Ferrocement is often believed to be a form of reinforced concrete. However, in spite of the similarities between the two materials there are still major differences, indicating that ferrocement requires a separate study to establish its structural performances. On the other hand, although a large amount of research has been carried out on ferrocement, its flexural behaviour is still not fully understood. The aim of this investigation is to study the structural behaviour of ferrocement plates under flexural loading and the influence of the different variables on the strength and deformation characteristics. The variables studied were the mesh number, strength, opening and distribution, presence of steel bars, and the thickness of the section and the mortar cover. The experimental programme included 49 plates, 1000x300 mm in dimensions, reinforced with woven type steel wire mesh and tested under two lines load. Deformation measurements were taken from first application of the load up till failure and about10000 crack measurements (crack width and spacing) were recorded. The crack width data were dealt with statistically. The effect of the variables on the crack width was studied, quantitatively, by comparing the rate of growth of crack width of the plates. It was found that ferrocement cracking behaviour is characterized by almost a full development of the cracks at relatively early stages of the load (about 30-50% of the ultimate load) and the crack width is smaller and more uniformly distributed than in reinforced concrete. The mesh number and yield strength influenced significantly the crack width and spacing. There was a limit for the mesh number after which the enhancement in the cracking performance of the plates slowed down noticeably. Crack width prediction equations were derived from these tests showed good correlation, whereas the published crack width formulae largely overestimated or underestimated the measured crack width. The strength and deformation were influenced mainly by the yield strength and fraction volume of reinforcement in the loading direction. The deflection is most likely to exceed the serviceability criteria before the crack width. For a span-deflection ratio of 180, the mean crack width was mostly below 20 microns, and the load was about 15-30% of the ultimate load. A procedure is proposed to analyse ferrocement sections under flexural loading. While application of reinforced concrete theory to predict the ultimate moment largely underestimated the experimental results, the proposed procedure predicted closely the experimental moment and deflection at first cracking, yielding and failure of the tested plates.

No

This thesis presents an experimental and theoretical study of the material and structural behaviour of a Steel-Fibre reinforced Reactive Powder Concrete (SF-RPC). The experimental program consisted of three phases. Phase 1 involved the development of a design mix for use throughout the remainder of the study. Phase 2 consisted of an in-depth investigation into the material properties of the mix. The final phase of the experimental component was the testing of 16 plain and prestressed SF-RPC beams. Twelve beams were tested under short-term loading to determine their cracking and ultimate moment capacity. The remaining 4 beams were used to investigate the time-dependent flexural behaviour of prestressed SF-RPC slabs. The material properties were measured using a range of short-term tests and included the compressive and flexural behaviour, static chord modulus of elasticity and crack mouth opening. In addition to the short-term tests, investigation into the time-dependent material behaviour was undertaken and included the creep and shrinkage characteristics of the material. The response of the material to various curing conditions was also investigated. The structural behaviour investigated included the short-term flexural moment-curvature response and load-deflection behaviour of beams and slabs along with the crack patterns of both plain and prestressed SF-RPC members. In addition to the investigations into the short-term flexural behaviour, a study into the time-dependent flexural behaviour was also undertaken. There are currently 2 available models for predicting the flexural response of plain and prestressed RPC cross-sections. The analytical phase of this investigation involved an evaluation of these models. Based on the experimental findings and analysis, a modified model was proposed for calculating the short-term flexural behaviour of plain and prestressed SF-RPC beams. The applicability of an age-adjusted effective modulus method for calculating the time-dependent deformations of prestressed SF-RPC slabs under various levels of sustained loads was also evaluated and found to be adequate with minor refinements.

