Composite materials, including Fibre Reinforced Polymer (FRP) bars, have been used for decades in the structural and civil engineering sectors over traditional steel reinforcement. The main reasons for this are that FRP composites possess a number of advantages. They are non-corrosive, non-conductive, and lightweight and possess high longitudinal tensile strength. This paper presents the results of an experimental investigation into the effects of the use of glass FRP (GFRP) bars as internal reinforcement on the behaviour of concretebeams with highstrengthconcrete (HSC) and ultra-highstrengthconcrete (UHSC). Both static and dynamic (impact) behaviours of the beam have been investigated. Twelve GFRP reinforced concrete (RC) beams were designed, cast and tested. Six GFRP RC beams were tested under static loading (three point bending) to examine the failure modes, load carrying capacity, deflection and energy absorption capacities. The other six GFRP RC beams were tested under impact loading using a drop hammer apparatus at various levels of impact energy. It was found that the use of UHSC in conjunction with larger amounts of tensile reinforcement showed higher levels of post-cracking bending stiffness. GFRP RC beams under static loading displayed a flexural response at failure. The GFRP RC beams under impact loading displayed a dynamic punching shear failure response at various levels of impact energy.
Link 180 elements were adopted to model the steel reinforcement bars. This element has two nodes with three degrees of freedom in the X, Y and Z direction translations at each node and capable of plastic deformation. Discrete representation to represent the reinforcement steel bars has been widely used due to its capability to adequately account for the bond-slip and dowel action phenomena as seen in Figure-3. As a result, it was used in this analysis to connect the steel bars elements to the concrete mesh nodes. Consequently, both concrete and steel bar mesh share the same nodes, with one exception in the region of lap splice and this will be discussed later inCombin39 element item.
The load – displacement variation of the tested FR-HSC beams are presented from Figures 5 to 8. It is clear from the graphs that load - deflection variation is linear approximately up to 65% of the ultimate load. The longitudinal reinforcement alone is responsible for the load resistance in the post cracking region. In the shear zone number of secondary cracks has appeared during the post cracking and pre-ultimate stage. Beyond the ultimate load, the load bearing capacity of the member decreased. The ultimate failure occurred with widening of a single potential crack in the shear span. In case of fibrous beams, the post ultimate deflections are found to be more than that of the non fibrous beams. This clearly indicates the post ultimate ductility of the members enhances with the addition of fiber.
Fibre Reinforced Polymer (FRP) is a relatively new composite material manufactured from fibres and resins and has proven to be efficient and economical for the development and repair of new and damaged structures in civil engineering and is also adequate for some architectural applications. The innovation of FRP allowed for materials other than steel to be used as confinement. The FRP allows the concrete to be externally wrapped with sheets, tapes or tubes. The most common types of FRP are carbon, glass and Aramid. Glass Fibre Reinforced Polymer (GFRP), Carbon Fibre Reinforced Polymer (CFRP) and many other types of reinforcing fibres in an epoxy, aluminium or polyamide matrix, have been used to retrofit the existing reinforced concrete structural members to enhance their load and displacement capacities, or in new structures to increase their strength, ductility and their resistance against environment [8, 9].
Abstract: One of the primary concerns about the design aspects is that how to deal with the shear reinforcement in the ultra-high performance ﬁber reinforced concrete (UHPFRC) beam. This study aims to investigate the shear behavior of UHPFRC rectangular cross sectional beams with ﬁber volume fraction of 1.5 % considering a spacing of shear reinforcement. Shear tests for simply supported UHPFRC beams were performed. Test results showed that the steel ﬁbers substantially improved of the shear resistance of the UHPFRC beams. Also, shear reinforcement had a synergetic effect on enhancement of ductility. Even though the spacing of shear reinforcement exceeds the spacing limit recommended by current design codes (ACI 318-14), shear strength of UHPFRC beam was noticeably greater than current design codes. Therefore, the spacing limit of 0.75d can be allowed for UHPFRC beams. Keywords: spacing limit, shear reinforcement, ultra-high performance ﬁber-reinforced concrete (UHPFRC), shear strength, shear test, failure modes.
