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Punching and Lateral Cyclic Behavior of Slab-Column Connections with Shearbands
Kang, Thomas H.-K.,Lee, Ju Dong,Lee, Bum Sik,Kim, Min-Jun,Kim, Kil-Hee American Concrete Institute 2017 ACI structural journal Vol. No.
<P>Given the increasing use of shear bands for slab-column connections as an alternative to stirrups and other types of shear reinforcement, punching and lateral cyclic behavior of reinforced concrete ( RC) slab-column connections with shear bands was experimentally investigated. A total of six half-scale specimens of RC interior slab-column connection subassemblies were constructed on the same day. Of six specimens, three were tested under monotonically increased gravity loads and three under the combined effects of constant gravity and reversed cyclic lateral loads. Control specimens had no shear reinforcement, while closed stirrups and modular shear bands without punched holes were used for the shear-reinforced specimens. The slabs were heavily reinforced to limit the degree of flexural yielding prior to punching failure, and associated with gravity shear ratios of approximately 0.5 when subjected to lateral loads. The test results and comparison with current design codes indicate that the performance of the shear bands was equivalent to or better than that of the closed stirrups and that the code provisions for stirrups are applicable to shear bands, with the exception of provisions for anchorage requirement.</P>
Kang, Thomas H.K.,Ary, Moustapha Ibrahim Korea Concrete Institute 2012 International Journal of Concrete Structures and M Vol.6 No.1
The main objectives of this research were to experimentally evaluate the impact of Carbon Fiber-Reinforced Polymers (CFRP) amount and strip spacing on the shear behavior of prestressed concrete (PC) beams and to evaluate the applicability of existing analytical models of Fiber-Reinforced Polymer (FRP) shear capacity to PC beams shear-strengthened with CFRP. The Ushaped CFRP strips with different spacing were applied externally to the test specimens in order to observe the overall behavior of the prestressed concrete I-beams and the mode of failure of the applied CFRP strips. Results obtained from the experimental program showed that the application of CFRP strips to prestressed concrete I-beams did in fact enhance the overall behavior of the specimens. The strengthened specimens responded with an increase in ductility and in shear capacity. However, it should be noted that the CFRP strips were not effective at all at spacing greater than half the effective depth of the specimen and that fracture of the strips was the dominant failure mechanism of CFRP. Further research is needed to confirm the conclusion derived from the experimental program.
Hybrid Effects of Carbon-Glass FRP Sheets in Combination with or without Concrete Beams
Thomas H.-K. Kang,Woosuk Kim,Sang-Su Ha,Dong-Uk Choi 한국콘크리트학회 2014 International Journal of Concrete Structures and M Vol.8 No.1
The use of carbon fibers (CF) and glass fibers (GF) were combined to strengthen concrete flexural members. In this study, data of tensile tests of 94 hybrid carbon-glass FRP sheets and 47 carbon and GF rovings or sheets were thoroughly investigated in terms of tensile behavior. Based on comparisons between the rule of mixtures and test data, positive hybrid effects were identified for various (GF/CF) ratios. Unlike the rule of mixtures, the hybrid sheets with relatively low (GF/CF) ratios also produced pseudo-ductility. From the calibrated results obtained from experiments, a new analytical model for the stress?strain relationship of hybrid FRP sheets was proposed. Finally, the hybrid effects were verified by structural tests of concrete members strengthened with hybrid FRP sheets and either carbon or glass FRP sheets.
A State-of-the-Art Review on Debonding Failures of FRP Laminates Externally Adhered to Concrete
Kang, Thomas H.K.,Howell, Joe,Kim, Sang-Hee,Lee, Dong-Joo Korea Concrete Institute 2012 International Journal of Concrete Structures and M Vol.6 No.2
There is significant concern in the engineering community regarding the safety and effectiveness of fiber-reinforced polymer (FRP) strengthening of RC structures because of the potential for brittle debonding failures. In this paper, previous research programs conducted by other researchers were reviewed in terms of the debonding failure of FRP laminates externally attached to concrete. This review article also discusses the influences on bond strength and failure modes as well as the existing experimental research and developed equations. Based on the review, several important conclusions were re-emphasized, including the finding that the bond transfer strength is proportional to the concrete compressive strength; that there is a certain bond development length that has to be exceeded; and that thinner adhesive layers in fact lower the chances of a concrete-adhesive interface failure. It is also found that there exist uncertainty and inaccuracy in the available models when compared with the experimental data and inconsistency among the models. This demonstrates the need for continuing research and compilation of data on the topic of FRP's bond strength.
