• Title/Summary/Keyword: prestressing ratio

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An Experimental Study on Structural Behavior of Concrete Box Girder Member with Transverse Prestressing (PSC 박스거더 교량부재의 횡방향 프리스트레싱에 따른 구조거동 실험연구)

  • Oh Byung Hwan;Choi Young Cheol;Choi Jung Sun;Lee Seong Cheol
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.11a
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    • pp.77-80
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    • 2004
  • In bridge deck systems, deflections and cracking can be controlled by longitudinal and transverse prestressing, There are some benefits, longitudinal cracking control, the thickness reduction of deck slab, the widening of deck width and the reduction of the cross section area, in transversely post-tensioned concrete box girder bridges. However, it has been not sufficient to study the structural behaviors of transversely post-tensioned concrete box girder. Therefore, It is needed to predict the structural behaviors by prestressing and static loading. In this study, the analytical and experimental load tests are carried out to study the effect of transverse prestressing on concrete box girder. For these objectives, four test specimens are fabricated with various tendon spacing and steel ratio of top slab. The analytical and experimental studies are performed to estimate effects of the prestressing and failure tests.

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Effects of Design Parameters on Structural Performance of Precast Piers with Bonded Prestressing Steels (부착 긴장재를 가진 조립식 교각 설계변수의 구조성능에 미치는 영향)

  • Shim, Chang-Su;Yoon, Jae-Young
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.30 no.1A
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    • pp.15-26
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    • 2010
  • Quasi-static tests were conducted to evaluate structural performance of precast piers prestressed by bonded prestressing steels. Combinations of prestressing bars and normal reinforcing bars, embedded steel tubes and prestressing strands were used as continuous steels crossing the joints of a precast pier. Main design parameters were steel ratio, magnitude of prestress force, and section details. Flexural strength and energy dissipation capacity of precast columns with higher steel ratio showed better performance due to continuous steels after opening of the joints. Precast piers with embedded members showed stable behavior after reaching maximum loads resulting in higher displacement ductility and energy dissipation capacity increased as the introduced prestress increased. Self-centering behavior at early stages and stress increase of confining reinforcements were observed from highly prestressed columns. Combination of prestressing steels and normal reinforcing bars should be used in design to prevent rapid strength degradation after reaching the maximum load.

Transverse Stress of Slabs due tp Longitudinal Prestressing in Prestressed Concrete Box Girders (프리스트레스트 콘크리트 박스 거더의 종방향 프리스트레싱에 의한 슬래브의 횡방향 응력)

  • Yang, In-Hwan
    • Journal of the Korea Concrete Institute
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    • v.15 no.5
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    • pp.679-688
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    • 2003
  • For box girders in which the longitudinal tendon is profiled in the inclined webs, longitudinal prestressing force will induce transverse effects as well as longitudinal ones. In this paper, the method to estimate transverse effects induced by longitudinal prestressing is proposed. The concept of transverse equivalent loading which is calculated through longitudinal prestressing analysis is developed. The transverse stress in slabs of box girders due to longitudinal prestressing are investigated. The comparison of numerical results of the proposed method and those of folded plate method represents that the method is reasonable. Numerical analyses are carried out depending on the parameters such as web inclination and ratio of girder length to tendon eccentricity. Analysis results show that when only prestressing are considered the magnitude of transverse stress in slabs of box girder is not so large. However, if the other stresses due to dead and live load et al. are superposed on these stresses, it may be that the longitudinal prestressing effects are significant.