The need for rapid construction or replacement of highway bridge decks can be addressed by precast concrete elements reinforced with Glass Fiber Reinforced Polymer (GFRP) bars with cast-in-place joints made using Ultra-High Performance Concrete (UHPC). This thesis investigates the bond between GFRP bars and UHPC and splice length optimization to obtain narrow joints and simplified bar geometries. Multiple linear regression analyses of existing bond data indicate that the bar’s Young’s Modulus and embedded length are the most significant parameters that influence the average bond strength of sand-coated GFRP bars in UHPC: increasing either decreases the average bond strength. Linear-elastic uncracked Finite Element analysis of pull-out specimens indicates that reinforcing bars with low Young’s Moduli have highly non-uniform bond distributions along their length and so exhibit high peak bond stresses and low average bond strengths. The higher average bond strengths observed for High Modulus (HM) GFRP bars compared to Low Modulus (LM) GFRP bars is likely because the HM GFRP bars have lower interlaminar shear strength. A methodology for GFRP reinforcement design that synthesizes provisions from the Flexural Design Method in the Canadian Highway Bridge Design Code including an additional new step to determine bar splice lengths in UHPC was developed. Splice lengths and bond resistance factors for HM GFRP bars in UHPC are determined by reliability analysis to resist either bar stresses due to the factored applied moments or the mean ultimate tensile strength of the bar. A significant reduction in splice length can be achieved if splices are designed to resist the bar stresses at factored applied moments. A new resistance factor of 0.5 for bond of GFRP bars in UHPC is also recommended.
Foster and Gilbert tested 16 high-strengthconcrete deep beams (Stephen & Gilbert, 1998). Variables considered in the investigation were shear-span to depth ratio, concretestrength (50 to 120MPa), and the provision of shear reinforcement. The investigation examines deep beam behavior and compares the experimental results with the ACI 318 code method and other methods. The results of the investigation show that ACI 318 prediction generally conservative for deep beams with high- strengthconcrete. Ashour (2000) proposed a numerical method of estimating the shear capacity of RC deep beams. Deep beams were considered to be in a state of plane stress. The concrete and steel reinforcement assumed to be rigid perfectly plastic. Shear failure mechanisms idealized as assemblage of moving rigid blocks separated by yield lines. Good agreement observed between the predicted shear capacity and experimental results.
ratio. Seven mixes were prepared for the fourteen beams. Each mix was used in two beams. The difference between the two beams that one has stirrups and the other one did not have stirrups. Shear span to depth ratio was 3.5 for all the specimens. Although the fiber decreased the workability of the fresh concrete, a small increase in the tensile strength of the concrete and in the modulus of elasticity was noted in the hardened concrete due to this addition of fibers. The shear strength was increased for all specimens that had fibers within them. The increase in shear strength was between 7.5% to 17% for the beams with stirrups and fibers. The increase in shear strength was much more significant for the beams without stirrups. For those beams the increase in shear strength was between 9% to 37%. The addition of fibers increased the cracking control. The crack patterns at the end of the testing were more intense for all the beams. The crack patterns at the end of the test for the beam with 2% steel fiber and without stirrups were similar to the beams with stirrups and without the addition of fibers. The addition of fibers in the beams increased its ductility. The increase in ductility was major for beam with 2% steel fiber and without stirrups. The inclusion of fibers increased the stiffness and reduces the deflection for all beams with fibers. The beams with fiber showed that maximum stirrups stress was less compared to the beams without stirrups. Also, it showed that stirrups contribution to the shear resistance was delayed due to the inclusion of fiber in the beams (the stress in the stirrups started at a very high shear force value in comparison to the beams without fibers).
