Effect of pipe-cooling system on thermal-mechanical behaviour of PC box bridge girders at hydration age
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(2020) 1:9
Advances in Bridge Engineering
ORIGINAL INNOVATION
Open Access
Effect of pipe-cooling system on thermalmechanical behaviour of PC box bridge girders at hydration age Chaojie Song, Gang Zhang*, Hao Wen and Yongfei Zhang * Correspondence: zhangg_2004@ 126.com School of Highway, Chang’an University, Xi’an 710064, Shaanxi, China
Abstract Prestressed concrete (PC) box bridge girders on the pier top is prone to generate thermal cracks due to large inner-outer temperature difference at hydration age. This paper presents an approach for investigating behaviour of PC box bridge girders at early age of curing. First, based on measured data from a typical PC box bridge girder, an inverse analysis method for adiabatic temperature rise function of concrete hydration heat is proposed using genetic algorithm and thermal analysis. Then, a thermo-hydro-mechanical coupling model is established, using the computer program ANSYS incorporating time-dependent wind speed and ambient temperature, to analyse thermal mechanical behaviour of PC box bridge girders considering pipecooling system. Subsequently, parametric studies are carried out to evaluate influence of cooling time, cooling water flow rate, cooling water temperature and cooling period on temperature and stress of PC box bridge girders during curing. Results from analysis show that the principal tensile stress generated in the vicinity of pipe increases more rapidly during cooling, while the temperature and principal tensile stress can be significantly reduced when cooling is terminated. Increasing cooling time, cooling water flow rate or decreasing cooling water temperature can reduce the highest temperature. However, unreasonable value of these cooling parameters will cause PC box bridge girders cracking due to excessive principal tensile stress around pipe. Both one-stage and two-stage cooling are effective measures to minimize the adverse effects of hydration heat in PC box bridge girders. Keywords: Prestressed concrete box bridge girder, Hydration heat, Finite element method, Pipe-cooling system, Thermal-mechanical behaviour, Parametric studies
1 Introduction In the mass concrete structures, large amount of heat generated by cement hydration is accumulated due to lower thermal conductivity of concrete. The interior of concrete under high temperature tends to expand, whereas surface of concrete close to ambient temperature tends to shrink, resulting in tensile stress on surface of PC box bridge girders. Cracks will occur on the concrete surface when the tensile stress exceeds the tensile strength (Zhu 2013). However, cracks are not permitted in PC box bridge girders because cracks have adverse effects on safety, integrity and durability of structure © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link
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