beams by monolayer prepreg composites with and without graphene reinforcement

Composite materials are widely used in different engineering fields and they are very efficient for engineering applications. Several composite materials are in use along with the technological innovations in materials and construction techniques. This study focuses on the monolayer prepreg (MP) composites and graphene-reinforced monolayer prepreg (GMP) composites and their structural contribution to the structural performance of concrete beams. The main objectives of the study are (1) to understand the mechanical properties of the MP and GMP composites, (2) to investigate the influence of graphene on the mechanical characterizations of the MP composites and (3) to compare the strengthening effectiveness and configurations of the MP and GMP composites applied to plain concrete (PC) beams. For this purpose, the MP and GMP composites are produced as continuous sheets and concrete beams are strengthened with these sheets considering four different internal and external strengthening configurations. The flexural behavior of the PC beams is compared to reinforced beams with MP and GMP composites through experiments, numerical simulations and statistical tests. The results indicate that the tensile strength of the MP composite increases by addition of graphene leading to more effective strengthening by the GMP composites, especially with external configuration, than the MP composites.

FLEXURAL IMPROVEMENT OF PLAIN CONCRETE BEAMS STRENGTHENED WITH HIGH PERFORMANCE FIBRE REINFORCED CONCRETE

Strengthening of concrete structures have become inevitable due to unavoidable factors such as fatigue and aggressive environmental conditions causing deterioration of concrete structures. Many researchers have turned in the direction of using various high strength and high performance concretes due to their high structural and durability properties, for the purpose of repair and strengthening of concrete structures against these aggressive conditions. As a result, this study carryout experimental, numerical and analytical investigation to study the behaviour of plain concrete (PC) beams strengthened with High Performance Fibre Reinforced Concrete (HPFRC) layer using three different jacketing configurations and tested in flexure. Results show significant improvement in both stiffness and load bearing capacity of plain concrete beams. Â http://dx.doi.org/10.4314/njt.v36i3.6

FLEXURAL IMPROVEMENT OF PLAIN CONCRETE BEAMS STRENGTHENED WITH HIGH PERFORMANCE FIBRE REINFORCED CONCRETE

Strengthening of concrete structures have become inevitable due to unavoidable factors such as fatigue and aggressive environmental conditions causing deterioration of concrete structures. Many researchers have turned in the direction of using various high strength and high performance concretes due to their high structural and durability properties, for the purpose of repair and strengthening of concrete structures against these aggressive conditions. As a result, this study carryout experimental, numerical and analytical investigation to study the behaviour of plain concrete (PC) beams strengthened with High Performance Fibre Reinforced Concrete (HPFRC) layer using three different jacketing configurations and tested in flexure. Results show significant improvement in both stiffness and load bearing capacity of plain concrete beams. http://dx.doi.org/10.4314/njt.v36i3.6

Non-linear Analysis Reinforced Concrete Flexure Members Using Elements with Axial – Shear Coupling

This paper explains the formulation of Applied Element Method (AEM) as applied to plain and reinforced concrete beams as two-dimensional structures by primarily implementing material non-linearity. Both concrete and steel reinforcement have non-linear stress-strain curve in the model. A multi linear curve is assumed for reinforcement and concrete is modeled as a progressively fracturing solid. Static linear analysis of a reinforced beam using this method was compared with finite element and coupled boundary element method solutions. Static non-linear analysis of plain concrete beam using this method was compared with results of fracture mechanics model and published experimental results. The results were in good agreement with established analysis methods and experimental data. Advantages of AEM which is simple and straightforward in the modeling of reinforced concrete members are also discussed.

3D numerical modelling of twisting cracks under bending and torsion of skew notched beams

The testing of mode III and mixed mode failure is every so often encountered in the dedicated literature of mechanical characterization of brittle and quasi-brittle materials. In this work, the application of the mixed strain displacement ε-u finite element formulation to three examples involving skew notched beams is presented. The use of this FE technology is effective in problems involving localization of strains in softening materials.The objectives of the paper are: (i) to test the mixed formulation in mode III and mixed mode failure and (ii) to present an enhancement in terms of computational time given by the kinematic compatibility between irreducible displacement-based and the mixed strain-displacement elements.Three tests of skew-notched beams are presented: firstly, a three point bending test of a PolyMethyl MethaAcrylate beam; secondly, a torsion test of a plain concrete prismatic beam with square base; finally, a torsion test of a cylindrical beam made of plain concrete as well. To describe the mechanical behavior of the material in the inelastic range, Rankine and Drucker-Prager failure criteria are used in both plasticity and isotropic continuum damage formats.The proposed mixed formulation is capable of yielding results close to the experimental ones in terms of fracture surface, peak load and global loss of carrying capability. In addition, the symmetric secant formulation and the compatibility condition between the standard irreducible method and the strain-displacement one is exploited, resulting in a significant speedup of the computational procedure.