Fibre-reinforced-polymer (FRP) composites have been widely used for the flexural strengthening of reinforced concrete (RC) structures. Flexural strengthening methods with FRP include external bonding of FRP composites (EB system) and insertion of FRP strips or bars into grooves cut into the concrete (near-surface-mounted or NSM system). Recently, a prestressed FRP strengthening system has been developed and investigated, whereby the FRP reinforcement is pretensioned prior to attachment to the concrete to maximize the use of the high tensile strength of the FRP reinforcement. Existing studies have shown that the ultimate load carrying capacity and serviceability were greatly improved in FRP flexural strengthened beams. However, the only disadvantage of the FRP strengthening system is the reduction of deformability compared to that of unstrengthened structures due to the limited strain capacity of the FRP reinforcement and premature debonding failure. Structures with low deformability may fail suddenly without warning to evacuate, resulting in catastrophic failure. Therefore, a study on the improvement of deformability is critical for the effective use of FRP strengthening systems. In this study, a partially bonded concept is introduced and applied to various FRP strengthening methods, with the specific objective of increasing deformability in FRP strengthened beams. The FRP reinforcement is usually completely bonded to the concrete tensile surface, while a portion of the FRP length is intentionally unbonded in the partially bonded system in order to improve deformability while sustaining high load carrying capacity. To investigate the general behaviour of the partially bonded system, a new analytical model has been developed because conventional section analysis used for analysis of the fully bonded system is not applicable due to strain incompatibility at the FRP reinforcement level within the unbonded length. The analysis shows that a partially bonded system has a high potential to improve deformability without the loss of strength capacity. An extensive experimental program was conducted to verify the analytical model and to investigate the actual behaviour of the partially bonded beams. A total of seventeen, 3.5m long, RC T-beams were constructed and tested. One of them is an unstrengthened control beam, while the other 16 beams consist of four test groups that were strengthened by different strengthening methods: non-prestressed EB, non-prestressed NSM, 40% prestressed NSM, and 60% prestressed NSM. To allow investigation of the effect of partially unbonding, each group has different unbonded lengths and includes a fully bonded beam. For the non-prestressed EB strengthened beams, the failure mode of all beams was premature FRP debonding failure without regard to the bond condition. The ultimate strength and the ultimate deformability of the partially bonded beams were improved compared to the fully bonded beam. This was because the typical intermediate debonding failure that occurred in the fully bonded beam was avoided due to intentional unbonding in the partially bonded beams. The analytical model predicted the general behaviour of the EB strengthened beams well except at the ultimate response due to the premature debonding failure. A three-dimensional nonlinear finite element (FE) analysis was performed utilizing interfacial elements and contact modeling to investigate the debonding failure of this system. The FE analysis represented the behaviour of the debonding failure and bond stress distributions at FRP-concrete interface of both the fully bonded and partially bonded beams well. For the non-prestressed NSM strengthened beams, the premature debonding failure that occurred in the EB strengthened beams was not observed, and almost the full capacity of FRP was exhibited. Prominent stiffness reduction was observed in terms of load-deflection diagrams at the post-yielding stage with the increase of the unbonded length. This stiffness reduction increased the deformability of the partially bonded beams for a given applied load after steel yielding in comparison to the fully bonded beam. The FRP started to slip at high load levels and the concrete crushed gradually with a gradual loss of the beam’s cross-section, inducing nonlinear behaviour near the ultimate state of the beams. To address this behaviour, an advanced analytical model utilizing idealized section model and slip model is proposed to consider the FRP slip and concrete gradual failure. Prestressed NSM strengthened beams were very effective to improve the cracking load, to decrease the deflection at service load, and to increase the ultimate load compared to non-prestressed NSM strengthened beams. This improvement was greater as the prestressing level increased. The partially bonded prestressed beams showed an improvement in deformability compared to the fully bonded prestressed beams while minimizing the reduction of the ultimate load carrying capacity and serviceability. The partially bonded system was more effective to improve the deformability at higher levels of prestressing force. Based on the model developed, a parametric study was performed varying the main parameters. This showed that the FRP strengthened beam that has an FRP area (Af) less than the balanced FRP area (Af,b) of the beam has a high potential to improve the deformability as the unbonded length increases. The balanced FRP area is increased as the concrete strength and the FRP prestressing force are increased, or as the area of the steel reinforcement decreases. Finally, design recommendations and procedures are proposed for the effective use of the partially bonded system to improve the deformability of FRP strengthened concrete beams.

