RC기둥의 내진성능에 미치는 겹침 이음상세의 영향

김철구,박홍근,김태완,엄태성 한국지진공학회 2016 한국지진공학회논문집 Vol.20 No.6

In regions of low-to-moderate seismicity, various types of lap splices are used for longitudinal reinforcement of columns at the plastic hinge zones. The seismic performance of such lap spliced columns, such as strength, deformation capacity, and energy dissipation, is affected by material strengths, longitudinal re-bar size, confinement of hoops, lap splice location, and lap splice length. In the present study, cyclic loading tests were performed for columns using three types of lap splices (bottom offset bar splice, top offset bar splice, and splice without offset bend). Lap splice length(40db and 50db) was also considered as test parameters. Ties with 90-degree end hooks were provided in the lap splice length. The test results showed that strength, deformation capacity, and energy dissipation of columns significantly differed depending on the details and the length of lap splices. The bottom offset bar splice showed high ductility and energy dissipation but low strength; on the other hand, the top offset bar splice and the splice without offset bend showed high strength but moderate ductility and energy dissipation.

소성힌지 구간에서 겹침이음된 RC기둥의 내진성능

김철구(Kim, Chul-Goo),엄태성(Eom, Tae-Sung),박홍근(Park, Hong-Gun),김태완(Kim, Tae-Wan) 대한건축학회 2015 大韓建築學會論文集 : 構造系 Vol.31 No.12

For small buildings designed to primarily resist gravity load, lap splices of longitudinal reinforcement are used in columns at the regions (e.g. at the bottom of the 1st floor) where flexural yielding is anticipated. Although not allowed under cyclic loading repeated in large inelastic range, such splices can be used as an alternative for the convenience of construction in small buildings where a limited ductility is required. In this study, cyclic loading test was performed for columns using lap splices at the plastic hinge regions. The length and offset bar details of lap splices and the ratio of shear span and section height (or aspect ratio) were considered as the test parameters. Non-seismic hoops of 90-degree end hooks were provided over the lap length. Test results showed that the strength and ductility of columns were significantly varied depending on the offset bar details and length of lap splices. In addition, the aspect ratio also had significant impact on the performance of lap splices due to change of the bond demand in the splice zone. The columns lap spliced in the plastic hinge zone were vulnerable to vertical cracking (or concrete splitting) along the lap length. Based on the test results and the review of existing studies, design recommendations for calculating lap spliced length of columns at plastic hinge zone were proposed.

이음 철근 사이 간격이 넓은 D13, D19 철근의 비접촉겹침이음 실험

문소현,천성철 한국콘크리트학회 2024 콘크리트학회논문집 Vol.36 No.1

In the Concrete Design Code of Korea, bars spliced by noncontact lap splices should not be spaced transversely farther apart than the lesser of one-fifth the required lap splice length or 150 mm. The structural behavior of noncontact lap splices with D13 and D19, which are spaced transversely farther apart than the provisions of the Concrete Design Code of Korea, was tested in this work. The test results showed that the behavior of noncontact laps is similar to the behavior of contact laps within the transverse spacing of spliced bars of 225 mm. Regardless of the spacing between spliced bars, the flexural cracks on the sides were similar for all specimens. The load-deflection relationships of all specimens were similar to the deflection curves of flexural members determined according to KDS 14 20 30, implying that all specimens deformed like ideal flexural members. As the spacing between spliced bars increases, there is no significant difference in the load-deflection relationships. Comparisons of test results of noncontact laps with the predictions by the design code provision, Orangun et al. (1977)’s equation, and the ACI Committee 408 equation show that the test-to-prediction ratios of 1.27, 1.54, and 1.23, respectively, indicating that the noncontact laps had sufficient strength. Consequently, noncontact laps within a 225 mm transverse spacing have equivalent strength and behavior and can be safely designed using the previous equations.

