All validated FE models included bond-slip modelling between the steel shear links and the concrete, as detailed in Section 5.6. Although the overall predictions were good (with an average experimental to FE model ratio of 1.17 and a standard deviation of 0.06), detailed analysis showed that some corrodedbeams had higher predicted shear force capacities than those of the uncorroded beams when other parameters were the same (see Figure 6.3.1b). This result disagrees with the experimental results. This discrepancy may be attributable to the bond-slip model. El- Maaddawy and Soudki (2003) suggested that the steel shear link-to-concrete bond initially increases, and then decreases due to corrosion level increase. The corrosion impact factor may be used to represent this behaviour numerically, and it may be related to the applied current density. For example, it showed that the bond stress increases until a shear link corrosion level of 14.8% (due to the rust forms), and decreases thereafter (due to the appearance of cracks). However, EI-Maaddawy and Soudki (2003) induced the corrosion with a current density of 250 µA/cm 2 . Hence, the
Concrete is the most common material for construction. The demand for concrete as a construction material l eads t o the increase of demand for Portland cement. Concrete is known as a significant contributor to the emission of greenhouse gases. The cement industry is the second largest producer of the greenhouse gas. The environmental problems caused by cement production can be reduced by finding an alternate material. One of potential material to substitute for conventional concrete is geopolymer concrete. Geopolymer concrete is an inorganic alumino-silicate polymer synthesized from predominantly silicon, aluminium and by product materials such as fly ash, GGBS (ground granulated blast furnace slag). Geopolymer concrete does not contain cement. Hybrid fibres were used in this study. Hybrid fibre is the combination of steel fibre and basalt fibre with different volume fractions. When these fibres are added to this special concrete it improves the ductile behaviour and energy absorption capacity. This is due to the property of steel and basalt fibre to bridge the crack development inside the concrete. The main objective of the study is to look into the shearbehaviour of hybrid fibrereinforced geopolymer concretebeams.
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 FibreReinforcedPolymer (CFRP) rods are placed inside pre- cut grooves and are bonded to the concrete with epoxy adhesive.  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,
The experimental program was comprised of a material testing phase and a beam testing phase. The material testing phase consisted of testing seventy-two (72) material samples under monotonic and cyclic axial loading, full strand testing, and corrosion measurements of prestressing strands corroded while embedded in concrete prism. Material testing achieved multiple objectives: (a) it identified the rate of accelerated corrosion of the prestressing strands, (b) it quantified the distribution of the applied nominal tensile force among the seven wires within a single 7-wire strand in a prestressed strand, (c) it determined the material fatigue properties, and the stress-strain behaviour of the strand wires, and (d) it quantified the stress concentration factor in the prestressing strand due to corrosion. The beam testing involved constructing thirty-seven (37) 3.6 m long pretensioned T-beams and testing them in a four-point bending configuration. Twelve (12) beams were tested under monotonic loading, and twenty-five (25) beams were tested under cyclic loading. The main testing variables included: the corrosion level, the applied stress range, and a repair or the lack of it.
Conversly, LWA are not strong as conventional aggregates. When the cracks star to develop; theses cracks will pass through th aggregate particles without any resistance. The failure is developed by the tensile stresses initiated within the aggregate particles as well as by the failure developed in the concrete paste surrounding the aggregate particles. The crack width and intensity are higher in LWC compared with NWC. Briefly, LWC is weak compared with NWC. Furthermore, the cracking strength or the tensile strength of LWC is significantly lower than the NWC of the same grade of concrete. This issue also influnce the shear capacity of LWC, bond between steel and concrete as well as the anchorage strength, etc. (Clarke, 2002). LWC has been used increasingly over the past decades (Aljaafreh, 2016). Table (1.1) summarises the most important LWC buildings constructed in the last 70 years. In the coming decades, it is therefore expected that structures constructed using LWC will occupy a significant proportion of the concrete infrastructures. When deteriorated, these structures may be retrofitted using efficient systems such as FRP reinforcement.