Effect of GGBFS on time-dependent deflection of RC beams

The paper presents the experimental investigations for studying the effect of ground granulated blast furnace slag (GGBFS) on the time-dependent deflection of reinforced concrete (RC) beams due to creep and shrinkage. The RC beams were reinforced with 2-10 mm bars at tension side and subjected to constant sustained two-point loading for the period of 150 days. The amount of cement replacement by GGBFS was varied from 0 to 60% with an increment of 20%. The total deflection was measured at different ages of up to 150 days under sustained loads. The experiments revealed that the time-dependent deflection of the reinforced concrete RC beams containing GGBFS was higher than that of plain concrete RC beams. At 150 days, the average creep and shrinkage deflection of RC beams containing 20%, 40% and 60% GGBFS was 1.25, 1.45 and 1.75 times higher than the plain concrete beams. A new model, which is an extension of authors\' earlier model, is proposed to incorporate the effect of GGBFS content in predicting the long-term deflection of RC beams. Besides validating the new model with the current data with higher percentage of tension reinforcement, it was also used to predict the authors\' earlier data containing lesser percentage of tension reinforcement with reasonable accuracy.

Behavior of Plain Concrete Beam subjected to Three Point Bending using Concrete Damaged Plasticity (CDP) Model

Concrete is an integral part of construction industry which is widely used throughout the globe. Concrete being heterogeneous in nature complicates the understanding of predicting its actual behavior under static or cyclic loading. Widespread use of concrete has increased the urge to accurately predict the response and design of concrete structures more accurately. In this paper, computer based simulation is carried out using Finite Element Analysis package- ABAQUS to study the Non-linear behavior of concrete by Concrete Damaged Plasticity (CDP) model. CDP model is a modified form of Drucker-Prager criterion and it takes into account the isotropic compressive and tensile plasticity of concrete to represent the inelastic behavior of concrete in association with its isotropic damaged elasticity. Tensile cracking and compression crushing in concrete are taken into consideration in this model. Load vs. Displacement curves were achieved for unreinforced concrete beams of various sizes subjected to three-point bending test. Also, effect of mesh refinement on CDP model has been studied so as to accurately predict the desired results

Feasibility study of using smart aggregates as embedded acoustic emission sensors for health monitoring of concrete structures

Acoustic emission (AE) is a nondestructive evaluation technique that is capable of monitoring the damage evolution of concrete structures in real time. Conventionally, AE sensors are surface mounted on the host structures, however, the AE signals attenuate quickly due to the high attenuation properties of concrete structures. This study conducts a feasibility study of using smart aggregates (SAs), which are a type of embedded piezoceramic transducers, as embedded AE sensors for the health monitoring of concrete structures. A plain concrete beam with two surface mounted AE sensors and two embedded SAs was fabricated in laboratory and loaded under a designed three-point-bending test. The performance of embedded SAs were compared with the traditional surface mounted AE sensors in their ability to detect and evaluate the damage to the concrete structure. The results verified the feasibility of using smart aggregates as embedded AE sensors for monitoring structural damage in concrete. Potentially, the low cost smart aggregates could function as embedded AE sensors, providing great sensitivity and high reliability in applications for the structural health monitoring of concrete structures.

Durability of bond between concrete beams and FRP composites made of flax and glass fibers

In this paper, the durability of flax and glass fiber-reinforced polymer (FRP) composites externally bonded to concrete beams is studied. A total of 100 plain concrete beam specimens (75mm×100mm×400mm) were prepared and bonded with flax and glass FRP strips to the tension side of the beams. The specimens were designed to have an adhesive debonding failure of the FRP from the concrete. The specimens were aged in water and dry heat conditions at 20and60°C for 21, 42, and 63daysandthen were tested under three-point bending. A set of specimens were also aged by freeze/thaw cycles. The load-deflection behaviors of the specimens were evaluated and the effects of heat, moisture, and freeze/thaw cycles on the peak load and ductility of the specimens were quantified. The study shows that the peak load retentions of the specimens with bonded flax and glass FRPs immersed in 60°C water for 63daysis 72% and 80% of their counterparts kept in dry heat condition, respectively. An analysis of variance was also performed to assess the significance of the aging effects on the physical and mechanical properties of the specimens. Also, a cross-sectional analytical modeling was performed to compute the FRP tensile force, strain, and bond strength of the specimens.

Heterogeneous Fracture Simulation of Three-point Bending Plain-concrete Beam with Double Notches

Plain concrete is regarded as a two-phase material comprising randomly distributed aggregates and mortar matrix. A series of three-point bending concrete beams with symmetric or asymmetric double notches are modeled using the modified random aggregate generation and packing algorithm. The cohesive zone model is used as the fracture criterion and the cohesive elements are inserted into both the mortar matrix and the aggregate-mortar interfaces as potential micro-cracking zones. The dead and alive crack phenomena are studied experimentally and numerically; and the influences of notch location, aggregate distribution and gradation on fracture are numerically evaluated. Some important conclusions are given.

