Experimental study on mechanical behaviors of damaged RC beams after reinforcement

Transcription

1 Applied Mechanics and Materials Submitted: ISSN: , Vols , pp Accepted: doi: / Online: Trans Tech Publications, Switzerland Experimental study on mechanical behaviors of damaged RC beams after reinforcement Congqi Li 1,a, Wenjie Ge 1,b, Dafu Cao 1, Linglong Pan 1 and Biyuan Wang 1 1 College of Civil Science and Engineering, Yangzhou University, Yangzhou , China a licq@yzu.edu.cn, b jshagwj@163.com Keywords: reinforced concrete beams, damage evaluation, reinforcement, mechanical property. Abstract. Based on 6 testing beams in site cast, the mechanical behaviors of RC beams after reinforcement are analyzed. Concrete-replacing and grouting were used to reinforce the damaged component. When the reinforcement materials reached sufficient strength and maturity, beams were subjected to experiments of bending bearing capacity. Cracking load and ultimate bearing capacity were analyzed relatively, drawing some conclusions which could use as the reference of reinforcing concrete structure after damage. Introduction Durability of reinforced concrete structures is a hot issue in today's world. After a few years, due to expose of wind and frost, snow and rain, by the nature of the role of physical, chemical and biological, and now had varying degrees of damage, mechanical properties of structural decay gradually. Normal use condition of the building has been greatly affected the concrete structure performance degradation, bearing capacity drops, structural safety and reliability can t be guaranteed. There is an urgent need for damaged concrete structures reinforced and repaired, providing safe and reliable guarantee for the subsequent use of the building [1~5]. Reinforcement of damaged RC beam Replacement concrete repair test. The concrete damage of original specimen upper compression zone is serious and exist penetrating crack, so the upper pressure zone using replacement method for repair of reinforced concrete. Firstly chisel compression damaged concrete, chisel in the section of the mid-span (Length 1500 mm, depth 100 mm). Then bend straightening longitudinal reinforcement. The concrete strength of replacement is the same as the original specimen. Grouting reinforcement test. Through the observation to understand members crack distribution after replacement repair. In order to make the sealing glue to bond with concrete better polished surface of the beam. Then use high-impact drills and other drilling tools drill cross on both sides along the fissures, Drilling angle should be 45, drilling depth 2/3 structure thickness, hole must be through the cracks, but not be structure through (except post-grouting structure), drilling and crack spacing should be 1/2 the thickness of the structure. Air compressor with a pressure of 6 MPa blowing to the grouting mouth, clean dust out the seam, observe the situation of cracks. In the crack surface sealed with epoxy quick drying cement in order to not run slurry when pouring epoxy slurry. In the drilled hole install grouting mouth. Using high pressure grouting machine (mouth) to prime epoxy resin slurry into the grouting hole, facade grouting sequence from bottom to top. The plane can start from one end, hole one by one, when the adjacent hole began to paste, pressure maintenance 3~5 minutes, stop the grouting hole (mouth), note the adjacent grouting hole, change to prime adjacent grouting hole. With fast dry cement grouting mouth for repair and seal processing All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-05/03/16,17:52:16)