Fibre-reinforced-polymer (FRP) composites have been widely used for the flexural strengthening of reinforced concrete (RC) structures. Flexural strengthening methods with FRP include external bonding of FRP composites (EB system) and insertion of FRP strips or bars into grooves cut into the concrete (near-surface-mounted or NSM system). Recently, a prestressed FRP strengthening system has been developed and investigated, whereby the FRP reinforcement is pretensioned prior to attachment to the concrete to maximize the use of the high tensile strength of the FRP reinforcement. Existing studies have shown that the ultimate load carrying capacity and serviceability were greatly improved in FRP flexural strengthened beams. However, the only disadvantage of the FRP strengthening system is the reduction of deformability compared to that of unstrengthened structures due to the limited strain capacity of the FRP reinforcement and premature debonding failure. Structures with low deformability may fail suddenly without warning to evacuate, resulting in catastrophic failure. Therefore, a study on the improvement of deformability is critical for the effective use of FRP strengthening systems. In this study, a partially bonded concept is introduced and applied to various FRP strengthening methods, with the specific objective of increasing deformability in FRP strengthened beams. The FRP reinforcement is usually completely bonded to the concrete tensile surface, while a portion of the FRP length is intentionally unbonded in the partially bonded system in order to improve deformability while sustaining high load carrying capacity. To investigate the general behaviour of the partially bonded system, a new analytical model has been developed because conventional section analysis used for analysis of the fully bonded system is not applicable due to strain incompatibility at the FRP reinforcement level within the unbonded length. The analysis shows that a partially bonded system has a high potential to improve deformability without the loss of strength capacity. An extensive experimental program was conducted to verify the analytical model and to investigate the actual behaviour of the partially bonded beams. A total of seventeen, 3.5m long, RC T-beams were constructed and tested. One of them is an unstrengthened control beam, while the other 16 beams consist of four test groups that were strengthened by different strengthening methods: non-prestressed EB, non-prestressed NSM, 40% prestressed NSM, and 60% prestressed NSM. To allow investigation of the effect of partially unbonding, each group has different unbonded lengths and includes a fully bonded beam. For the non-prestressed EB strengthened beams, the failure mode of all beams was premature FRP debonding failure without regard to the bond condition. The ultimate strength and the ultimate deformability of the partially bonded beams were improved compared to the fully bonded beam. This was because the typical intermediate debonding failure that occurred in the fully bonded beam was avoided due to intentional unbonding in the partially bonded beams. The analytical model predicted the general behaviour of the EB strengthened beams well except at the ultimate response due to the premature debonding failure. A three-dimensional nonlinear finite element (FE) analysis was performed utilizing interfacial elements and contact modeling to investigate the debonding failure of this system. The FE analysis represented the behaviour of the debonding failure and bond stress distributions at FRP-concrete interface of both the fully bonded and partially bonded beams well. For the non-prestressed NSM strengthened beams, the premature debonding failure that occurred in the EB strengthened beams was not observed, and almost the full capacity of FRP was exhibited. Prominent stiffness reduction was observed in terms of load-deflection diagrams at the post-yielding stage with the increase of the unbonded length. This stiffness reduction increased the deformability of the partially bonded beams for a given applied load after steel yielding in comparison to the fully bonded beam. The FRP started to slip at high load levels and the concrete crushed gradually with a gradual loss of the beam’s cross-section, inducing nonlinear behaviour near the ultimate state of the beams. To address this behaviour, an advanced analytical model utilizing idealized section model and slip model is proposed to consider the FRP slip and concrete gradual failure. Prestressed NSM strengthened beams were very effective to improve the cracking load, to decrease the deflection at service load, and to increase the ultimate load compared to non-prestressed NSM strengthened beams. This improvement was greater as the prestressing level increased. The partially bonded prestressed beams showed an improvement in deformability compared to the fully bonded prestressed beams while minimizing the reduction of the ultimate load carrying capacity and serviceability. The partially bonded system was more effective to improve the deformability at higher levels of prestressing force. Based on the model developed, a parametric study was performed varying the main parameters. This showed that the FRP strengthened beam that has an FRP area (Af) less than the balanced FRP area (Af,b) of the beam has a high potential to improve the deformability as the unbonded length increases. The balanced FRP area is increased as the concrete strength and the FRP prestressing force are increased, or as the area of the steel reinforcement decreases. Finally, design recommendations and procedures are proposed for the effective use of the partially bonded system to improve the deformability of FRP strengthened concrete beams.

