Top PDF Ultimate shear of RC beams with corroded stirrups and strengthened with FRP

Ultimate shear of RC beams with corroded stirrups and strengthened with FRP

Ultimate shear of RC beams with corroded stirrups and strengthened with FRP

Abstract: Transverse reinforcement plays a key role in the response behavior of reinforced concrete beams. Therefore, corrosion of steel stirrups may change the failure mode of elements from bending to shear, leading to a brittle and catastrophic crisis. It is important to strengthen reinforced concrete beams with corroded stirrups to enhance the shear resistance. This paper presents a formulation, based on the modified compression field theory, to estimate the ultimate shear of reinforced concrete beams strengthened with FRP, because of stirrup corrosion. The detrimental effect of corrosion on steel stirrup yield strength was taken into account by introducing an empirical decay law. The effective strain of FRP reinforcement was adequately evaluated by considering both debonding and tensile stress rupture. The proposed model was validated against collected experimental results, showing a good ability to evaluate shear strength. Moreover, a numerical analysis was carried out to highlight the role of the key parameters predicting the ultimate shear.
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Strut-and-Tie Method for Prediction of Ultimate Shear Capacity of Shear-Strengthened RC deep beams with FRP

Strut-and-Tie Method for Prediction of Ultimate Shear Capacity of Shear-Strengthened RC deep beams with FRP

behave differently from shallow beams and generally their ultimate capacity is controlled by shear strength. The conventional design formulas not be useable for this type of RC beams. Some semi rational methods such as Strut-and-tie method have proposed to analysis and design of deep beams. Strut- and-tie modeling is the most rational and simple method for designing nonflexural members currently available. Specific strut- and-tie models need to be developed, whereas shallow beams are characterized by linear strain distribution and most of the applied load is transferred through a fairly uniform diagonal compression field. Design of nonflexural members using strut-and-tie modeling incorporates lower bound theory of plasticity assuming that both the concrete and the steel are perfectly plastic. The behavior and dimensional properties of steel are well known and the strength of members failing in tension can be predicted with some degree of certainty. The foundation of the method was laid by Ritter in 1899. Ritter’s original goal was to explain that stirrups in reinforced concrete members provided more than dowel action in resisting shear. Mörsch (1909) expanded on Ritter’s model by proposing that the diagonal compressive stresses in the concrete need not be discrete zones, but could be a continuous field. Foster, S.J et al
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Shear Behaviour of Slender RC Beams with Corroded Web Reinforcement

Shear Behaviour of Slender RC Beams with Corroded Web Reinforcement

Figure 3.13 shows a plot of the applied load vs. diagonal tensile strain crossing the inclined cracks within the middle instrumented region (300 mm from the support). Again, these beams exhibited stiff response until diagonal cracking occurred followed by a nonlinear response up to failure. At the ultimate load, it is clear that the corroded beams exhibited more shear deformation (or inclined crack opening) in comparison to the un-corroded beam. The un-corroded beam (D12-0%-UR) had diagonal tensile strain initiation at higher diagonal cracking load in comparison to the corroded beams. This was opposite to what was observed for beams with deformed corroded stirrups. As the corrosion level increased, the diagonal cracking load decreased due to the weakening of the bond between the concrete cover and the corroded stirrups. In this case, the outside layer (concrete cover) was partially engaged with the concrete core of the beam (which is inside the closed stirrups). As such the diagonal shear stresses in the corroded beams were mostly transmitted through the beam core leading to a reduction in the strength and the stiffness at higher corrosion level.
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Numerical Study on FRP Strengthened RC Deep Beams with Openings

Numerical Study on FRP Strengthened RC Deep Beams with Openings

The study conducted by Tamar El Maaddawy et.al [1] reported that the use of externally bonded carbon fiber polymer composite sheets was found to be very effective in upgrading the shear strength of RC deep beams. The strength gain caused by the CFRP sheets was in the range of 35% - 73%. Qudeer Hussain et.al [2] conducted an experimental study on Shear strengthening of RC deep beams with openings using sprayed glass fiber reinforced polymer composites. Mechanical anchors were used to prevent the de-bonding of FRP from the beam surface. From the studies, it was reported that the use of mechanical anchors were effective in preventing the de-bonding failure thereby increasing the ultimate load carrying capacity of the deep beams. M. R Islam et.al [3] reported that the use of FRP systems leads to a much slower growth of the critical diagonal cracks and enhances the load carrying capacity of the beam to a level quite sufficient to meet most of the practical upgrade requirements.
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An Artificial Neural Network Model for Estimating the Shear Contribution of RC Beams Strengthened by Externally Bonded FRP

