Cracked Beams Research Articles

Flexural behavior of hybrid fibre-reinforced geopolymer composites (FRGC)-jacketed RC beams

Fibre-reinforced geopolymer composites (FRGC) are drawing interest as potential repairing and strengthening materials for concrete elements due to their desirable properties. They are known to have good mechanical bond with the concrete substrate and steel reinforcement, good fire resistance, greater durability in corrosive environments, and lower creep and shrinkage characteristics. However, the main challenge in their practical application is the lack of design standards and the structural performance of FRGC-rehabilitated concrete elements has not been fully investigated. In this paper, the result obtained from an experimental study on the flexural behavior of reinforced concrete (RC) beams jacketed by hybrid FRGC is reported. Six repair and strengthening configurations were adopted in this study including jacketing at the bottom, two and three sides of the beam with at least 25 mm thick FRGC layer. Twelve FRGC-jacketed and two control beams were subjected to four-point bending test to determine their loading performance, cracking response, ductility and energy absorption capacity. In addition, an analytical model was developed to predict the ultimate moment capacity of the jacketed beams. The results showed that FRGC-jacketing technique increased the cracking, yielding and ultimate load of the initial RC beams by up to 167%, 62% and 62% respectively. Among the seven repair and strengthening patterns, the bottom and three-sides jacketing provided less ductile response, nevertheless, it offered a 32% increase on the energy absorption value of the initial RC beam. It also indicated that all jacketed RC beams displayed no sign of overlay delamination up to failure, confirming a bond excellence between the FRGC and concrete substrate. The model predicting the flexural moment capacity of the FRGC jacketed beams compared reasonably with the experimental results with error value of 4–7%.

Evaluation of Smeared Constitutive Laws for Tensile Concrete to Predict the Cracking of RC Beams under Torsion with Smeared Truss Model.

In this study, the generalized softened variable angle truss-model (GSVATM) is used to predict the response of reinforced concrete (RC) beams under torsion at the early loading stages, namely the transition from the uncracked to the cracked stage. Being a 3-dimensional smeared truss model, the GSVATM must incorporate smeared constitutive laws for the materials, namely for the tensile concrete. Different smeared constitutive laws for tensile concrete can be found in the literature, which could lead to different predictions for the torsional response of RC beams at the earlier stages. Hence, the GSVATM is used to check several smeared constitutive laws for tensile concrete proposed in previous studies. The studied parameters are the cracking torque and the corresponding twist. The predictions of these parameters from the GSVATM are compared with the experimental results from several reported tests on RC beams under torsion. From the obtained results and the performed comparative analyses, one of the checked smeared constitutive laws for tensile concrete was found to lead to good predictions for the cracking torque of the RC beams regardless of the cross-section type (plain or hollow). Such a result could be useful to help with choosing the best constitutive laws to be incorporated into the smeared truss models to predict the response of RC beams under torsion.

FLEXURAL BEHAVIOR OF REINFORCED LIGHTWEIGHT CONCRETE BEAMS MADE WITH ATTAPULGITE AND ALUMINUM WASTE

Lightweight concrete reduces the total dead load of structural elements and seismic loads significantly. This paper presents the production Attapulgite Lightweight aggregate concrete (ALWAC) and its effect on the flexural behavior of reinforced concrete beams. Attapulgite was treated with sodium hypochlorite of 6% concentration for 24 hours. The variable considered was the aluminum waste (AW), used as a fiber, of fraction (0, 0.5 and 1%) by concrete volume. Behavior was investigated in terms of cracking and ultimate load, load-deflection relationship, failure mode, crack patterns and flexural ductility. The mechanical properties of the ALWAC were studied. It was observed that, Attapulgite improves the mechanical properties of concrete when comparing the experimental value with theoretical ones for the reference mixture. AW has a disparate effect on the mechanical properties of ALWAC. The increase in the proportions of AW showed an increase in the cracking load and decrease in the ultimate load by 37.14% and 22.45 %, respectively, at AW of 1%. Experimental value of ultimate load in all beams was higher than the theoretical value (ACI simplified method). AW increases the deflection at the same magnitude of applied load, and reduces the number and propagation of the flexural cracks in beams. All beams exhibited a typical tension failure mode and failed in ductile manner.

