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Non-Iterative Moment Capacity Equation for Reinforced Concrete Beams with External Post-Tensioning
Lee, Swoo-Heon,Shin, Kyung-Jae,Kang, Thomas H.-K. American Concrete Institute 2014 ACI structural journal Vol.111 No.5
<p>The stress of unbonded steel in post-tensioned concrete beams at the ultimate stage is needed to determine their moment capacity, but it is difficult to accurately predict the stress of external posttensioning steel. This is because the unbonded steel stress is governed by total steel elongation, which depends on the beam deflection and other interrelated variables. The bulk of the previously developed analytical methods are applicable only for internal tendons encased in concrete. Given the lack of analytical models for externally post-tensioned beams, in this study, a simplified non-iterative equation for the stress at ultimate in external tendons or other steel materials is developed. During this process, flexural responses of yield and ultimate moments and their corresponding deflections are also predicted. A major effort is made to simplify such a process and propose a generalized non-iterative moment capacity equation for reinforced concrete beams with external post-tensioning.</p>
고장력 인장봉으로 보강된 RC보의 전단해석에 관한 연구
이수헌(Lee Swoo-Heon),김병준(Kim Byung-Jun),박민석(Park Min-Suk),신경재(Shin Kyung-Jae) 대한건축학회 2009 大韓建築學會論文集 : 構造系 Vol.25 No.3
The objective of this study is to develop equations or the method that can predict the strengthening effect on shear capacity of RC beams with high tension bars. The shear capacity of these beams is defined as summation of shear force by concrete, stirrup and high tension bars. To estimate the shear force by concrete and stirrup, Zsutty equation is used. As like other paper, the Zsutty shear equation produces satisfactory predictions as compared to ACI code equation. And the strengthening effect on shear capacity is achieved through the geometrical method. The basic concept of this method is that externally unbonded high tension bars are converted to a vertical component which affects the shear capacity. This geometrical equation contains three parameters such as the area, inclined angle and specified yield strength of high tension bars. Especially, the high tension bars of experimental specimens in this paper didn`t reach the yield point. Therefore it is necessary to estimate the stress of high tension bars at nominal flexural strength for more exact predicting results. There are two ways to estimate this stress; the flexural design code equations of prestressed concrete in ACI 318-05 and the relation equations between load and deflection. In flexural design code, experimental result of theoretical result is about 0.56~0.62. On the other hand, the relation equations betweem load and deflection show that experimental result of theoretical result is about 0.96~1.01 agreement. This paper presents equations to estimate the stress in high tension bars at nominal flexural strength. From the comparison of experimental and predicted shear capacity, an exact agreement is achieved in proposed method.
반복횡하중에 따른 철근콘크리트 모멘트골조의 거동 및 반응수정계수 분석
이수헌(Lee Swoo-Heon),신경재(Shin Kyung-Jae),김동백(Kim Dong-Baek),이희두(Lee Hee-Du) 대한건축학회 2012 大韓建築學會論文集 : 構造系 Vol.28 No.8
The average number of earthquake activities per year around the peninsula is about fifty times during the last five years according to the Korea Meteorological Administration. Nevertheless, the damage caused by the earthquake was not serious because the earthquake magnitude was not severe. It is required to make provision for old structural system with non-seismical detail at this time while the incidence of earthquake is gradually increasing. There are more than 80% school buildings of the reinforced concrete moment frame constructed before considering seismic design code in Korea. In this study, three RC frames designed only for gravity loads, including a frame simulated for non-seismical school building, were prepared based on KBC 2009: one ordinary moment frame (OMF) and two intermediate moment frames (IMFs). One of IMFs was strengthened with carbon fiber reinforced polymer (CFRP) at the base of column. A total of three frames were tested under cyclic loading according to ACI374.1-05. As a result, the CFRP increases the load-carrying capacity, ductility ratio and energy dissipation ratio but the strength and response modification factor were not increased as expected. Additionally, the plastic rotation of three models significantly exceeded the criteria of FEMA 356.
이수헌 ( Lee Swoo-heon ),김보우 ( Kim Bo-woo ) 한국구조물진단유지관리공학회 2017 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.21 No.2
Externally post-tensioning steel rods led to a 25~66% increase of load-carrying shear capacity in damaged reinforced concrete beams when compared to a control beam. And the shear strength of a beam with two deviators was larger than that of a beam with one deviator. That shows how important a deviator location is for strengthening effect.