HPC can be achieved by further lowering water-to-cement ratio, but without its certain adverse effects on the properties of the material. However, from a structural point of view, one understands usually that high strength, high ductility and high durability, which are regarded as the most favorable factors of being a construction material, are the key attributes to HPC. For adequate ductility in beam-column junction, use closely spaced hoops as transverse reinforcement was recommended in the ACI-ASE committee 352 report (ACI 2002). However, due to congestion of reinforcement, casting of beam-column joints will be difficult and will lead to honeycombing in concrete at these joints.FIBRE reinforcedconcrete (FRC) can sustain a portion of its resistance following cracking to resist more cycles of loading. Since beam-column joints in building frames have a crucial role in the structural integrity of building, they must be provided with adequate stiffness and strength to sustain load transmitted from beams and columns.
Godat et al (2010), studied to obtain a clear understanding of size effects for Carbon Fiber-ReinforcedPolymer (CFRP) shear-strengthened beams. Their experimental research presented here, investigated the shear performance of rectangular reinforcedconcretebeams strengthened with CFRP U-strips as well as one completely wrapped with CFRP sheet. Seven rectangular RC beams were grouped into three test series, three control beams, three beams with U-Shaped CFRP jacket and beam with completely wrapped external CFRP sheets. The cross sections were; first series 100mmx200mm with length 900mm, second series 200x400mm of length 1800mm and third series 300mmx600mm with beam length 2700mm. All beams were heavily reinforced in bending, no steel stirrups were installed in the right shear span of interest but in the left shear span. It was placed to ensure that the failure would occur in the shear span of interest. From these results, they observed that the larger beam size, CFRP sheet provided less improvement in the shear capacity. They investigated the cracking behaviour of these specimens. Their research presented a Comparison between Test Results and Predictions from Design Guidelines.
Matta, F., Nanni, A., Galati, N. & Mosele, F. (2007). Size Effect on Shear Strength of ConcreteBeamsReinforced with FRP Bars. Proc. 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures (FraMCoS-6), June 17-22, 2007, Catania, Italy, Taylor & Francis, Vol. 2, pp.1077-1084.
The Strain Energy (SE) in a FRP strengthened RC beam section consists of three components which are summed in the proposed model. 1) SE in the RC beam due to flexure; 2) SE in the RC beam due to axial force and 3) SE in the FRP plate. Energy released from all of these components with the extension of flaw should be considered; the beam is divided into short segments and the energy releases in each segment are calculated. Since the strain distributions of the segments outside the fractured zone cannot be altered by the extension of the flaw, unless the load changes, it is assumed that only the segments within the fractured zone contribute for the energy released from the system. It is now possible to consider the energy state of the beam before and after the flaw extension. The elastic strain energy is given by the assumption that the beam would unload elastically from any loaded state, using the effective stiffnesses calculated as in Section 4. There would be some permanent deformation. By accounting for the energy that is dissipated in the concrete, either in flexural-tension cracking, or nonlinear elasticity, and by yielding of the tensions reinforcement, it is possible to
Monotonic flexural tests until failure were carried out to determine the failure bond stress for each type of FRP reinforcing bar in this study and to establish the bond stress profile. All prestressed and non-prestressed beams were tested under a four-point static bending regime using a hydraulic 500 kN Uniroyal testing frame. The flexural tests were completed under displacement control at a displacement rate of 1.0 mm/minute. The shear span was 500 mm for all beams. The beam had roller support at one end and a hinge support at the other. Two steel plates (120 mm x 50 mm) were located between the support and the beam. The importance of these plates is to minimize the compression forces produced at the support location at the bottom face of the beam. These compression forces might increase the frictional forces on the GFRP bar, which lead to increase the bond stress between the concrete and the GFRP reinforcement. Figure 3.12 shows the support with extra steel plates. The beam was levelled in the loading frame and centred over the support centrelines. Measurements of load, mid-span deflection (LVDT 1), bar slip at the end of the beam (LVDT 2 and LVDT 3), strain in the GFRP bar, and strain in the concrete at the end of the shear span were collected at a 0.5 second time increments using a National Instruments Data Acquisition System connected to a computer. Figure 3.13 shows the test setup.
