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Control of Tensile Stress in Prestressed Concrete Members Under Service Loads
Deuck Hang Lee,Sun-Jin Han,Hyo-Eun Joo,Kang Su Kim 한국콘크리트학회 2018 International Journal of Concrete Structures and M Vol.12 No.4
In current design codes, crack control design criterion for prestressed concrete (PSC) members is stricter than conventional reinforced concrete (RC) members. In particular, it is stipulated that the net tensile stress of prestressing strands should be controlled under 250 MPa in the serviceability design of PSC members belonging to the Class C category section that is expected to be cracked due to flexure under service load conditions as defined in ACI318 code. Thus, the cracked section analysis is essentially required to estimate the tensile stress of the prestressing strands under the service loads, which requires very complex iterative calculations, thereby causing many difficulties in the applications of the Class C PSC members in practice. Thus, this study proposed a simple method to estimate the net tensile stress of the prestressing strands (△fps) under the service load conditions, and also provided a summary table to be used for checking whether the net tensile stress (△fps) exceeds the stress limit (250 or 350 MPa) with respect to the magnitude of effective prestress (fse).
Lee, Deuck Hang,Han, Sun-Jin,Kim, Kang Su,LaFave, James M. ELSEVIER (APPLIED SCIENCE) 2017 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.173 No.-
<P><B>Abstract</B></P> <P>A shear strength estimation model for reinforced concrete (RC) beams, the so-called dual potential capacity model (DPCM), has previously been proposed by the authors. In this study, the DPCM is extended to estimate the shear strength of RC beams strengthened in shear by using externally-bonded fiber-reinforced polymer (FRP) composites. The proposed model has been derived so as to take into account the effects of the type of FRP composite, fiber-bonding configuration, and fiber layout, and it can also determine the critical shear failure modes of RC beams strengthened by externally-bonded FRP composites. To verify the accuracy of the proposed model, shear test results of 227 RC beams strengthened by externally-bonded FRP composites were collected from previous studies, and it is shown that the analysis results estimated by the DPCM agree well with those test results.</P>
Lee, Deuck Hang,Park, Min-Kook,Oh, Jae-Yuel,Kim, Kang Su,Im, Ju-Hyeuk,Seo, Soo-Yeon 테크노프레스 2014 Computers and Concrete, An International Journal Vol. No.
Prestressed hollow-core slabs (HCS) are widely used for modern lightweight precast floor structures because they are cost-efficient by reducing materials, and have excellent flexural strength and stiffness by using prestressing tendons, compared to reinforced concrete (RC) floor system. According to the recently revised ACI318-08, the web-shear capacity of HCS members exceeding 315 mm in depth without the minimum shear reinforcement should be reduced by half. It is, however, difficult to provide shear reinforcement in HCS members produced by the extrusion method due to their unique concrete casting methods, and thus, their shear design is significantly affected by the minimum shear reinforcement provision in ACI318-08. In this study, a large number of shear test data on HCS members has been collected and analyzed to examine their web-shear capacity with consideration on the minimum shear reinforcement requirement in ACI318-08. The analysis results indicates that the minimum shear reinforcement requirement for deep HCS members are too severe, and that the web-shear strength equation in ACI318-08 does not provide good estimation of shear strengths for HCS members. Thus, in this paper, a rational web-shear strength equation for HCS members was derived in a simple manner, which provides a consistent margin of safety on shear strength for the HCS members up to 500 mm deep. More shear test data would be required to apply the proposed shear strength equation for the HCS members over 500 mm in depth though.
Flexural strength of prestressed concrete members with unbonded tendons
Lee, Deuck Hang,Kim, Kang Su Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.38 No.5
It is difficult to accurately predict the flexural strength of prestressed members with unbonded tendons, unlike that of prestressed members with bonded tendons, due to the unbonded behavior between concrete and tendon. While there have been many studies on this subject, the flexural strength of prestressed members with unbonded tendons is still not well understood, and different standards in various countries often result in different estimation results for identical members. Therefore, this paper aimed to observe existing approaches and to propose an improved model for the ultimate strength of prestressed members with unbonded tendons. Additionally, a large number of tests results on flexural strength of prestressed members with unbonded tendons were collected from previous studies, which entered into a database to verify the accuracy of the proposed model. The proposed model, compared to existing approaches, well estimated the flexural strength of prestressed members with unbonded tendons, adequately reflecting the effects of influencing factors such as the reinforced steel ratio, the loading patterns, and the concrete strength. The proposed model also provided a reasonably good estimation of the ultimate strength of over-reinforced members and high-strength concrete members.
장방형 단면을 갖는 프리텐션부재의 프리스트레스 도입시 허용압축응력
이정연(Lee Jeong-Yeon),이득행(Lee Deuck-Hang),김강수(Kim Kang-Su),황진하(Hwang Jing-Ha),임주혁(Lim Joo-Hyuk),이진섭(Lee Jin-Seop) 대한건축학회 2011 大韓建築學會論文集 : 構造系 Vol.27 No.5
Prestressed concrete structural system is the one of the best alternatives to satisfy deflection requirements for the long and slender span members. Especially, pre-tension member can be precasted at factory that reduces construction waste by minimizing the onsite work and construction duration, which is considered as an eco-friendly and economical structural method. However, the economic efficiency of the pre-tension system heavily depends on the transfer time as the pre-tensioned member need to acquire an proper compressive strength at transfer. Unfortunately, the allowable compressive stresses in many codes of practice are based on only experience without theoretical consideration, which also are often very conservative. To solve out such problems, this research proposed the allowable compressive stress based on ultimate strength design method, considering main variables such as shapes of cross section, intensity of prestress, and eccentricity of tendons.
이득행 ( Lee Deuck Hang ),김강수 ( Kim Kang Su ) 한국구조물진단유지관리공학회 2009 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.13 No.1
In existing post-tension(PT) slab system, anchorage is typically located at the edge of slab, and temporary installations of additional froms are required to set the anchorage. In previous research, authors proposed the top jacking anchorage system to improve the constructability of existing PT methods. The stress distribution at anchorage zone, however, is very different from the existing systems because jacking at interior slab induces tensile stresses at the back of anchorage. Structural design provisions have not yet suggested the design details suitable for proposed anchorage system. Therefore, this research presents a detailed design example including reasonable reinforcement details resisting against the spalling, bursting, and tensile stresses at the back of anchorage based on code requirements and strut-tie model.