- Dept. of Civil Engineering
Isfahan University of Technology (IUT)
Isfahan
Iran
Davood Mostofinejad
Isfahan University of Technology, Civil Engineering, Department Member
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Abstract The externally-bonded reinforcement on grooves (EBROG) has been recently developed as a substitute for the conventional externally-bonded reinforcement (EBR) technique used to retrofit reinforced concrete (RC) structural members... more
Abstract The externally-bonded reinforcement on grooves (EBROG) has been recently developed as a substitute for the conventional externally-bonded reinforcement (EBR) technique used to retrofit reinforced concrete (RC) structural members with fiber-reinforced polymer (FRP) composites. While the presently available bond-slip models predict the bond-slip behavior of FRP composites adhered to the concrete surface via the conventional EBR method, there is a lack of reports in the literature on rigorous bond-slip model for FRP composites attached to concrete surfaces via the EBROG technique. Using a nonlinear regression on experimental data, the current research attempts to introduce an empirical model for such bond-slips. For this purpose, FRP composite strips were bonded to 68 concrete prism specimens retrofitted through the EBR and EBROG technique, before subjecting them to the single lap-shear experiment (108 tests in all). The test parameters included compressive strength of concrete, grooves dimensions (width and depth), composite strip width, and composite stiffness. A bilinear bond-slip model was proposed. Maximum shear stress, fracture energy, and associated slip were determined by analyzing on-groove and out-of-groove stresses and strains via the image processing method of particle image velocimetry (PIV). Finally, analysis of variance and different statistical tools were employed to validate the results obtained from the bond-slip model developed.
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AbstractIn recent years, the grooving method in the form of “externally bonded reinforcement on groove” (EBROG) has been introduced as an alternative method of the conventional externally bonded re...
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ABSTRACT: The use of fibre-reinforced polymer (FRP) composites to strengthen existing concrete structures is rapidly expanding. One of the important reasons that lead to initial failure is non-preparation of the concrete surface before... more
ABSTRACT: The use of fibre-reinforced polymer (FRP) composites to strengthen existing concrete structures is rapidly expanding. One of the important reasons that lead to initial failure is non-preparation of the concrete surface before attaching the FRP laminate. In ...
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In this study, an analytical method for the dam break flow of non-Newtonian fluids is extended to model self-compacting concrete flow in the L-box test. The rheology of fresh self-compacting concrete is expressed by a Bingham model. To... more
In this study, an analytical method for the dam break flow of non-Newtonian fluids is extended to model self-compacting concrete flow in the L-box test. The rheology of fresh self-compacting concrete is expressed by a Bingham model. To simplify the mathematical formulation, inertia forces and the effect of rebar are neglected and the fluid is assumed to be homogeneous. Several self-compacting concrete mixtures with different yield stresses are also tested to measure the L-box blocking ratio. The proposed model arrested profiles satisfactorily coincide with the experimental results. A relation between yield stress and the L-box blocking ratio is also derived. A comparison between the predicted values of yield stress and the experimental results shows that the proposed model successfully evaluates the yield stress of the tested samples. Moreover, it is observed that the proposed model is valid in the case of an L-box with rebar. Finally, a plot of the relative yield stress against L-box blocking ratio is presented that can be practically used for workability design of self-compacting concrete.
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Structural repair and strengthening have long been dynamic and challenging activities in construction work. One of the most commonly used methods for such repairs is the application of fiber-reinforced polymer (FRP) sheets to strengthen... more
Structural repair and strengthening have long been dynamic and challenging activities in construction work. One of the most commonly used methods for such repairs is the application of fiber-reinforced polymer (FRP) sheets to strengthen RC or even steel ...
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Reinforced concrete (RC) flat slabs are widely being applied to almost every building structure due to their distinct advantages. Nevertheless, there has not yet been a definitive method to precisely foresee the governing slab failure... more
Reinforced concrete (RC) flat slabs are widely being applied to almost every building structure due to their distinct advantages. Nevertheless, there has not yet been a definitive method to precisely foresee the governing slab failure modes. This research was targeted at predicting the main failure mode of RC slab-column connections subjected to unbalanced moment and various vertical shear forces, for the first time. Thus, the failure modes of the connections were deviated by comparing the unbalanced moment capacity at punching shear failure controlled by the codes and unbalanced moment strength at the flexural mechanism checked by the yield line theory (YLT). The procedure was validated by the results of experimental tests carried out at authentic research in the literature. Afterward, 200 case studies were done on the connections under moment transfer at 20%, 40%, and 60% of gravity shear ratios (GSRs), regarding the alteration of flexural reinforcement ratio from zero to 3.0%. Op...