Bending crack behaviour of plain concrete beams externally reinforced with TRC

This paper presents the experimental study of concrete beams in bending, externally strengthened with Textile Reinforced Cementitious materials (TRC) with varying contact area with the concrete. In order to study the pure influence of the TRC on the concrete substrate, only non-internally-reinforced concrete beams are considered. The crack pattern evolution is monitored with Digital Image Correlation, and the influence of the contact width between the concrete substrate and the external reinforcement is investigated. The results show that the TRC reinforcement has an important crack bridging capacity, and consequently that its application over the full beam width is beneficial for the loadbearing capacity and the limitation of the crack widths of the concrete beam.

Effect of flexural crack on plain concrete beam failure mechanism A numerical simulation

The flexural failure of plain concrete beam occurs along with development of flexural crack on beam. In this paper by using ABAQUS, mechanism failure of plain concrete beam under three steps have been simulated. The cracking moment has been analytically calculated and applied on the both sides of the fixed beam, and flexural crack has been simulated on beam. Displacement, von Mises, load reaction, displacementcrack length, von Mises-crack length and von Mises-displacement of beams have been graphical depicted. Results indicated that, the flexural crack governs beam mechanism failure and its effects on beam resistance failure. It has been found that the flexural crack in initial stage it developed slowly and changes to be fast at the final stage of collapsing beam due to reduction of the flexural resistance of beam. Increasing mechanical properties of concrete, collapse displacement is reduced.

Shear and flexural behaviour of prestressed and non-prestressed plain and SFRC concrete beams

The present study aims at improving the shear and flexural strength of the concrete by the addition of steel fibres. Also the study investigates the effect of prestressing on the shear and flexural strength of concrete. In this research work, 20% of fly ash (class-C) is added as a replacement of binder to its weight and 1.5% steel fibres by weight of concrete. Based on the experimental results, it can be seen that the load carrying capacity of steel fibre increased by 30–50% than the plain beam for non-prestressed. And load carrying capacity is increased approximately by 30–90% than the plain prestressed concrete beam. The use of steel fibres in a concrete mix was found to increase the crack resistance of the beams. Crack width was not more than 6mm and 3mm in case of the non-prestressed and prestressed steel fibre reinforced concrete beams respectively. Hence, based on experimental results it can be concluded that prestressed steel fibre reinforced concrete beams help to improve the shear strength, flexural strength, and crack resistance.

FIBER Bragg Grating (FBG) sensor for estimation of Crack Mouth Opening Displacement (CMOD) in concrete

Crack mouth opening displacement (CMOD) is one of the important parameters for characterizing the fracture properties in concrete. Amongst various optical fiber senors, Fiber Bragg gratings are (FBG) being used for structural health monitoring in the recent times. Very few reports exist in literature for use of CMOD estimation using FBG sensors. We report here, the use of FBG based sensor for the estimation of CMOD in plain concrete beams prepared as per recommendations of Reunion Internationale des Laboratoires et Experts des Materiaux, Systems de Construction et Ouvrages (RILEM) and subjected to three point bend test in a digitally controlled Universal Testing Machine (UTM). The results are compared with Linear Variable Differential Transformer (LVDT) and a good agreement is found. The FBG sensor's resolution is better than LVDT beyond the peak stress.

FE investigations of the effect of fluctuating local tensile strength on coupled energetic–statistical size effect in concrete beams

The effect of fluctuating local tensile strength on a coupled energetic–statistical size effect in plain concrete beams under bending was numerically investigated. First, the influence of varying autocorrelation length of the random field describing a spatial variation of local tensile strength was studied. Next, the influence of the coefficient of variation of local tensile strength was analyzed. The numerical FE investigations were performed for unnotched concrete beams of similar geometry under quasi-static three point bending within elasto-plastic model assumptions, accounting for non-local softening. The FE analyses were carried out for four different beam sizes. In the calculations, the tensile strength took the form of spatially correlated random field described by a Gaussian distribution.

Estimating crack widths in steel fibre-reinforced concrete

The use of steel fibres as reinforcement for sprayed concrete tunnel linings offers significant potential savings in time and cost. These provide a degree of crack control and an increase in ductility to the otherwise brittle material, and while the properties of steel fibre-reinforced concrete (SFRC) are well understood, its ability to control cracks is not quantifiable or justifiable in the design of concrete sections. This paper describes the novel application of particle image velocimetry (PIV) to the study of cracking in plain concrete and SFRC four-point flexural beam tests. Strain hardening under bending was observed, as was the propagation of multiple cracks (multicracking) in SFRC beams, in contrast to the brittle failure of the plain concrete specimen. The stress–strain behaviour of the material was quantified by means of digital photographs of the test, and Young's modulus of the SFRC was found to be similar to that of plain concrete. Cracks on the side of the beam as small as 0·05 mm and up to 4 mm were measured with an error < 0·02 mm, making PIV a viable option for crack width analysis for the basis of SFRC design assisted by testing, supported by BS EN 1990.