콘크리트 압축강도 및 매입깊이에 따른 긴 칼블럭앵커의 뽑힘강도 평가

박준렬 ( Jun-ryeol Park ),양근혁 ( Keun-hyeok Yang ),김상희 ( Sang-hee Kim ),오나경 ( Na-kyung Oh ) 한국구조물진단유지관리공학회 2021 한국구조물진단유지관리공학회 논문집 Vol.25 No.6

2017년 경주지진은 블록이나 벽돌의 전도 및 탈락을 발생시켜 많은 인명피해 및 재산피해를 야기했다. 이에 칼블럭앵커나 치장벽보강 나선앵커를 활용한 보강기법들이 제시되었지만 길이가 짧거나 시공오차에 대한 대응의 어려움 등 문제가 발생하였다. 따라서 본 연구는 기존의 칼블럭앵커을 개선한 긴 칼블럭앵커를 제안하고 뽑힘강도 평가 실험을 수행하였다. 실험 변수는 콘크리트 압축강도와 매입깊이로 설정하였다. 앵커 인발시험결과, 긴 칼블럭앵커의 뽑힘강도는 콘크리트 실험체의 압축강도가 증가함에 따라 증가하였으며, 긴 칼블럭앵커의 매입깊이는 큰 영향이 없었다. 오히려 나사산 길이가 뽑힘강도에 더 큰 영향이 있는 것으로 나타났다. In 2017, the Gyeongju earthquake caused many casualties and considerable property damage by overturning and dropping blocks and bricks. Various reinforcement techniques were proposed, but some problems, such as short length or difficult construction, were encountered. Therefore, this study proposes a long-rawlplug screw anchor to improve the existing rawlplug anchor and conducts an experiment to evaluate the pullout strength. Variables in the pullout test were the compressive strength of concrete and the embedded length of the long-rawlplug screw anchor. According to the results, the pullout strength of the long-rawlplug screw anchor increased as the compressive strength of concrete increased, and they were not affected by the embedded length. Rather, it was found that the screw length of the long-rawlplug was important to the pullout strength.

Bond performance of steel rebar embedded in 80–180 MPa ultra-high-strength concrete

Yoo, Doo-Yeol,Shin, Hyun-Oh Elsevier 2018 Cement & concrete composites Vol.93 No.-

<P><B>Abstract</B></P> <P>Ultra-high-strength concrete (UHSC) has attracted attention from engineers because of its great capability on reducing the size of reinforced concrete columns. However, the bond performance of steel rebar embedded in UHSC has not been examined enough yet, although it is a fundamental information for structural design. So, this study comprehensively investigates the bond performance of deformed steel rebar embedded in high-strength concrete (HSC), very-high-strength concrete (VHSC), and UHSC with compressive strengths ranging from 80 to 180 MPa. Different bar diameters (12.7, 15.9, and 19.1 mm), embedment lengths (0.5, 1.0, and 1.5 × bar diameter), cover depths (1, 2, and 3 × bar diameter and center), steel fiber volume fractions (0, 0.5, 1.0, and 1.5%), and yield strengths of steel rebar (normal-strength vs. high-strength) were all considered. Test results indicate that the average bond strength increased significantly with an increase in the compressive strength of the concrete and decreased slightly with an increase in the bar diameter. Average bond strengths of steel rebars in HSC, VHSC, and UHSC were all increased by increasing the embedment length. The cover depth marginally influenced the bond strength when pullout failure was generated, and it significantly increased the bond strength when splitting failure occurred. The incorporation of steel fibers most effectively increased the bond strength in the UHSC mixture, compared with the HSC and VHSC mixtures. Lastly, the widely used prediction models for average bond strength were not accurate for concrete with a compressive strength greater than 80 MPa; thus, a new, appropriate model needs to be proposed in the near future.</P>

An Experimental Study on the Flexural Bonding Characteristic of a Concrete Beam Reinforced with a GFRP Rebar