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This paper deals with evaluating the rehabilitation convenience of a damaged RC beam under the combined shear-torsion effect and retrieving its shear-torsion capacity by using FRP rolled strips. To this end, 9 specimens with 2.85 m... more
This paper deals with evaluating the rehabilitation convenience of a damaged RC beam under the combined shear-torsion effect and retrieving its shear-torsion capacity by using FRP rolled strips. To this end, 9 specimens with 2.85 m lengths and clamped-clamped boundary conditions were made and tested under combined shear and torsion up to fracture (from zero loading eccentricity, corresponding to pure shear, to infinite eccentricity, due to pure torsion). Five of the specimens were ordinary (control) specimens considered as reference and four of them were strengthened with FRP strips from the beginning. Also, four of the ordinary specimens were rehabilitated after fracture by rubbing cement mortar on the cracked faces, then strengthened and tested like other specimens. Results indicated that rehabilitating and strengthening the beam will not only retrieve the initial shear-torsion capacity, but also increase the ultimate capacity up to 60 %. The increased capacity for the specimens s...
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Four 6.5 m long two span continuous beams were tested to investigate the feasibility of using FRP grids as shear reinforcement. The beams were longitudinally reinforced with equal amounts of CFRP reinforcement while transversely two beams... more
Four 6.5 m long two span continuous beams were tested to investigate the feasibility of using FRP grids as shear reinforcement. The beams were longitudinally reinforced with equal amounts of CFRP reinforcement while transversely two beams were reinforced with steel stirrups and two with CFRP grids. The two spans of each beam had identical amount and disposition of reinforcement, and were symmetrically loaded with a point load at the center of each span. For the beams with steel stirrups, the so-called A(v)/s = 2.0 mm while for the ones with CFRP grade the equivalent quantity was 1.75 mm. The elastic modulus of the grid was half the elastic modulus of the steel. The beams were monotonically loaded to destruction and they all failed in flexure. Despite their lower shear reinforcement ratio, the beams with the CFRP grid performed as well as those with the steel stirrups. They actually failed at 10% higher load that the beams with steel stirrups. Strain values of up to 0.4% were increased in the grids. Recognizing the practical convenience of grid shear reinforcement over custom manufacturing of stirrups, and considering their satisfactory performance, as observed in the present testing program, the use of FRP grids as shear reinforcement is indeed feasible.
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Concrete shear walls are the most prevalent structural systems resisting lateral loads due to earthquakes in high-rise buildings. Very large in-plane stiffness of shear walls provides an excellent drift control in the structure. However,... more
Concrete shear walls are the most prevalent structural systems resisting lateral loads due to earthquakes in high-rise buildings. Very large in-plane stiffness of shear walls provides an excellent drift control in the structure. However, structural damages and early code shortcomings threaten the efficiency of existing structural walls against earthquake. Recently, fiber reinforced polymer (FRP) materials have been used considerably in strengthening and retrofitting of structural elements. High tensile strength and excellent tensile modulus along with other unique features of FRP materials make them the first alternative in the strengthening projects. However, the literature shows that few analytical and/or experimental studies have been conducted on the strengthening of slender reinforced concrete (RC) shear walls with FRP materials so far. In this paper, the effect of strengthening of boundary elements in slender RC shear walls with FRP on the overall behavior of shear walls is in...
