DESIGN METHOD OF REINFORCED CONCRETE MEMBERS WITH THERMAL CRACKING

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In order to help establish design method of reinforced concrete structure subjected to external load combined with thermal stress due to hydration heat of cement, investigations were performed experimentally and unmerically on thermal stress and flexural deformation of concrete beams constructed in two stages. Furthermore, the effect of thermal stress on reinforcement stress, crack width and yielding moment of the beams were investigated, which were restrained flexurally and perfectly, and thereafter loaded.(1) The average curvatures at peak temperature and at stabilized temperature depend on rigidity of the first stage concrete. All three creep models (CEB/MC 90, JSCE,Iwaki et al) did not predict the average curvatures both at peak and at room temperature with satisfactory accuracy.(2) Temperature change in young concrete block produced higher reinforcement stress and wider crack width in serviceability state than those in the companion beams cured in room temperature when residual flexural deformation was restrained perfectly, which were underestimated by conventional method.(3) Larger existing block did not necessarily cause higher reinforcement stress as well as wider crack width due to temperature change than smaller one because residual flexural deformation of the beam with smaller existing block is considerably larger than that with larger one.From the results the necessity considering the effects of thermal stress in serviceability limit state design for concrete members made in two stages were shown. The effects are estimated based on free flexural deformation, degree of restraint and flexural rigidity considering cracks of reinforced concrete members.