2 Applied Mechanics and Materials Vols Test plan Test methods. In order to analyze the basic mechanical properties of flexural members after reinforcement replacement and bonding properties of new to old concrete, six beam tests were carried out. In order to ensure the quality of the same reinforcement, all replacement parts adopt C25 concrete. Member section are made of rectangular section 180 mm 300 mm, length is 2700 mm, calculated span is 2400 mm. Tensile longitudinal reinforcement and vertical reinforcement, configure the same as the stirrup, respectively, 3φ12,2φ10 and All specimen details are shown in table 1. Table 1 Basic parameters of the test component NO. Original concrete strength Failure length Failure location Failure degree L-3 C Bearing left Complete L-5 C Bearing left Complete L-9 C Mid-span Complete L-10 C Full length Complete HL-6 C Mid-span Partial HL-10 C Full length Partial Test equipment and loading system. Test beam is design as simply supported beam. In order to prevent concrete local crushing before the damage, steel plates were laid respectively in support and loading point. Three points loading was adopted. Reinforcement effectiveness analyses Mechanical performance comparison and analysis. For the repair of damaged RC beams, the most concerned is the mechanical properties after repair components, comparative analysis of the mechanical properties before and after reinforcement are shown in Table 2. Table2 Contrastive analysis of the mechanical performance before and after repair M cr 0 M u 0 M cr r M u r NO. [kn m] [kn m] [kn m] [kn m] M 0 0 cr /M u M r r cr /M u M r 0 cr /M cr M r 0 u /M u L L L L HL HL Note: the M cr0 is the original specimen cracking moment, M r cr is after repair specimen cracking moment, M u0 is the ultimate bending moment of original specimen, M ur is the ultimate bending moment of the specimens after repair. As can be seemed from Table 2, damaged specimen's cracking load of reinforced component did not change a lot. The highest cracking load still is the half-bonded specimen, the support of unbonded followed, the lowest is the mid-span of unbonded. Bearing capacity of semi-bonded specimen was well restored, ultimate bearing capacity of two semi-bonded specimen tested in this experiment achieved original 94% and 96% respectively; effects of unbonded specimen have great difference, the best one achieved 95% of the original, while the worst only about 1/3 of the original; Differences of unbonded parts also have some impact on the repair effects, specimen support's repair effects of unbonded is better than mid-span. Repaired specimen's ratio of cracking load and ultimate load has some different degrees of rise, the increased most one is the specimen of unbonded in the mid-span, about 2~3 times of the original, the rest are increased small, just a slight increase. Repaired specimen's ratio of cracking load and ultimate load is more consistent, about 30% of the ultimate load.

3 1332 Progress in Industrial and Civil Engineering III Failure pattern Beam L-3 failure pattern comparison and analysis. Damage form of beam L-3 is shown in Fig.3, reinforced beams failure modes was similar to failure mode of original component as follows, cracks are basically the same as the original failure pattern in the bond failure section; in pure bending section contains three cracks at the same condition with the original failure pattern. Difference is that: in pure bending section has a dense crack development, other are relatively sparse, does not like the original failure pattern evenly distributed; Pure bending crack is not within the period of each article to carry out high, only 3 more than half of the high beam; Outside the bonding failure section of the beam bending shear fracture develop better than the original failure pattern, bending-shear crack height more than half of the beam height. Fig.3 Comparison of failure pattern (L-3). Beam L-5 failure pattern comparison and analysis. Damage form of beam L-5 is shown in Fig.4, reinforced beams L-3's failure modes was similarly to failure mode of original component as follows, cracks are basically the same as the original failure pattern in pure bending section. Difference is that: Some cracks occur in the original form of the damage zone near the side of the bond failure, not appear in the specimen after restoration; Bond failure zones inclined cracks' toward gentler than original failure pattern, eventually into the pure bending section;cracks in the middle section of bond failure better than the original,the original only to 1/2 high beam crack, Cracks in the middle section of bond failure better than the original, originally only to crack 1/2 beam height, those repaired specimens crack through from the bottom of beam to top. Fig.4 Comparison of failure pattern (L-5). Beam L-9 failure pattern comparison and analysis. Damage form of beam L-9 is shown in Fig.5, cracks of primary failure modes in pure bending section not appear on the repaired specimen, replaced by the emergence of new cracks in the vicinity of the original crack; numbers of crack in pure bending segment increased a lot more than original failure modes, cracks in pure bending specimens after reinforced segment increased 3, there is a crack carry a higher altitude; when near the ultimate bearing capacity, some cracks appeared in original failure modes outside bond failure section, not appear on the specimen after the repair; Cracks in the middle section of bond failure better than the original, originally only to crack 1/3 high beam, repaired specimen crack high more than 5/6 beam height.

