粮食群仓的环境振动测试和角仓边仓振动响应分析

Ambient vibration test of grain group silos and vibration response analysis of the corner and side silos

为了获取群仓准确的动力特性参数从而更合理地进行群仓的抗震设计,从粮食储藏工程考虑,对实际工程中一组三排五列的粮食群仓的振动特性进行了分析。基于结构振动理论和有限元数值分析,考虑结构对称性、荷载对称性和工程实际情况,制定了环境振动测试粮食群仓的优化方案;利用最小二乘法、五点三次平滑法和数字滤波的方法对测试信号进行了处理,得到了有效的测点加速度响应数据。基于控制理论和振动系统的运动方程,引入变换矩阵,推导了环境振动下利用测点加速度响应数据进行粮食群仓振型计算的公式,从而得到前四阶振型及对应的频率,各阶振型形态和模拟结果相同;前四阶频率计算值分别为2.28、3.45、6.37、8.26 Hz,对应模拟值分别为2.35、3.56、6.31、8.16 Hz,模拟值与计算值误差分别为3.07%、3.19%、0.94%、1.21%。进一步对角仓和边仓的振动反应进行分析,结果发现:两个仓体的第一阶振型均沿着粮食群仓整体的短轴方向,以剪切型为主,振型幅值基本一致,相邻仓体间的约束作用对一阶振动反应几乎没有影响;两个仓体的第二阶振型均沿着粮食群仓整体的长轴方向,仍以剪切型为主,但振型幅值不同,边仓小于角仓;两个仓体的第三阶振型形态为绕粮食群仓整体中心的扭转,短轴方向测点转动幅值大于长轴方向测点;随着相邻仓体间约束作用增强,两个仓体的第四阶振型形态和振型幅值均不同,角仓和边仓呈现不同的振动特性,角仓上靠近边仓测点振型以弯曲型为主,振型幅值相对较小,其他测点以剪切型或弯剪型为主,振型幅值相对较大;边仓受相邻3个仓体的约束作用,测点振型幅值都较小,而且靠近相邻仓体测点振型以弯剪型为主,中间列测点以剪切型为主。研究结果表明:相邻仓体间的相互约束作用对二阶及以上振型影响较大,根据振型形态和振型幅值分组进行粮食群仓中仓体的抗震设计更加切合实际,节约材料,降低成本。

Accurate dynamic parameters are essential to more reasonably design grain group silos under earthquake action.In this study,the vibration characteristics of large-scale grain silos were analyzed,considering 15 silos in three rows and five columns in a grain storage project.The specific procedure was as follows:1)A feasible optimization scheme was proposed for the ambient vibration test of grain group silos using structural vibration and finite element method(FEM),together with the structural and load symmetry in the actual engineering condition.2)The measuring points were drawn in the corner silo(No.11)and the side silo(No.12),and then the point elevation and orientation were all listed in the tables.The acceleration signals of measuring points were obtained after the test.The least square,five-point three-smoothing,and digital filtering were then used to efficiently process the measured data.3)The mode shapes of grain group silos were derived using control theory and motion equation of vibration via the acceleration data and transformation matrix.The first four mode shapes and frequencies were calculated to draw for the corner silo(No.11)and the side silo(No.12).The results demonstrated that the mode shapes were all the same.In the first four mode frequencies,the calculated values were 2.28,3.45,6.37 and 8.26 Hz,respectively,and the simulated values were 2.35,3.56,6.31 and 8.16 Hz with an error of 3.07%,3.19%,0.94%,and 1.21%,respectively.In the vibration responses of the corner silo(No.11)and the side silo(No.12),the first mode shapes of the two silos were all along the short axis direction of the whole grain silos with the same shear deformation and the same amplitude,indicating that there was little effect of adjacent silos on the first vibration response.The second mode shapes of two silos were all along the long axis direction of whole grain silos with the same shear deformation but a different amplitude.The constraint effect among the corner silo(No.11)and the adjacent silos was weaker than that of the side silo(No.12)and the adjacent silos.Therefore,the vibration amplitude of the former was larger than that of the latter.The third mode shapes of two silos were torsion shapes around the center of grain group silos,while,the rotational amplitude of the measuring point in the short-axis direction was greater than that in the long-axis direction.The fourth mode shapes of the two silos were significantly different,due to different interactions among the corner silo(No.11)and the adjacent silos and that of the side silo(No.12)and the adjacent silos.Bending mode shapes of the measuring points of the corner silo(No.11)near the side silo,and the amplitudes were relatively small,but the other points were mainly shear or flexural shear mode shapes,and the amplitudes were relatively larger.The reason was that three adjacent silos constrained the side silo(No.12)to the small amplitudes.Bend-shear mode shapes were found in the measuring points near the adjacent silos,but the points of the middle column were mainly shear mode shapes.Each silo in the grain group silos represented different interactions with the adjacent silos at the measuring positions,indicating a significant impact on the second order and above modes.A seismic design of grain group silos can be expected to divide into several parts for better materials cost-saving,according to the shape and amplitude of vibration mode.