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Abstract Numerous studies have been so far conducted to better understand the behavior of fiber-reinforced polymer (FRP) sheets adhered to the concrete surface. In most studies, effective bond length has been known as an important... more
Abstract Numerous studies have been so far conducted to better understand the behavior of fiber-reinforced polymer (FRP) sheets adhered to the concrete surface. In most studies, effective bond length has been known as an important concept, which beyond this length, loading capacity cannot be increased. To more scrutinize on effective bond length of FRP-concrete joints, in the present study the bond behavior of FRP-concrete joints was investigated and an attempt was made to determine the effective bond length of the joints. To this end, first, 24 concrete prisms of three grades of different compressive strengths were made and strengthened with various ranges of thickness, elastic modulus, and type of FRP composites; and the specimens were subjected to the single-shear test. The particle image velocimetry (PIV) technique was employed to obtain the load-slip curves and the strain and slip profiles along the joints. An attempt was made to detect the beginning of debonding through investigating the bond behavior of FRP-concrete, and consequently, the effective bond length was measured. A simplified analytical method was then developed to predict the effective bond length such that it be independent of the bond-slip relationship. Finally, comparisons were made between the values predicted by the well-known models and those obtained from the experimental results. Moreover, the new procedure suggested in this study was found capable to predict the effective bond length with reasonable accuracy.
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Abstract The growing interest in fiber-reinforced polymer (FRP) composites in recent years for use in strengthening concrete structures bears witness to their efficiency and ease of use. A major is...
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The fiber/matrix interface in fiber reinforced concrete (FRC) enhances due to the geometry of fiber surface. This work benefits from freedom of fiber engineering due to the availability of fiber production facilities. Non‐indented,... more
The fiber/matrix interface in fiber reinforced concrete (FRC) enhances due to the geometry of fiber surface. This work benefits from freedom of fiber engineering due to the availability of fiber production facilities. Non‐indented, indented, flat tape, and fibrillated macro polypropylene fibers were produced. The effect of fiber surface indentation and fibrillation on FRCs flexural performance was investigated. Concrete flexural strength due to the effect of fiber young modulus was found to increases by 94 and 61%, when indented and fibrillated fibers are used, respectively. The energy absorption capacity of samples containing indented and fibrillated fibers due to the effect of surface fibrillation were found to be 5.5 and 12.5 times more than that of control concrete, respectively. The mechanical performance of FRCs was modeled using finite element model. The model generated and experimental results showed acceptable compatibility. Thus, the model can be concluded to be a successf...
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In some of biaxial voided slabs, spherical or ellipsoidal plastic balls enclosed in steel cages are used to eliminate ineffective concrete. To investigate the bending and shear behavior of this system, five full‐scale specimens were cast... more
In some of biaxial voided slabs, spherical or ellipsoidal plastic balls enclosed in steel cages are used to eliminate ineffective concrete. To investigate the bending and shear behavior of this system, five full‐scale specimens were cast including two bending specimens for investigating bending capacity and cracking distribution as well as three shear specimens used to study the shear capacity, cracking distribution, and concrete casting effect on the shear behavior. Moreover, the effects of the steel cage rods were studied on the bending and shear capacity. It was found that while both solid and biaxial voided specimens exhibited almost similar failure mode, both the bending and shear capacity of biaxial voided specimens were affected by the steel cages. In contrast, the voided specimens exhibited a significantly lower shear capacity than the solid ones while the different concrete casting methods had no effects on the capacity and behavior of biaxial voided specimens. Finally, a c...
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A new generation of cementitious composite materials as ultra-high performance concrete (UHPC) possessing notable mechanical characteristics, has demonstrated a high potential to be widely used in practice. In this research, first, the... more
A new generation of cementitious composite materials as ultra-high performance concrete (UHPC) possessing notable mechanical characteristics, has demonstrated a high potential to be widely used in practice. In this research, first, the compressive strengths of UHPC composites with various mixture designs and by exploitation of different curing conditions (water, autoclave, and heat curing) were investigated. Based on the results, it was perceived that the stepwise method proposed herein led the compressive strength of the samples to rise from 76 MPa to 212 MPa exhibiting an augmentation of about 179%. Furthermore, to scrutinize the impact of fiber hybridization on the behavior of UHPC composites in flexure, polyvinyl alcohol (PVA) and modified polypropylene (PP) fibers with different volume fractions were incorporated into the cementitious matrix. The maximum increase in flexural strength owing to the contribution of added fibers was observed to be 128%. The previous studies have shown that hybrid PVA-PP has no effects on enhancement in the mechanical properties of engineered cementitious composites (ECC); however, through this research, it was figured out that such hybrid fibers have a remarkable influence on the improvement of flexural strength, toughness, and energy absorption capacity of UHPC. According to the load-deflection curves, it can be expressed that all the hybrid PVA-PP fiber-reinforced cementitious composites examined in this study possess strain-hardening properties associated with bending. Furthermore, the strain-hardening behavior in UHPFRC incorporating PVA and modified PP fibers is more pronounced in comparison to that of ECC. The results demonstrate that such hybridization is a promising technique and yields a composite material with superior mechanical characteristics.
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Abstract The durability of environment-friendly concrete containing two types of waste material is investigated. Glass powder and microsilica with high silica content were selected to compare their effects on the durability of... more
Abstract The durability of environment-friendly concrete containing two types of waste material is investigated. Glass powder and microsilica with high silica content were selected to compare their effects on the durability of self-consolidating concrete (SCC) and ordinary concrete with the same packing density in the acidic medium. Experimental results show that microsilica and glass powder do not contribute to concrete corrosion reduction and the most important variable would be superplasticizer content. According to this result, ordinary concretes with lower superplasticizer content show better performance in HCl medium than SCCs. For a quantitative analysis and even to elicit the optimum values for minimum corrosion from the experimental results, an artificial neural network (ANN) and particle swarm optimization (PSO) were used. The minimum mass-loss was related to 15.68% for the volume of permeable pores and the optimum value for compressive strength would be in the range of 32–34 MPa.
Research Interests: Environmental Engineering, Materials Science, Cleaner Production, Concrete, Recycled Construction Materials, and 13 moreConcrete Technology, Construction Waste Management, Durability of Concrete, Manufacturing Engineering, Self-Consolidating Concrete, HCL, Materials waste in construction projects, Interdisciplinary Engineering, Cement and Concrete Materials, Innovative Materials and Sustainable Concrete Construction, Glass Powder, Acid Attack test, and Microsililca(Concrete Technology, Construction Waste Management, Durability of Concrete, Manufacturing Engineering, Self-Consolidating Concrete, HCL, Materials waste in construction projects, Interdisciplinary Engineering, Cement and Concrete Materials, Innovative Materials and Sustainable Concrete Construction, Glass Powder, Acid Attack test, and Microsililca)
(Concrete Technology, Construction Waste Management, Durability of Concrete, Manufacturing Engineering, Self-Consolidating Concrete, HCL, Materials waste in construction projects, Interdisciplinary Engineering, Cement and Concrete Materials, Innovative Materials and Sustainable Concrete Construction, Glass Powder, Acid Attack test, and Microsililca)
Abstract Using glass powder to manufacture eco-friendly self-consolidating concrete (SCC) has been developed and improved in recent years. While researchers have determined the effect of glass powder on rheological properties of the green... more
Abstract Using glass powder to manufacture eco-friendly self-consolidating concrete (SCC) has been developed and improved in recent years. While researchers have determined the effect of glass powder on rheological properties of the green concretes, the sensitivity of SCC to this powder content yet remains to be investigated. This study introduced the concepts of insensitive design, and subsequently, the ranges of water to powder ratio, sodium lignosulfonate plasticizer (LS), and glass powder were determined and optimized by the artificial neural network and particle swarm optimization, respectively. The results showed the possibility of producing SCC with the least possible sensitivity to water, glass powder, and plasticizer variations. The best water to cement ratio to design an insensitive SCC derived between 0.33 and 0.34, but the reduction in the compressive strength was inevitable for the augmented water-to-cement ratio. The effect of glass powder on alkali-silica reactions (ASR) and compressive strength was also investigated to clear the way for the incorporation of glass powder in SCC. The results indicated that the ASR reduced to 52% by substituting 30% glass powder.
