To validate the finite model, a comparison study with published experimental results was done. Verification of FE results passes through a gradual path. The first step consists of modeling for simply supported beamreinforced of steel bar with geometry details was shown in Figure 1. The applied load and corresponding maximum deflection at mid-span were got. The second step is comparing the FE result with experimental through the load-deflection curves, as shown in Figure 5. For the analysis of the result of Mises stress for beams as shown in, Figure 4-a. The maximum of stress appears in the support and around the loading plate also appears greater stress, changing from max- to min. Similar to the arched truss force model of the beam with web reinforcement, the stress distribution between two supports forms Stress arch. Since the force of beam shoulder is small, Mises stress is lower, and Mises stress in the bottom of the beam is lower under the effect of reinforcement (FRP) See Figure (4-b). For the same caseload, the displacement of nodes in the middle and its time variation is shown in Figure (4-c). The result appears, with the increase of calculation time, span deflection growth gradually accelerated. Since reinforcedconcrete in the elastic phase have high strength and strong rigidity, the amount of change in mid-span of deflection is small in the beginning; after entering the plastic stage, the material property of reinforcedconcrete declines, and therefore the acceleration of the deflection of the beam speeds up, thereby forming an acceleration in the mid-span deflection curve. This shows that the simulation is of a reliable theoretical basis, very credible. In addition, the cracks and failures pattern as shown in Figure (4-d), is a good agreement with experimental results.
Over the several last decades, strengthening of existing structures including reinforcedconcrete beams, slabs, walls and columns through the externally bonded reinforcement (EBR) and the near surface mounted (NSM) methods with fiber reinforced polymer (FRP) has been successfully utilized in civil engineering applications due to its efficiency, effectiveness and ease of application for strengthening concrete structures in both flexure and shear. A laminate or textile bond onto the surface of concrete elements in externally bonded method (EPR) while the near surface mounted method consists of placing fiber reinforced polymer bars into grooves precut on the concrete members and embedding them with a high-strength adhesive . The efficiency of using FRP for strengthening of reinforced members according to the near surface mounted (NSM) method is widely proven in comparison to the externally bonded reinforcement (EBR) due to the fact that, the tensile strength of fiber reinforced polymer is better exploited . Moreover, application of fiber reinforced polymer (FRP) with the near surface mounted (NSM) method is an alternative to the externally bonded reinforcement technique to mitigate the risk of premature debonding failure [8, 9], deterioration of FRP materials, protection against environmental corrosion and temperature, better aesthetics, as well as delimit any imperfection accommodate to the installation procedure [10, 11]. Fracture of flexural components (FRP materials), detachment of FRP sheets from the structural elements and flaking of concrete in EBR scheme of strengthening lead an additional difficulty arising from the fact that only limited amount of FRP can be used to increase the beam flexural capacity . However, application of near surface mounted technique is appropriate only if the cover of the internal reinforcement is sufficiently thick for the groove size to be accommodated . It worth mentioning that, the performance of the near surface mounted bars in strengthening of existing reinforcedconcrete elements is affected by local bond slip behavior, surface characteristics of FRPbars and treatments of reinforcement and grooves, interactions of FRP rods with the surrounding materials, geometry of FRPbars, and the concrete cover [7, 13].
Steel bar reinforcement in idealized as axial rod element by taking the discrete engineering models Spar Link Element (LINK8) with similar characteristics as the original, but a line reinforcement [20-23]. This element has 2 points with 3 degrees of freedom at any point in the x, y, and z, and is able to deform plastically. The reinforcement is assumed to be capable of transmitting axial forces only, and perfect bond is assumed to exist between the concrete and the reinforcing bars. To provide the perfect bond, the link element for the steel reinforcing bar was connected between nodes of each adjacent concrete solid element, so the two materials share the same nodes. Model of stress-strain relationship of steel used is a model Bilinear Isotropic Hardening that the material data is shown in Table 3.