지진하중을 받는 주철근 겹침이음된 철근콘크리트 교각의 곡률분석

정영수,박창규,송희원 한국지진공학회 2006 한국지진공학회논문집 Vol.10 No.1

지난 1982년 우라카와 근해지진 및 1995년 효고현 남부 지진 등에 의하여 주철근이 겹침이음된 많은 교각들이 주철근 겹침이음부의 활동에 의한 휨-전단파괴를 발생하였음을 경험하였다. 철근콘크리트 교각의 내진성능은 소성힌지구간의 변형능력에 좌우되고 있으며, 이는 곡률연성도로서 평가된다. 우리나라에서는 1992년 내진 설계가 도입된 이후 철근콘크리트 교각의 주철근겹침이음에 대한 규정이 없었으나, 2005년 도로교 설계기준에서 주철근겹침음을 50% 이내에서 허용하고 있다. 본 연구는 단면 직경이 600 mm이고 형상비가 2.5 및 3.5인 주철근 겹침이음이 있는 철근콘크리트 교각에 대하여 지진시 소성힌지부의 곡률분포 및 곡률연성도에 대하여 조사하였다. 실험은 일정한 축력 P=0.1f{ck}A_g가 재하된 상태에서 변위제어 방식으로 준정적실험을 실시하였다. 실험결과 반복하중에 의한 주철근 겹침이음부에 활동이 발생하면, 주철근 겹침이음 구간 내의 곡률이 주철근 겹침이음이 없는 경우와 다르게 나타났다. 다시 말하면 주철근 겹침이음 실험체의 겹침이음 구간 중의 하부 곡률은 주철근 겹침이음이 없는 실험체의 경우보다 큰 값을 보이고 있으며, 상부는 작은 값을 보였다. 이로 인하여 교각실험체의 손상은 겹침이음 구간의 하부에 집중되어 휨파괴되는 모습으로 보이는 양상을 보였다. Through the 1982 Urahawa-ohi and the 1995 Kobe earthquakes, a number of bridge columns were observed to develop a flexural-shear failure due to the bond slip as a consequence of premature termination of the column longitudinal reinforcement. Because the seismic behavior of RC bridge piers is largely dependent on the performance of the plastic hinge legion of RC bridge piers, it is desirable that the seismic capacity of RC bridge pier is to evaluate as a curvature ductility. The provision for the lap splice of longitudinal steel was not specified in KHBDS(Korea Highway Bridge Design Specification) before the implementation of 1992 seismic design code, but the lap splice of not more than 50%, longitudinal reinforcement was newly allowed in the 2005 version of the KHBDS. The objective of this research is to investigate the distribution and ductility of the curvature of RC bridge column with the lap splice of longitudinal reinforcement in the plastic hinge legion. Six (6) specimens were made in 600 mm diameter with an aspect ratio of 2.5 or 3.5. These piers were cyclically subjected to the quasi-static loads with the uniform axial load of P=0.1f_{ck}A_g. According to the slip failure of longitudinal steels of the lap spliced specimen by cyclic loads, the curvatures of the lower and upper parts of the lap spliced region were bigger and smaller than the corresponding paris of the specimen without a lap splice, respectively. Therefore, the damage of the lap spliced test column was concentrated almost on the lower part of the lap spliced region, that appeared io be failed in flexure.

섬유에 의한 원형 철근콘크리트 교각의 내진성능향상

정영수,이재형 中央大學校 建設環境硏究所 2002 環境科學硏究 Vol.13 No.1

철근콘크리트 교각의 시공시 주철근의 겹침이음은 내진성능면에서 바람직하진 않지만, 실제의 시공에서는 불가피하게 시공되는 경우가 허다하다. 더욱이, 1992년 도로교표준시방서의 내진설계기준 설정 이전에 설계 시공된 철근콘크리트 교각은 주철근의 겹침이음이 소성힌지구간에 위치하여 현행 내진성능기준을 거의 만족하지 못하리라 예상된다. 본 연구는 철근콘크리트 교각의 내진성능에 영향을 미치고 있는 변수들로서 소성힌지구간의 주철근 겹침이음, 축방향력의 크기 및 횡구속철근비 등을 선택하여 준정적(Quasi-Static)실험에 의하여 철근콘크리트 교각의 내진성능을 평가하였다. 그리고, 유리섬유보강에 의한 내진성능향상효과 및 중약진지역에 적절한 내원설계기법 등에 관한 실험적 연구를 병행하였다. 형상비 4.0으로 제작된 9개의 시험체는 비내진, 중저진, 내진 성능을 가지는 3종류의 횡구속철근비, 0%, 50%, 100%의 3종류 주철근 겹침이음량, 및 3종류의 축방향력 0.1fckAg, 0.15fckAg, 0.2fckAg 등을 변수로 선택하여 실험을 수행하였으며, 실험결과 50%이상의 주철근 겹이음량, 소성힌지구간의 주철근겹이음 등은 바람직하지 않은 것으로 판단되었다. It has been known that lap splicing in the longitudinal reinforcement of bridge columns is not desirable for seism performance. However, lap splicing is sometimes unavoidable in practice. Lap splices were usually located at the alas tinge regions of most bridge columns constructed before the 1992 seismic design provision of Korea Roadway Bride Design Specification. This research is to evaluate the seismic performance of reinforced concrete bridge piers with lap splicing of longitudinal reinforcement at the plastic hinge region, to develop the enhancement scheme of their seismic capacity by retrofitting with glassfiber sheets, and to develop an appropriate limited ductility design concept in low or moderate seismicity region. Nine test specimens in the aspect ratio of 4.0 were made with three confinement ratios and three types of lap splicing. Quasi-Static tests under three different axial load levels were conducted. The results of a threes types of tests indicated that displacement ductility ratios of test columns with lap splicing were significantly reduced and lap splices of longitudinal reinforcement steels were not desirable in the plastic hinge region of bridge columns.

