粮食筒仓储粮和卸粮状态下的仓壁侧压力试验研究

为了研究粮食筒仓在储粮状态下的仓壁静态侧压力及中心卸粮状态下的仓壁动态侧压力,该研究利用仓身直径400 mm、仓壁高度700 mm的模型筒仓,以小麦为储料,分别进行了100%、80%和50%仓容3种状态下的静态储粮及中心卸粮的侧压力测试试验,并将仓壁压力实测结果与中国、欧洲和美国相关规范的计算值进行对比。试验结果表明:100%、80%和50%仓容时,仓壁静态侧压力实测值与中国规范计算值的偏差率最小,与美国规范计算值的偏差率最大,其中,距储粮顶面600(100%仓容状态)、160(80%仓容状态)和250 mm(50%仓容状态)处的仓壁静态侧压力实测值超过中国规范的计算值,经过修正后,仓壁静态侧压力实测值均小于规范的计算值;仓壁静态侧压力实测值均小于欧洲和美国规范;在相同高径比时,储粮仓容越小,仓壁静态侧压力实测值与各国规范静态侧压力计算值偏差率越大。与中国规范相比,欧洲和美国规范更偏于安全。仓壁动态侧压力试验结果表明:对于相同高径比的筒仓,中心卸粮情况下,在小麦顶面处于整体流动状态时,不同初始仓容卸粮至同一高度时,同一测点的动态侧压力不同,100%仓容卸粮至50%仓容时C1测点(距仓壁下边缘100 cm处)的动态侧压力为3.376 kPa,80%仓容卸粮至50%仓容时C1测点的动态侧压力为1.528k Pa;小麦由整体流动变为管状流动的过程中均出现超压现象,100%、80%和50%仓容的最大超压系数分别为2.76、2.90和2.68;100%、80%和50%仓容出现管状流动状态的高度位置逐渐下降,说明管状流动的出现位置与初始的储粮仓容相关,初始仓容越小,粮食上表面出现管状流动的位置越低;相同卸粮口卸粮时,出粮高度随时间的变化曲线斜率均约为16.1,即卸粮速率一致;下部测点出现动态侧压力峰值的时间滞后于上部测点。试验结果可为筒仓规范的编制修订提供依据,为粮食筒仓设计提供参考。

Experimental study on side pressure of grain silo under storage and discharging state

Abstract: Pressure especially dynamic pressure on the silo wall is crucial for the silo design, and it is difficult and intractable to study and discuss the pressures on the silo wall during discharging. In order to study the static pressure in the state of grain storage and the dynamic pressure under the state of central discharging, the model silo with a diameter of 400 mm and height of 700 mm which based on a reinforced concrete silo was made by aluminum. Taking the wheat as the storage material, the pressure tests of static storage and central discharging were carried out under the conditions of 100%, 80% and 50% volume of silo respectively, and the measured results of pressure were compared with the calculation results of relevant standards of China, Europe and the United States The experiments results of the static side pressure showed that the deviations rate between the measured value of the static side pressure of the model silo with the calculated value of China stangards were the smallest, while it was biggest compared with the United States standard. The three measured values of the static side pressure were more than the calculated values of China''s standard, that was 600 mm away from the top surface of the storage under 100% of silo volume, 160 mm away from the top surface of the storage under 80% of silo volume and 250 mm away from the top surface of the storage under 50% of silo volume, but the measured values were less than the calculated values after security correction. The measured values of static side pressure of the model silo were all less than those of European and the United States standards, the European and the United States standards were more security than China''s, the China''s standard safety margin should to be adjusted. The test results of the dynamic side pressure of the silo wall showed that the dynamic side pressure of the same measuring points were different when the top of storage was in the whole flow state for the different initial silo volume when the storage was discharged to the same height, The dynamic side pressure of C1 was 3.376 kPa when the 100% silo volume was discharged to 50% silo volume, and it was 1.528 kPa when the 80% silo volume was discharged to 50% silo volume. The phenomenon of overpressure occurred in the process of wheat from mass flow to tubular flow. The maximum overpressure coefficients of the 100%, 80% and 50% silo volume were 2.76, 2.90 and 2.68. The positions of occurring tubular flow gradually decreased at 100%, 80% and 50% silo volumes, it indicated that the location of tubular flow was related to the initial storage volume, the smaller the initial storage volume, the lower the location of tubular flow occurred on the top surface of storage. When discharging at the same port, the slope of the curve of grain height with time was about 16.1, i.e. the rate of grain unloading was the same, and the peak time of dynamic side pressure at the lower measuring points was later than that of the upper measuring points The study could provide a basis for the compilation and revision of silo standard and a reference for the design of grain silo.