As Figure 2 shows all reinforced tested beams failed in shear. The number of flexural cracks formed up to the ocurrence of the shear failure crack increased with the increase of the content of steel fibres. Furthermore, it is visible that the inclination of the shear failure crack (angle of the shear crack plan with the beam longitudinal axis) decreased with the increase of the content of fibres, which justifies the resulting benefits of fibre reinforcement, since larger area of crack, bridged by fibres, is available, and more favorable inclination of the fibre resisting tensile force is moblized for the shear resistance. Moreover, due to the crack opening arrestment offered by fibres briding the shear crack plans, a diffuse crack pattern occurred in the vicinity of the shear failure crack, contributing for the increase of energy dissipation and for the more ductile failure mode observed in HSSFRC beams, in comparison to HSC beams.
assisting in the preservation of the ductility and the overall integrity of the concrete member. Another positive aspect of the addition of 1% of steel fibres was that the ultimate shear strength of the beams increased by about 60 to 210 percent, while the ductility increased by 20 to 150% compared to the equivalent beams with 0% of fibres. The authors also stated that the LWC beam deformations were reduced due to the addition of 1% steel fibres. Furthermore, the first cracking loads of flexure and shear, number of cracks with smaller width were greater in SFRC beams than in reference concrete counterparts. The presence of 1% of fibres also stopped the expected significant tensile splitting between the concrete and longitudinal reinforcing bars in shear-tension failure particularly. Moreover, the addition of steel fibres mitigated the fast propagation of cracks experienced in reference concretebeams. The researchers also proposed a truss model for projecting the ultimate shear resistance of the reinforced concretebeams. They also concluded that fibres played as shear reinforcement by transforming the shear failures into flexural failures for beams (containing 1.6 or 2.8% of tension reinforcing bars) tested at large shear span-to-depth ratios. Although steel fibres enhanced the cracking patterns, deformations and beam capacities, shear failure did occur prior to flexure. Upon inspection of the model, it was found that the model also predicted the values of shear resistance, which were acceptable for both normal weight and lightweight concretebeams.
This paper presents the criteria for the shear design of highstrengthconcrete (HSC) beams in moment resisting frames (MRFs). The formulation of an analytical model is provided for the case of beams with longitudinal reinforcement in the presence of transverse stirrups. The model is of additive type, in the meaning that the shear resistance of the beam is evaluated as the sum of several contributions. In particular, the contribution of concrete, longitudinal rebars, and transversal reinforcement are taken into account. Furthermore, for assessing the concrete contribution, a classical approach is followed, according to which two effects arise in the shear mechanism: the arc and the beam effect. The features of these two resisting mechanisms are particularized to the case of HSC in steel reinforced beams and the maximum concrete contribution is limited to the maximum compressive strength of the concrete strut in biaxial state of stress. Moreover, for the evaluation of the resistance contribution of the longitudinal steel rebars in tension, the model takes into account the residual bond adherence between HSC and steel reinforcement and the spacing between subsequent cracks. The results are compared with the prescriptions currently provided in the main building codes and with different analytical models existing in the literature. For the comparison, the analytical expressions are applied to a set of experimental data available in the literature and design observations are made on the geometrical percentage of steel bars, the resistance of materials, the residual bond stress and the depth-to-shear span ratio.
Abstract-- This study highlights the effect of additional reinforcements in the idealized core zone of fibrous highstrengthconcretebeams for resisting pure torsional loading. The transverse and longitudinal reinforcements were added in the area considered as idealized core zone which is supposed to be in tension condition plus the traditional reinforcements located in the main idealized shear flow zone. Four fibrous highstrength under-reinforced concrete solid beams were cast and tested under pure torsion to verify the influence of secondary shear flow zone on the torsional resistance. The tested beams were designed according to ACI318-14. The transverse and longitudinal reinforcements were kept constant in the idealized main shear flow zone while the covered area in the idealized core zone by reinforcements was added as a different percentage of this zone. The test results show that torsional resistance at peak load and torsional resistance provided by reinforcement and fibre were improved up to 14.18% and 146%, respectively, due to covering of 85.4% of the idealized core zone area by transverse and longitudinal reinforcements. In addition, due to contribution of reinforcement in the idealized core zone, the strains in transverse and longitudinal reinforcements were reduced up to 60% and 69.4%, respectively.