An Artificial Neural Network Model for Estimating the Shear Contribution of RC Beams Strengthened by Externally Bonded FRP

The first study in shear strengthening of RC beams with FRP was performed by Berset [5]. He tested some RC beams in both of control specimens and FRP-strengthened specimens type and developed a simple analytical model for shear contribution of FRP composite, which in this model, FRP treated similar to steel stirrups. Uji [6] tested RC beams strengthened by FRP with bonding FRP on their side faces either vertical or inclined. In this study, Uji focused on debonding shear stress. In another work, Veilhaber and Limberger [7] tested some large scale RC beams, and the test results indicated that even small amounts of external reinforcement could avoid brittle shear failure. Chajes et al. [8] tested 12 beams, four as control specimens and eight as strengthened RC beams with aramid, E-glass, and graphite fibers. The tests results indicated that FRP composite increases in the ultimate strength of about 60 to 150 percent. Sato et al. [9] tested some
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Study on behaviour of corroded RC beams repaired in shear with NSM CFRP rods

Study on behaviour of corroded RC beams repaired in shear with NSM CFRP rods

The cost increase due to the rehabilitation of the deteriorated RC structures reaches to millions of euros each year. The corrosion of the steel bars in the RC elements leads to a reduction in the cross sectional area of the steel reinforcement and a significant reduction in its ductility which leads to the early failure of steel bars, [1, 2]. The near surface mounted reinforcement technique (NSM) is one of the promising techniques used nowadays. In the NSM technique, the Carbon Fibre Reinforced Polymer (CFRP) rods are placed inside pre- cut grooves and are bonded to the concrete with epoxy adhesive. [3] presented a testing program in order to assess the increasing of the shear capacity can happen by using the NSM FRP reinforcement technique, this test program tested the beams in two regions. The increase of the shear capacity was between 22% - 44% for beams strengthened with NSM reinforcement,
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Strengthening of Shear Deficient RC T-Beams with Externally Bonded FRP Sheets

Strengthening of Shear Deficient RC T-Beams with Externally Bonded FRP Sheets

Chaallal et al. (1998) investigated a comprehensive design approach for reinforced concrete flexural beams and unidirectional slabs strengthened with externally bonded fiber reinforced plastic (FRP) plates. The approach complied with the Canadian Concrete Standard. This was divided into two parts, namely flexural strengthening and shear strengthening. In the first part, analytical models were presented for two families of failure modes: classical modes such as crushing of concrete in compression and tensile failure of the laminate, and premature modes such as debonding of the plate and ripping off of the concrete cover. These models were based on the common principles of compatibility of deformations and equilibrium of forces. They can be used to predict the ultimate strength in flexure which can be achieved by such elements, given the FRP cross-sectional area, or conversely, the required FRP cross- sectional area to achieve a targeted resisting moment for rehabilitated flexural elements. In the second part, design equations were derived to enable calculation of the required cross- sectional area of shear lateral FRP plates or strips for four number of plating patterns: vertical strips, inclined strips, wings, and U-sheet jackets.
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A practical method for determining shear crack induced deformation in FRP RC beams

A practical method for determining shear crack induced deformation in FRP RC beams

During the tests on side A, several shear cracks developed on side B but crack opening was effectively controlled (maximum width=0.01 mm) by the post-tensioned steel strapping around the latter side. During the tests on side B, the flexural and shear cracks developed during the tests in side A propagated and penetrated deeper towards the loading point as the applied load increased. After the formation of diagonal cracks, the strain recorded in the shear stirrups increased rapidly and, eventually, failure occurred. As expected, all beams with stirrups were dominated by a shear diagonal failure. This was accompanied by stirrup rupture and concrete spalling at the beams’ soffit (Fig. 4b,c). The measured ultimate capacities of the beams with stirrups ranged between 77 and 134 kN.
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Effective Strain of RC Beams Strengthened in Shear with FRP