축방향철근의 겹침이음길이에 따른 원형 RC교각의 내진성능평가

박광순,서형열,김태훈,김익현,선창호 한국지진공학회 2014 한국지진공학회논문집 Vol.18 No.4

The plastic hinge region of RC pier ensures its nonlinear behavior during strong earthquake events. It is assumed that the piers secure sufficient strength and ductility in order to prevent the collapse of the bridge during strong earthquake. However, the presence of a lap-splice of longitudinal bars in the plastic hinge region may lead to the occurrence of early bond failure in the lap-splice zone and result in significant loss of the seismic performance. The current regulations for seismic performance evaluation limit the ultimate strain and displacement ductility considering the eventual presence of lap-splice, but do not consider the lap-splice length. In this study, seismic performance test and analysis are performed according to the cross-sectional size and the lap-splice length in the case of longitudinal bars with lap-splice located in the plastic hinge region of existing RC bridge columns with circular cross-section. The seismic behavioral characteristics of the piers are also analyzed. Based upon the results, this paper presents a more reasonable seismic performance evaluation method considering the lap-splice length and the cross-sectional size of the column.

주철근 겹침이음 비율에 따른 RC교각의 연성능력 평가

박광순,주형석,신현목,김문겸 한국지진공학회 2008 한국지진공학회논문집 Vol.12 No.6

국내외의 실험을 통해 알려진 바와 같이 RC교각의 연성능력은 소성힌지구간에 위치한 주철근 겹침이음 비율 및 횡방향 구속철근이 보유한 횡구속력에 따라 차이를 보이고 있다. 내진설계가 반영되지 못한 기존 교각의 경우 소성힌지구간의 겹침이음 비율에 따라 강도 및 연성능력의 저하에 미치는 영향이 크다. 우리나라에서는1992년 내진설계가 도입된 이후 철근콘크리트 교각의 주철근 겹침 이음에 대한 규정은 없었으나, 2005년 도로교 설계기준에서 주철근 겹침이음을 50% 이내에서 허용하고 있다. 기존 교량의 내진성능 평가 요령에 있어서도 이를 반영하여 교각의 연성능력을 평가하고 있지만 주철근 겹침이음 비율을 단순 유 무에 따라서 구분하여 평가하고 있고 평가기법 또한 명확하게 정립되어 있지 못하다. 따라서 본 연구에서는 비내진 교각의 겹침이음 비율별 연성능력평가를 위하여 현재까지 국내에서 수행된 연구실험결과를 분석하고, 교각의 비선형성 및 주철근의 겹침이음을 고려하기 위하여 섬유요소를 이용한 단면해석으로 RC교각의 연성능력을 산정시 적절한 콘크리트의 극한변형률을 제시하였다. As internal and external seismic experiment results, the seismic performance of RC bridge piers is largely dependent on the ratio of lap-spliced bars to all longitudinal reinforcing bars in plastic hinge regions, and confining effects of transverse reinforcements. Capacity and displacement ductility of non-seismically designed existing RC piers are reduced by lap splices in plastic hinge regions. The provision for the lap splice of longitudinal reinforcing bars was not specified in KBDS (Korean Bridge Design Specifications) before the implementation of 1992 seismic design code, but the ratio of lap-spliced bars to all longitudinal reinforcing bars in plastic hinge regions is restricted to 50% in the 2005 version of KBDS. This paper presents a seismic assessment of RC piers at lap-splicing ratios of 0%, 50%, and 100%. Through a comparison of experimental and analytic results of RC piers, we introduce an appropriate ultimate strain of confined concrete in plastic hinge regions with lap-splices, and propose a method for estimating displacement ductility ratios of non-seismically designed existing RC piers using fiber element analysis.

이음된 초고강도 강섬유보강콘크리트 보의 휨강도에 관한 실험적 연구

배백일 ( Baek-il Bae ),손동희 ( Dong-hee Son ),최현기 ( Hyun-ki Choi ),정형석 ( Hyung-suk Jung ),최창식 ( Chang-sik Choi ) 한국구조물진단유지관리공학회 2021 한국구조물진단유지관리공학회 논문집 Vol.25 No.6

