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Prior research has not explored the creation of concrete with superior thermal insulation properties using calcium oxide-activated materials. Furthermore, the impact of substituting large proportions of sand with worn rubber powder and PET on the mechanical and thermal characteristics of high-performance geopolymer concrete remains uninvestigated. This study addresses these gaps by examining the development of geopolymeric concrete with enhanced thermal insulation properties using calcium oxide-activated materials. A novel mixing method has been devised to improve the compaction of thermally insulating concrete, which includes calcium oxide-activated slag. For the purposes of this research, worn rubber powder and PET powder have replaced 10%, 20%, 30%, 40%, and 50% of the aggregates. The mechanical properties of the concrete were determined through compressive strength, four-point bending, and tensile strength tests. Lastly, the thermal conductivity coefficient was tested to ascertain the thermal properties of the developed concrete.The findings revealed that in the developed concrete, substituting 10% of the aggregates with worn rubber powder or PET powder increased the energy absorption capacity of the concrete by 143% and 107%, respectively, while its mechanical properties decreased by 10% and 7%, respectively. Moreover, using 50% worn rubber powder and PET as aggregate substitutes reduced the samples’ thermal conductivity by 70% and 60%, respectively.

Fiber-reinforced polymer (FRP) sheets are lightweight and offer high tensile strength and durability under harsh environmental conditions. For this reason, FRP sheets are used extensively for the strengthening of concrete structures. Concrete structures reinforced with FRP composites commonly experience debonding failure of the reinforcement sheet before the tensile capacity of the FRP sheet has been fully utilized. One method used to prevent the debonding of FRP sheets is the use of FRP anchors. FRP anchors are made by rolling the FRP sheet and impregnating it with epoxy resin as a matrix. One end of the FRP anchor then is placed into a hole drilled in the concrete and the other end is fanned out across the FRP composite. In this research the bond technique, method of fan application, length of fan part, the anchor cross-section to reinforcement sheet cross-section ratio, and converting the failure mode to FRP rupture for straight FRP anchors were investigated. The FRP anchors were examined by the externally-bonded reinforcement (EBR) method and the externally-bonded reinforcement on grooves (EBROG) technique. To strengthen the specimens, FRP with a net thickness of 0.131 mm (SikaWrap-230C), a bond length of 70 mm, and a width of 48 mm was used. In the EBROG technique, two grooves with widths of 10 mm, depths of 10 mm, and spaced 20-mm apart were cut on the concrete surface. The matrix phase of the composite was Quantom-EPR 3301 epoxy resin. FRP composites were prepared by the wet lay-up method. To determine the bond behavior of FRP anchors, 15 single-lap shear tests on T-shaped specimens were conducted. The results showed that, in EBR method an increase in the anchor cross-section had a positive effect on the bond strength, so an increase of about 58% in bond strength of the EBR-60-3 specimens was observed. The failure mode in EBR specimens was debonding. The load-slip curves of the EBR joints showed that in the first part, the load increases sharply and linearly up to the initiation of debonding; In the second part, slippage increased significantly and the slope of the curve decreased. The use of straight FRP anchors significantly increased the bond strength and the final slip values compared to the control specimens. In the EBROG method, anchors with a cross-section ratio of twice eliminated the debonding and the failure mode for this group was the rupture of the FRP sheet. The load-slip curves for the EBROG method ascended and did not exhibit the almost two-line behavior of the EBR specimens. The load-slip curves consisted of an ascending branch with an initial slope that was greater than at the end. The slippage of the EBROG specimens was significantly lower than for the EBR specimens. This small amount of slip versus the high bond strength reveals the high stiffness of the bond. A comparison of the EBR and EBROG methods shows that the EBROG eliminated debonding at lower FRP fan and bond length values. Also, the bond strength of the EBROG specimens with FRP anchors increased by 136% compared to the EBR specimens. In this research, an embedment depth of 50 mm transferred stress to the concrete without pulling out the fibers.

