수정압축장이론에 의한 탄소보강근-콘크리트 부재의 면내전단강도 평가

강수태,양은익,최명성 한국구조물진단유지관리공학회 2024 한국구조물진단유지관리공학회 논문집 Vol.28 No.4

이 연구에서는 전단벽과 같은 면내 전단을 받는 경우에 대해, 종방향 보강근비를 2.96%로 일정하게 하고, 횡방향 보강근비를 0.30 에서 2.98%까지 변화시켰을 때, CFRP 보강근을 사용한 콘크리트 부재의 거동특성을 MCFT 이론에 기반하여 평가하고, 철근을 사용한 콘크리트 부재의 경우와 비교하여 분석하고자 하였다. 보강근비 0.30에서 1.19% 사이에서는 CFRP 보강근을 사용한 경우가 철근을 사용한 경우보다높은 전단강도를 보였으며, 그 이상의 1.79% 및 2.98%에서는 상대적으로 낮은 전단강도를 나타내었다. 최대전단변형률은 낮은 보강근비에서철근을 사용한 경우가 더 크게 나타났으며, 0.97% 이상에서는 CFRP 보강근을 사용한 경우에 더 크게 나타났으며 보강근비가 커질수록 철근대비 전단변형률 증가율이 더 크게 나타났다. 철근 및 CFRP 보강근의 기계적 성질 차이로 인해 발생하는 보강근에서의 변형률 차이 및 요소에서의 주변형률 차이 분석을 통해 보강근비 변화에 따른 철근 및 CFRP 보강근을 사용한 경우의 전단강도 및 전단변형률 변화를 비교하여 분석할 수 있었다. In this study, when subjected to in-plane shear such as a shear wall, the behavior characteristics of a concrete member using CFRP rebars were investigated when the longitudinal reinforcement ratio was kept constant at 2.96% and the transverse reinforcement ratio was changed from 0.30 to 2.98%. The evaluation was conducted based on MCFT theory and analyzed by comparison with the case of concrete members using steel rebars. When the reinforcement ratio ranged from 0.30 to 1.19%, concrete members employing CFRP rebars exhibited higher shear strength compared to those using steel rebars. In contrast, at high reinforcement ratios of 1.79 and 2.98%, it was observed that the shear strength of the member with CFRP rebar was lower compared to the member with steel rebar. Maximum shear strain was observed to be higher for members reinforced with steel rebars at lower reinforcing bar ratios, while for ratios of 0.97% and above, CFRP rebars resulted in higher maximum shear strain. As the reinforcement ratio increases, the use of CFRP rebar instead of steel rebar results in a greater increase in maximum shear strain. By analyzing the difference in strain in the reinforcing bar as well as the difference in principal strain in the element caused by differences in the mechanical properties of the steel rebar and CFRP rebar, the shear strength and shear strain when using steel rebar and CFRP rebar with different reinforcement ratios can be compared and analyzed.

Direct Shear Strength of Rebar-coupler Anchor Systems for Steel-plate Composite (SC) Walls

Efe G. Kurt,Amit H. Varma,Young M. Sohn 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.4

This paper focuses on the direct shear behavior of rebar-coupler anchor systems, and their use for anchorage of steel-plate composite (SC) walls to the concrete basemat of safety-related nuclear facilities. Large-scale rebar-coupler anchor specimens were tested under direct shear loading until failure. The results included the applied load-slip displacement responses of the specimens, the direct shear strength, and the observed failure mode. The American Concrete Institute (ACI) 349 code equation for calculating the direct shear strength of embedded anchors was compared with the direct shear strengths from the tests. The code equation underestimated the direct shear strength of the anchor system, because shear failure was assumed to occur in the rebars, whereas experimental observations indicated that shear fracture failure occurred in the couplers rather than the rebars. The design equation was updated to utilize the net shear area of the couplers instead of the rebars, after which the direct shear strengths from the tests could be calculated with reasonable accuracy. The experimental results were also used to propose an empirical model for the shear force vs. slip displacement response of rebar-coupler anchor systems.

