• Title/Summary/Keyword: 프리플렉스 부재

Search Result 5, Processing Time 0.022 seconds

A Study on the Optimum Design of Three Span Continuous Preflex Composite Girder Bridge (3경간 연속 Preflex 합성형교의 최적설계에 관한 연구)

  • Koo, Min Se;Chang, Suong Su;Jeong, Jin Il
    • Journal of Korean Society of Steel Construction
    • /
    • v.10 no.1 s.34
    • /
    • pp.125-135
    • /
    • 1998
  • This study presents a design method for three-span continuous preflex composite girder bridges (3S-PCB) which imposes prestresses in the negative moment region by lifting or lowering interior supports and the design method is automated by a computer program which incorporates optimal design procedure. The objective function for the design of 3S-PCB minimizes the cost of construction materials and the constraint functions represent the limited dimensions of the design section and the allowable stress for each structural member as given in the specifications. Optimal design procedure used in this study is a modification of existing sequential unconstrained minimization technique (SUMT), a numerical analyses procedure for two-span continuous preflex composite bridges. The optimized design sections determined for each span length are compared with those of simple preflex composite beams (SPCB) and the optimal girder depth is determined by defining the relationship between girder depth and construction material costs.

  • PDF

Experimental and Analytical Evaluation of the Seismic performance of a Concrete Box Structure Strengthened with Pre-flexed Members (프리플렉스 부재를 이용한 콘크리트 박스 구조물 내진보강에 관한 실험 및 해석적 평가)

  • Ann, Ho-June;Song, Sang-Geun;Min, Dae-Hong;An, Sang-Mi;Kong, Jung-Sik
    • Journal of the Computational Structural Engineering Institute of Korea
    • /
    • v.29 no.5
    • /
    • pp.397-403
    • /
    • 2016
  • During the rapid economic growth in Korea since the 1970s, many underground facilities were constructed such as under passes and railways. Seismic design has been mandated in 1988, but the structures built before 1988 were not reflected on the seismic design. Accordingly, these underground structures require effective seismic reinforcing methods to ensure safety when the earthquake happens. By these reasons, in this study, using the proposed pre-flexed members, RC box structure was analyzed for seismic reinforcement of the corner. This method is based on a principle that enlarging the resistance against the external force by installing the pre-flexed member to the box structure corner. To evaluate validity, a newly developed member with CornerSafe was compared with traditional type reinforcement using experiments and finite element analysis. In finite element mode, nonlinearity of steel was modeled based on J2 plasticity model and concrete was based on CEB FIP MODEL CODE 1990. Also, composite ratios of box and pre-flexed member were computed for design application. The reinforcement and box structure were analyzed under the bond condition completely attached by the tie, and the results of experiment and finite element analysis were same in the force-displacement curve.

Strength Method Using Pre-flexed Members for the Corner of Underground Box Structures under Additional Surface Load (추가 상재하중을 받는 지중박스구조물의 우각부에 대한 프리플렉스 부재를 이용한 보강공법)

  • Chung, Jee Seung;Lee, Jin Hyuk;Kim, Ki Am
    • Journal of the Korean Society of Safety
    • /
    • v.31 no.5
    • /
    • pp.102-108
    • /
    • 2016
  • This paper presents a new strength method of underground box structures under additional surface load. An L-bracing using pre-flexed steel member threads called the "Pre-flex strength method" is used to improve capacity of the RC box structure under earth pressure due to additional surface load. The pre-flexed steel member is fixed the top and bottom of the structure after chemical anchor was installed by drilling hole on the box structure. The structural performance was evaluated analytically. 3 types of underground RC box structure were used; $2.0m{\times}2.0m$, $3.0m{\times}3.0m$ and $4.0m{\times}4.0m$. For the performance evaluation, structure analysis were performed on moment and shear resisting structures with and without pre-flex strength method. Numerical results confirmed that the proposed strength member system installed on underground RC box structures enhanced the strength capacity. The feasible region of the proposed pre-flex strength method in accordance with the earth pressure due to additional surface depth was evaluated.

A Case Study on Earthquake Resistant Reinforcement Method for the Corner of Existing Underground R.C Box Structures using Pre-flexed Member System (프리플렉스 부재를 이용한 기존 철근콘크리트 지중박스구조물 우각부에 대한 내진보강공법 사례연구)

  • Chung, Jee-Seung;Kim, Jin-Gu;Lee, Jin-Hyuk
    • Journal of the Korean Society of Safety
    • /
    • v.31 no.3
    • /
    • pp.68-74
    • /
    • 2016
  • This paper presents a new strengthening method of underground box structures against seismic loads for anti-seismic capacity improvement. A threaded steel member with pressure devices(so called 'Pre-flexed member system') is used to improve seismic capacity of the RC box structure. The pre-flexed member system is fixed the corner of opening after chemical anchor was installed by drilling hole on the box structure. The structural performance was evaluated analytically. Two bracing types of strengthening methods were used; conventional bracing method and I-bracing pressure system. For the performance evaluation, seismic analyses were performed on moment and shear resisting structures with and without strength member system. Numerical results confirmed that the proposed pre-flexed member system can enhance the seismic capacity of the underground RC box structures.

Numerical Evaluation of Stress Loss Rates and Adjusting Coefficients due to Internal and External Constraints of Concrete Long-Term Deformation (콘크리트 장기변형의 내·외부 구속에 의한 응력 손실률 및 수정계수 평가의 전산구조해석)

  • Yon, Jung-Heum;Kim, Hyun-Jin
    • Journal of the Korea Concrete Institute
    • /
    • v.25 no.4
    • /
    • pp.429-438
    • /
    • 2013
  • An object oriented numerical analysis program of axial-flexural elements and the step-by-step method (SSM) has been developed to analyze concrete long-term behaviors of structures constrained internally and externally. The results of the numerical analysis for simple and continuous prestressed (PS) concrete box and composite girders, pre-cast slab of continuous steel composite girder, and simple preflex composite girder show that the adjusting coefficient decreases by increasing constraint. The loss rates of pre-tension force were not sensitive but those of pre-compression force were increased rapidly by decreasing adjusting coefficient. This indicates that the design based on the loss rate of pre-tension can over-estimate the pre-compression force in a concrete section constrained internally and externally. The adjusting coefficients which satisfy results of the numerical analysis are 0.35~0.95, and it can be used as an index of constraint of concrete long-term deformation. The adjusting coefficient 0.5 of Bridge Design Specifications can under-estimate residual stress of PS concrete slab, and the coefficient 0.7 or 0.8 of LRFD Bridge Designing Specifications can under-estimate the loss rates of continuous PS concrete girders. The adjusting coefficient of hybrid structures should be less then 0.4.