Numerous studies have been devoted to the investigation of the deterioration and behavior of fiber-reinforced polymer (FRP) sheets (made from a variety of materials such as carbon, glass, or aramid) bonded onto the concrete substrate under a variety of adverse environments. Results indicate that environmental conditions might exercise significant and undesirable effects on FRP-concrete bond performance. In many corrosive environments, there are the potential risks of premature debonding and failure of the bonding interface in externally bonded FRP-strengthened concrete structures. The effects of freeze–thaw cycles on the fiber-reinforced polymer (FRP)-to-concrete bond strength were investigated using the particle image velocimetry (PIV) technique. For this purpose, 18 specimens were prepared, including 12 specimens strengthened with carbon FRP (CFRP) strips as well as six control specimens subjected to 200 and 500 freeze–thaw cycles, each consisting of four steps according to ASTM C 666. In the first stage, the temperature was held constant at 5°C for 4.2 h. The next step involved rapid freezing to ‒18°C for 2.4 h. In the third step, the temperature was held constant at ‒18°C for 2.4 h. Finally, the temperature was raised and maintained at 5°C for 3 h in the fourth step. The freeze–thaw under wet conditions was selected in order to create harsher conditions than the dry freeze–thaw conditions would. According to ASTM C 666, the specimens were stored in saturated lime water from the time of their removal from the molds until the time of freezing and thawing tests started. In addition, the nominal freezing and thawing cycle consisted of alternately lowering the temperature of the specimens from +5 to −18°C and raising it from −18 to +5°C in not less than 2 nor more than 5 h. The freezing and thawing chamber was equipped with a user defined program. The temperature range of the chamber was −30°C to +65°C. The temperature was controlled by a sensor, which can be immersed either into the sample or into the water in which the sample was placed. The specimens were strengthened via externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) methods. After the concrete prisms had been subjected to 200 and 500 freeze–thaw cycles, they were placed in the single shear test machine. During each test run, a tensile force was applied to the FRP composite while the concrete block was restrained from movement. The single shear test machine consisted of a hydraulic jack with a capacity of 400 kN that provided the required force for the single shear test. Moreover, a load-cell with a capacity of 50 kN was used to measure the force applied to the specimens. In the current investigation, the specimens were subjected to a quasi-static loading of 2 mm/min in accordance with ASTM D3039/D3039M. The results of PIV measurements revealed that, compared with the specimens strengthened via the EBR method, the EBROG-strengthened specimens exhibited considerably enhanced bond performance. When subjected to 200 and 500 freeze–thaw cycles, the EBR-strengthened specimens experienced a 3% and 9% decrease in their bond strength, respectively; the EBROG-strengthened specimens experienced no decrease in bond strength and increases in the range of 7%–19% when subjected to 200 and 500 cycles, respectively.

Various methods have been developed for the retrofit and strengthening of RC beams. One of the successful methods is the near-surface mounting (NSM) method. In this method, the reinforcing rebar is inserted and glued into the groove in the concrete cover. This groove is created in the tensile face of the beam. The relative protection of reinforcing materials, which are less exposed to mechanical damage, shock and fire loading is an important advantage of this strengthening method. Pre-stressing can close the cracks caused by the weak flexural strength of the member and reduce its excess deflection. The proposed strengthening method in this research was near surface mounting of pre-stressed rebars to enhance the flexural behavior of RC beams. The test program consisted of testing 5 RC beams of 200×200 ×1700 mm. One was the control sample and was tested without strengthening. Four other beams were first pre-loaded to the cracking stage and, after unloading, were strengthened by near surface mounting of the steel bars. The beams were tested under four-point bending. The applied load and the corresponding displacement in the middle of the beam were measured. In the flexural strengthening of the beams by proposed NSM method, end-anchorage and epoxy adhesive, both provided the proper bond. Tightening the end nuts with the aid of a torque meter, was the selective method to pre-stress the reinforcing bar. The results showed that this method was very effective for the flexural strengthening of RC beams, so the final load capacity of beam samples increased about twice as much as the control sample. The proposed method also led to the closure of the bending cracks and the reduction of the samples’ deflection, as well as the increase in energy absorption of the samples.

Fiber strands due to their flexibility, high aspect ratio, cross-section varieties and degree of crystallinity are adequately strong to be used as reinforcement in composites such as concrete. Newly introduced fiber reinforced concretes (FRC) are the cementitious materials that exhibit reinforcing features in all directions. FRCs due to their interesting properties are enormously favored by civil and structural engineers. Natural and synthetic fibers can be employed in concretes, shutcretes and mortars. The interface between the added fibers and the cementitious matrix fundamentally influences the properties of the FRCs. Fibers are classified into hydrophobic and hydrophilic. The former fibers have negligible moisture absorbent capacity while exhibiting acceptable mechanical properties. Hydrophobic fibers are incapable of forming adequate adhesion with cementitious matrix. Properties such as low weight, strength parity in wet or dry conditions and inertness in acid or alkaline environments are among the salient properties of polypropylene (PP) fibers. PP as a hydrophobic fiber has gained wide acceptance as concrete reinforcement. The hydrophobicity of fibers, such as PP, has been always been disadvantageous for the use of these fibers in concrete structures. Treatments such as chemical surface modification imparts hydrophilic property to PP fibers. Thus the modified PP fibers can successfully adhere to concrete matrix. In this research melt-spinning technology as the most widely used manufacturing technique for production of the PP fibers was used. Pure and grafted anhydride maleic PP granules were used to produce both hydrophobic and hydrophilic PP fibers. The produced fibers were characterized according to relevant standards prior to be added to concrete samples at identical fiber volume fraction. The results pointed to the positive effect of the induced hydrophilic properties in the fibers as far as the fiber-matrix adhesion was concerned. The ability of the chemically modified fibers to absorb water when wetted with the moisture present in the concrete, greatly improved the adhesion of the added fibers with the concrete matrix. The effect of hydrophilicity of PP fibers on mechanical properties of reinforced concrete was investigated by comparing concrete samples prepared by modified and unmodified fibers. Results showed that in comparison to control concrete sample, addition of modified hydrophilic fibers to concrete enhances compressive, tensile and flexural strength of concrete by 11%, 43% and 75% respectively. It was found that compressive, tensile and flexural strength of concrete samples containing the chemically modified fibers were respectively higher by 5%, 8% and 5% in comparison to the concrete samples containing unmodified hydrophobic fibers. Addition of fibers is more effective in enhancement of flexural strength of resultant concrete. This is due to the fiber bridging phenomena that prevent both crack formation and propagation. Addition of fibers also improves load bearing capacity of the resultant concrete, which in turn leads to enhancement of flexural strength of the concrete. Results also showed that addition of hydrophobic polypropylene fibers leads to 66% increase in the flexural strength of the samples. The increase in flexural strength of the concrete samples containing hydrophilic fibers in comparison to the control sample was found to be 75%.

A wide variety of systems have been introduced so far for the construction of roofs, as one of the most essential structural components of buildings. A conventional roofing system is the solid slab that offers adequate rigidity to distribute gravitational and seismic loads, while it is also relatively resistant against fire. However, its main drawback is its overweight that increases the associated seismic loads. To resolve this problem, modifications were proposed that resulted in different types of biaxial voided slabs. In one such system, spherical and ellipsoidal plastic balls enclosed in steel cages were used to eliminate ineffective concrete. Due to the novelty of the system, however, little was known about the bending behavior of the roof thus constructed. Most of previous studies have been conducted on spherically-shaped voids ignoring ellipsoidal ones. This is while the effect of supporting cages on voids has not been investigated at all. The present study was, therefore, designed and implemented to study the behavior of biaxial voided slabs containing ellipsoidal plastic balls and the effect of supporting cages on bending behavior. To investigate these aspects of the system, two full-scale bending specimens were cast for investigating bending capacity, cracking distribution, and deflection in solid and biaxial voided slabs. Moreover, the effect of cage longitudinal rods was studied on the ultimate capacity of the bending specimens. Finally, the experimental results were then examined by ACI 318-14 recommendations to put forth suggestions for using the ACI 318-14 equations in designing biaxial voided slabs. It was found that while both solid and biaxial voided specimens exhibited almost similar bending behavior and the same failure mode. Also, the bending behavior of biaxial voided specimen was affected by the steel cages used. So, to use the ACI 318-14 equations, if this longitudinal cage bar is considered, the percentage difference between experimental and calculated results reached just one percent.