AFRP rebar로 보강된 콘크리트 깊은보의 전단강도

이영학,김민숙,조장세,김희철 한국지진공학회 2009 한국지진공학회논문집 Vol.13 No.6

본 연구는 아라미드 섬유 보강 폴리머(Aramid Fiber Reinforced Polymers, 이하 AFRP)rebar로 보강된 콘크리트 깊은보의 전단강도를 평가하기 위하여 전단경간비, 보강비, 유효깊이, 주근을 변수로 총 8본의 시험체에 대한 전단 실험을 수행하였다. ACI 318-08의 스트럿-타이 모델(이하 STM)을 이용한 전단강도와 아치작용을 고려한 제안식에 의한 전단강도를 비교-평가하였으며, 그 결과 AFRP rebar로 보강한 경우, Steel rebar로 보강한 경우보다 전단강도가 증가하는 것으로 나타났다. 전단강도 산정에 있어 ACI 318-08 STM을 이용한 해석이 상대적으로 정확했으며, 실험결과를 토대로 스트럿의 크기효과를 고려한 유효압축강도 산정 모델을 제안하였다. 이를 본 실험에 적용시킨 결과 기존 기준 및 제안식을 이용한 전단강도 산정방법보다 합리적인 결과를 얻을 수 있었다. This study carried out a shear experiment on concrete deep beam reinforced AFRP to investigate the shear strength of deep beam. The test was conducted on 8 specimens, and the variables were shear span ratio, reinforcement ratio, effective depth, and rebar type. We compared shear strength using ACI 318-08 STM with proposed equations that considered arching action according to shear span ratio. As a result, it was found that shear strength of deep beam reinforced AFRP rebar presented higher shear strength than steel rebar. ACI STM's predictions are more accurate than other predicting equations, and thus this research proposed model versus effective compressive strength of the concrete strut that considered strut size effect based on test results. The predictions obtained using the proposed model are in better agreement than previous equations and codes.

Seismic Behavior of Low-rise Concrete Shear Wall with Single Layer of Web Reinforcement and Inclined Rebars: Restoring Force Model

Jian-Wei Zhang,Wen-Bin Zheng,Wan-Lin Cao,Hong-Ying Dong,Wan-Di Li 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.3

In order to study the restoring force model of low-rise concrete shear wall with single layer of web reinforcement and inclined rebars, a series of specimens were investigated by quasi-static tests. Based on the fitting of experimental data and theoretical analysis, the restoring force model considering four characteristic points (crack point, yield point, peak point and failure point) and degradation of unloading stiffness was established. The hysteretic rule of restoring force model was determined by analyzing characteristic of hysteresis curve for cyclic loading tests. The results show that skeleton curves and hysteresis curves calculated by the restoring force model are in good agreement with the test curves, which can provide reference for the elastic-plastic dynamic analysis of low-rise concrete shear walls with single layer of web reinforcements and inclined rebars. Shaking table tests of two low-rise concrete shear walls were also conducted to investigate dynamic performance and the seismic damage mechanism of low-rise concrete shear wall with single layer of web reinforcement and inclined rebars. Research on dynamic nonlinear simplified model of SAP2000 shows thatthe proposed restoring force model can be used to analyze the elastic and elastic-plastic dynamic response for the low-rise concrete shear wall with single layer of web reinforcement and inclined rebars.

하이브리드 FRP 리바의 역학적 특성

박찬기 ( Park Chan Gi ),원종필 ( Won Jong Pil ) 한국농공학회 2003 韓國農工學會誌 : 전원과 자원 Vol.45 No.2

Over the last decade fiber-reinforced polymer (FRP) reinforcement consisting of glass, carbon, or aramid fibers embedded in a resin such as vinyl ester, epoxy, or polyester has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. But reinforcing rebar for concrete made of FRP rebar has linear elastic behavior up to tensile failure. For safety a certain plastic strain and an elongation greater than 3% at maximum load is usually required for steel reinforcement in concrete structures. The same should be required for FRP rebar. Thus, the main object of this study was to develop new type of hybrid FRP rebar Also, this study was evaluated to the mechanical properties of Hybrid FRP rebar. The Manufacture of the hybrid FRP rebar was achieved by pultrusion, and braiding and filament winding techniques. Tensile and interlaminar shear test results of Hybrid FRP rebar can provide its excellent tensile strength-strain behavior and interlaminar stress-strain behavior.

FRP bar 보강 교량바닥판의 전단연결재 강도평가에 관한 연구

김철환 ( Kim Cheol-hwan ),이성태 ( Yi Seong-tae ) 한국구조물진단유지관리공학회 2022 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.26 No.2

철근콘크리트 교량 바닥판은 균열발생시 철근의 부식으로 바닥판의 파손이 진행되기 때문에 최근에는 철근을 원천 배제한 FRP bar 보강 바닥판이 현장에 다수 도입되고 있으나, 전단연결재의 설계기준과 연구사례는 철근보강 바닥판에 집중되어 있어 FRP 보강근이 전단연결재에 미치는 영향을 파악하기는 어려운 실정이다. 본 연구에서는 FRP rebar로 보강된 바닥판의 전단연결재 표준 시험체를 제작하고 Push-out 테스트를 수행하였으며, 스터드 직경별 파괴하중 도출하여 전단연결재에 대한 강도평가 실험식을 제안하였다.