Student, MSc Structural Engineering: Department of Civil Engineering, School of Civil, Environmental and Geospatial Engineering, Jomo Kenyatta University of Agriculture and Technology- Nairobi Kenya. -----------------------------------------------------------------------***-------------------------------------------------------------------- ABSTRACT: Present infiltration of substandard steel reinforcing bars on local market have had a serious concern and impacts on strength and stability of buildings and other engineering structures that are being built with them. Some buildings have collapsed in both Rwanda and in neighboring countries where most of rebars are imported from and investigations have pinpointed substandard steel reinforcing bars. Primary objective of this study was to investigate the flexural performance behavior of concrete beams reinforced with steel bars available in Rwanda, where 24 samples of concrete beams reinforced with steel bars of 12mm and 10 mm ϴ separately were investigated for flexural performance behavior. The steel bars from four different sources available in Rwanda were randomly picked from warehouses, examined for their mechanical properties compliance to standard codes in a separate study and results were used to investigate RC beam flexural performance. Results obtained showed that the ultimate load of RC beams made of Y12 mm were in range of 114.6 KN to 142.6 KN while their respective flexural strength ranged from 25.7 N/mm2 to 33.4 N/mm2 as compared to design load of 111.8 KN and design flexural strength of 25.1 N/mm2 respectively. The flexural load of RC beam made of Y10 mm was found to be in range of 93 KN to 131.5 KN while their respective flexural strength ranged from 20.89N/mm2 to 32 N/mm2 as compared to design load of 78.2 KN and design flexural strength of 17.6 N/mm2 respectively. Incidentally both experimental ultimate load and flexural strength of RC beams met their respective design requirements despite poor performance of steel bars that failed at 45.8%.
fraction (0%, 0.5%, 1% and 2%). The deflection, compressive concrete strain at mid-span of the one-way slab were measured and recorded. The testing results were compared with control specimens reinforced by GFRP reinforcing bars and with no added BMF. The testing results of the specimens were compared to the analytical equation for deflection’s prediction. Experimental and numerical results showed a general improvement in the flexural behavior of concrete one-way slabs by adding more BMF and increasing the reinforcement ratio. On the other hand, there were no major differences between BFRP and GFRP reinforcing bars. The main difference between them was because of the surface of FRP reinforcing bars. The ribbed surface of GFRP reinforcing bars gives better flexure for concrete one-way slabs than the sand coated surface of BFRP reinforcing bars, especially in over-reinforced samples. Test results clearly showed that both FRP reinforcing bars and BMF can be used as alternative materials for steel reinforcement in concrete structures. 6.2 CONCLUSION
During the test and at the end of a load increment, the growth of cracks was marked on each beam. This was carried out to identify the direction of crack propagation and to determine the differences in crack patterns of the beams. Figure 2.16 shows the typical gradual formation of cracks in a test beam (BGN-A2-02). The thick lines in the figure are used to identify the cracks that were formed at failure. The slope of the inclined crack at failure is shown on the figures of the crack patterns. The cracks were drawn to scale as in the actual tests. The extent t of a crack at the end of a load increment was marked by a short horizontal line. The loads shown at each crack tip corresponds to the actuator load in kilo-newton (KN). This load was twice the value of the load at each loading point. For all beams, the first flexural cracks initiated at the bottom of the beam in the constant moment region, where the flexural tension stress was the highest and the shear stress was zero. The observed flexural cracks propagated vertically upward to the level of the neutral axis, which reflected the absence of shear stress. As the load was increased, additional flexural cracks were developed within the shear span. Due to the presence of shear stresses, these flexural cracks became progressively more inclined and propagated towards the load points. These types of cracks are known as flexural-shear cracks. These cracks extended rapidly through the beam leading to the so-called diagonal-tension failure. The duration between the formation of an inclined crack and failure of a beam was small. ASCE-ACI Committee 426 (1973) reported that for beams with shear span-to-depth ratio between 2.5 and 6.0, the inclined flexural cracks extend to form a diagonal tension crack. This behavior was observed for most of the beams in the current study. Photographs of the crack patterns for all beams at failure are shown in Appendix I.