This paper examines the structural behavior of the reinforced concrete beams strengthened in shear experimentally and simulates using finite element analysis. Then, the effect of employing concrete with different compressive strengths and different ratios of transverse reinforcements is studied using the case analyses. In the experimental part, four reinforced concrete beams are divided into two series of with and without internal steel reinforcements and the effect of carbon-fiber-reinforced polymer (CFRP) laminates is investigated by near-surface mounted (NSM) technique as the shear strengthening method. For this purpose, rectangular beams with the dimensions 2000×300×200 mm are designed and monolithically tested in four point loading test up to failure and the load-displacement curves of the mid-span as well as their failure modes are compared with each other. All the beams were reinforced with 3 steel tension bars of 20 mm at the bottom and 2 steel compression bars of 12 mm at the top with end hooks. If stirrups are applicable, 6 mm diameter steel closed hoops spaced at designated distances, are applied. For strengthening using the NSM method, thin slots with 8 mm width and 10 mm depth are made on lateral faces of concrete cover. In order to install composite laminates, the CFRP strips after impregnating with strong epoxy resin are folded and embedded in these grooves. After curing the specimens, all the beams are subjected to a 2000 kN capacity hydraulic jack with the loading rate of 2.5 kN/Min. The ready-mix commercially concrete was delivered to the structural laboratory for casting the specimens with 28-day concrete strength of 30 MPa. The ACI code formulations were used for calculating the shear capacity of the beams before their casting and a suitable span to depth ratio was selected to inhibit deep beam failure. The experimental results indicate that using NSM technique enhances the shear capacity up to 41% and 69% in the beams with and without stirrups, respectively. Test results show that the NSM shear strengthened specimens failed by CFRP laminate rupture. Moreover, simulation of the test specimens by modeling the probability of FRP de-bonding using interface element and orthotropic behavior of laminates shows that the results of the proposed model are consistent with experimental results. In the numerical part, two case studies are carried out; in the first case analysis, three concrete compressive strengths of 20, 30 and 50 MPa are selected and in the second one, three steel stirrup spacing of 65, 130 and 190 mm are applied.  Numerical case analyses show that as the compressive strength of concrete decreases, the failure mode the probability of de-bonding increases and as the stirrup percentage increases, the axial strain of CFRP laminates decreases. Numerical case analysis clarifies that by decreasing the distance of internal shear reinforcements from 195 mm to 65 mm, the maximum axial strain of CFRP laminate decreases about 45%. Load-deflection curves in the case analysis also show that by increasing the transverse steel ratio, ultimate displacement enhances and deformability capacity improves.

The use of concrete with ultra high performance reinforced steel fiber has been investigated in numerous studies. However, most research has focused on the use of steel fibers as reinforced. In this study, the replacement of steel fibers with polypropylene fibers and synthetic fibers (barchip) was investigated in the parameters of the mechanical properties of this concrete. The same use was also made of two hybrid fibers, as well as hybrid with steel fibers has been investigated. The total fiber content in each mixing plan is considered to be 1.5% vol. A total of 28 specimens 70x70mm cubes and 14, 100x200mm cylindrical specimens were made for compressive strength testing and 28 specimens of 70x70x 350mm were used to test the flexural strength. The compressive and flexural strength tests were measured at 7 and 28 days. the compressive strength of samples made at 28 days of age at all levels of the fibers used was more than 100 MPa ., the highest rupture stress relates to 28-day steel fiber reinforced specimens of 23.9 MPa.