Influence of Nano-silica and Crack Width on Corrosion Parameters of Pre-cracked Reinforced Concrete Beams

This paper presents an experimental study on the durability of both sound and cracked reinforced concrete (RC) beam specimens. Using nano-silica (NS) can improve the durability properties of reinforced concrete. So, RC beams with three nano-silica percentages of 0 %, 1.5 %, and 3 % were prepared. In addition, to consider the effect of cracking on corrosion, crack widths between 0.1 mm and 0.5 mm, and cover depths of 30 mm and 45 mm were considered. All beam specimens were subjected to 5 % NaCl solution and monitored weekly for half-cell potentials (HCP). The presented results include the HCP evaluation and diffusion factor values in sound and cracked concrete beams exposed to chloride attack. The experimental results indicated that the chloride diffusion coefficient increases with extending crack width. Nano-silica improved the permeability characteristics of concrete, HCP and also diffusion factor values. Regressive models of the chloride diffusion factor and HCP values were proposed for influencing parameters, i.e., nano-silica and crack width with two different cover depths.

Characteristic analysis of acoustic emission monitoring parameters for crack propagation in UHPC-NC composite beam under bending test

Ultra high performance concrete (UHPC) has more outstanding mechanical properties and durability than normal concrete (NC) materials. Currently, analysis methods for the mechanical properties of UHPC structures and UHPC composite structures, such as measuring structural deflection, strain, and observing crack propagation, are relatively single. Acoustic emission (AE) technique is a non-destructive testing method that evaluates the damage state of structures effectively. The variation characteristics of AE parameters can be used to analyze the damage process and the failure precursor information of the structures. On this basis, AE technique was used to monitor the crack propagation of the UHPC-NC composite beam under four-point bending test in this study. Results showed that the U-shape UHPC layer gave full play to its high strength and ductility characteristics under bending, which was mainly manifested in reducing the number and width of cracks of the UHPC-NC composite beam, reducing the mid-span deflection and increasing the cracking load (Pcr) and ultimate load (Pu). AE ringing counts, energy, and b-value showed different and easily distinguishable variation characteristics at each failure stage of UHPC-NC composite beam and can be considered the optimal AE monitoring parameters. RA-AF association analysis can be used to further analyze the failure mode of UHPC-NC composite beam. AE monitoring method can be considered an alternative to traditional monitoring methods for the real-time monitoring of crack propagation in UHPC-NC composite beams.

Flexural behaviour of high strength basalt FRP rebar concrete

In this paper, the flexural behaviour of under-reinforced M70 grade basalt FRP rebar concrete beams in terms of first crack load, pre-cracking and post-cracking behavior, deflection pattern, crack development pattern and ultimate load carrying capacity is evaluated. Loads at first crack in basalt FRP rebars beams are higher than the normal steel rebar concrete beams confirming that basalt FRP rebars beams offer greater resistance to cracking. The ultimate flexural strength of basalt FRP rebar concrete beams have improved when compared to normal steel rebar concrete beams. First crack formation was delayed in basalt FRP rebar concrete beams due to which fatigue strength is increased which in turn increases the time taken for first crack occurrence and thereby increasing the load carrying capacity. The deflection at the mid span decreased in basalt FRP rebar concrete beams which indicates the improved flexural stiffness of the elements thereby reducing the structural member’s deformability, increasing strength and hence controlling deflection. Mid-span deflections at peak load reduced in basalt FRP rebar concrete beams. The ultimate deflection in case of basalt FRP rebar concrete beams is less than that of normal steel rebar concrete beams.

Free vibration of the double tapered cracked beam

This study presents the free vibration analysis of a double tapered beam having linearly varying both thickness and width, by using finite element and component mode synthesis methods. To determine the natural frequency and mode shape of the double tapered cracked beam, the stiffness and mass matrices of the beam have been obtained. The crack in the beam is modeled as a massless spring, and the beam is divided into two subcomponents from the crack section. The stiffness of spring has been derived from the linear elastic fracture mechanics theory as the inverse of the compliance matrix calculated using stress intensity factors and strain energy release rate expressions. It has been observed that natural frequencies and mode shapes vary depending on the location of the crack, the depth of the crack and the aspect ratios of the beam. The results of the present study and those in the literature are compared and a great deal of consistency has been found.

