Journal of the Korea Concrete Institute (콘크리트학회논문집)

Korea Concrete Institute (한국콘크리트학회)
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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

  • Received : 2013.01.23
  • Accepted : 2013.03.19
  • Published : 2013.08.31
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Abstract

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.

콘크리트 장기변형이 합성단면과 부재의 경계조건에 의해 내 외부 구속된 구조물에 단계별계산법(SSM)을 적용하 기위해 축-휨 요소가 적용된 객체지향 전산구조해석 프로그램이 개발되었다. 단순 및 연속 지지된 PS 콘크리트 박스 및 합성거더, 연속 강합성거더의 조립식 바닥판, 단순 프리플렉스 합성거더에 대한 SSM의 전산구조해석 결과 구속정도가 클수록 수정계수는 감소하였다. 수정계수의 감소에 대해 선인장의 손실률에는 큰 변화가 없으나, 선압축의 손실률은 급격히 증가하였다. 연속보의 내부지점에서 선압축의 손실률은 더욱 증가하였다. 이는 선인장의 손실에 기초한 설계는 내 외부 구속 정도가 큰 구조물에 대한 선압축의 손실을 과소평가할 수 있음을 보여준다. 전산구조해석을 만족하는 크리프의 수정계수는 0.35~0.95의 값이었으며, 수정 계수는 콘크리트 장기변형의 내 외부 구속의 정도를 나타내는 지표로 사용될 수 있다. 도로교설계기준의 수정계수 0.5는 긴장력이 도입된 강합성단면의 조립식 바닥판에 대해서는 부적절하며, 2007년 도입된 AASHTO LRFD 도로교설계기준(2008)과 한계상태에 대한 도로교설계기준의 긴장력 손실에 적용된 수정계수 0.7과 0.8은 PS 콘크리트 합성거더의 연속화에 대한 손실률을 과소평가한다. 복합구조 합성단면의 수정계수는 0.4 이하의 값이 적절하다.

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References

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