오홍섭,심종성,강태성,권혁우 대한토목학회 2011 KSCE Journal of Civil Engineering Vol.15 No.7

This study was conducted to examine the bond strength of a beam reinforced with a GFRP (Glass Fiber Reinforced Polymer) rebar through a four-point bending test, adopting the British standard. The variables were made to have a bonding length 5 times (5 d_b), 10 times (10 d_b), and 15 times (15 d_b) that of the nominal diameter of a GFRP rebar. This was done to analyze the relationship between the bonding strength and the slip. The results of the test reveal that pull-out failure was dominant in the 5 d_b and 10d_b specimens. Both patterns of the pull-out failure and concrete-splitting failure appeared in the 10 d_b specimen. On the other hand, the 15d_b specimen showed only concretesplitting failure at the end of its bonding length. Therefore, it was proven in this study that the available bonding length of GFRP rebar under a bending condition in a static test is over 15 d_b. Further research should be conducted on this subject, though, particularly a fatigue bending test and an FEM (Finite Element Method) parameter study, and a bonding model must be developed

Seismic behavior of steel tube reinforced concrete bridge columns

Tian Tian,Wenliang Qiu,Zhe Zhang 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.1

This paper reports an experimental study that was accomplished to assess the seismic behavior of steel tube reinforced concrete bridge columns (SBCs). The motivation of this study was to verify a supposition that the core steel tube may be terminated at a rational position in the column to minimize the material cost while maintaining the seismic behavior of this composite column. Four SBC specimens were tested under combined constant axial load and cyclic reversed lateral loads. The unique variable in the test matrix was the core steel tube embedment length, which ranged from 1/3 to 3/3 of the column effective height. It is observed that SBCs showed two distinctly different failure patterns, namely brittle shear failure and ductile flexural failure. Tests results indicate that the hysteretic responses of SBCs were susceptible to the core steel tube embedment length. With the increase of this structural parameter, the lateral strength of SBC was progressively improved; the deformability and ductility, however, exhibited a tendency of first increase and then decrease. It is also found that in addition to maintained the rate of stiffness degradation and cumulative energy dissipation basically unchanged, both the ductility and deformability of SBC were significantly improved when the core steel tube was terminated at the mid-height of the column, and these were the most unexpected benefits accompanied with material cost reduction.

GFRP Rebar로 보강된 콘크리트보의 피로 휨·부착성능에 관한 실험적 연구

오홍섭,심종성,강태성 한국구조물진단유지관리공학회 2008 한국구조물진단유지관리공학회 논문집 Vol.12 No.1

본 연구에서는 철근과 같은 기계적 맞물림 현상을 활용하기 위하여 이형리브가 형성되어 있는 GFRP 보강근을 제작하여 철근대체 재료로 사용하기 위해 FRP 보강근의 부착성능을 규명하고자 한다. 하지만 지금까지 많은 기존 연구자들이 부착성능에 대한 실험으로 단순 1방향(수직, 수평)인장실험으로 철근과 콘크리트 또는 FRP 보강근과 콘크리트사이의 부착특성을 고찰하여 두 재료 사이의 부착-슬립에 관한 제안식을 도출해왔다. 국내에서는 아직까지 GFRP 보강근의 부착에 대한 관심이 증대대고 있는 실정이지만 피로부착에 관한연구는 미흡한 편이이어서 GFRP 보강근의 피로 연구가 필요로 하다. 본 연구에서는 BRITISH STANDARD에서 규정하고 있는 방법에 의하여 휨 부착 시험체를 제작하여 정적 휨 부착실험 최대파괴하중의 70% ~ 90%의 하중으로 반복하중재하 후 정적실험을 통하여 GFRP로 보강된 콘크리트 피로부착 성능을 검증하였다 This study is to examine bond strength of beam reinforced with GFRP rebar under 4-point fatigue bending test by adopting BRITISH STANDARD. The variables were made to have bonding length of 5times(5db), and 15times(15db) of the nominal diameter of GFRP rebar and were done to analyze the relationship between the bonding strength and the slip. In the result of the test, pull-out failure was dominant in the 5db specimen, patterns of the pull-out failure and concrete shear failure appeared in the 15db specimen showed only concrete shear failure at the end of bonding length. Therefore, The strain development consist of three different stage : A rapid increases form 0 to about 10% of total fatigue life. A uniform increases form 10% to about 70%~90%. Then a rapid increases until failure, if failure takes place. It seems that stress level has not influence on the secant modules of elasticity. And also according to the outcome the existing strengthening method came out to be the most superiority in S-N graphs.