Effective Strain of RC Beams Strengthened in Shear with FRP

The failure modes of reinforced concrete (RC) beams strengthened in shear with fiber reinforced polymer (FRP) sheets or strips are not well understood as much as those of RC beams reinforced with steel stirrups. When the beams are strengthened in shear with FRP composites, beams may fail due to crushing of the concrete before the FRP reaches its rupture strain. Therefore, the effective strain of the FRP plays an important role in predicting the shear strength of such beams. This paper presents the results of an analytical and experimental study on the performance of reinforced concrete beams strengthened in shear with FRP composites and internally reinforced with conventional steel stirrups. Ten RC beams strengthened with varying FRP reinforcement ratio, the type of fiber material (carbon or glass) and configuration (continuous sheets or strips) were tested. Comparisons between the observed and calculated effective strains of the FRP in the tested beams failing in shear showed reasonable agreement.
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Behaviour of Strengthened RC Beams in Shear

Behaviour of Strengthened RC Beams in Shear

Since last few years, the demand of strengthening is going on increasing due to variety of reasons. The various reasons for deterioration of structural members include change in loading condition, improper design or execution, change of functionality of building etc. Construction of new structure post demolishing old one will not only be uneconomical but also it might have adverse effect on the adjoining structures. Thus, it is not advisable. Rather it is better to enhance the load bearing capacity of the present deteriorating structure. Beams are the most important members of any structure. They are designed for flexure and checked for shear. However, the flexural failure of beam is preferred against the shear failure which leads to catastrophic failure. Various materials are now available in the market for strengthening of RC Beams. A study has been carried out wherein 5 beams were casted of 2000 mm length, 200 mm width & 270 mm depth followed by testing after strengthening. In the current experiment, materials used for strengthening are weaved mesh and welded mesh, using mechanism of Ferro-cement & Micro-Concrete. Further loads and deflections were measured and the results show improvement in load carrying capacity of strengthened beam as compared to non-strengthened beam.
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Strength of RC and PSC Beams with High Strength Stirrups

Strength of RC and PSC Beams with High Strength Stirrups

shear can be resisted by either concrete or shear reinforcement. In the case where a concrete contribution is constant and high strength shear reinforcement is employed, the spacing of the shear reinforcement can be larger. Hence, there is a strong possibility that the diagonal crack width is increased. This is supported by ACI 318-11, which specifies that yield strength of shear reinforcement is limited to 420MPa in order to control the diagonal crack width. This is also supported further by the report of ASCE-ACI Committee 445 on Shear and Torsion, describing that the ACI 318 shear design approach is based on a parallel truss model with 45 degree constant inclination diagonals supplemented by an experimentally obtained concrete contribution, and hence it limits the maximum shear contribution of shear reinforcement to prevent diagonal crushing failures of the web concrete before yielding of the shear reinforcement (Lee and Lim (2011)).
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Structural performance of FRP strengthened concrete beams

Structural performance of FRP strengthened concrete beams

the centres of the beams were cut (width of 5 mm and depth of 75 mm) with an electronic saw. These saw-cuts were planned to induce debonding failure in beams because the highest tensile stress can be fully transferred to FRP. After cutting, the beams were flexurally strengthened withone or two sheets of CFRP or GFRP, the sizes of which were 130 mm in width and 300 mm in length. All the beams were tested under three-point loading with an effective span of 450 mm. Mohammed Rashwan et al. (2015) examined thesize effect of reinforced concrete beams strengthened with CFRP and GFRP sheets in flexure. Two types of FRP sheets were considered in this study; Carbon and Glass fibre reinforced polymer sheets (CFRP and GFRP). FRP sheets were bonded to the soffit of the beams using a two-part epoxy. Tara Sen and Jaganatha Reddy (2013) investigated the flexural and tensile behavior of reinforced concrete beams strengthened using natural textile jute fibre and it was compared with CFRP and GFRP strengthening systems. A total of fourteen beams were cast in three groups. Among these three groups, the first group comprised of control specimens and the other two groups were strengthened RC beams. Rami Hawileh et al. (2014) studied the behavior of reinforced concrete beams strengthened with externally bonded hybrid fibre reinforced polymer systems. The experiment consisted of casting and testing five beams of size 120X240X1840 mm. One beam served as the control beam and four beams were strengthened in flexure with GFRP, CFRP and Hybrid FRP sheets. The beams were tested under four-point bending. The results were presented in terms of observed failure modes, load versus mid-span deflection and load versus FRP strain relationship at mid-span. Thomas Kang et al. (2014) examined the hybrid effects of FRP laminates
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Tests and Design Provisions for Reinforced-Concrete Beams Strengthened in Shear Using FRP Sheets and Strips