A State-of-the-Art Review on Debonding Failures of FRP Laminates Externally Adhered to Concrete
Thomas H.-K. Kang,Joe Howell,Sanghee Kim,Dong Joo Lee 한국콘크리트학회 2012 International Journal of Concrete Structures and M Vol.6 No.2
There is significant concern in the engineering community regarding the safety and effectiveness of fiber-reinforced polymer (FRP) strengthening of RC structures because of the potential for brittle debonding failures. In this paper, previous research programs conducted by other researchers were reviewed in terms of the debonding failure of FRP laminates externally attached to concrete. This review article also discusses the influences on bond strength and failure modes as well as the existing experimental research and developed equations. Based on the review, several important conclusions were re-emphasized, including the finding that the bond transfer strength is proportional to the concrete compressive strength; that there is a certain bond development length that has to be exceeded; and that thinner adhesive layers in fact lower the chances of a concrete-adhesive interface failure. It is also found that there exist uncertainty and inaccuracy in the available models when compared with the experimental data and inconsistency among the models. This demonstrates the need for continuing research and compilation of data on the topic of FRP’s bond strength.
Flexural Testing of Reinforced Concrete Beams with Recycled Concrete Aggregates
Kang, Thomas H.-K.,Kim, Woosuk,Kwak, Yoon-Keun,Hong, Sung-Gul American Concrete Institute 2014 ACI structural journal Vol.111 No.3
<p>Owing in part to the fact that appropriate structural design guides for recycled concrete materials have not been established, only approximately 14% of all waste concrete is made into aggregate and recycled. This is an inefficient method of recycling the concrete materials, under-utilizing an important and valuable asset. To promote the use of recycled concrete aggregates (RCAs), flexural tests of 28 reinforced high-strength and normal-strength concrete beams were performed. The main objectives of this research were the structural investigation of flexural performance and the evaluation of the potential application of RCA for concrete structures. In comparing the RCA specimens to the natural aggregate specimens, the overall crack patterns were similar to each other. The flexural behavior was also not affected significantly by the use of RCA up to 30% RCA replacement ratio. The current test data and data from other researchers' studies were examined in evaluating the flexural strength of reinforced concrete beams with RCA.</p>
Shear-Strengthening of Reinforced & Prestressed Concrete Beams Using FRP
Thomas H.-K. Kang,Moustapha Ibrahim Ary 한국콘크리트학회 2012 International Journal of Concrete Structures and M Vol.6 No.1
The main objectives of this research were to experimentally evaluate the impact of Carbon Fiber-Reinforced Polymers (CFRP) amount and strip spacing on the shear behavior of prestressed concrete (PC) beams and to evaluate the applicability of existing analytical models of Fiber-Reinforced Polymer (FRP) shear capacity to PC beams shear-strengthened with CFRP. The Ushaped CFRP strips with different spacing were applied externally to the test specimens in order to observe the overall behavior of the prestressed concrete I-beams and the mode of failure of the applied CFRP strips. Results obtained from the experimental program showed that the application of CFRP strips to prestressed concrete I-beams did in fact enhance the overall behavior of the specimens. The strengthened specimens responded with an increase in ductility and in shear capacity. However, it should be noted that the CFRP strips were not effective at all at spacing greater than half the effective depth of the specimen and that fracture of the strips was the dominant failure mechanism of CFRP. Further research is needed to confirm the conclusion derived from the experimental program.
Reinforced Concrete One-Way Slabs with Large Steps
Kang, Thomas H.-K.,Kim, Sanghee,Hong, Seongwon,Hong, Geon-Ho,Park, Hong-Gun American Concrete Institute 2017 ACI structural journal Vol.114 No.4
<P>To evaluate the performance of relatively large steps in reinforced concrete one-way slabs in terms of the flexural behavior of the stepped slabs, a total of 12 specimens with various shapes of steps and different reinforcing details in steps were tested. The primary purpose of this research is to investigate the structural behavior of one-way slabs with steps and to evaluate the performance of steps in slab depending on various details. In comparing the conventional one-way slab with the stepped slab, it was found that: 1) the specimen without supplementary reinforcement in the step showed a very low moment strength and significant damage; 2) the specimens with diagonal reinforcement in the step exhibited substantial early cracks, experienced hinging of the step, and demonstrated a substantial loss of moment strength; and 3) the specimens with a combination of U-bars, inverted U-bars, L-bars, and inverted L-bars performed very well, reaching almost 100% of moment strength of the one-way slab. The U-bars and inverted U-bars were effective in controlling the diagonal cracks, while the L-bars and inverted L-bars were effective in preventing yielding of the slab reinforcement near the step. Based on the crack pattern and the analysis of the structural performance, the design guidelines of reinforcement details of stepped slabs were proposed.</P>