그라우트 충전식 철근이음의 강도와 연성에 관한 비교분석

金載承,金亨其,朴福萬,劉承圭 明知大學校 産業技術硏究所 2005 産業技術硏究所論文集 Vol.24 No.-

In this study, the tensile strength and ductility of 306 grout-filled splice sleeve specimen were compared and analyzed in order to afford the data for a reasonable and economical design of this system. The experimental variables analyzed in this study were embedment length of reinforcing bars, compressive strength of grout, sleeve geometry, loading pattern and final failure mode of specimen Following main conclusions are obtained: 1) The strength and ductility of grout-filled splice sleeve tends to be improved with increasing compressive strength of grout and embedment length of reinforcing bars, Specially this tendency appears apparent in specimens of bond failure rather than rebar failure. 2) The results of this study show that the sleeve geometries have influences on the bond strength and ductility of grout-filled splice sleeve. 3) It is verified that the tensile strength required in ACI and domestic code is retained when the compressive strength of grout over 700kgf/㎠ is used with embedment length of reinforcing bars over 4.5d and that the tensile strength required in AIJ code is retained in case when the embedment length of reinforcing bars is 0.8 times the rebar diameter longer than in ACI code. 4) It is verified that over 2% ductility is maintained When the compressive strength of grout over 700kgf/㎠ is used with embedment length of reinforcing bars over 4.5d. 5) The ductility of grout-filled splice sleeve tends to be improved with increasing tensile strength of grout filled splice sleeve. Specially this tendency appears apparent in specimens of bond failure rather than rebar failure.

고강도 모르타르 충전식 스플라이스 슬리브의 인장강도와 연성에 관한 실험적 연구

김형기(Kim Hyong-Kee) 대한건축학회 2002 大韓建築學會論文集 : 構造系 Vol.18 No.12

In this study, totally 60 full-sized specimens were made and tested under monotonic loading in order to afford the data for a reasonable and economical design of grout-filled splice sleeve. The experimental variables adopted in this study were embedment length of reinforcing bars, compressive strength of filled mortar and size of reinforcing bars. After test was performed, the results were compared and analyzed along with previous test of author. The followings were found: 1) It is verified that the tensile strength required in ACI and domestic code is maintained either when the embedment length of reinforcing bars over 4.2d is used with compressive strength of mortar over 700kgf/㎠ or when the embedment length of reinforcing bars over 4.7d is used with compressive strength of mortar over 600kgf/㎠. 2) It is verified that over 2% ductility is maintained either when the embedment length of reinforcing bars over 4.2d is used with compressive strength of mortar over 700kgf/㎠ or when the embedment length of reinforcing bars over 5.2d is used with compressive strength of mortar over 600kgf/㎠. 3) Splice sleeve which are designed to maintain the embedment length of reinforcing bars over 6.5d are conservative in respect of tensile strength and ductility. When splice sleeve are produced anew, it is considered that the more economical splice sleeve which reduce the length of splice sleeve can he made.