Influence of transverse rebar on shear behavior of Y-type perfobond rib shear connection

Kim, Sang-Hyo,Kim, Kun-Soo,Han, Oneil,Park, Jun-Seung Elsevier 2018 Construction & building materials Vol.180 No.-

<P><B>Abstract</B></P> <P>This study experimentally investigated the effects of transverse rebar on the shear behavior of Y-type perfobond rib shear connectors. Push-out tests were performed on 12 specimens for which the strength and diameter of transverse rebar were utilized as variables. Test results from a previous study were used to confirm the shear strength and ductility of the Y-type perfobond rib shear connectors, along with the initial cracking and failure modes of the concrete. The results showed that shear strength increased as the diameter of the transverse rebar increased, and this effect was amplified in concrete with lower compressive strength.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Behavior of Y-type perfobond rib shear connections with various strength and diameter of transverse rebar were evaluated. </LI> <LI> Push-out tests were conducted to evaluate the shear resistance and ductility of Y-type perfobond rib shear connections. </LI> <LI> Push-out test results were compared with predicted results by existing models. </LI> <LI> Failure modes of Y-type perfobond rib shear connections were classified into three types. </LI> </UL> </P>

Experimental investigation on optimal shear strengthening of RC beams using NSM GFRP bars

M. Ramezanpour,R. Morshed,A. Eslami 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.67 No.1

Several techniques have been developed for shear strengthening of reinforced concrete (RC) members by using fiber reinforced polymer (FRP) composites. However, debonding of FRP retrofits from concrete substrate still deemed as a challenging concern in their application which needs to be scrutinized in details. As a result, this paper reports on the results of an experimental investigation on shear strengthening of RC beams using near surface mounted (NSM) FRP reinforcing bars. The main objective of the experimentation was increasing the efficiency of shear retrofits by precluding/postponing the premature debonding failure. The experimental program was comprised of six shear deficient RC beams. The test parameters include the FRP rebar spacing, inclination angle, and groove shape. Also, an innovative modification was introduced to the conventional NSM technique and its efficiency was evaluated by experimental observation and measurement. The results testified the efficiency of glass FRP (GFRP) rebars in increasing the shear strength of the test specimens retrofitted using conventional NSM technique. However, debonding of FRP bars impeded exploiting all retrofitting advantages and induced a premature shear failure. On the contrary, application of the proposed modified NSM (MNSM) technique was not only capable of preventing the premature debonding of FRP bars, but also could replace the failure mode of specimen from the brittle shear to a ductile flexural failure which is more desirable.

Experimental investigation on optimal shear strengthening of RC beams using NSM GFRP bars

Ramezanpour, M.,Morshed, R.,Eslami, A. Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.67 No.1

Several techniques have been developed for shear strengthening of reinforced concrete (RC) members by using fiber reinforced polymer (FRP) composites. However, debonding of FRP retrofits from concrete substrate still deemed as a challenging concern in their application which needs to be scrutinized in details. As a result, this paper reports on the results of an experimental investigation on shear strengthening of RC beams using near surface mounted (NSM) FRP reinforcing bars. The main objective of the experimentation was increasing the efficiency of shear retrofits by precluding/postponing the premature debonding failure. The experimental program was comprised of six shear deficient RC beams. The test parameters include the FRP rebar spacing, inclination angle, and groove shape. Also, an innovative modification was introduced to the conventional NSM technique and its efficiency was evaluated by experimental observation and measurement. The results testified the efficiency of glass FRP (GFRP) rebars in increasing the shear strength of the test specimens retrofitted using conventional NSM technique. However, debonding of FRP bars impeded exploiting all retrofitting advantages and induced a premature shear failure. On the contrary, application of the proposed modified NSM (MNSM) technique was not only capable of preventing the premature debonding of FRP bars, but also could replace the failure mode of specimen from the brittle shear to a ductile flexural failure which is more desirable.

Theoretical Formula of Ultimate Shear Strength for RC Beams without Transverse Reinforcement by Using External Vertical Prestressing Rebars

Xingwei Xue,Meizhong Wu,Peng Zhou,Junlong Zhou 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7

External vertical prestressing rebars (EVPRs) can effectively improve shear strength of concrete structures by the way of providing vertical compressive stress to the concrete and acting as stirrups. The objective of this study is to obtain a shear strength prediction model of EVPRs strengthening concrete beam without transverse reinforcement enhanced by modifying the ACI-318 and Critical Shear Crack Theory (CSCT). At the same time, this article analyzes the contribution of the strength of the shear strength, including the EVPRs as stirrups, compression zone of concrete, dowelling action, aggregate interlock and residual tensile strength. The results indicate that the shear strength prediction model can fit well with the experimental data and EVPRs can effectively enhance shear strength.