Reinforcement corrosion is the most common deterioration problem observed in reinforced concrete (RC) structures located at coastal or cold regions. The corrosion process can impact the performance of these structures by inducing damage on the bonding action between concrete and steel, either by the splitting of the concrete cover due to the volumetric expansion of corrosion products or the lubricant effect at the steel/concrete interface as the corrosion by-products accumulate. The current research aims at investigating corrosion-induced deterioration of bond between steel and concrete through finite element (FE) analysis of the flexural behaviour of corroded RC components. By treating the concrete cover as a thick-wall cylinder subjected to internal pressure, the analytical evaluation of impaired bond capacity is studied first and verified against published bonding tests. Then, the formulation of a numerical model is performed using ABAQUS, wherein a link element to simulate the bond behaviour is formulated and implemented through the ABAQUS user-subroutine (UEL) feature according to the validated analytical model. By introducing corrosion-induced damages, i.e., smaller cross-sectional area of reinforcement, splitting of concrete and bond deterioration, in the FE analyses, the results of the numerical model show good agreement with experimental observations. Upon validation of the analytical and FE models, a parametric investigation is conducted, wherein the effects of concrete strength, dimension of reinforcing bars, properties of oxide products, different corrosion damage mechanisms and the corrosion location along the longitudinal reinforcement on the flexural behaviour of RC beams are studied. The results show that the analytical evaluation for bond degradation is impacted by the selection of the post-cracking material model and the thickness of cover that determine the ‘holding capacity’ after cracking initiation. Also, the density of rust by-products affects the results of the analytical model at high corrosion levels. From the FE model results, it was observed that each damage mechanism due to corrosion contribute to different levels of flexural degradation, although the flexural strength degradation is mainly due to the loss of bonding action. The parametric study also demonstrates that flexural members which have reinforcement corrosion initiated near the supports suffer greater deterioration in flexural capacity than those with damages at mid span. Finally, based on these observations, suggestions for the application of both analytical and numerical models are made.

The final thesis consists of three main parts, each covering a certain aspect of investigation. First chapter presents an extensive literature review, covering such aspects as: application of FRP (fiber reinforced polymer) materials in modern-day civil engineering, characteristics of FRP reinforcement for reinforced concrete structures, advantages and drawbacks of FRP rebars compared to traditional materials, peculiarities of flexural behavior of FRP reinforced members, review of existing empirical stress-strain calculation algorithms and building codes for concrete members reinforced with FRP. Second part aims at presenting gathered experimental data consisting of 51 FRP reinforced flexural members under 4 point bending scheme. Taking into account such parameters as reinforcement ratio, load intensity and elasticity modulus of FRP reinforcement, statistical analysis on a number of calculation algorithms and building codes is performed in order to evaluate their credibility and reliability for use in real-world structures. The final part of the work presents a Simplified Discrete Crack model developed in VGTU Department of Bridges and Special Structures. The model is applied for a series of collected beams. The results are compared with theoretical predictions made by different design codes and experimental values. The final thesis consists of: 90 pages of text (without appendixes), 46 pictures, 17 tables. 3 appendixes are included. Literature list consisting of 82... [to full text] / Baigiamąjį magistro darbą sudaro trys pagrindinės dalys. Pirmajame skyriuje pateikiama literatūros apžvalga, kurioje nagrinėjamos temos susijusios su pluoštinės armatūros panaudojimu lenkiamiems betoniniams elementams. Apžvelgiamos tokių elementų panaudojimo galimybės, privalumai ir trūkumai, deformacijų skaičiavimo metodai bei matematiniai modeliai. Antrajame skyriuje nagrinėjama surinkta polimerine armatūra armuotų sijų eksperimentinių duomenų imtis. Siekiant įvertinti skirtingų skaičiavimo metodų patikimumą ir pritaikomumą ne plienine armatūra armuotiems elementams, atliekama lyginamoji statistinė analizė. Jos metu įvertinama armavimo procento, apkrovimo lygio bei pluoštinės armatūros tamprumo modulio įtaka. Trečiojoje darbo dalyje surinktai eksperimentinių duomenų imčiai pritaikytas VGTU Tiltų ir Specialiųjų Statinių Katedroje sukurtas Diskrečiųjų plyšių modelis. Gautos priklausomybės palygintos su kitų skaičiavimo normų rezultatais bei eksperimentiniais duomenimis. Gauti rezultatai parodė, kad pritaikius tikslesnius praslydimo bei armatūros ir betono sąveikos ruožuose tarp plyšių modelius, diskrečiųjų plyšių modelis gali būti sėkmingai taikomas polimerine armatūra armuotų elementų elgsenai prognozuoti.

