钢筋混凝土高烟囱切口支撑部失稳力学分析

MECHANICAL ANALYSIS OF CUTTING-SUPPORT DESTABILIZATION OF HIGH REINFORCED CONCRETE CHIMNEY

根据烟囱自重纵向平衡,分析切口爆破后自重突加载荷在支撑部的受压范围,并以突加载荷受压区高度系数kλ≥0.85判断支撑部被突加载荷破坏;在烟囱倾倒时支撑部受大偏心受压脆性破坏而形成"塑性铰",其倾倒失稳的名义保证率k≥1.5判断确保烟囱倾倒;烟囱自重和拉区弯矩形成的载荷与压区抗力的纵向平衡,也决定了后移中性轴的极限位置,若其保持在筒腔内,支撑部的"塑性铰"在烟囱微倾阶段将保持;而此时支撑部前剪区的破坏状况,决定倒向偏差,当定向窗口角在30°以下,切口高在2.4 m以下,其引起的倒向偏离仅在2°以内;支撑部的后剪滑动失稳系数Ks决定初倾阶段的后坐,Ks估算和实例说明高位切口50 m以上烟囱支撑部有后剪可能。为保证烟囱在纵向稳定下的倾倒,切口圆心角宜取210°～230°;为防止高位切口后剪,下切口宜在该切口爆破后1.5～4.0 s前起爆。

According to longitudinal balance of own weight of chimney,the compressive region by sudden load of its own weight on cutting-support after blasting is analyzed;and the damage of the support from sudden load can be estimated by kλ≥0.85,which is height coefficient of the compressive region.While the chimney breaks down,brittle failure will be seen in the support position with large eccentric pressure;and plastic joint is formed.According to the nominal ensure coefficient k≥1.5i,t can be judged that the chimney falls in.The limit position of backward moving neutral axis is determined by longitudinal balance of chimney weight and moment formed by loads in tensile region and resistance force on compressive region.If the limit position of the neutral axis is in the canister,the plastic joint of the support will remain when the chimney tilts slightly.At the time the damage of front shear region of support determines the dipping direction of chimney.When the angle of direction window is not greater than 30°and height of cutting is less than 2.4 m,the error of dipping direction will not be more than 2.° The initial dipping backward sitting is estimated by sloping coefficient Ks of backward shear of support.It is demonstrated by practical examples and estimation that backward shear is able to take place above the cutting on high chimney,which is higher than 50 m.In order to ensure the chimney not to tilt in longitudinal direction,the radius angle of the cutting is 210°-230.°To prevent the cutting on high site from backward shear,lower cutting should be blasted after 1.5-4.0 seconds when the cutting blasts.