4 Applied Mechanics and Materials Vols Fig.5 Comparison of failure pattern (L-9). Beam L-10 failure pattern comparison and analysis. Damage form of beam L-10 is shown in Fig.6, reinforced beams L-10's failure modes and failure mode are similar to the original, the position and direction of development of pure bending section occur 2 main cracks. Difference is cracks of primary failure modes in pure bending section not appear on the reinforced specimen, replaced by the emergence of new cracks in the vicinity of the original crack; numbers of crack more than the original failure pattern, little cracks in the original form of damage, only two main cracks in pure bending section, cracks in pure bending specimens of reinforced increased 1, three points loading point and bending shear section all occur 1 crack, and crack of the three points loading point height is higher, more than 5/6 beam height. Fig.6 Comparison of failure pattern (L-10). Beam HL-6 failure pattern comparison and analysis. Damage form of beam HL-6 is shown in fig.7, reinforced beams HL-6 s failure modes and failure mode are similar to the original, fracture spacing is uniform; Cracks partly appeared in the pure bending section of the original form of destruction, also appeared in the specimen after reinforced;bending and shear location s cracks are similar to original failure pattern. Difference is some high cracks in the pure bending section of original failure pattern not appear on the repaired specimens. Replaced by some new cracks appeared around the original cracks, those new cracks' height slightly less than original failure pattern. Numbers of crack has increased than original pattern, two flexural cracks increased in the mid-span, the height of cracks reached 2/3 beam height. Cracks in the edge of the original pattern from the bottom to top, not appear in reinforced specimen; cracks' height in bending shear section higher than original failure pattern, those cracks are all more than 1/2 beam height, highest crack more than 2/3 beam height, original pattern's vertical cracks change into diagonal cracks. Fig.7 Comparison of failure pattern (HL-6).

5 1334 Progress in Industrial and Civil Engineering III Beam HL-10 failure pattern comparison and analysis. Damage form of beam HL-10 is shown in Fig.8, reinforced beams HL-10 s failure modes and failure mode are similar to the original, cracks appeared in the pure bending section of the original pattern, also appeared in reinforced specimen; one crack in the three points loading point is similar to original failure pattern. Difference is some high cracks in the pure bending section of original failure pattern not appear on reinforced specimens. Replaced by some not very high cracks and developed densely in reinforced specimen, the height of those cracks is more than 2/3 beam height. numbers of crack in the bending shear section significantly less than original failure pattern, development is relatively concentrated, the height is taller than original failure pattern, those cracks' height are all higher than 1/2 beam height, direction of original pattern's vertical cracks change into diagonal cracks. Conclusions Fig.8 Comparison of failure pattern (HL-10). Based on the reinforcement test of damaged specimen with different degrees of adhesion failure and research of bending strength destruction test, drawing the following conclusions: Specimen's cracking load of after replacement and grouting repair basically the same as the original specimen. The highest cracking load still is the half-bonded specimen, the support of unbonded followed, the lowest is the mid-span of unbonded. Most new cracks appeared in the around of larger force reinforcement, old concrete cracking is a characteristic of repaired specimen damage. The used reinforcing materials has a good crack resistance, the cracking load of concrete specimens still depends on its own stiffness and tensile strength. In the process of strengthening, attention should not only pay to the main crack of original damage, but also need paid to those small cracks in the original pattern, these small cracks are not obvious, but caused the loss of part of the section stiffness, easier to crack damage when loaded. Small cracks of those reinforced specimen developed higher to the main crack of damaged specimen. Replacement of concrete and grouting reinforcement method play a great role in the limitation on cracks, almost all of the original specimen failure pattern existence through crack; after reinforcement, reinforcement replacement segment not occur through crack; cracks in the grouting parts of repaired specimen are few and not high. It is shown that the bonding of grouting materials and concrete is very good, has good restriction to the development of cracks. Acknowledgments The authors appreciate the support of the national natural science foundation of China ( , ), the Natural Science Foundation of Jiangsu Province, China(BK ), the science and technology projects of ministry of housing and urban-rural development (2013-K4-17), the natural science fund for colleges and universities in Jiangsu Province (13KJB560015), the science and technology projects fund of Yangzhou City ( ), the open foundation of Southeast University, Key laboratory of concrete and pre-stressed concrete structure of Ministry of Education.

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7 Progress in Industrial and Civil Engineering III / Experimental Study on Mechanical Behaviors of Damaged RC Beams after Reinforcement /