STUDIES ON THE EFFECTS OF ENVIRONMENTAL CONDITION ON LONG-TERM DEFORMATION AND CRACK WIDTH OF REINFORCED CONCRETE MEMBERS

对钢筋混凝土梁在持续受弯荷载作用下的变形和开裂性能进行了试验研究，试验条件为：（1）室温20（]SY. ±-. [)1 60（]SY. ±. [)5（2）70（]SY. ±. [)5%;（3）实验室感染;（4）田间感染。在此基础上，采用作者提出的数值计算方法，对温湿交变作用下钢筋混凝土受弯构件的时变变形和裂缝宽度进行了计算。主要结果如下：（1）蠕变主要受季节性温度升高的影响，而不一定依赖于相对湿度。由于降雨的影响，土壤的干缩应变是实验室的近一半，而土壤的干缩应变在暴露于水的过程中发生可逆的变化。(2)曲率和压应变都与徐变和干缩密切相关。采用有效弹性模量法分析时，特别是在现场试验中，低估了配筋梁的曲率和压应变。基于惠特尼蠕变速率定律的分步计算方法在一定程度上提高了计算精度。(3)现场荷载作用下干缩对裂缝宽度增长的有效速率大于室内荷载作用下干缩对裂缝宽度增长的有效速率。这意味着裂缝不一定与干燥收缩应变的大小成比例地扩大。

Deformational and cracking behaviors of reinforced concrete beams subjected to sustained flexural load were experimentally investigated under four different environmental conditions, that is, (1) in the room with the temperature of 20(]SY.+-。[)1ﾟC and relative humidity of 60(]SY.+-。[)5%, (2) in that with 70(]SY.+-。[)5%, (3) in the laborato-ry and (4) in the feild. Furthermore, computations of time-dependent deformations and crack widths of reinforced concrete flexural member under alternating temperature and humidity were performed, using numerical method developed by authors. Main results were abtained as follows ;(1) Creep was promoted mainly by seasonal temperature rise and did not necessarily depend upon relative humidity. Drying shrinkage strain in the feild, which changed reversibly during exposure to water, resulted in nearly a half of that in the laboratory due to rainfall.(2) Both curvature and compressive strain depended closely on creep and drying shrinkage. Curvatures and compressive strains of beams with compressive reinforcement were underestimated especially in the field by analysis used effective elastic modulus method. A step-by-step method based on Whitney's rate of creep law was effective in improving the procedure in terms of accuracy to a certain extent.(3) Effective rate of drying shrinkage to increase of crack width under load in the field was larger than that in the laboratory. This means that cracks do not necessarily widen in proportion to the magnitude of drying shrinkage strain.