Evaluating the pull-out load capacity of steel bolt using Schmidt hammer and ultrasonic pulse velocity test

Saleem, Muhammad Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.5

Steel bolts are used in the construction industry for a large variety of applications that range from fixing permanent installations to temporary fixtures. In the past much research has been focused on developing destructive testing techniques to estimate their pull-out load carrying capacity with very little attention to develop non-destructive techniques. In this regards the presented research work details the combined use of ultrasonic pulse velocity and Schmidt hammer tests to identify anchor bolts with faculty installation and to estimate their pull-out strength by relating it to the Schmidt hammer rebound value. From experimentation, it was observed that the load capacity of bolt depends on its embedment length, diameter, bond quality/concrete strength and alignment. Ultrasonic pulse velocity test is used to judge the quality of bond of embedded anchor bolt by relating the increase in ultrasonic pulse transit time to the presence of internal pours and cracks in the vicinity of steel bolt and the surrounding concrete. This information combined with the Schmidt hammer rebound number, R, can be used to accurately identify defective bolts which resulted in lower pull-out strength. 12 mm diameter bolts with embedment length of 70 mm and 50 mm were investigated using constant strength concrete. Pull-out load capacity versus the Schmidt hammer rebound number for each embedment length is presented.

Evaluating the pull-out load capacity of steel bolt using Schmidt hammer and ultrasonic pulse velocity test

Muhammad Saleem 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.5

Steel bolts are used in the construction industry for a large variety of applications that range from fixing permanent installations to temporary fixtures. In the past much research has been focused on developing destructive testing techniques to estimate their pull-out load carrying capacity with very little attention to develop non-destructive techniques. In this regards the presented research work details the combined use of ultrasonic pulse velocity and Schmidt hammer tests to identify anchor bolts with faculty installation and to estimate their pull-out strength by relating it to the Schmidt hammer rebound value. From experimentation, it was observed that the load capacity of bolt depends on its embedment length, diameter, bond quality/concrete strength and alignment. Ultrasonic pulse velocity test is used to judge the quality of bond of embedded anchor bolt by relating the increase in ultrasonic pulse transit time to the presence of internal pours and cracks in the vicinity of steel bolt and the surrounding concrete. This information combined with the Schmidt hammer rebound number, R, can be used to accurately identify defective bolts which resulted in lower pull-out strength. 12 mm diameter bolts with embedment length of 70 mm and 50 mm were investigated using constant strength concrete. Pull-out load capacity versus the Schmidt hammer rebound number for each embedment length is presented.

Effect of embedment length on pullout behavior of amorphous steel fiber in Portland cement composites

Kim, Baek-Joong,Yi, Chongku,Ahn, Yu-ri Elsevier 2017 Construction and Building Materials Vol.143 No.-

<P><B>Abstract</B></P> <P>For using amorphous steel fibers (ASF) in Portland cement composites, the performance of ASF was evaluated by a pullout test and compared to that of a hooked-end steel fiber (HSF). The embedment length of the fiber (5.0, 8.0, and 12.5mm), compressive strength of the mortar, and number of fibers were considered the test variables. The results showed that a single ASF had a greater maximum applied load (<I>P<SUB>max</SUB> </I>) than a single HSF; however, at a mortar compressive strength of 30–42MPa, its bond strength (<I>τ<SUB>max</SUB> </I>) and pullout energy (<I>E<SUB>f</SUB> </I>) decreased by 40.9–55.8% and 16.9–79.7%, respectively, compared to those of a single HSF. Furthermore, in the pullout failure mode, the <I>E<SUB>f</SUB> </I> of 4 ASFs, which have a volume fraction equivalent to a single HSF, was 2.10–3.04 times higher than that of a single HSF. Based on the <I>E<SUB>f</SUB> </I> of ASFs, an embedment length of 5–8mm is recommended to provide the most effective ASF reinforcement effect to a mortar with a compressive strength of up to 40MPa.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Review on the fiber reinforcement in cement composites. </LI> <LI> Effect of embedment length on bond behavior is experimentally investigated. </LI> <LI> Optimum fiber geometry of the amorphous steel fiber. </LI> </UL> </P>