By connecting the maximum story drift points corresponding to each displacement level, the load-story drift envelope curve is obtained. In Figure 14a and b, the load-story drift envelope curve of the specimens reinforced with steel and FRF are illustrated. ACI Committee  suggested provisions for a connection to be accepted as an element of a moment resistant frame in seismic regions. Based on this code, in the third cycle in which the drift of 3.5% is obtained, the maximum applied load in each loading direction should not be less than 75% of the maximum lateral strength in the aforesaid direction to satisfy the fracture criterion. Moreover, the observed energy ratio should not be less than 0.125, and the secant stiffness about zero (the secant stiffness corresponding to the drifts ranged from -0.35% to 0.35%) should not be less than 5% of the initial stiffness at the first cycle of the aforesaid direction. Based on Figures 14a and b and the requirements of ACI Committee , the seismic behavior of the specimens were assessed. Accordingly, the behavior of the specimens reinforced with the steel bars is acceptable. Moreover, the specimens reinforced with the FRPbars satisfied the acceptance criteria of ACI Committee , and the behavior of the specimen 7 and 8 with high strength concrete were acceptable as well. Note that; the specimens 5 and 6 did not satisfy the criteria of the 3.5% drift. Hence, they could not be accepted. According to Corley’s suggestions , the performance of specimens 5 and 6 was not satisfactory. Corley  suggested the third cycle in which the drift of 3% was occurred for satisfying the fracture criterion. In this displacement, the connection behavior ought to be stable. Specimens 5 and 6 were not able to reach the drift of 3% although the behavior of specimen 5 was stable in drifts beyond 3% due to the compressive forces. Based on the load-story drift envelope curves, usage of GFRP bars in connection showed an acceptable drift capacity, assuming a minimum drift demand of 3% as suggested in the literature for ductile frame structures .
According to West (2011), three possible modes of failure of the FRPreinforced beams exist, i.e. balanced failure, compression failure and tension failure. The modes of failure of concretebeamreinforced with FRP rebars greatly depend on the FRP reinforcement ratio compared to the reinforcement ratio achieved when the concrete crushes and FRP rupture simultaneously, i.e. a balanced reinforcement ratio. FRP reinforcement, when subjected to axial tension exhibits a linear elastic behaviour until failure. It is little, or no warning for these elements as the FRP elements would rupture before concrete crushing in compression for under reinforced beams, leading to the sudden and often catastrophic failure mode. For over-reinforced sections, the usual crushing of concrete would predominate, similar to steel reinforced sections. On the case of balanced sections, both the concrete and FRP rebar would achieve failure at the same time, albeit brittle in nature. Both modes of failures of FRPreinforcedconcretebeam are brittle due to the linear elastic behaviour of the FRP reinforcement bar. In 1993, Nanni (1993) stated that the concrete crushing failure mode is marginally more desirable for flexural members reinforced with FRP reinforcement bars. The ACI 440.1R standard (2006) recognises the two principal modes of failure for the design of flexural members reinforced with FRPbars, as far as strength and serviceability criteria are satisfied. Benmokrane et al. (1996) investigated the experimental and theoretical comparison between the flexural behaviour of concrete beams reinforced with glass FRP and steel counterpart by adopting the same analytical formulations put forward by Benmokrane et al. (1995) to determine the ultimate moment. Gao et al. (1998) undertook investigation focusing on the effects of reinforcement ratio on cracking patterns, deformation, flexural capacities, and modes of failure of GFRP
In this study, the comparison was made between the shear performance of steel and GFRP RC beams which identified as BSM and BGM respectively. Totally sixteen RC beams were designated with different amount and types of longitudinal reinforcement bars, a/d and steel stirrup ratios (refer Table 1). Eight specimens were longitudinally reinforced with 16 mm diameter of steel bars, while another eight specimens reinforced with 16 mm diameter of GFRP bars. The beam dimension was 200 mm wide, 400 mm deep with 2000 mm and 3000 mm long due to two types of shear span length (a = 550 mm and 1100 mm). The beams were designed accordingly to available design codes and guidelines in the literature [8-10]. Two design codes of “Structural Use of Concrete – BS8110- 1:1997” and “Building Code Requirements for Structural Concrete and Commentary – ACI 318-08” were used for the design of steel RC beams. Since the designation of FRPreinforcedconcrete beams are slightly differ from conventional beams, the code provisions according to the “Guide for the Design and Construction of Structural ConcreteReinforced with FRPBars – ACI 440.1R-06” was used.