Energy absorption capacity is the salient property of concrete. In this work the effect of cross -sectional area of melt spun polypropylene fibers together with that of fibers diameter on behavior of fiber reinforced concrete was investigated. Variation on fiber dimensions was achieved by varying fiber spinning draw ratio and speed of melt feeding pumps. Variations in fiber diameter affect fiber specific area which in turn influences the adhesion of the fibers to the matrix in FRC. In order to evaluate the FRC behavior, the area under load versus displacement was studied. It was found that energy absorption capacity excessively increases as the cross-sectional area of the fibers decreases. The increase in the energy absorption was at least 6 times of that of reference specimen. It is while in the concrete mix containing the fibers with the least cross-sectional area, the increase in the energy absorption was 14 times the corresponding value in the reference mix. This was concluded to be due to the increase in contact area between the finer fibers and the matrix due to increase in number of fibers for a given fiber volume fraction in the concrete. Results also showed that the increase in energy absorption capacity of the FRC leads to higher workability of the concrete after appearance of the initial crack and ultimate failure of the concrete. Finally it was observed that load bearing capacity of the samples prior to disintegration was high.

Using of polymeric fibers for reinforced concrete structures has significantly developed in recent years. Polymeric fibers start their contribution in the behavior of concrete members after cracking. In order to a careful investigation into post-cracking behavior need to apply fracture mechanic concept (growth of cracks) in reinforced concrete members. For this purpose, in this research 14 concrete prisms (100×100×400 mm in dimensions) with 35 mm notch depth (at the center of tensile side) for four-point flexural strength test were fabricated. Fiber composition, geometry and hybridization percent were varied in these samples. Derived outputs illustrated that macro polypropylene (PP) fiber has no significant effect on concrete ductility, whereas it leads to increase the flexural strength. But micro polyester (PET) and PP fibers have more effective performance during forming cracks in concrete members. PET and PP fibers have a more suitable function during concrete cracking and the samples containing these fibers have no significant drop in their bearing while the cracking is started. In addition, samples reinforced with PP and PET fibers indicated that by increase in macro fibers, the flexural strength were increased where as ductility indices decreased. In general, samples reinforced with %60 of PP macro fibers and %40 PET micro fibers have the best performance.

The current study is focused on strengthening of reinforced concrete (RC) beams using CFRP straps installed in pre-cut grooves. The method which is referred as near surface mounted (NSM) benefits considerable advantages in comparison with the conventional externally bonded reinforcement (EBR) method and provides better normal and shear stress transfer between the FRP and concrete substrate. The advantages of NSM method compared to EBR are investigated in this paper from viewpoints of loading capacity، serviceability and better use of FRP materials. Five simply-supported RC beams were cast and tested in the laboratory of Department of Civil Engineering of Isfahan University of Technology (IUT). One of the beams was un-strengthened (base specimen) while one was strengthened without prestressing and the other three were strengthened with CFRP straps with prestress up to 5، 20، and 30 percents of the nominal capacity of the composite. The results revealed that the prestressed beams show higher values of cracking and yield loads compared to strengthened specimen without prestressing. The cracking loads for the specimens with 5، 20، and 30 percents prestressing were respectively 117%، 127. 5%، and 144. 5% higher than that of base specimen; while the cracks in prestressed strengthened specimens were more limited with smaller crack width. Furthermore، the strengthened beams by prestressed CFRP had higher ultimate loading capacities and their failures happened at smaller deflections. The ultimate loads for the specimens strengthened by CFRP prestressed up to 5، 20، and 30 percents of their ultimate capacity were 11. 5%، 14. 7%، and 15% higher، respectively، compared with that of base specimen.

Reinforced concrete (RC) beams strengthened in flexure with a bonded fiber reinforced polymer (FRP) plate may fail by debonding mechanism, in which the FRP plate is detached from the beam surface in lower levels of ultimate strain of FRP. This paper presents a new method based on the smeard crack approach for finite element simulation of debonding process. For this purpose, first the problems involved in numerical simulation of debonding were investigated. Then, a technique based on cohesive elements implied in the software was used. To evaluate the proposed technique, 4 experimental RC beams strengthened with FRP plates were modeled. The results showed that the predicted ultimate loads and the whole behavior of the beams under the loads were in very good agreement with experimental data.

