钢管混凝土轴心受压构件的徐变预测模型及其徐变性能分析

CREEP CALCULATION AND BEHAVIOR ANALYSIS OF CONCRETE-FILLED STEEL TUBULAR MEMBER UNDER AXIAL COMPRESSION

为研究混凝土徐变对钢管混凝土轴心受压构件长期受力性能的影响,考虑构件截面内力重分布,建立了钢管混凝土轴心受压构件截面应力和应变以徐变系数为参数的随混凝土龄期变化关系的理论模型,结合已有试验数据和国内外常用12种混凝土徐变预测模型对该模型进行验证,并找到了适用于钢管混凝土轴心受压构件的徐变预测模型——Huo模型;在此基础上,计算并分析了钢管混凝土轴心受压构件混凝土龄期为10000 d的截面应力和应变;通过对混凝土强度等级、环境年平均相对湿度、初始加载龄期、含钢率、构件长度、截面应力水平等因素的不同取值,分析了各因素对钢管混凝土轴心受压构件徐变性能的影响程度及规律。结果表明:当钢管混凝土轴心受压构件的轴力不大于其极限承载力的60%时,随着加载龄期的增长,钢管截面应力逐渐增大,最大变化量达61.4%,而混凝土截面应力逐渐减小,最大变化量达26.2%;加载初期构件应变增长迅速,1000 d以后应变增长速度减慢,构件最终应变是初始应变的1.61倍;在轴压比相同的条件下,钢管混凝土轴心受压构件的徐变应变终值随着混凝土强度等级的提高而逐渐增大,随着含钢率的增大显著减小,随着初始加载龄期、环境年平均相对湿度、构件长度的增大而逐渐减小,轴压比不大于0.6时,其徐变应变终值随轴压比增长。研究成果可为钢管混凝土轴心受压构件在正常使用阶段徐变计算以及徐变变形控制提供依据。

In order to analyze the effect of concrete creep on long-term behavior of concrete-filled steel tubular member under axial compression, the theoretical model of stress and strain at a member cross-section which changes with concrete age was deduced by taking the internal force redistribution into account. Based on the comparison between the experimental results and the calculated ones, the new model was verified and model Huo is selected as the most suitable model among the existed 12 types of creep coefficient calculation model. The stress and strain at the cross-section of a concrete-filled steel tubular member under axial compression were analyzed until the age of 10000 days, and the factors affecting the creep behavior were discussed, including concrete strength, environmental relative humidity, loading age, steel ratio, member length and cross-section stress level. The results show that, as the age grows, the stress of the steel pipe increases gradually with the maximum increment being 61.4% of the initial stress, and the concrete stress decreases with the maximum stress reduction being 26.2% when the axial force is less than 60% of its ultimate bearing capacity; the creep strain of the concrete-filled steel tubular member increases quickly at the beginning, and slows down after 1000 days, and the ultimate strain is about 1.60 times of the initial one. With the same axial compression ratio, the creep strain of the concrete-filled steel tubular member increases gradually with the core concrete strength grade improving; the creep strain of the concrete-filled steel tubular member decreases significantly with the increasing of steel ratio; with the increases of environmental relative humidity, loading age and member length, the creep strain of the concrete-filled steel tubular member increases. Axial compression ratio has the most significant influence on the creep of concrete-filled steel tubular member under axial compression. The creep strain increases with the increasing of axial compression ratio when the compression ratio is less than 0.6. The study provides useful references for the creep calculation and creep control of concrete-filled steel tubular members under axial compression.