ReinforcedConcretebeams consisting of two concrete layers of different strengths fall into the category of composite structures and may therefore be analyzed using known methods for composite materials. When extending the hybrid concept to composite concrete members and due to advances in concrete technology, it is relatively easy to produce composite sections which possess high compressive strength, high ductility, high energy absorption and high tensile strength at the same time, these characteristics can be achieved by placing two or more different types or strengths of concrete layers together so that each layer is used to its best advantage and as a result, the concrete section becomes a "hybrid" section or the Layered concrete section. It was shown that these beams are effective when the design compressed zone depth corresponds to a case when the ReinforcedConcrete section carries a maximum bending moment, but brittle failure of compressed concrete is avoided. High strength concrete is widely used in structures despite its relatively low tensile strength and weak deformation capability. Steel fibers increase the energy absorption of concrete and ductility of bending elements’ sections. This feature is especially important for sections withstanding ultimate loads (including dynamic ones). Therefore, Steel Fibre High Strength Concrete becomes a material with high resistance to cracking and relatively high ductility. High Performance Concrete (HPC) is an engineered concrete possessing the most beneficial properties during fresh as well as hardened concrete stages. HPC is far superior to conventional cement concrete as the ingredients of High Performance Concrete contribute most optimally and efficiently to the various properties. (Lalit Rathee and Naveen Hooda
carrying capacity for this shear reinforcement arrangement. The low strength performance is due to the high amount of kenaf fibre in the beam, which absorbs the water and delay the internal hardening of the concrete. Consequently, the strength of the beam with the highest amount of fibres is lower than the one with 1% of fibre content. A similar pattern was observed in the case of the beam with reduced in shear reinforcement (S=200mm) as illustrated in Figure-6. It is apparent that the beam with reduced in shear reinforcement produced better strength as compared to the beam without fibre (refer to Figure-6). The aforementioned results suggest that kenaf and steel fibres demonstrate its prospective characteristics as part of shear reinforcement in the KFSF-RC beams.
mm and a span length of 1770 mm, while the simply supported span was 1470 mm. A shear span to effective depth ratio of 3.5 was used. This study was found to be stimulating, as it fixated on something, which was quite different as compared to all other studies in the same scope. An assessment of the ability of crimped and hooked-end steel fibres to be used as minimum shear reinforcement in RC beams prepared with two different grades of concrete was completed. To accomplish this, the control samples were made from the beams, which were believed to be satisfactory. The fibre-reinforcedbeams also showed fluctuating degrees of multiple cracking at ultimate loads. The shear strength of the FRC beams was found to be more than a low value endorsed in the literature. The grade of concrete was found to be of little importance in this regard. A comparison of the strength of the two types of deformed fibres revealed that the beamsreinforced with the hooked-end fibres were found to have up to 38% higher shear strength than the crimped fibres. A simple model for shear strength was also suggested for the calculation of the behaviour of fibrereinforcedconcrete. The proposed model was tested along with seven other shear strength models. The seven models were selected from the literature. The proposed model predicted fairly good values. However, a model proposed by other researchers from the selected literature was found to be projecting a better approximation. Imam et al. (1995) presented an analytical model for predicting the shear strength of reinforced high-strength concretebeams. The dimensions of all the specimens were constant and valued at 200 mm × 350 mm. All beams had span length of 3600 mm. All specimens were singly reinforced without stirrups. The author classified the beams into four groups based on three factors (a/d, V f , and ) in different levels. These beams
Abstract—This study presents the flexural behaviour of rectangular concretebeamsreinforced with surface treated Glass FibreReinforcedPolymer (GFRP), Grooved bars and Sand sprinkled reinforcing bars. Beams cast with standard mix of M30 grade concrete, with a reinforcement ratios of 0.73%, and compared with that of conventional steel reinforcedbeams. Totally five rectangular beams of size 125 mm x 250 mm x 3200 mm were cast. The flexural study was carried under static two point loading. The experimental prediction was focused on observation of ultimate load capacity, cracks propagation and crack widths and failure modes of beams. The results indicate that both type of GFRP reinforcements are at par with the conventional steel reinforcements.