Performance of BFRP RC beams using high strength concrete

This research investigates the flexural behavior and serviceability performance of basalt fiber-reinforced polymer (BFRP) reinforced concrete (RC) beams cast with normal- and high-strength concretes (NSC and HSC). Carbon FRP (CFRP) and steel-reinforced concrete beams were also included for comparison purposes. Four-point bending tests were performed on a total of 14 slender beams with dimensions of 180 mm × 230 mm × 2200 mm. The main aim was to examine the improvement in the performance of BFRP RC beams using HSC and to assess its compatibility with the recommendations and guidelines of the ACI440 Code. The test results were reported and discussed in terms of flexural capacity, deflection, crack width, reinforcement and concrete strains, and failure modes. The results revealed that the flexural capacities of BFRP beams were slightly underestimated by ACI440.1R-15 while reasonable predictions were observed for the cracking moments in HSC and NSC. The use of HSC as compared to NSC enhanced the cracking and ultimate moments of all BFRP RC beams by 10% and 16%, respectively. Furthermore, the average bond-coefficient (kb) value for BFRP-RC beams was found to be 0.70 which is much lower than the conservative kb value suggested by the ACI440 guidelines for sand-coated FRP bars.

Behaviour of steel beams retrofitted with anchored carbon-fibre-reinforced polymer strips

Steel bridge beams can be damaged due to increased traffic loads and environmental impacts. An experimental study on the use of bonded and mechanically anchored carbon-fibre-reinforced polymer (CFRP) strips was undertaken to assess the retrofitting of such steel beams. The number of mechanical anchors used in the ends of the bonded strips was varied from zero to eight. The steel beam samples were tested under four-point loading. Loading was applied as an increasingly high static load and a low repetitive fatigue load. The load–displacement behaviour under the effects of static and fatigue loading and the strain distributions along the strips were measured and interpreted. The results showed that retrofitting cracked steel beams with CFRP strips is an effective method. In addition, retrofitting with anchored strips increased the performance of cracked beams under the effects of both static and fatigue loading.

Bending behaviour of reinforced concrete/engineered cementitious composite beams

Engineered cementitious composites (ECCs) are fibre-reinforced cementitious composite materials with ultra-high ductility. Their excellent tensile properties can make up for the defects of the poor tensile properties and easy cracking of concrete materials. ECCs can thus be used to replace concrete material in the tensile regions of structural components, and the high tensile strength of ECCs can be utilised to form ECC–reinforced concrete (RC) composite beams with good crack controllability. In the work reported in this paper, six ECC–RC composite beams with different ECC cross-section replacement ratios (0, 0·2, 0·4, 0·6, 0·8 and 1·0) were tested to examine the effects of the ECC cross-section replacement ratio on the flexural capacity, deformation and cracking of the composite beams. The experiments showed that the plane section assumption is valid for ECC–RC composite beams in the elastic stage. Compared with an ordinary RC beam, the bearing capacity and ductility of the composite beams were significantly improved and the crack width was reduced. It was found that there is an optimal replacement interval for the ECC cross-section replacement ratio, from which a balance between excellent mechanical properties and economic use of ECC materials may be obtained.

Lengthwise fracture of functionally graded beams: a study of stress relaxation effects

The present paper is focussed on analyzing the strain energy release rate for a lengthwise crack in a cantilever beam that exhibits stress relaxation. The beam is continuously inhomogeneous in the thickness direction. A linear viscoelastic model is used for treating the stress relaxation. The balance of the energy is analyzed in order to derive a time-dependent solution to the strain energy release rate. The equilibrium of the lower crack arm and the un-cracked beam portion is considered to determine the curvatures and the coordinates of the neutral axes which are involved in the solution. The compliance method is applied in order to verify the solution to the strain energy release rate. A time-dependent solution to the strain energy release rate is derived also for the case of material exhibiting different viscoelastic behaviour in tension and compression. The solutions derived are used to investigate the evolution of the strain energy release rate with the time. The influence of the crack location along the thickness of the beam and the material inhomogeneity on the time-dependent strain energy release rate under stress relaxation is also investigated.

Modeling of crack opening mode sif for a crack in a thin-walled structural channel beam

The analysis of engineering methods for determining stress intensity factors (SIF) for defective elements of open profile (channels) under bending is carried out. Mathematical models are created and dependences for calculation of SIF are deduced using two methods: using nominal stresses in net-section and using change of the inertia-moment of the profile cross-section. The obtained results are compared with the data of SIF for the crack in the channel obtained during simulation modeling using finite element method.

Damage indices evaluation for one-dimensional guided wave-based structural health monitoring

Damage detection in structures and systems is essential for monitoring parameters that can affect their integrity. This paper evaluates the efficiency of four damage indices (DIs) commonly used with temporal wave signals. The root mean square deviation, mean absolute percentage deviation, covariance, and correlation coefficient deviation DIs are presented, and a normalization is then proposed. An Euler-Bernoulli beam is used as a guided wave modelled with the spectral element method and excited by a toneburst signal. It includes the theoretical background of the throw-off beam, undamaged and cracked beam spectral elements. The DIs for a single crack position and a map varying crack depth and positions are calculated with deterministic and random temporal signal responses derived from noise addition. Results showed that DIs could identify and quantify the damage conditioned to the pulse location point and the influence of noise in the estimation, which leads in an analysis comparable to practical applications.

FEM evaluation of reinforced concrete beams by hybrid and banana fiber bars (BFB)

This research study highlights composite materials that consist of two parts—a matrix and fiber—and that have become commonly used in building materials. There are two types of fiber: synthetic fibers, such as carbon, glass, aluminum, aluminum oxide, boron, etc., and natural fibers, such as banana, jute, coir, silk, bamboo, coconut, etc. While synthetic fibers are the most common and are used despite their high cost, this study researches banana fibers, which are generally made from plant wastes and are therefore less costly. This study is based on the identification of banana fibers and their impact on the flexure behavior of concrete. The experiment tested ten models of concrete beams with various parameters using an experimental program and a finite element analysis (ANSYS) to study (1) the performance of banana fiber bars in reinforced beams, (2) the influence of hybrid fibers that contain banana and glass fiber, and (3) the effect of banana fiber bars on beams compared to traditional steel bars. The results demonstrate that using banana fibers has a significant effect in reducing cracking in concrete beams. From this research, it is clear that natural fibers increase flexure strength, which contributes to reduced depth of concrete sections and develops an innovative technique of reinforcement.

Dynamic analysis of multiple cracked Timoshenko beam under moving load–analytical method

When cracks start to surface in the surrounding areas of the structure, they create a local softness zone and influences on the dynamic response of the structure. The beams are more susceptible to shear and flexural cracks because of being subjected to shear and bending stress. In this study, the dynamic response of the single-span and multi-span damped beam under moving load with multi-crack and elastic boundary condition is studied based on Timoshenko’s theory. The Green’s function method is used to calculate the dynamic response of the cracked beam. In addition, the Green’s function method provides a solution for the differential equations. Moreover, the effects of the crack on the essential characteristics of the multi-span beams, especially the natural frequencies, are investigated. In this study, crack by itself is modeled in different situations and its effect on the behavior of the beam is analyzed. Also, the elastically restrained beam is modeled and its effect on the behavior of the beam is assessed. Because of the fact that the Euler–Bernoulli theory is also used in most beams, in this study, the results of the numerical examples are compared with the Euler–Bernoulli theory. Several examples are analyzed for a better understanding of the Timoshenko cracked beam.

Experimental Study on Dynamic Amplification Factor of Simple-Supported Reinforced Concrete Beams Under Impact Loading Generated by an Impulse Hammer

The empirical formulas of dynamic amplification factor (DAF) specified in current bridge codes only consider the span or fundamental frequency of reinforced concrete (RC) girders in highway. Although investigations have been carried out on different bridges with considering the road roughness, vehicle–bridge interactions and travelling velocity, but most of them have been done numerically. In this study, experimental study of DAF was carried out on three simple-supported RC beams with different fundamental frequencies and different damage stages, i.e. without damage, cracked and yielded. Impulse hammer with four hammer heads of different hardness, i.e. black, red, green and brown, were used to generate impact forces with increasing duration. The impact tests were first carried out on the RC beams without any damage by impact hammer with different hammer heads. Then the RC beams were loaded by a concentrated static force at the mid-span to crack. Impact tests with different hammer heads were repeated on the cracked RC beams. Finally, the cracked beams were further loaded by a concentrated static force to yield of the longitudinal reinforcement. The impact tests were repeated on the yielded beams again. Load cells installed at the supports of the RC beams were used to measure the reaction force generated by the hammer, then DAF was calculated directly by dividing the peak reaction force with the peak impact force. Data obtained from tests, theoretical analysis and specification in codes were compared to examine the DAFs. Results show that the ratio of duration of the impact force and the period of the beams performed a significant effect on the DAFs of the beams.