Confining RC columns by FRP composites with fibers oriented in the hoop direction is the most common method of strengthening columns. In the present study, however, the application of CFRP composites with fibers aligned along the column’s axis to improve compressive strength of RC columns has been investigated. Global buckling of composite with longitudinal fibers may result in debonding of FRP from column surface, and thus, the compressive load carrying capacity of the strengthened column would not be increased considerably. To limit the global buckling of composite under compression, a newly introduced strengthening method, named as Grooving Method (GM), was utilized in the present study and its effect on postponing the buckling of CFRP fibers when aligned along the column axis was investigated. For this purpose, 12 circular RC columns with diameter of 150 mm and height of 500 mm were tested under axial compression. Experimental results showed that while the effect of installing CFRP with conventional EBR method was negligible on the columns’ load capacity, the grooving method considerably enhanced the columns’ maximum loads.

A major challenges in flexural strengthening of reinforced concrete beams by FRP laminates is FRP sheet debonding from the concrete substrate, which leads to the premature failure of strengthened structural member. Surface preparation of concrete before FRP sheets installation is a suitable method to postpone debonding, however the effectiveness of the method is limited by the problems such as practical costs and environmental pollution. Grooving is an innovative technique to overcome debonding of FRP laminates from concrete surface, which has been recently used in Isfahan University of Technology (IUT). In this paper, the effect of some factors influencing the grooving capability aiming at reducing the debonding potential of FRP sheets from the concrete surface is addressed. These factors include the width and the depth of the grooves. In the experimental study, thirty-three prism specimens of dimensions 100×100×500 mm were subjected to 4-point flexural loading. The surfaces of the specimens have been grooved. After reinforcing the specimens by CFRP sheets, the four point flexural tests were carried out to measure the ultimate loading capacity. The results indicate that debonding can be completely prevented or highly limited by applying specified width and depth for the grooves.