Tests and Design Provisions for Reinforced-Concrete Beams Strengthened in Shear Using FRP Sheets and Strips

Figure 9a and b present a schematic configuration of a beam retrofitted in shear with side-bonded EB FRP. Based on experimental observations (e.g., the failed specimen in the current study), the debonded FRP area can be defined as a trapezoidal area, as illustrated by the shaded area in Fig. 9a for side-bonded EB FRP and in Fig. 9c for U-jacket EB FRP. The schematic configuration shown in Fig. 9 is repre- sentative of a multiple-shear-crack pattern. It was previously mentioned that the bond effect of several cracks intersecting the FRP is not easy to determine and therefore not well documented. As an alternative, an equivalent rectangular area assuming a 45 single crack was used to replace the assumed trapezoidal bonding area in the distributed multi- ple-line shear-crack pattern (Fig. 9b, d). The dimensions of the equivalent rectangular area are equal to the FRP effective length and the FRP effective width. The concept of FRP effective length has already been established and is defined as the length of the FRP beyond which the bond force will not increase. The effective bond length can be calculated using the Neubauer and Rosta´sy (1997) equation:
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Shear Strength of Reinforced Concrete Beams Without Stirrups

Shear Strength of Reinforced Concrete Beams Without Stirrups

mentioned that plenty of theoretical and research studies have concentrated on beams without transverse reinforcement as it is widely accepted that the understanding of their shear failure mechanism will provide valuable knowledge for the clarification of failure mechanism in beams with transverse reinforcement. However, a fundamental theory to explain the shear failure of beams without transverse reinforcements is yet to be found. Current shear design procedures are commonly considered unacceptable and efforts are being done to revise them. Even though some efforts have met success at the national level, none of the national revisions have been accepted as a widely accepted revision. Thus, attempts are being done to identify the common elements of the various national methods in order to bring together their differences and produce an established shear design procedure.
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Effect of Fiber Orientation on Shear Behavior of RC Beams Externally Strengthened with CFRP

Effect of Fiber Orientation on Shear Behavior of RC Beams Externally Strengthened with CFRP

The use of fiber reinforced polymer (FRP) as a strengthening material is one of the applied strengthening techniques of reinforced concrete beams. This results from a number of advantages, such as excellent strength to self-weight ratio, high tensile strength, large fatigue resistance capacity, and high durability, [1] and [2]. Reinforced concrete (RC) beams strengthened with carbon and glass fiber-reinforced polymer (CFRP and GFRP) composites introduces a promising solution to improve shear and flexural capacities and ductility, as well as altering the mode of rupture, [3-6].
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Non-Linear Finite Element Analysis of FRP Strengthened RC Beams Using ANSYS

Non-Linear Finite Element Analysis of FRP Strengthened RC Beams Using ANSYS

The use of FRP (Fiber Reinforced Plastics) plates for strengthening and repairing of RC structures represents an interesting alternative for steel plates. FRP materials are lighter than steel. They present a high strength to mass ratio. They are corrosion- resistant and are generally resistant to chemical attacks. This technique has been widely investigated, and several examples of existing structures retrofitted using epoxy-bonded composite materials can be found in the literature .