Experimental, numerical and analytical studies on a novel external prestressing technique for concrete structural components

  • Lakshmanan, N.;Saibabu, S.;Murthy, A. Rama Chandra;Ganapathi, S. Chitra;Jayaraman, R.;Senthil, R.
    • Computers and Concrete
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    • v.6 no.1
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    • pp.41-57
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    • 2009
  • This paper presents the details of a novel external prestressing technique for strengthening of concrete members. In the proposed technique, transfer of external force is in shear mode on the end block thus creating a complex stress distribution and the required transverse prestressing force is lesser compared to conventional techniques. Steel brackets are provided on either side of the end block for transferring external prestressing force and these are connected to the anchor blocks by expansion type anchor bolts. In order to validate the technique, an experimental investigation has been carried out on post-tensioned end blocks. Performance of the end blocks have been studied for design, cracking and ultimate loads. Slip and slope of steel bracket have been recorded at various stages during the experiment. Finite element analysis has been carried out by simulating the test conditions and the responses have been compared. From the analysis, it has been observed that the computed slope and slip of the steel bracket are in good agreement with the corresponding experimental observations. A simplified analytical model has been proposed to compute load-deformation of the loaded steel bracket with respect to the end block. Yield and ultimate loads have been arrived at based on force/moment equilibrium equations at critical sections. Deformation analysis has been carried out based on the assumption that the ratio of axial deformation to vertical deformation of anchor bolt would follow the same ratio at the corresponding forces such as yield and ultimate. It is observed that the computed forces, slip and slopes are in good agreement with the corresponding experimental observations.

A Comparitive Study on the Ultimate Tendon Stress of Unbonded Tendon According to Various Codes (규격별 비부착 긴장재의 극한응력식에 대한 비교 연구)

  • 유성원;서정인
    • Proceedings of the Korea Concrete Institute Conference
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    • 2002.05a
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    • pp.501-506
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    • 2002
  • The unbonded prestressed concrete(PSC) members exhibit very different structural behavior from that of bonded PSC members because of having different tendon stress increment. Recently, AASHTO changed the provision of ultimate tendon stress with unbonded tendons, because some researches tried to improve the provision of ultimate tendon stress with unbonded tendons. The purpose of the present study is to compare various Codes with the ultimate failure stresses of prestressing(PS) steels for the unbonded PSC members. To this end, Some national Codes have been collected and analyzed. A series of major influencing variables have been included in the analysis. It was found that the span-depth ratio, neutral axis depth-effective depth ratio, concrete compressive strength, effective prestress, and prestressing steel ratio have great influence on the ultimate failure stress of PS steel in unbonded PSC members. The Comparison indicates that existing formulas including ACI and domestic Code's equations shows some unwarranties. The present study allows more realistic analysis and design of prestressed concrete structures with internal unbonded tendons.

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Prediction of Prestressing Steel Stress at Ultimate State of Prestressed Concrete Members with External Unbonded Tendons (외부 프리스트레스트 콘크리트 부재의 극한상태에서의 강선응력예측식 제안)

  • 오병환;유성원
    • Journal of the Korea Concrete Institute
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    • v.11 no.6
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    • pp.13-24
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    • 1999
  • The external, unbonded prestressed concrete(PSC) members exhibit very different structural behavior from that of internal bonded PSC members because of eccentricity change and slip occurrence during loading process. The purpose of the present study is to propose the ultimate failure stresses of prestressing (PS) steels for those external unbonded PSC members. To this end, a comprehensive analysis has been made using the nonlinear finite element analysis program developed recently for external unbonded PSC members by authors. A series of major influencing variables have been included in the analysis. It was found that the span-depth ratio, neutral axis depth-effective depth ratio, load geometry, amount of ordinary steel, and prestressing steel ration have great influence for the ultimate failue stress of PS steel is preposed and is compared with experimental dat as well as existing formulas for internal unbonded members. The Comparison indicates that the proposed equation agrees relatively well with experimental data and that existing formulas including ACI and AASHTO equations show some discrepancies from experimental ones. The present study allows more realistic analysis and design of prestressed concrete structures with external unbonded tendons.

