하중재하 시점 및 긴장력 변화를 고려한 철도교 PSC 합성보의 장기 솟음 분석
Long-term Camber Analysis of PSC Composite Beam for Railway Bridge Considering Changes in Loading Time and Prestressing Force
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초록
프리스트레스트 콘크리트 철도 교량에서 발생하는 과다한 솟음 문제를 분석하는 연구의 일환으로, 이 논문에서는 콘크리트 구조물의 시간에 따른 솟음 산정 프로그램을 작성하여, 긴장력과 자중이 가해지는 시점과 작용 기간 및 활하중 크기의 변화에 대한 솟음의 크기 변화를 분석한다. 초기 콘크리트 강도 확보 기간, 양생 후 긴장력 및 하중이 작용하는 시점, 긴장력의 시간에 따른 감소 등 시간에 대한 변수를 해석에서 고려하기 위하여 증분 시간단계해석 방법을 적용하고, 크리프 계수 및 긴장력 손실 산정식은 국내 교량설계기준의 수식을 적용한다. 철도교량 PSC 합성보 예제에 적용하여 다양한 재하시점에 따른 즉시 처짐과 재하기간에 따른 크리프 처짐을 구하고, 철도 활하중의 여유도를 고려하여 긴장력을 감소시키는 경우의 솟음 감소 효과를 검토한다. 수치 예제를 통하여 초기 긴장력을 도입하는 시점이 빠르고 슬래브 타설 시점 사이의 기간이 길어지거나 이들이 조합되면 시공 단계별 솟음의 크기가 커지고, 실제 열차 중량을 고려하여 활하중을 감소시키는 경우에 솟음이감소됨을 보인다.
Abstract
As part of a study to analyze the excessive camber occurring in prestressed concrete railway bridges, this paper develops a time-dependent camber analysis program for concrete structures and analyzes the change in camber according to the variation of applying time and duration of prestressing force and self-weight as well as the change in live load. The incremental time-step analysis method is applied in order to consider time-related variables such as the strength of concrete in early stage, the applying time and duration of the prestressing force and loads, and the decrease in prestressing force over time. The equations for calculating the creep coefficient and loss of prestressing force are applied according to the domestic bridge design codes. By applying the developed method to an example PSC composite beam for railway bridge, the instantaneous deflection at various loading points and the long term creep deflection for the loading period are obtained. Also the effect of reducing the camber is examined when the prestressing force is reduced considering the degree of allowance of the railway live load. Through numerical examples, it can be shown that the camber increases if the initial prestressing force is introduced early or the period to the slab placement is long or a combination of the two. When the live load is reduced by taking into account the actual train weight, the camber is reduced.
참고문헌 (10)
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