One of possible and discovered reason is the size effect of the structure members, which was introduced by Okamura . Another possible problem is the shear carrying capacity’s design concept used as the strength of concrete at either failure or shear crack load and sum up with shear resistance of web reinforcement. It is possible that a small amount of web reinforcement cannot maintain the shear strength resist by concrete to be the same up to yielding point of stirrup itself . However, there is still not a simple, albeit analytically derived formula to predict and with accuracy the shear strength of slender beams. In addition many of the factors that influence the determination of the required minimum amount of shear reinforcement are not yet known . Unlike flexural failures, reinforced concrete shear failures are relatively brittle and particularly for members without stirrups can occur without warning because of this, the prime objective of shear design is to identify where shear reinforcement is required to prevent such a failure and then in a less-critical decision how much is required. Shear reinforcement, usually called stirrups links together the flexure tension and flexure compression sides of a member and ensures that the two sides act as a unit.
Today, the structural Engineers are facing the problem of ensuring the safe structures which will withstand for the impact loads in addition to static loads. Many concrete structures are often subjected to short duration dynamic loads. These loads originate from sources such as impact from missiles and projectiles, wind gusts, earthquakes and machine vibrations. The need to accurately predict the structural response and reserve capacity under such loading had led researches to investigate the mechanical properties of the component materials at such high rates of strain. Impact is a complex dynamic phenomenon involving crushing shear failure and tensile fracturing. It is also associated with penetration, Perforation, Fragmentation and scaling of the target being hit. The use of fibers was found to be advantageous in both static and impact conditions. One method to improve the resistance of concrete when subjected to impact or impulsive loading is by the incorporation of randomly distributed short fibers. Concrete so reinforced is called Fibre Reinforced Concrete (FRC). Many investigators
The lattice model was initially developed by Niwa et al. (1994), and can be expressed using a fi- nite element formulation by smearing out concrete and reinforcement lattices into a continuum. The main characteristic of the lattice model is the possi- bility to change the direction of the local coordinate (or the inclination angle of the lattice component) in proportion to the progress of fracture in the connec- tion between the stress field of the global and local coordinate system. This model provides the freedom to change the inclination angle of longitudinal rein- forcement lattice components. Thus it is possible to evaluate the dowel effect by controlling the inclina- tion angles of the reinforcement lattice components. In addition, it is possible to evaluate the resisting mechanism of transverse reinforcement, which may not be vertical. With regard to the resisting mecha- nism of concrete, the shear transfer of the crack sur- face can be evaluated not by using the shear stress- strain relationship, but by using the shear lattice. For each crack surface, two shear lattices S1 and S2 are provided. The shear force along a crack is carried by these shear lattices. The effect of aggregate interlock is dependent on the relative movement of concrete on two sides of the crack and thus S1 and S2 will be- come active as shown in Figure 4. In this shear transfer mode, the roughness of the crack surface is represented by the roughness angle θ of the crack surface. Itoh et al. (2000) suggested a value θ = π/3 for NSC based on a comprehensive study comparing the lattice model and the panel test results of Vec- chio & Collins (1986). For HSC with smoother crack surfaces, a smaller value of θ should be
environments. FRP bars are non-corrosive, light weight, non-magnetic and have high longitudinal strength and low thermal and electric conductivity. This paper experimentally investigated the flexural behaviour of highstrengthconcrete (HSC) and ultra-highstrengthconcrete (UHSC) beams reinforced with glass fiber reinforced polymer (GFRP) bars that has not been addressed in the literature before. Beams of 2400 mm long, 100 mm wide and 150 mm high were tested under quasi-static loading (three point loading). Influence of reinforcement ratio and compressive strength of concrete (HSC and UHSC) on the load carrying capacity, deflection, energy absorption, strains in the concrete and reinforcement, and failure modes were investigated. Test results found that over-reinforced HSC and UHSC GFRP bar reinforced concrete (GFRP-RC) beams showed an amount of pseudo ¿ductility¿ compared to under-reinforced HSC and UHSC GFRP-RC beams, where failure was brittle, without any prior warning. Energy absorption capacities were found to be higher for UHSC GFRP-RC beams for the same amount of reinforcement compared to HSC GFRP-RC beams. FRP design recommendations in ACI (2015) and CSA (2012) were compared with experimental data. FRP design recommendations for the calculation of flexural strength were found to be conservative (load-carrying capacity was under-predicted by 36% for both HSC GFRP-RC beams and UHSC GFRP-RC beams). However, FRP design recommendations for the calculation of deflection at the load carrying capacity were found to be un-conservative (deflections were under- predicted by an average of 10-22% for the HSC GFRP-RC beams and UHSC GFRP-RC beams). Disciplines