Strength and ductility performance of corroded steel bars in concrete exposed to 2D chloride ingress

AbstractThis paper presents the residual tensile strength test results of corroded high yield steel bars. Single steel bars were embedded at a cover depth of 20 mm in 150 × 150 × 625 mm long cracked concrete beam specimens made with 70/30 PC/FA and 50/50 PC/SL binders with a constant w/b ratio of 0.40. The steel bars were placed in the cross-section centre and near the orthogonal edge of the beams, and selected beam faces epoxy-coated in order to simulate, respectively, 1D and 2D chloride ingress. The beams were subjected to 2-week wetting (with 5% NaCl) and 2-week air-drying cycles in the laboratory for 110 weeks after which the corroded steel bars were extracted, assessed for corrosion morphology, and tested in tension for ultimate strength, fracture strength and ductility performance. The steel bars in concretes exposed to 1D chloride ingress had isolated corrosion pits while both general and isolated corrosion pits were observed in specimens exposed to 2D chloride ingress. The residual ultimate and fracture tensile strengths, and ductility of corroded steel reinforcing bars in concretes exposed to 2D chloride ingress are lower than those for steel bars in concretes exposed to 1D chloride ingress.

Numerical and FEM Investigation on Dynamic Response of Damaged Cantilever Structures Carrying Transit Load

In the present investigation, the effects of crack related features such as crack position, crack height, as well as the mass and the velocity of the moving load on the vertical deflection of the damaged beams under the effect of moving load are analyzed. The governing equations of motion for cracked beams subjected to moving load have been obtained and they have been solved by applying the Duhamel integral technique. The responses of the structures due to the consequences of crack depth, crack location, moving speed, and moving mass are also determined. At first, the results between undamaged and damaged beams have been compared. Then, a comparative study between double and triple cracked beams has been conducted in order to understand the consequence of third crack on the dynamic characteristics of the beam. The mass-beam structural system has been modelled mathematically with the presence of open and transverse cracks with different crack configuration (crack depth and locations). Several numerical examples have been executed. In order to confirm the validity of the formulation, finite elements analysis has been carried out. The results gathered from the numerical analysis along with finite element analysis for undamaged, double, and triple cracked beams have been plotted for comparative results analysis. It has been concluded that the aforementioned parameters (crack depth, crack location, moving mass and moving speed) play an important role on the dynamic behaviour of the damaged structures.

Numerical modeling on varying patch repair size of cracked beam using engineered cementitious composites

PurposeThis study aims to investigate the size effect of the patched repairing material applied to the cracked beam.Design/methodology/approachNumerical analysis was conducted on a simply supported cracked beam with a dimension of 200 × 25 × 15 cm using ABAQUS software. The behavior of concrete and engineered cementitious composites (ECC) in the simulation are described as concrete damage plasticity model. Linear elastic-plastic model was used to represent the behavior of rebar steel. The type of patching consisted of the varying ratio of lengths and depths, including patching length to total length ratios of 0.2, 0.3 and 0.4, and patching depth to total depth ratios of 0.2, 0.3, 0.4 and 0.5.FindingsResults show that variations in the patching length and depth ratios affect the maximum flexural load, stiffness and ductility of the repaired beam. It was also found that repairing the cracked beam by using ECC provides higher flexural load of the beam than the use of conventional concrete, owing to the superior tensile strength of ECC.Originality/valueECC is the cementitious-based mortar that contains the special selected poly vinyl alcohol fiber having high tensile strength. ECC has been known to exhibit high ductility, high tensile strength and improve durability performance. Thus, ECC is suitable as repairing material for patching cracked beam. By investigating the size of the patched repairing material applied to the cracked beam, the structural performance of repairing beam and the effectiveness of the various patching size were achieved.

Residual life estimation of healthy and cracked composite beam using experimental and numerical modal analysis methods

Preventive maintenance is beneficial to minimize unexpected breakdowns in industries with continuous production. Composite structures are used for naval applications like ship hulls and marine propellers. In most of the industries, composite structural health analysis using experimental and numerical model are available for damage detection and estimate the residual life of composite beams. The present work is focusses on identification of damage and estimate residual life of composite healthy and cracked beams. Free vibrational analysis is carried out on composite beam made of glass fiber reinforced polymer (GFRP) with a different crack orientation. A fast Fourier transform (FFT) spectrum analyzer associated with engineering data management (EDM) software utilized for experimental analysis to detect presence of damage in cracked composite beam. FEM software called Analysis of composite pre/post (ACP) available in ANSYS R3 is used to compare the natural frequency results of healthy composite beam with cracked composite beam with different ply orientations. For validation of numerical modal evaluation, the consequences acquired from ANSYS R3 FEA software are in comparison with experimental results received by impact hammer method. The fatigue life of a damaged composite beam is estimated the use of “Hwang and Han’s” fatigue life equation.