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Abstract Recent advances in construction engineering have made the design of safe structures possible and attracted an increasing attention to the use of concrete for its beneficial properties. This has, in turn, instigated a lot of... more
Abstract Recent advances in construction engineering have made the design of safe structures possible and attracted an increasing attention to the use of concrete for its beneficial properties. This has, in turn, instigated a lot of efforts aimed at improving the physical and chemical properties of concrete. This is while increasing numbers of industry are producing waste products that warrant to be reused in order to avoid their dumping into the environment. One way to prevent accumulation of waste products in the environment is to use them as useful substitute materials in concrete. Along these lines, the use of ceramic wastes in concrete has been widely investigated. Porcelain ceramic is a new generation of ceramics that is highly heat resistant and offers a great resistance against pressure; however, these ceramics cannot be recycled to return to the production line in factories and are inevitably dumped into the environment as waste products. In the present research, two types of porcelain and ordinary red ceramics were used as substitutes for coarse aggregates in concrete. For this purpose, 65 specimens were cast to test their compressive, tensile, and flexural strengths as well as their water absorption. It was found that porcelain tile waste was able to increase concrete compressive strength by up to 41% while the red ceramic one increased it by up to 29%. Additionally, porcelain was found capable of increasing tensile and flexural strengths by up to 41% and 67%, respectively. Water absorption tests revealed that while porcelain increased concrete water absorption by up to 54%, red ceramic waste increased it by 91%. The superior performance of porcelain over that of red ceramic waste was attributed to the high porosity of red ceramics.
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Abstract Combination of microsilica and nanosilica (colloidal silica) are considered to design a high strength self-consolidating concrete to resist in the sulfuric acid medium. Artificial intelligence was used to predict and compare the... more
Abstract Combination of microsilica and nanosilica (colloidal silica) are considered to design a high strength self-consolidating concrete to resist in the sulfuric acid medium. Artificial intelligence was used to predict and compare the behavior of these two pozzolans in a sulfuric acid medium. Contour plots were used to investigate the products combination better. Thermogravimetric analysis (TGA) was also used to find the calcium hydroxide range while using these two pozzolans. TGA revealed that colloidal silica did not contribute to cement hydration within seven days of curing while a combination of them boosted calcium hydroxide consumption. The results show that more substitution of the pozzolans could lead to lower mass loss while nanosilica has marginal effect on the residual compressive strength. The results also revealed that 7 percent substitution of microsilica showed the same effect as 2 percent nanosilica replacement.
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Experimental studies show that an indeterminate structure or a continuous concrete beam does not fail when critical sections reach their ultimate strengths. Therefore, if a structure has adequate ductility, stress and moment... more
Experimental studies show that an indeterminate structure or a continuous concrete beam does not fail when critical sections reach their ultimate strengths. Therefore, if a structure has adequate ductility, stress and moment redistribution will take place in the flexural members by developing plastic hinges at critical sections. This causes the other points of beams to achieve their ultimate strengths and capacities. Besides, moment redistribution allows designers to adjust the bending moment diagram computed by elastic analysis. The usual result is a reduction in the values of negative moments at the support face as well as an increase in the values of positive moments along the span. In the current investigation, a parametric study on moment redistribution in continuous RC beams with equal spans under uniform loading was performed. First, the governing equation for the allowable percent of moment redistribution was extracted using ductility demand and ductility capacity concepts. ...
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ABSTRACT The present paper describes an experimental investigation of moment redistribution of continuous beams in 6 two-span RC frames strengthened with CFRP laminates. Design variables were the number of CFRP layers, and the... more
ABSTRACT The present paper describes an experimental investigation of moment redistribution of continuous beams in 6 two-span RC frames strengthened with CFRP laminates. Design variables were the number of CFRP layers, and the configuration of the laminates. To prevent debonding of the CFRP laminates at the end region and at the beam-column connection, U-shaped CFRP anchorages were provided for all of the frame specimens. Furthermore, mechanical anchorages of steel plate strips and bolts were added to the laminates in one frame of these specimens. Test results showed that a maximum moment redistribution of 56% occurred in the strengthened frames. Furthermore, the load carrying capacities of the strengthened frames increased from 20% to 38%, while the flexural capacities had an increase of 9% to 20% and 35% to 55% at the negative and positive moment regions, respectively.
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Abstract Shear is the predominant failure mode in most reinforced concrete (RC) short columns under seismic loads. The overall structural performance of short columns can be improved by shear stren...