Self consolidating concrete (SCC) is widely used in the construction industry. SCC is a high performance concrete with high workability and consistency allowing it to flow under its own weight without vibration and making the construction of heavily congested structural elements and narrow sections easier. Fiber reinforced polymer (FRP) reinforcement, with its excellent mechanical properties and non-corrosive characteristic, is being used as a replacement for conventional steel reinforcement. In spite of the wide spread of SCC applications, bond and flexural behaviour of SCC beams reinforced or prestressed with FRP bars has not been fully studied. Furthermore, the ACI 440.1R-06 equation for determining the development length of FRP bars is based on Glass FRP (GFRP) bars and may not be applicable for Carbon FRP (CFRP) bars. This research program included an experimental and analytical study to investigate the flexural and bond behaviour of SCC beams reinforced with FRP bars and SCC beams prestressed with CFRP bars. In the experimental phase, fifty-six beams were fabricated and tested. Sixteen of these beams were prestressed with CFRP bars and forty beams were reinforced with non-prestressed GFRP or CFRP bars. Four concrete batches were used to fabricate all the specimens. Three mixes were of self consolidating concrete (SCC) and one mix was of normal vibrated concrete (NVC). The test parameters for the non-prestressed beams were the concrete type, bar type and bar diameter, concrete cover thickness and embedment length while the test parameters for the prestressed beams were the concrete type and the prestressing level (30%, 45% and 60%). The transfer length of the prestressed CFRP bars was determined by means of longitudinal concrete strain profile and draw-in methods. All beams were tested in four-point bending to failure. Measurements of load, midspan deflection, bar slip if any at the beam ends, strain in reinforcing FRP bar at various locations, and strain in concrete at the beam midspan were collected during the flexural test. The concrete compressive strength at flexural tests of SCC mix-1, mix-2, and mix-3 were 62.1MPa, 49.6MPa and 70.9MPa, respectively and for the NVC mix was 64.5MPa. The material test results showed that SCC mixes had lower modulus of elasticity mechanical properties than the NVC mix. The modulus of elasticity of the SCC mixes ranged between 65% and 82% of the NVC mix. The modulus of rupture of the SCC mixes was 86% of the NVC mixes. The test results for beams prestressed with CFRP bars revealed that the variation of transfer length of CFRP bars in SCC versus their prestressing level was nonlinear. The average measured transfer lengths of 12.7mm diameter CFRP bars prestressed to 30%, 45% and 60% was found to be 25db, 40db, 54db, respectively. Measured transfer lengths of the 12.7mm diameter CFRP bar prestressed to 30% in SCC met the ACI440.4 prediction. However, as the prestressing level increased, the predicted transfer length became unconservative. At a 60% prestress level, the measured/prediction ratio was 1.25. Beams prestressed with CFRP bars and subjected to flexural testing with shear spans less than the minimum development length had local bar slippage within the transmission zone. Beams that experienced local bond slip, their stiffness was significantly decreased. A modification to the existing model used to calculate the transfer and development lengths of CFRP bars in NVC beams was proposed to account for the SCC. The test results for beams reinforced with FRP bars indicated that the average bond strength of CFRP bars in NVC concrete is about 15% higher than that of GFRP bars in NVC. The ACI 440.1R-06 equation overestimated the development length of the CFRP bars by about 40%, while CAN/CSA-S6-06 equation was unconservative by about 50%. A new factor of (1/1.35) was proposed to estimate the development length of the CFRP bars in NVC when the ACI440.1R-06 equation is used. Beams made from SCC showed closer flexural crack spacing than similar beams made from NVC at a similar loading. The deflection of beams made from SCC and reinforced with CFRP bars was found to be slightly larger than those made from NVC. The average bond stresses of GFRP and CFRP bars in SCC were comparable to those in NVC. However, FRP bars embedded in SCC beams had higher bond stresses within the uncracked region of the beams than those embedded in NVC beams. In contrast, FRP bars in SCC had lower bond stresses than FRP bars in NVC within the cracked region. The average bond strength of GFRP in SCC was increased by 15% when the concrete cover thickness increased from 1.0db to 3.0db. Cover thicknesses of 2db and 3db were found to be sufficient to prevent bond splitting failure of GFRP and CFRP bars in SCC, respectively. Bond splitting failure was recorded when the cover thickness dropped to 1.5db for the GRP bars and to 2.0db for the CFRP bars. An insignificant increase in average bond stress was found when the bar diameter decreased from 12.7mm to 6.3mm for the CFRP bars, and a similar increase occurred in GFRP bars when the bar diameter decreased from 15.9mm to 9.5mm. New models to calculate