Development of DCOC Algorithm Considering the Variation of Effective Depth in the Optimum Design of PRC Continuous Beam (PRC연속보 최적설계에서 단면의 유효깊이 변화를 고려한 DCOC알고리즘 개발)

  • 조홍동;한상훈
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.15 no.2
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    • pp.281-291
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    • 2002
  • This paper describes the minimum cost design of prestressed reinforced concrete (PRC) hem with rectangular section. The cost of construction as objective function which includes the costs of concrete, prestressing steel, non prestressing steel, and formwork is minimized. The design constraints include limits on the minimum deflection, flexural and shear strengths, in addition to ductility requirements, and upper-Lower bounds on design variables as stipulated by the specification. The optimization is carried out using the methods based on discretized continuum-type optimality criteria(DCOC). Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables - effective depth, eccentricity of prestressing steel and non prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. In this paper the effective depth is considered to be freely-varying and one uniform for the entire multispan beam respectively. Also the maximum eccentricity of prestressing force is considered in every span. In order to show the applicability and efficiency of the derived algorithm, several numerical examples of PRC continuous beams are solved.

Development of Optimum Design Program for PPC Structures using DCOC (이산성 연속형 최적성 규준을 이용한 PPC 구조의 최적설계프로그램 개발)

  • 한상훈;조홍동;이상근
    • Computational Structural Engineering
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    • v.10 no.4
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    • pp.315-325
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    • 1997
  • This paper describes the application of discretized continuum-type optimality criteria (DCOC) and the development of optimum design program for the multispan partially prestressed concrete beams. The cost of construction as objective function which includes the costs of concrete, prestressing steel, non-prestressing steel and formwork is minimized. The design constraints include limits on the maximum deflection, flexural and shear strengths, in addition to ductility requirements, and upper and lower bounds on design variables as stipulated by the design Code. Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables-effective depth, eccentricity of prestressing steel and non-prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. The self-weight of the structure is included in the equilibrium equation of the real system, as is the secondary effect resulting from the prestressing force. An iterative procedure and computer program for updating the design variables are developed. Two numerical examples of multispan PPC beams with rectangular cross-section are solved to show the applicability and efficiency of the DCOC-based technique.

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Creep Strain of Containment Concrete Structure (원자로 격납건물 콘크리트의 크리이프 변형 특성)

  • 방기성;정원섭;조명석;송영철
    • Proceedings of the Korea Concrete Institute Conference
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    • 1996.10a
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    • pp.95-100
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    • 1996
  • Creep, drying shrinkage, modulus of elasiticity and Poisson's ratio of concrete are influenced by a number of factors such as mix type, member thickness, curing condition and loading cases. Particularly, creep and shrinkage in concrete have yet to be studied due to its complicated time-dependent properties. In this study, the concrete creep tests were carried out at varous ages of loading-7, 28, 90, 180 and 365 days in order to investigate and quantify its long-term properties. The test procedures and analysis of the test results were also described herein. The results of this study will enable A/E to calculate effective prestressing forces considering time-dependent prestressing loss and evaluate the structural integrity of the prestressing system using the representative values derived from this property test.

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Shear Strength of Prestressed PC-CIP Composite Beams without Vertical Shear Reinforcements (수직전단보강이 없는 PS 콘크리트와 현장타설 콘크리트 합성보의 전단강도)

  • Kim, Chul-Goo;Park, Hong-Gun;Hong, Geon-Ho;Kang, Su-Min;Suh, Jung-Il
    • Journal of the Korea Concrete Institute
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    • v.26 no.4
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    • pp.533-543
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    • 2014
  • Currently, composite construction of prestressed Precast Concrete (PC) and Cast-In-Place (CIP) concrete with different concrete strengths are frequently used in the modular construction. However, current design codes do not clearly define shear design methods for such composite beams. In this present study, simply supported prestressed PC-CIP composite beams without vertical shear reinforcement or only with horizontal shear reinforcement were tested to evaluate the effect of prestressing on the shear strength and the shear design method for such composite members. The test variables were the area ratio of PC and CIP concretes, prestressing force, shear span-to-depth ratio, and shear reinforcement ratio. The results showed that the shear strength was increased by the increase of prestressing force and prestressed PC area, and the decrease of shear span-to-depth ratio.