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Abstract Use of bacteria in concrete is an eco-friendly technique to enhance concrete durability. Since the concrete is a dry and alkaline medium, the present study implemented air-entrained concrete to protect bacteria against this harsh... more
Abstract Use of bacteria in concrete is an eco-friendly technique to enhance concrete durability. Since the concrete is a dry and alkaline medium, the present study implemented air-entrained concrete to protect bacteria against this harsh environment. For this purpose, electrical resistivity experiments were conducted using 90- and 120-days old concrete specimens. Rapid chloride permeability tests were also performed on 90-days specimens. The experiments were designed using fractional factorial split plot (FFSP) to decrease the number of tests while the results remain reliable. Results obtained based on FFSP statistical analyses indicated that inclusion of bacteria enhanced the electrical resistivity and reduced the chloride permeability of concrete. Even better results were achieved with high air content percentages since the bacteria exhibited a better performance near the air voids. Furthermore, it was shown that surface treatment with bacteria increased concrete electrical resistivity and further reduced its chloride penetration for specimens cured in a medium containing minerals. In addition, lower porosity was observed in scanning electron microscopy (SEM) analysis when the specimens contained bacteria.
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AbstractConcrete is one of the most widely used materials in building structures; hence, improving its durability is important. Corrosive agents affecting concrete durability find their way into co...
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The effects of such environmental conditions as alkali media at temperatures of 23℃, 40℃, and 60℃ were investigated on the fiber reinforced polymer-to-concrete bond strength. For this purpose, 42 specimens were strengthened via the... more
The effects of such environmental conditions as alkali media at temperatures of 23℃, 40℃, and 60℃ were investigated on the fiber reinforced polymer-to-concrete bond strength. For this purpose, 42 specimens were strengthened via the externally bonded reinforcement and the externally bonded reinforcement on grooves techniques. The specimens were later subjected to the single-shear test after the specified durations of exposure to an alkaline medium. The particle image velocimetry technique was used to investigate such bond characteristics of the strengthened specimens as load-slip behavior, strain profiles, and strain fields along the fiber reinforced polymer-to-concrete bond. Experimental results showed that the specimens strengthened via the externally bonded reinforcement on grooves method exhibited ultimate bond loads by up to 50% higher than those strengthened via the externally bonded reinforcement method.
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One of the most common practices for strengthening the reinforced concrete structures is the application of FRP (Fiber Reinforce Plastic) sheets to increase the flexural and shear strengths of the member. The elastic modulus of FRP is... more
One of the most common practices for strengthening the reinforced concrete structures is the application of FRP (Fiber Reinforce Plastic) sheets to increase the flexural and shear strengths of the member. The elastic modulus of FRP is considerably higher than that of concrete. This will result in debonding between the FRP sheets and concrete surface. With conventional surface preparation of concrete, the ultimate capacity of the FRP sheets can hardly be achieved. New methods for preparation of the bonding surface have shown improvements in reducing the premature debonding of FRP sheets from concrete surface. The present experimental study focuses on the application of grooving method to postpone debonding of the FRP sheets attached to the side faces of concrete beams for shear strengthening. Comparison has also been made with conventional surface preparation method. This study clearly shows the efficiency of grooving method compared to surface preparation method, in preventing the d...
Concrete shear walls are the most common system resisting against seismic loads in the world. These elements carry the lateral loads by a combination of the axial, shear and flexural responses. Change in the seismic code requirements,... more
Concrete shear walls are the most common system resisting against seismic loads in the world. These elements carry the lateral loads by a combination of the axial, shear and flexural responses. Change in the seismic code requirements, subjecting intensive dynamic loads such as explosion or earthquake and other destructive effects make the shear walls weak for continuing service life. In the recent years FRP materials have attracted much interest. FRP application in retrofitting projects is appealing because of their unique properties. Nevertheless, a review on the previous studies shows that despite the squat walls, very limited analytical and/or experimental studies have been conducted on the FRP strengthening of the slender RC shear walls under monotonic loading so far. In this paper it is focused on the strengthening of boundary elements with FRP and it’s effect on the wall behavior. The finite element software is calibrated and verified using available experimental data. Nonline...