混凝土受压徐变模型及应力—应变关系研究

发布时间：2018-05-24 06:29

  本文选题：混凝土 + 徐变模型　； 参考：《哈尔滨工业大学》2016年博士论文

【摘要】：混凝土徐变是指在荷载持续作用下,混凝土变形随持荷时间延长而增大的现象。徐变不但影响混凝土结构构件的正常使用性能,而且高应力徐变会影响混凝土结构构件的承载能力。现有混凝土受压徐变模型适用范围偏窄,无法预估高强混凝土试件徐变和高应力构件徐变;尚未建立考虑徐变影响的混凝土受压应力-应变全曲线方程,无法考虑徐变对混凝土试件峰值压应变的影响;缺乏对混凝土徐变卸载瞬时应变恢复和滞后应变恢复规律的认识,无法准确分析轴压柱持荷过程中截面应力重分布及受压钢筋对柱徐变的影响。基于上述考虑开展研究工作,完成了龄期28d时轴心抗压强度20.9MPa~40.9MPa、应力水平0.154~0.725、加载龄期30d~512d、持荷时间39d~589d的188个混凝土受压试件徐变试验及徐变后的受压破坏试验。基于试验数据,完善了混凝土徐变模型,探索了卸载后徐变试件应变恢复规律,建立了考虑徐变影响的混凝土受压应力-应变全曲线方程。具体分述如下:(1)基于国内外徐变试验数据,分别建立了混凝土立方体抗压强度、加载龄期、环境温度、环境相对湿度、构件理论厚度对徐变的影响系数公式。应用上述公式,将54个混凝土试件的线性徐变试验数据转化为龄期28d时标准立方体抗压强度30MPa、加载龄期28d、环境温度20℃、环境相对湿度60%、构件理论厚度50mm这一基准条件下的徐变试验数据,继而提出基准条件下的线性徐变计算模型。将0.35作为线性徐变和非线性徐变分界点,将0.76作为收敛型非线性徐变和发散性非线性徐变的分界点。对应力水平介于0.35~0.76的非线性徐变,基于134个混凝土试件的非线性徐变试验数据,提出随应力水平提高呈指数函数增大的非线性徐变增大系数计算公式。从而扩大了所建立徐变模型的适用范围,可实现混凝土标准立方体抗压强度15MPa~180MPa、徐变加载龄期1d~3650d、环境温度-20℃~80℃、环境相对湿度3%~100%、理论厚度20mm~270mm、应力水平0~0.76混凝土试件徐变的分析与计算。(2)基于114个试件徐变后卸载试验数据,发现当混凝土强度一定时,瞬时应变恢复系数(瞬时应变恢复与徐变加载瞬时应变的比值)随应力水平的增大而减小,滞后应变恢复稳定时间随应力水平的增大而延长,滞后应变恢复与卸载前发生的徐变应变呈正比,滞后应变恢复随时间的推移而减缓。建立了瞬时应变恢复和滞后应变恢复的相关计算公式,并将其用于考察轴压柱在持荷过程中截面应力重分布及受压钢筋对柱徐变的影响。(3)基于188个混凝土试件徐变后受压破坏试验数据,提出了混凝土试件经历徐变后继续加载至受压破坏四阶段应力-应变全曲线方程和经历徐变后卸载至零再加载至受压破坏六阶段应力-应变全曲线方程。经历不同应力水平徐变的试件受压破坏时峰值应力处对应的总应变约在2400×10-6~4500×10-6之间,相对于同批次同龄期参比用试件短期加载峰值压应变提高20%~120%。建立了合理考虑徐变影响的混凝土试件峰值压应变的计算公式,为合理应用高强热轧钢筋作为受压钢筋提供了参考依据。
[Abstract]:Concrete creep is the phenomenon that the deformation of concrete increases with the prolonged loading time under the continuous load of the concrete. The creep not only affects the normal performance of the concrete structural members, but also the high stress and creep will affect the bearing capacity of the concrete structural members. The existing concrete compression and creep model has narrow application range and can not predict the high strength. The creep of concrete specimens and the creep of high stress components have not been established, and the effect of creep on the compressive stress-strain curves of concrete has not been established, and the effect of creep on the peak compressive strain of concrete specimens can not be considered, and the lack of understanding of the instantaneous strain recovery and the hysteresis strain recovery of concrete creep and unloading can not accurately analyze the holding of axial compression columns. The stress redistribution of the section and the influence of the reinforced bar on the creep of the column in the process of loading. Based on the above consideration, the axial compression strength 20.9MPa~40.9MPa, the stress level 0.154~0.725, the loading age 0.154~0.725, the loading age 30d~512d, the 188 concrete compression test of the loading time 39d~589d and the compression failure test after the creep are completed. Based on the test data, the concrete creep model is perfected, the strain recovery law of the creep specimens after unloading is explored, and the stress strain full curve equation of concrete under the influence of creep is established. The detailed description is as follows: (1) based on the data of the creep test at home and abroad, the concrete cube compressive strength, loading age and environment are established respectively. The formula of the influence coefficient of temperature, relative humidity and theoretical thickness of component to creep is used to convert the linear creep test data of 54 concrete specimens into standard cube compressive strength 30MPa for age 28d, loading age 28d, ambient temperature 20, ambient humidity 60%, and component theoretical thickness 50mm. According to the creep test data, the linear creep calculation model under the reference condition is put forward. 0.35 is used as the boundary of the linear creep and the nonlinear creep, and 0.76 is the demarcation point of the nonlinear creep and the divergent nonlinear creep of the convergent type. The nonlinear creep of the force level is between the 0.35~0.76 and the nonlinear creep of the 134 concrete specimens. By changing the test data, the formula of the nonlinear creep enlargement coefficient which increases with the increase of the stress level is proposed. Thus the application range of the creep model is expanded, and the compressive strength of the concrete standard cube is 15MPa~180MPa, the age of creep loading is 1d~3650d, the ambient temperature is -20 C ~80 C, and the environmental relative humidity is 3%~100%, On the analysis and calculation of the creep of the thickness 20mm~270mm and the stress level 0~0.76 concrete specimens. (2) based on the data of the unloading test after the creep of the 114 specimens, it is found that the instantaneous strain recovery coefficient (the ratio of instantaneous strain recovery to the instantaneous strain of the creep) decreases with the increase of the stress level when the concrete strength is fixed, and the lag strain is restored to stability. Time is prolonged with the increase of stress level, and the hysteresis strain recovery is proportional to the creep strain before unloading, and the hysteresis strain recovery slows with the passage of time. The correlation calculation formula of the instantaneous strain recovery and the hysteresis strain recovery is established, and is used to investigate the stress redistribution and the compression steel of the axial compression column during the loading process. The influence of the reinforcement on the creep of the column. (3) based on the creep test data of 188 concrete specimens after creep, the full curve equation of the stress-strain curve and the six stage of the stress strain of the concrete specimen after the creep are continued to be loaded to the four stage of the compression failure and the stress strain curve equation after the creep after the creep to zero reloading to the compression failure. The total strain corresponding to the peak stress is about 2400 x 10-6~4500 x 10-6 when the stress level creep is subjected to the compression failure, and the calculation formula for the peak pressure stress of the concrete specimen with the influence of the creep is set up for the reasonable application of the high strength hot rolling for the reasonable application of the calculation formula of the peak pressure stress of the concrete specimen with the influence of the creep. The reinforcement provides a reference for the reinforced bar.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TU528
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本文编号：1928038