the development length of GFRP and CFRP bars embedded in SCC were proposed based on the experimental results. These models capture the average bond stress profile along the embedment length. A good agreement was found between the proposed model and the experimental results. Analytical modeling of the load-deflection response based on the effective moment of inertia (ISIS Canada M5) was unconservative for SCC beams reinforced with CFRP bars by 25% at ultimate loading. A new model for bond stress versus Ma/Mcr (applied moment to cracking moment) ratio was developed for GFRP and CFRP bars in SCC and for CFRP bars in NVC. These bond stress models were incorporated in a new rigorous model to predict the load-deflection response based on the curvature approach. The FRP bar extension and bond stress models were used to calculate the load-deflection response. With these models 90% of the calculated deflections were found to be within ± 15% of the experimental measured results for SCC beams reinforced with FRP bars. Analytical modeling of the load-deflection for NVC and SCC beams prestressed with CFRP bars are proposed done. The moment resistance was calculated using Sectional Analysis approach. The deflection was calculated using simplified and detailed methods. The simplified method was based on the effective moment of inertia while the detailed method was based on effective moment of inertia and effective centroid. The experimental results correlated well with the detailed method at higher loads range. This study provided an understanding of the mechanism of bond and flexural behaviour of FRP reinforced and prestressed SCC beams. The information presented in this thesis is valuable for designers using FRP bars as flexural reinforcement and also for the development of design guidelines for SCC structures.

Self consolidating concrete (SCC) is widely used in the construction industry. SCC is a high performance concrete with high workability and consistency allowing it to flow under its own weight without vibration and making the construction of heavily congested structural elements and narrow sections easier. Fiber reinforced polymer (FRP) reinforcement, with its excellent mechanical properties and non-corrosive characteristic, is being used as a replacement for conventional steel reinforcement. In spite of the wide spread of SCC applications, bond and flexural behaviour of SCC beams reinforced or prestressed with FRP bars has not been fully studied. Furthermore, the ACI 440.1R-06 equation for determining the development length of FRP bars is based on Glass FRP (GFRP) bars and may not be applicable for Carbon FRP (CFRP) bars. This research program included an experimental and analytical study to investigate the flexural and bond behaviour of SCC beams reinforced with FRP bars and SCC beams prestressed with CFRP bars. In the experimental phase, fifty-six beams were fabricated and tested. Sixteen of these beams were prestressed with CFRP bars and forty beams were reinforced with non-prestressed GFRP or CFRP bars. Four concrete batches were used to fabricate all the specimens. Three mixes were of self consolidating concrete (SCC) and one mix was of normal vibrated concrete (NVC). The test parameters for the non-prestressed beams were the concrete type, bar type and bar diameter, concrete cover thickness and embedment length while the test parameters for the prestressed beams were the concrete type and the prestressing level (30%, 45% and 60%). The transfer length of the prestressed CFRP bars was determined by means of longitudinal concrete strain profile and draw-in methods. All beams were tested in four-point bending to failure. Measurements of load, midspan deflection, bar slip if any at the beam ends, strain in reinforcing FRP bar at various locations, and strain in concrete at the beam midspan were collected during the flexural test. The concrete compressive strength at flexural tests of SCC mix-1, mix-2, and mix-3 were 62.1MPa, 49.6MPa and 70.9MPa, respectively and for the NVC mix was 64.5MPa. The material test results showed that SCC mixes had lower modulus of elasticity mechanical properties than the NVC mix. The modulus of elasticity of the SCC mixes ranged between 65% and 82% of the NVC mix. The modulus of rupture of the SCC mixes was 86% of the NVC mixes. The test results for beams prestressed with CFRP bars revealed that the variation of transfer length of CFRP bars in SCC versus their prestressing level was nonlinear. The average measured transfer lengths of 12.7mm diameter CFRP bars prestressed to 30%, 45% and 60% was found to be 25db, 40db, 54db, respectively. Measured transfer lengths of the 12.7mm diameter CFRP bar prestressed to 30% in SCC met the ACI440.4 prediction. However, as the prestressing level increased, the predicted transfer length became unconservative. At a 60% prestress level, the measured/prediction ratio was 1.25. Beams prestressed with CFRP bars and subjected to flexural testing with shear spans less than the minimum development length had local bar slippage within the transmission zone. Beams that experienced local bond slip, their stiffness was significantly decreased. A