unconservative. To improve the predictions of strut-and-tie models, Nehdi et al. (2008) and Kim et al. (2014) proposed new effective- ness factors for struts in FRP-reinforced deep beams and derived the factors based on data from experimental studies involving mod- erate-scale test specimens (d ¼ 150–350 mm). An extensive study on the strength modeling of deep beams with FRPreinforcement was performed by Andermatt and Lubell (2013a), who used a data- base of 36 moderate- and large-scale tests (d up to 889 mm) to evaluate the accuracy of five sectional models — CSA S6-06 (CSA 2006), Hoult et al. (2008), CSA S806-02 (CSA 2002), ISIS Design Manual (ISIS Canada Research Network 2007), and ACI 440.1R- 06 (ACI 2006) — and three strut-and-tie models, two of which were based on CSA A23.3-04 (CSA 2004) and one on ACI 318-08 (ACI 2008). Based on the results, it was concluded that the sectional models gave poor predictions of capacity for specimens having a = d ratios smaller than 2.5. A strut-and-tie model based on the CSA A23.3-04 (CSA 2004) provisions produced most accurate strength predictions with and average experimental-to-predicted ratio of 1.20 and COV of 21%. At the same time, this model resulted in two rather unconservative predictions (experimental-to-predicted ratios ≈ 0 . 66 ) for specimens with high-strengthconcrete and a = d ≈ 2 . 04 . For the same two beams, the ACI 318-08 (ACI 2008) strut-and-tie provisions produced ratios as low as 0.28, and the average ratio and COV for the whole database were, respectively, 1.02 and 51%. Although all these comparisons were performed with simple strut-and-tie models applied to simply supported test specimens, caution was expressed regarding the use of strut-and-tie models for more complex members with FRPreinforcement. Be- cause strut-and-tie models are based on the lower-bound approach of the theory of plasticity, they require that the structure possesses the ability to redistribute internal stresses and adapt to the model. In conventional deep beams, this stress redistribution is facilitated by the plastic properties of the reinforcing steel. However, because FRPreinforcement is brittle-elastic, the ability of FRP-reinforced structures to adapt to complex strut-and-tie models may be limited. Further research on this topic is recommended.
A solid element, SOLID65, is used to model the concrete in ANSYS. The solid element has eight nodes with threetransitional degrees of freedom at each node. In addition, the element is capable of simulating plastic deformation, cracking in three orthogonal directions, and crushing. The steel plates at the supports for the beams are modeled using Solid185 elements. This element has eight nodes with three degrees of freedom at each node – translations in the x, y, andz directions. In order to obtain the internal strains in the reinforcement bars and keep them in their right positions, the discrete technique using the 3D spar Link180 element is followed. This element has two nodes with three degrees of freedom translations in the x, y, and z directions. This element is also capable of plastic deformation.
The mid-span experimental deflections of C1-4, C2-4, G1-6 and G1-8 FRP reinforced concrete simply supported beams tested by Kassem et al.  are compared with the predictions from the numerical technique and ACI 440; see Fig. 6. Geometrical dimensions, reinforcement details and material properties of FRP reinforced concretebeams considered are given in Table 2. All beams were subjected to two symmetrical point loads and reinforced with various types and amounts of FRP bottom longitudinal reinforcement. The deflections results obtained from the present numerical technique and ACI 440 are in good agreement with the test results for the applied loads up to failure. However, the numerical technique gives a better prediction of deflections than the ACI model. Fig. 6 also indicates that the present technique is able to predict both the pre and post cracking deflections up to beam failure.
GFRP and CFRP composites, depending upon the capacities needed at the various locations on the beams. The use of fibers with various thicknesses creates discontinuities, which are not desirable in the FE analysis. To overcome that, a constant overall thickness of FRP composite was used in the models. To keep the model equivalent, overall stiffness of the FRP materials, the elastic and shear modulus assigned to each FRP layer were modified to achieve the overall stiffness such as: