承台大体积混凝土里表温差梯度与温差应力有限元模拟

Finite element simulation of inside-outside temperature gradient and thermal stress for abutment mass concrete

针对大体积混凝土因水化热引起的早期开裂问题,以内蒙古老山沟公路大桥承台为依托,建立了大体积混凝土三维有限元模型,分析了粉煤灰掺量、浇筑温度、环境温度与养护措施对承台中心温度、里表温差与表面拉应力的影响。模拟结果表明:混凝土表面拉应力随粉煤灰掺量增大而减小,当掺量超过30%时,降幅增大,中心温度、里表温差和表面拉应力均随其掺量增大而减小,可见掺加粉煤灰可有效降低混凝土水化热,防止表面温差裂缝的产生;当浇筑温度从5℃到30℃变化时,中心最高温度从40.3℃升至58.1℃,里表最大温差从8.6℃升至19.0℃,表面最大拉应力从0.93 MPa升至1.66 MPa,且随浇筑温度的增大,中心最高温度和里表最大温差产生的时间有所提前,表面拉应力呈线性增大趋势;里表温差和表面拉应力都随环境温度增大而减小,且表面拉应力与环境温度基本呈线性关系;养护条件越好,里表温差越小,表面拉应力明显降低,且前期表面拉应力增速减慢,峰值出现时间推迟,有利于裂缝控制。

Aimed at the earlier temperature cracks of mass concrete during construction, a 3D finite element model of mass concrete was built based on the abutment of Laoshangou Highway Bridge in Inner Mongolia, and the effects of content of fly ash, pouring temperature, environmental temperature, and maintenance measure on central temperature, temperature difference between inside and outside, and surface tensile stress of abutment were analyzed. Simulation result shows that the surface tensile stress of concrete increases with the content decrease of fly ash, the decline increases when the content exceeds 30%, and the central temperature, the temperature difference between inside and outside, and the surface tensile stress decrease with the increasse of adding dosage of fly ash, so effective adding fly ash can reduce the hydration heat of concrete and prevent the occurrence of cracks due to the surface temperature difference. When the pouring temperature increases from 5 ℃ to 30 ℃, the highest central temperature of concrete increases from 40.3 ℃ to 58.1 ℃, the maximum temperature difference between inside and outside increases from 8. 6℃ to 19.0 ℃, and the maximum tensile stress increases from 0. 93 MPa to 1.66 MPa. The highest central temperature of concrete and the maximum temperature difference between inside and outside appear in advance, and the surface tensile stress increases linearly along with the increase of pouring temperature. The temperature difference between inside and outside and the surface tensile stress decrease with the increase of environmental temperature, and the relationship between the surface tensile stress and the environmental temperature is linear basically. The better curing condition is, the smaller the temperature difference between inside and outside is, the slower the increase speed of surface tensile stress is, the later the occurred time of maximum surface tensile stress is, which are beneficial to control the cracks. 1 tab, 31 figs, 23 refs.