EXPERIMENTAL STUDY ON BOND BEHAVIOR BETWEEN NSM CFRP RODS AND STONE FOR COMPOSITE STONE BEAMS
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It is a new technique to embed near-surface mounted(NSM) CFRP rods in a stone beam to improve the flexural performance of the beam,and it can be used for retrofitting existing stone structures.26 pull-out specimens were tested to investigate the bond behavior between CFRP rods and the stone.The main experimental parameters were the diameter of CFRP rod,the bonded length and the thickness of epoxy cover.Test results indicate that there are three typical failure modes,namely tensile rupture of CFRP rod,CFRP rod-epoxy interface-interfacial failure and fracture in the stone along the groove corner.The failure mechanism is influenced by the bonded length,the thickness of adhesive cover and the diameter of CFRP rod.An epoxy cover thicker than 0.5Db has no significant influence on the ultimate load of pull-out specimen.The ultimate load of pull-out specimen increases with the increase of bonded length,whereas the average bond strength decreases with the increase of bonded length.The basic anchorage length is related to the diameter of CFRP rod,which is 30Db and 35Db respectively for bars with diameter of 5mm and 7mm.Keywords:
Rod
Groove (engineering)
Ultimate load
Concrete cover
Retrofitting
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A butt-joint was formed between two pipes of dissimilar materials, steel and aluminum, by winding a wetted roving of carbon fiber with epoxy at ±45° angle. On the curing of the epoxy, a tight carbon fiber reinforced polymer (CFRP) sleeve was formed, joining the ends of the pipes. The CFRP butt-joint was characterized for two kinds of loads: tensile and bending. Based on the joint strength performance, the specimens were categorized into two groups, thin and thick CFRP sleeved specimens. In the tensile testing, the thin sleeved specimen failed through the breakage of the CFRP sleeve at the joint plane because the axial stress developed in CFRP sleeve exceeded the ultimate strength of the CFRP. However, the thick sleeved specimens resisted the axial load in the sleeve and the weaker adherend, the aluminum pipe, slipped out of the CFRP sleeve. In the flexural testing, the thin CFRP sleeved specimens also failed by failure of the CFRP sleeve at the joint plane while the specimens of thick CFRP sleeve failed by the formation of a plastic hinge near the edge of the CFRP sleeve.
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Retrofitting clay brick masonry using Deep Mounted (DM) Carbon Fibre Reinforced Polymer (CFRP) strips embedded in grooves filled with a ductile adhesive considerably increases the out-of-plane flexural capacity of slender unreinforced masonry walls. In order to investigate the bond-slip behaviour of CFRP-strips in a viscous-elastic adhesive, an extensive experimental program was initiated. Direct pull-out tests were conducted with clay brick masonry. Two parameters were investigated, namely, the type of adhesive (2 types) and the groove widths (10 and 15 mm). The second part of the experimental program focused on the pull-out capacity when surface treatment (primering or sandblasting) was applied to the CFRP-strips. In literature dealing with bond behaviour the critical bond length was found using masonry prisms of approximately 350 mm in height. In the current study with CFRP strip application in conjunction with ductile epoxy, the critical bond length was not reached for specimens of nearly 1000 mm in length. This finding was an indication of a significantly improved stress distribution over the length of the embedded CFRP-strip as the appearance of peak stresses was prevented. No premature brick splitting was initiated despite the depth of the groove being 65% of the specimen thickness, whereas in literature this phenomenon was reported for groove depths of only 30%.
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Groove (engineering)
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This paper presents the experimental results of flexural and compression steel members strengthened with carbon fiber reinforced polymers (CFRP) sheets. In the flexural test, the five specimens were fabricated and the test parameters were the number of CFRP ply and the ratio of partial-length bonded CFRP sheets of specimen. The CFRP sheet strengthened steel beam had failure mode: CFRP sheet rupture at the mid span of steel beams. A maximum increase of 11.3% was achieved depending on the number of CFRP sheet ply and the length of CFRP sheet. In the compression test, the nine specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the length of the specimen. From the tests, for short columns it was observed that two sides would typically buckle outward and the other two sides would buckle inward. Also, for long columns, overall buckling was observed. A maximum increase of 57% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 60 transversely.