The second set of 3 beams was designed with no shear reinforcement so that the beams would fail in shear. Two of the beams were wrapped with FRP fabric wrap while one acts as control. One of the wrapped beams was wrapped with one layer 90 o to the horizontal while the other was wrapped with two layers; one at 45 o and the other at –45 o to the horizontal. Load carrying capacity and load-deflection behaviour of all beams tested were observed. From the results of the experiments it can be seen that the load carrying capacity of the strengthened beams wrapped at 90 o to the horizontal almost doubled when compared while the other wrapped beam more than double its load carrying capacity.
based on the function and properties of fibre, where one type of fibre provides strength or toughness in the concrete structure , while the another provides durability ,load resistance. From the last few decade, there are a remarkable increase in the interest towards the use of HFRC. The hybrid fibres are an interesting material for construction industry. A large number of research work has been done on durability of hybrid fibers in concrete in recent years. The life span of concrete structure is normally upto 50 to 100 years. The fibres bridging the cracks contribute to increase the strength, the failure strain and the toughness of the composite. The various properties of hybrid fibre increase the durability of concrete structure and the life-span of concrete structure will increase. The shear stress acts parallel or tangential on section of a material. When a hybrid fibrereinforcedconcrete beam is subjected to bending load, the fibers above the neutral axis are in compression and the fibers located below the neutral axis are in tension. A hybrid concrete beam with longitudinal steel when subjected to external loads will develop diagonal tensile stresses, which will tend to produce cracks. The cracks are vertical at the centre and inclined on the other parts of the beam. The stress due to which the inclined cracks are formed in the beam is known as diagonal tension stresses.
Experimental results on beam tests, performed by Gustafsson and Karlsson (2006), were used for comparison with design results obtained when designed according to, the FIB model code, RILEM TC-162-TDF (2003) and the Spanish EHE-08 in order to determine the accuracy of the design methods. The comparison showed that the different methods had little variation in the design results. When compared to the experimental results, underestimations, up to 12.5%, in ultimate moment resistances and both under- and overestimations in shear resistances, depending on the diameter of the ordinary reinforcement bars, were revealed. These over- underestimations might be caused by the use of the simplified linear post cracking behaviours, presented by the design codes and guidelines. It should also be mentioned that mean values of the experimental results were used due to the large variation in the material behaviour of the beam specimen. This variation in the ultimate moment resistance was up to 9.5% for beams with the same material properties and could also be a cause for the underestimations obtained.
Another tool which was used to capture and analyze data for this research project was the use of Digital Image Correlation (DIC). DIC has proven to be an accurate method to capturing strain profiles, among other data, for both brittle and ductile material [29,30]. It is especially effective for brittle materials such as concrete and masonry, because it can catch strain concentrations and cracks which strain gauges could miss due to the material’s brittle nature. It works by taking pictures over a time interval during the test, (in this case every five seconds), and then comparing the pictures to previous ones while tracking the pixels. This is accomplished through analytical software, such as GOM Correlate . The pictures are loaded into the software and pixels are analyzed to measure the distance which they travel in relation to each other. If they travel closer together it creates a compression value, and away from each other creates a tension value. The pixels which it tracks are arranged into blocks based on a size and number of pixels which the researcher decides on. The smaller the pixel block size, the finer the 2-D strain profile becomes. This essentially allows the researcher to analyze the beam as if there are hundreds or even thousands of strain gauges active on the concrete.