According to West (2011), three possible modes of failure of the FRPreinforced beams exist, i.e. balanced failure, compression failure and tension failure. The modes of failure of concretebeamreinforced with FRP rebars greatly depend on the FRP reinforcement ratio compared to the reinforcement ratio achieved when the concrete crushes and FRP rupture simultaneously, i.e. a balanced reinforcement ratio. FRP reinforcement, when subjected to axial tension exhibits a linear elastic behaviour until failure. It is little, or no warning for these elements as the FRP elements would rupture before concrete crushing in compression for under reinforced beams, leading to the sudden and often catastrophic failure mode. For over-reinforced sections, the usual crushing of concrete would predominate, similar to steel reinforced sections. On the case of balanced sections, both the concrete and FRP rebar would achieve failure at the same time, albeit brittle in nature. Both modes of failures of FRPreinforcedconcretebeam are brittle due to the linear elastic behaviour of the FRP reinforcement bar. In 1993, Nanni (1993) stated that the concrete crushing failure mode is marginally more desirable for flexural members reinforced with FRP reinforcement bars. The ACI 440.1R standard (2006) recognises the two principal modes of failure for the design of flexural members reinforced with FRPbars, as far as strength and serviceability criteria are satisfied. Benmokrane et al. (1996) investigated the experimental and theoretical comparison between the flexural behaviour of concrete beams reinforced with glass FRP and steel counterpart by adopting the same analytical formulations put forward by Benmokrane et al. (1995) to determine the ultimate moment. Gao et al. (1998) undertook investigation focusing on the effects of reinforcement ratio on cracking patterns, deformation, flexural capacities, and modes of failure of GFRP and steel reinforcedconcrete beams. Theoretical correlations for the prediction of crack width, maximum deflection, and ultimate load carrying capacity were proposed based on the experimental investigation. When determining the ultimate flexural capacity of the beams, the researchers considered the effect of the compression reinforcement. Nevertheless, the effect was discounted as it was deemed negligible. From serviceability perspective, FRP and steel reinforcedconcrete elements behave differently. Deflection and crack width are normally relatively small compared to similar elements reinforced with FRP Bakis et al., (2002). The low elastic modulus of the FRP rebars results in large deflections and crack width compared to steel reinforcing bars (Kara & Ashour, 2012). Tests on basalt FRP reinforcement by Gohnert et al. (2014) concluded that four times the amount of basalt FRP was needed to achieve the same stiffness as that of the conventional steel reinforcements.
In comparison among types of FRP, GFRP possesses the lowest tensile strength but it has the advantage of being least expensive. However, this composite material has proven to have high strength and to be noncorrosive and lightweight relative to the conventional steel. Research works related to the use of GFRP bars to replace longitudinal steel bars have been performed [3-6]. Nevertheless, very little research has been conducted to study the shear behaviour of FRP RC beams due to the difficulty in understanding its mechanism of failure. In addition, due to the incomparable strength of steel and FRP, different consideration of design concepts would affect the shear performance of the beam. Test results have shown that GFRP RC beams without shear reinforcement failed in shear for over-reinforced beams, whereas beam in under-reinforced section failed in flexure with excessive deflection . Even, beam with GFRP stirrups failed in a flexure- shear mode, and it also indicate that as the amount of longitudinal bars increases the shear strength is also increased . Thus, according to previous study, further research is needed in understanding the shear performance of GFRP beams with different test variables.