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It is necessary to take measures to prevent the carbon fiber-reinforced polymer(CFRP) plate debonding from the CFRP-strengthened steel beam due to the stress concentration at the two ends of the plate.In this paper,different lengths,widths and thickness of CFRP plates are used in the strengthening experiment to strengthen the bending steel beams,and set U-shaped carbon fiber reinforced polymer sheet anchor at the two ends of the plate.Test results show significant increases in the bending capacity and stiffness of steel beams strengthened with CFRP plates.The increases are related with the area of strengthening,the thickness of CFRP plate and the anchor at the end.The larger of the strengthening area,the thicker of the CFRP plate,and the greater of the strengthening effect.The U-shaped carbon fiber reinforced polymer sheet anchor at the end of CFRP plate may prevent debonding to some extent and increase the effectiveness of the strengthening.
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Bond tests were conducted on 10 concrete beams strengthened with near-surface mounted (NSM) prestressed carbon fiber reinforced polymer (CFRP) rods under different fatigue load levels. In the NSM technique, grooves are cut on the tension side of the beams. The CFRP rods are then placed inside the grooves and prestressed. Then an epoxy adhesive is placed inside the groove to provide a bond between the concrete and the CFRP rod. The test variables included the type of CFRP rod (spirally wound or sand-coated) and the fatigue load level. The beams were tested in four-point bending. Unlike the bond failures for beams strengthened with nonprestressed CFRP rods, bond failure for beams strengthened with prestressed CFRP rods and tested under fatigue loading was by slipping between the CFRP rod and the epoxy that started at the support and propagated inward toward the loading point. The sand-coated rods showed a better bond fatigue performance than the spirally wound rods, where at a given load level the beams strengthened with sand-coated rods had longer fatigue lives than the beams strengthened with spirally wound rods. Also, for a given number of cycles, the beams strengthened with prestressed CFRP rods failed in bond at a lower applied load range than the beams strengthened with a nonprestressed CFRP rod. At onset of excessive slip (failure), the force distribution in the CFRP rod in the end region was the same for a given rod type. Thus, the shear stress value and distribution in the region close to the support was the same at onset of excessive slip (failure) for a given rod type regardless of the applied load level.
Rod
Ultimate load
Tension (geology)
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Firstly,the bending strength theory of carbon fiber reinforced plastic(CFRP) wire was founded through analyzing the mechanical behaviors of CFRP wire in saddle,and influences of CFRP wire diameter and bending radius on bending strength were studied by theoretical formula.Then,the critical bending radius of CFRP wire was calculated,bending performance of CFRP wire in saddle was studied,the ultimate bending tensions with three kinds of bending radii were measured.Finally,the theoretical analysis results and test results were compared.The results show that the bending tensile efficiency of CFRP wire in saddle of long-span suspension bridge is more than 90%.Calculated values of bending strength of CFRP wire agree well with test values.If the bending radius is fixed,the bending strength decreases with the increase of diameter of CFRP wire,and the decreasing tendency presents linear.If the diameter of CFRP wire is fixed,the bending strength increases with the bending radius,and the increasing tendency presents non-linear.The critical bending radius of CFRP wire increases with the diameter of CFRP wire,and the increasing tendency presents linear,the bending angle of CFRP wire has no influence on ultimate bending tensile.
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Pure bending
Saddle
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The reinforced concrete beam embedded with CFRP plate at the lower surface of the beams are designed,and the experiment of the flexural behavior are carried out with different embedded way,and the effect of the reinforced material length and the reinforcement layer on the reinforced impact is analyzed.The load-deflection curves of the specimen,the load-strain curves of cross bar and the load-deformation relationship of CFRP are measured,and the failure modes of the specimens are analyzed.The results show that the embedded reinforcement can improve the bending bearing capacity,change the failure mode of the specimen,and the reinforcement effect can be improved as the length of the CFRP plate and the reinforcement volume increasing.
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Near Surface Mounted (NSM) reinforcement is becoming a viable material for strengthening existing concrete structures in flexure. This paper presents the test results of 4 concrete beams strengthened with different bond length NSM bar. The ultimate load bearing capacity increases 15.17%, 26.74%, 65.42% according to the bond length compared to the control beam. The stiffness and crack restrict can improve with the bond length. The failure mode is the concrete cover debonding where as the resin, CFRP bar and the compressive concrete remain intact.
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Concrete cover
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STRIPS
Brittleness
Ultimate load
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