외적 포스트텐셔닝 보강에서 데비에이터의 위치에 따른 전단보강효과
이수헌(Lee, Swoo-Heon),신경재(Shin, Kyung-Jae),이희두(Lee, Hee-Du) 대한건축학회 2018 大韓建築學會論文集 : 構造系 Vol.34 No.6
This paper described the shear strengthening effect by deviator location in pre-damaged reinforced concrete (RC) beams strengthened with externally post-tensioning steel rods. Three reinforced concrete beams as control beam and eight post-tensioned beams using external steel rods were tested to fail in shear. The externally post-tensioning material was a steel rod of 22 mm diameter, and it had a 655 MPa yield strength and an 805 MPa tensile strength. Specimens depend on multiple variables, such as the number of deviators, location of deviator, and load pattern. The pre-damaged loads up to about 2/3 of ultimate shear capacities were applied to specimens using displacement control and the diagonal shear crack just occurred at these loading levels. And then, the post-tensioning up to when a strain of steel rod reaches about 2000 με was continuously applied to beam. A displacement control was changed to a load control during post-tensioning. The post-tensioning resulted in increase of load-carrying capacity and restoration of existing deflection. Also, it prevented the existing diagonal cracks from excessively growing. Two deviators effectively improved the load capacity when compared with in case of test which one deviator at mid-span installed. When deviators were located near region which the diagonal crack occurred on, the strengthening impact by post-tensioning was greater.
손상입은 철근콘크리트 보의 외적 포스트텐셔닝에 의한 휨 보강
이수헌(Lee, Swoo-Heon),이희두(Lee, Hee-Du),이창수(Lee, Chang-Soo),신경재(Shin, Kyung-Jae) 대한건축학회 2017 大韓建築學會論文集 : 構造系 Vol.33 No.7
An experimental work was undertaken to observe and assess the behavior of damaged reinforced concrete (RC) beams with external post-tensioning steel rods. Six simply supported beams - two control beams and four comparable beams post-tensioned using externally steel rods - were tested in three-point bending. The main parameters are the diameter of external post-tensioning rods (ø22 mm and ø28 mm) and the ratio of tension steel reinforcement (p =0.0106 and 0.0166). For the post-tensioned beams, V-shaped profiles were used with a deviator located at the bottom of mid-span, and the post-tensioning force was applied to beams in order to overcome the low load-carrying capacity and existing deflection. The post-tensioning force acting on the steel rods was applied by tightening nuts of anchorage and its value was monitored by attached strain gauges. The initial strain of about 2000µε was chosen for post-tensioning force because it is about the maximum strain that two adult men can apply without struggle. Test results indicate that the externally post-tensioning increased the load-carrying capacity by about 40~101% and the flexural stiffness by about 27~43% compared to control beams. On the other hand, the larger steel reinforcements and external rods of the section disturbed the yielding of external rod at ultimate strength.
원형개구부가 있는 강판 전단벽 시스템을 적용한 학교 건축물의 내진성능평가
이유현(Lee, Yu-Hyeon),이수헌(Lee, Swoo-Heon),이희두(Lee, Hee-Du),신경재(Shin, Kyung-Jae) 대한건축학회 2018 大韓建築學會論文集 : 構造系 Vol.34 No.1
After the Gyeongju earthquake, school buildings were designated as earthquake shelters. However, the ratio of designed for seismic of domestic school buildings is only 23.2% in Korea, and it is necessary to secure the seismic safety of those. Therefore, in this paper, a target building was selected before the seismic design criteria was established and the seismic performance of the building was evaluated. After the evaluation, reinforcement of the building was carried out using seismic retrofit systems which was previously tested. For this purpose, the evaluation was carried out using OpenSees program and the reliability of the seismic retrofit systems was also verified. In this way, we can more precisely reproduce the response of the building in case of actual earthquake and predict damage of the earthquake in the future.
사전균열이 발생한 철근콘크리트 보의 외적 포스트텐셔닝 전단보강에서 보강깊이의 효과
이수헌(Lee, Swoo-Heon),신경재(Shin, Kyung-Jae),이희두(Lee, Hee-Du) 대한건축학회 2018 大韓建築學會論文集 : 構造系 Vol.34 No.11
This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.
포스트텐셔닝 강봉으로 보강한 손상된 철근콘크리트 보의 전단강도
이수헌 ( Lee Swoo-heon ),신경재 ( Shin Kyung-jae ),이희두 ( Lee Hee-du ),박성근 ( Park Seong-geun ) 한국구조물진단유지관리공학회 2017 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.21 No.1
The shear strength of damaged reinforced concrete beams using externally post-tensioning steel rods increased by 25∼57% compared to control beam. ACI 318-14 (simpled and detailed approaches) specifications for prestressed concrete beams conservatively predicted the nominal shear strength.