Razaqpur et al.  proposed an analytical model for computing the deflection of FRPreinforcedconcrete beams based on an assumed tri-linear variation for the moment-curvature response. In their model, the deflections of FRPreinforcedconcrete beams were computed assuming the entire beam to be fully cracked, followed by an adjustment for uncracked regions. However, the tension stiffening effect is ignored in this approach. In another investigation, Gravina and Smith  developed an analytical method to analyze the flexural behavior of statically indeterminate concrete beams reinforced with FRPbars. Their approach is able to model the progressive formation of flexural cracks and their spacings, and was found to be highly dependent on the input parameters such as the bond characteristics of FRPbars and surrounding concrete.
comparison with steel, are a lower modulus of elasticity and a linear elastic behaviour up to rupture, which implies the lack of plasticity in the behaviour of FRP . From among research studies conducted on flexural behavior and serviceability performance of concrete beams reinforced with FRPbars one can refer to [5-15]. Among the research studies conducted on pullout behavior of GFRP bars in concrete and bond stress-slip behavior of GFRP bars in concrete respectively one can refer to  and , and Studies conducted on shear behavior of concrete beams reinforced with GFRP bars include references [18, 19]. The present study focuses on investigating the effectiveness of FRP reinforcing on the pushover behaviour of RC beams using FE modeling technique. The FE meshes, boundary conditions and nonlinearity implementation methods have been calibrated/validated by comparing the predictions of the available experimental data. Subsequently, effects from FRP reinforcing on the bending response of RC beams were studied. Moreover, two groups of FRP and steel reinforced beams, with same reinforcement ratio, have been selected to investigate the effect of FRP reinforcement on the moment capacity of RC beams. Geometrical and material nonlinearities in the concrete material, steel reinforcements and also FRP reinforcement have been taken into consideration. In the study effects from the variation of span/depth ratio, the reinforcement ratio and the effective depth of the beam are that the new issues that have been addressed.
Abstract: This paper reports and compares experimental studies on flexural performance of concrete beams reinforced with hybrid fiber reinforced polymer (FRP) and steel HRB bars with this study and other literatures. The objective of this study is to examine the effect of hybrid FRPs on structural behavior of retrofitted RC beams and to investigate if different sequences of BFRP and GFRP bars of the hybrid FRPs have influences on improvement of strengthening RC beams, Total 3 steel reinforcedconcrete beams and 8 hybrid reinforced beams were designed using only HRB steel bars and hybrid G/BFRP-steel bars respectively. The flexural bearing capacity, the maximum crack width and the deflection of the test beams were obtained and analyzed. Results show that the ultimate bending moment of hybrid reinforced is slightly less than that of steel reinforcedconcretebeam with the same reinforcement ratio. It can be concluded that it is feasible to replace the corner steel bars of concrete members with FRPbars without reducing the flexural bearing capacity. However, the deflection and maximum crack of hybrid reinforcedconcrete beams are much higher than those of steel reinforcedconcrete beams at the same load levels. The theoretical calculation method can effectively predict the flexural bearing capacity, crack spacing, maximum crack width and deflection of hybrid reinforcedconcrete beams, which can be used in engineering design reference.
The beam elements were 150 mm wide, 250 mm high, 2550 mm long, with the distance between the end-supports being 2300 mm (see Figure 1). The shear span (767 mm) was reinforced with steel stirrups to avoid shear failure, while no shear reinforcement was provided in the constant bending moment zone. GFRP and CFRP rebars with nominal diameter of 6 mm were used as top reinforcement within the shear span to hold the stirrups in place. The clear concrete cover to the main rebars was 25 mm in all cases. Each beam series was designed to be under-reinforced, balanced or over-reinforced, with failure occurring by rupture of bars or crushing of concrete. The geometric and reinforcement details of GFRP and CFRP RC beams are given in Figure 1 and Table 2. The reinforcement ratio of the corresponding beam and slab series is almost identical to enable comparison between the deflection behaviour of beam and slab elements with similar reinforcement ratios.
