DESIGN METHOD OF REINFORCED CONCRETE MEMBERS WITH THERMAL CRACKING

为了建立钢筋混凝土结构在外荷载和水泥水化热温度应力共同作用下的设计方法，对分两个阶段施工的混凝土梁的温度应力和弯曲变形进行了试验和数值研究。在此基础上，研究了温度应力对钢筋应力、裂缝宽度和屈服弯矩的影响。(1)峰值温度和稳定温度下的平均曲率取决于第一阶段混凝土的刚度。所有三种蠕变模型（CEB/MC 90，JSCE，Iwaki等）都没有以令人满意的精度预测峰值和室温下的平均曲率。(2)在残余弯曲变形得到较好抑制的情况下，新浇筑混凝土试块在正常使用状态下的钢筋应力和裂缝宽度均高于常温养护的混凝土试块，而传统方法低估了这一点。(3)由于小砌块梁的残余弯曲变形远大于大砌块梁，大砌块并不一定比小砌块梁引起更高的钢筋应力和更大的温度裂缝宽度，从而说明了分两阶段进行混凝土构件正常使用极限状态设计时考虑温度应力影响的必要性。考虑钢筋混凝土构件的裂缝，根据自由弯曲变形、约束程度和抗弯刚度估算了影响。

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.