modification to the existing model used to calculate the transfer and development lengths of CFRP bars in NVC beams was proposed to account for the SCC. The test results for beams reinforced with FRP bars indicated that the average bond strength of CFRP bars in NVC concrete is about 15% higher than that of GFRP bars in NVC. The ACI 440.1R-06 equation overestimated the development length of the CFRP bars by about 40%, while CAN/CSA-S6-06 equation was unconservative by about 50%. A new factor of (1/1.35) was proposed to estimate the development length of the CFRP bars in NVC when the ACI440.1R-06 equation is used. Beams made from SCC showed closer flexural crack spacing than similar beams made from NVC at a similar loading. The deflection of beams made from SCC and reinforced with CFRP bars was found to be slightly larger than those made from NVC. The average bond stresses of GFRP and CFRP bars in SCC were comparable to those in NVC. However, FRP bars embedded in SCC beams had higher bond stresses within the uncracked region of the beams than those embedded in NVC beams. In contrast, FRP bars in SCC had lower bond stresses than FRP bars in NVC within the cracked region. The average bond strength of GFRP in SCC was increased by 15% when the concrete cover thickness increased from 1.0db to 3.0db. Cover thicknesses of 2db and 3db were found to be sufficient to prevent bond splitting failure of GFRP and CFRP bars in SCC, respectively. Bond splitting failure was recorded when the cover thickness dropped to 1.5db for the GRP bars and to 2.0db for the CFRP bars. An insignificant increase in average bond stress was found when the bar diameter decreased from 12.7mm to 6.3mm for the CFRP bars, and a similar increase occurred in GFRP bars when the bar diameter decreased from 15.9mm to 9.5mm. New models to calculate the development length of GFRP and CFRP bars embedded in SCC were proposed based on the experimental results. These models capture the average bond stress profile along the embedment length. A good agreement was found between the proposed model and the experimental results. Analytical modeling of the load-deflection response based on the effective moment of inertia (ISIS Canada M5) was unconservative for SCC beams reinforced with CFRP bars by 25% at ultimate loading. A new model for bond stress versus Ma/Mcr (applied moment to cracking moment) ratio was developed for GFRP and CFRP bars in SCC and for CFRP bars in NVC. These bond stress models were incorporated in a new rigorous model to predict the load-deflection response based on the curvature approach. The FRP bar extension and bond stress models were used to calculate the load-deflection response. With these models 90% of the calculated deflections were found to be within ± 15% of the experimental measured results for SCC beams reinforced with FRP bars. Analytical modeling of the load-deflection for NVC and SCC beams prestressed with CFRP bars are proposed done. The moment resistance was calculated using Sectional Analysis approach. The deflection was calculated using simplified and detailed methods. The simplified method was based on the effective moment of inertia while the detailed method was based on effective moment of inertia and effective centroid. The experimental results correlated well with the detailed method at higher loads range. This study provided an understanding of the mechanism of bond and flexural behaviour of FRP reinforced and prestressed SCC beams. The information presented in this thesis is valuable for designers using FRP bars as flexural reinforcement and also for the development of design guidelines for SCC structures.

Yes / Flexural performance of concrete beams reinforced with steel–FRP composite bar (SFCB) was investigated in this paper. Eight concrete beams reinforced with different bar types, namely one specimen reinforced with steel bars, one with fiber-reinforced polymer (FRP) bars and four with SFCBs, while the last two with hybrid FRP/steel bars, were tested to failure. Test results showed that SFCB/hybrid reinforced specimens exhibited improved stiffness, reduced crack width and larger bending capacity compared with FRP-reinforced specimen. According to compatibility of strains, materials’ constitutive relationships and equilibrium of forces, two balanced situations, three different failure modes and balanced reinforcement ratios as well as analytical technique for predicting the whole loading process are developed. Simplified formulas for effective moment of inertia and crack width are also proposed. The predicted results are closely correlated with the test results, confirming the validity of the proposed formulas for practical use. / National Natural Science Foundation of China (51678514), China Postdoctoral Science Foundation (2018M642335), the Science and Technology Project of Jiangsu Construction System (2018ZD047), the Cooperative Education Project of Ministry of Education, China (201901273053), the Blue Project Youth Academic Leader of Colleges and Universities in Jiangsu Province (2020), the Six Talent Peaks Project of Jiangsu Province (JZ038, 2016) and the Yangzhou University Top Talents Support Project