A general overview of previous research in the behavior of FRPbars in reinforcedconcrete structures was presented in this paper. Due to the increased use of FRPbars in concrete structures, the performance of FRPbars has been an important research topic in recent years. This research investigated the material characteristics and mechanical properties of different type of FRPbars in RC structures. In current study one of the most significant aspects is to understanding the behavior of bond between FRPbars and concrete. Subsequently the main experimental, numerical and analytical studies were presented. Moreover, FRP in concrete allows engineers to increase or decrease margins of safety depending on environmental and stress conditions, generic FRP type and required design life. At the end, the proposed study is to improve the understanding of FRPbars in RC construction and this research brings new challenges for professionals and who are working in the field of structural design and strengthening of reinforcedconcrete structures.
analytical investigation of flexural behaviors of concrete beams reinforced with glass-reinforced-polymer (GFRP) bars were studied. The GFRP rebar having the tensile strength of 902 MPa and Young’s modulus of 46 GPa. The beams were 1800 mm long with a rectangular cross section of 150 mm in width and 200 mm in depth. Totally Four beams were tested. One beam was reinforced with glass-FRPbars, two beams were reinforced with both glass-FRPbars and steel and one was reinforced with steel, serving as a control specimen. The beams were tested to failure in four-point bending over a clear span of 1600 mm. The test results were reported in terms of ultimate load carrying capacity, deflection and cracks. The experimental results were used to predict the load vs. deflection of Concrete beams reinforced with hybrid bars. The measured load vs. deflections was analyzed and compared with the predicted FEM model using ABAQUS. The results indicate that the reaction forces and deflections obtained from the finite element model (FEM) were well matched with the experimental results.
In these days ,the concrete structures in building industry are research attention require to investigate in this field. So it needs to be applied according to international standards; for this reason the use of new technology seems essential in building industry, there for developments that have occurred in field of material technology, researchers are using their main priority. Based on this newly materials such as that FRP composite and behavior of them that main topic of this paper. Because of the advantages such as resistance to corrosion, high tensile strength, low weight and insulation against electromagnetic waves can be expressed in these materials. so in the first step in this paper to provide a new method of structure design we treat about concrete material , reinforcement bars of the beam that the one the main elements of structure.
The first crack load was increased about (50%) for specimen DRS2 and (100%) for specimens DRS4 in comparison with first crack of specimen (NR). The steel ring delayed first crack load through preventing the concrete dome to deform under load. The 4mm steel ring contributes to some extent in reducing the deflection in post crack stage larger than the specimen with 2mm steel ring. When using steel rib at dome bottom, there is clear increasing of the first crack load in comparison with reference specimen; the specimens DRRS4 (with 4mm rib) achieved first crack load at 25 kN, while specimen DRS4 (with steel ring only) achieved first crack load at 20 kN. On the other hand, the specimen DRRS2 (with 2mm rib) achieved first crack load at 20kN, while specimen DRS2 (with steel ring only) achieved first crack load at 15 kN. The steel rib added some additional bracing against dome deterioration.
Twelve large-size, low aspect ratio, rectangular, RC shear wall specimens (denoted SW1 to SW12) were built and tested as part of a NEES research project on conventional  and composite structural walls [8, 9,11] with low aspect ratios at the NEES facility at the University at Buffalo . The construction and testing of the 12 specimens were executed in two phases: Phase I (SW1-SW7) and Phase II (SW8-SW12). The Phase I walls were constructed and tested first. The Phase II walls were designed after preliminary analysis of data from the testing of the Phase I walls. The test results from the phase I walls (SW1 to SW7) are used to validate the numerical model and only the properties of these walls are reported in this paper.