D e s p i t e e x t e n s i v e f i e l d a p p l i c a t i o n s o f F R P p l a t e s, n o t a l l b e h a v i o r a l a s p e c t s o f t h i s c o n s t r u c t i o n m a t e r i a l h a v e y e t b e e n f u l l y u n d e r s t o o d. O n e n e g l e c t e d a s p e c t i s t h e i r r u p t u r e a n d t h e c a u s e s f o r t h e i r d e b o n d i n g o f f t h e c o n c r e t e s u r f a c e t o w h i c h t h e y a r e a d j o i n e d u n d e r u n e x p e c t e d a n d p r e m a t u r e l o a d s. A l l p l a t e d e b o n d i n g t y p e s i n R C b e a m s c a n b e g e n e r a l l y c o n s i d e r e d a s a k i n d o f d i s c o n t i n u i t y. F r o m t h i s v i e w p o i n t, p l a t e-e n d d e b o n d i n g c a u s e s d i s c o n t i n u i t y i n t h e s t r e n g t h e n i n g s h e e t, a n d h i g h e r t h i c k n e s s e s o f t h e s t r e n g t h e n i n g s h e e t c a u s e s i n t e n s i f i e d d i s c o n t i n u i t y i n t h e c o n c r e t e m e m b e r t h i c k n e s s. F u r t h e r m o r e, f l e x u r a l a n d s h e a r c r a c k s c a u s e d i s c o n t i n u i t y i n t h e c o n c r e t e m e m b e r, c a u s i n g c r a c k w i d t h t o i n t e n s i f y d i s c o n t i n u i t y a n d, f i n a l l y, l e a d i n g t o t h e d e b o n d i n g o f t h e s t r e n g t h e n i n g s h e e t. D i f f e r e n t a r r a n g e m e n t s o f f l e x u r a l b a r s i n t h e c o n c r e t e b e a m l e a d t o d i f f e r e n t c r a c k d i s t r i b u t i o n s d u r i n g l o a d i n g. T h e d i f f e r e n c e i n d i s t r i b u t i o n i n v o l v e s, n o t o n l y c r a c k s p a c i n g, b u t, a l s o, c r a c k w i d t h; b o t h o f w h i c h a r e d i s c o n t i n u i t i e s i n t h e b e a m. O n t h e o t h e r h a n d, c r a c k s a n d c r a c k p r o p a g a t i o n a l s o l e a d t o m o i s t u r e a n d d e s t r u c t i v e i o n s p e n e t r a t i o n a n d, t h e r e b y, t o c o r r o s i o n o f t h e e m b e d d e d r e i n f o r c e m e n t i n c o n c r e t e m e m b e r s.I n t h i s s t u d y, t h e e f f e c t s o f d i f f e r e n t a r r a n g e m e n t s a n d l a y o u t s o f i n t e r n a l s t e e l r e i n f o r c e m e n t o n d e s i g n d e- b o n d i n g l o a d s a n d t h e c r a c k i n g p a t t e r n o f R C b e a m s s t r e n g t h e n e d w i t h C F R P s h e e t s a r e e x p e r i m e n t a l l y i n v e s t i g a t e d. A t o t a l o f n i n e 3-m l o n g b e a m s w e r e t e s t e d u n d e r 3- p o i n t l o a d i n g. T h r e e d i f f e r e n t b a r s i z e s w e r e u s e d t o r e i n f o r c e t h e b e a m s, i.e.$5P h i$14, 3$P h i$18 a n d 2$P h i$22 w h i l e t h e r e i n f o r c e m e n t r a t i o s i n a l l b e a m s w e r e a l m o s t t h e s a m e. T h e f i r s t t h r e e b e a m s w e r e u s e d a s b a s e s p e c i m e n s a n d j u s t f o r c o m p a r i s o n. T h e s e c o n d t h r e e s p e c i m e n s w e r e l o a d e d, a f t e r s t r e n g t h e n i n g w i t h t w o l a y e r s o f C F R P u p t o f a i l u r e. F i n a l l y, t h e l a s t t h r e e b e a m s w e r e l o a d e d, b e f o r e s t r e n g t h e n i n g u p t o 70% o f t h e m a x i m u m l o a d i n t h e l i n e a r p a r t o f t h e l o a d-d e f l e c t i o n r e s p o n s e. T h e n, t h e b e a m s w e r e r e l o a d e d a n d s t r e n g t h e n e d w i t h t w o l a y e r s o f C F R P a n d l o a d e d a g a i n u p t o f a i l u r e. T h e r e s u l t s s h o w e d t h a t s m a l l e r-s i z e s t e e l b a r s c a u s e m o r e u n i f o r m d i s t r i b u t i o n o f c r a c k s a l o n g t h e b e a m, a c c o m p a n i e d b y l o w e r c r a c k w i d t h s. F u r t h e r m o r e, t h e a x i a l s t r a i n d i s t r i b u t i o n i n t h e C F R P s t r e n g t h e n i n g p l a t e h a d m o r e u n i f o r m d i s t r i b u t i o n i n b e a m s w i t h f e w e r t e n s i l e s t e e l b a r s. N o s i g n i f i c a n t d i f f e r e n c e s w e r e o b s e r v e d a m o n g s p e c i m e n s w i t h v a r i o u s b a r s i z e s, i n t e r m s o f t h e p e e l i n g l o a d o f t h e C F R P p l a t e s.

This paper is focused on the results of the experimental investigation and numerical analysis for changing the precast RC beam-column connections with corbels to flexural connections using fiber reinforced polymers (FRPs). The experimental study has a special focus on the flexural strength and debonding effect of boundary layer of FRP sheets attached onto the corbels and other parts of precast connections. In the current study, four half-scale external beam-to-column connections including one conventional fixed connection, and three simple precast connections with corbels strengthened withFRP sheets were casted and tested. The FRP sheets were attached in different layouts with different thicknesses. Static concentrated loads were applied on the tip of the beam simultaneously with a constant axial load on the column, and were continued up to ultimate failure. To fulfill the numerical phase of this study, non-linear static analysis on the 3-D model of the connections were performed using Ansys 8.1. A comprehensive comparison was then performed between different strengthening methods with FRP sheets using different FRP configurations, different thicknesses and dimensions, also using full mechanical anchorages. The results showed that simple precast connections could be changed to flexural connections using FRPs, whereas the sufficient development length and thickness, configuration of FRP sheets, and suitable mechanical anchorage are quiteeffective to prevent the FRP debonding. The test results of this study showed that the suitable use of FRP sheets increased the flexural capacity of a simple precast joint more than 80% of that of a full flexural RC joint.