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Experimental and Finite Element Studies on CFF Strengthened RC Rectangular Beams in Shear

Experimental and Finite Element Studies on CFF Strengthened RC Rectangular Beams in Shear

Seven full-scale rectangular shear beams bonded externally using bi-directional discrete CFF strips were tested under three and four point bending systems at the Abstract: This paper presents the experimental and finite element (FE) results of Reinforced Concrete (RC) rectangular beams in shear bonded externally using Carbon Fibre Fabric (CFF) reinforcement. In the experimental study, all, except control, beams were strengthened/repaired with CFF reinforcement at laboratory environment. These beams were tested under four point bending system for failure. Moreover, to validate the obtained experimental results, the study used two-dimensional model to simulate the shear behaviour of the CFF repaired/strengthened beams using LUSAS finite element analysis software. The experimental results confirm that the CFF repaired and initially strengthened beams attained a gain of 37.28% - 77.95% and 60.71% - 77.34% for shear span to effective depth ratio of 2.5 and 4.0, respectively. The results of FE prediction were compared against the experimental results obtained from the experimental investigation. It was generally found that the comparison between the predicted FE and experimental results show satisfactory correlation in terms of load- displacement profile.
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State of the art review of FRP strengthened RC slabs

State of the art review of FRP strengthened RC slabs

The aim of this study is to investigate the structural flexural performance of one-way slab with cut-outs. Six slabs including cut-outs contained one control un- strengthened slab along with five strengthened slab. These slabs were strengthened using either Near Surface Mounted (NSM) steel bars or Externally Bonded Carbon Fiber Reinforced Polymer (EB-CFRP) at the tension side, while four out of them were strengthened by either NSM-steel bars (one slab) or an overlay of Engineered Cementitious Composites (ECC) material (three slabs) at the compression side. The test results showed that properly designed and detailed end anchors for EB-CFRP sheets prevented the de- bonding of both ends of the sheets till the CFRP sheets ruptured around the mid-span of the slab. They enabled the CFRP sheets to utilize their full tensile capacity resulted in the full restoration of the flexural capacity of both slabs strengthened with CFRP sheets in the tension side. After the CFRP sheet ruptured, de-bonding of both CFRP sheets for both slabs were observed and extended to the end anchors locations. Among all strengthened slabs, slab that adopted NSM-steel bars along with ECC overlay technique showed the highest flexural capacity. It restored the ultimate flexural capacity of un-strengthened slab including cut-out and outperform its capacity than that of the reference slab without cut-out by about 23%. Using thin layer of ECC material of 20% the slab total thickness in the compression side ensured the full restoration of the flexural capacity due to cut-out when combined with either NSM steel bars or EB-CFRP sheets in the tension side [10].
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Behavior of FRP-Strengthened RC Beams with Large Rectangular Web Openings in Flexure Zones: Experimental and Numerical Study

Behavior of FRP-Strengthened RC Beams with Large Rectangular Web Openings in Flexure Zones: Experimental and Numerical Study

was calculated to be 128 mm. However, as seen in Fig. 6, maximum spacing of 350  mm was used for specimens BS2-O2-CPL, which exceeded the 128  mm calculated from Eq. (6). Therefore, buckling occurred for plates of specimen BS2-O2-CPL. In brief, plate buckling could have been mitigated by the use of either lesser rod spac- ing (not exceeding 128 mm) or plates with larger thick- ness. The validated FE modeling was utilized to study the effect of steel plate parameters on performance of strengthened RC beams with web opening located in the zone of high flexure with high shear (case of center-point loading). In this regard, four new strengthening schemes (scheme-3 to scheme-6) were numerically investigated. Details of proposed schemes are shown in Figs. 16 and 17 for beams with 450 and 900 mm opening, respectively. It is clear that scheme-3 is the same as scheme-2 but with reduced rod spacing (maximum spacing of 125 mm was provided as seen in Figs. 16a and 17a). As depicted from Figs. 16b and 17b, strengthening scheme-4 is the same as scheme-2 but with larger plate thickness of 6.0 mm and reduced rod spacing (maximum spacing of 150 mm was (6) smax = πt p
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Punching Shear Strength Development of Bubble Deck Using FRP Stirrups

Punching Shear Strength Development of Bubble Deck Using FRP Stirrups

slab and bubble deck. But weight of bubble deck slab is low compared to solid slab, so punching shear capacity of bubble deck is very low. This study deals with what will be the effect of strengthening system such as CFRP and GFRP to improve the load carrying capacity of bubble deck slab and to find which FRP is better. Finite element software ANSYS 16.0 is used for nonlinear analysis of bubble deck slab.

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