본 연구에서는 이음된 초고강도 강섬유보강콘크리트 부재의 휨거동을 검토하고, 현행설계기준의 초고강도 강섬유보강콘크리트 구조물의 이음 설계에 대한 안전성을 평가하기 위해 총 6개의 보에 대한 가력 실험을 수행하였다. 주요 변수는 섬유의 혼입여부와 이음 길이로 설정하였다. 혼입된 섬유는 강섬유로 2%의 부피비로 결정하였으며, 이음길이는 8db와 16db로 결정하여 실험체를 제작하였다. 실험 결과 섬유로 보강되지 않은 실험체들은 이음부에서 급격한 하중지지능력을 상실하고 철근의 항복을 경험하지 못하였으나, 섬유로 보강된 경우 16db의 이음길이가 확보되면 주인장철근의 항복을 경험할 수 있으며, 적절한 휨강도를 발현할 수 있는 것으로 나타났다. 본 연구의 실험결과를 바탕으로 현행설계기준 및 초고강도콘크리트 구조설계지침의 이음길이 산정식들을 검토한 결과 모두 보수적인 평가를 하고 있는 것으로 나타났다. This study examines the bending behavior of lap-spliced ultra-high-strength fiber-reinforced concrete members and evaluates the safety of the design codes for ultra-high-strength fiber-reinforced concrete structures. An experiment on a total of six beams was performed. The main variables were the fiber-inclusion and the lap-spliced length at the center of the beams. The steel fibers in a volume fraction of 2% were used, and the lap-splice lengths were determined to be 8db and 16db. As a result of the test, the specimens not reinforced with fiber lost abrupt load-bearing capacity at the lap region and did not experience yielding of the reinforcing bar. In the case of fiber-reinforced concrete, if a lap-splice length of 16db is secured, the yielding of the main reinforcing bar can be experienced, and appropriate flexural strength can be expressed. Based on the experimental results of this study, as a result of reviewing the lap-splice length calculation formulas of the current design standards and the ultra-high-strength concrete structural design recommendations, it was found that all of them were evaluated conservatively.

Seismic performance and damage assessment of reinforced concrete bridge piers with lap-spliced longitudinal steels

Chung, Young S.,Park, Chang K.,Lee, Eun H. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.1

It is known that lap splices in the longitudinal reinforcement of reinforced concrete (RC) bridge columns are not desirable for seismic performance, but it is sometimes unavoidable. Lap splices were practically located in the potential plastic hinge region of most bridge columns that were constructed before the 1992 seismic design provisions of the Korea Bridge Design Specification. The objective of this research is to evaluate the seismic performance of reinforced concrete (RC) bridge piers with lap splicing of longitudinal reinforcement in the plastic hinge region, to develop an enhancement scheme for their seismic capacity by retrofitting with glassfiber sheets, and to assess a damage of bridge columns subjected to seismic loadings for the development of rational seismic design provisions in low or moderate seismicity region. Nine (9) test specimens with an aspect ratio of 4 were made with three confinement ratios and three types of lap splice. Quasi-static tests were conducted in a displacement-controlled way under three different axial loads. A significant reduction of displacement ductility was observed for test columns with lap splices of longitudinal reinforcements, whose displacement ductility could be greatly improved by externally wrapping with glassfiber sheets in the plastic hinge region. A damage of the limited ductile specimen was assessed to be relatively small.

T형 교각의 겹침이음을 고려한 콘크리트 교량의 지진취약도 분석

안효준,조백순,박주현,이종한 대한토목학회 2023 대한토목학회논문집 Vol.43 No.3

The collapse of bridges due to earthquakes results in many casualties and property damages. Thus, accurate prediction and preparation are required for the behavior of bridges during earthquakes. In particular, columns play an important role in the seismic behavior of bridges. The risk of collapse due to an earthquake increases when there is a problem of the insufficient lap splice in the column. In this study, to analyze the characteristics of the lap splice in the column, a numerical model was defined for the insufficient lap-spliced columns and verified using experimental data. The developed column model was applied to a commonly used RC slab bridge. Nonlinear static analysis for the column was performed to evaluate the change in the performance of the column according to the lap-spliced length. In addition, this study assessed the effect of the lap-spliced length on the seismic fragility analysis. 교량은 지진에 의해 붕괴가 일어나면 많은 수의 인명피해와 재산피해가 발생할 수 있어 정확한 지진거동 예측과 대비가 필요하다. 특히, 교각은 교량의 지진거동에 있어서 지배적인 역할을 한다. 또한, 교각의 겹침이음 길이 부족과 같은 설계적인 문제가 있다면 지진에 대한 위험성이 더욱 증대하게 된다. 본 연구에서는 교각에서 겹침이음 특성을 분석하기 위해, 겹침이음 길이가 부족한 교각의 수치해석 모델을 정의하고 실험데이터를 통해 검증하였다. 제시된 교각 모델을 일반적으로 사용되는 RC 슬래브 교량에 적용하였다. 교각의 비선형 정적해석을 수행하여 겹침이음에 따른 성능점 변화를 평가하였다. 또한, 지진취약도 곡선을 산정하여 교각의 겹침이음 길이에 따른 지진취약도 비교분석을 수행하였다.