| Column-supported reinforced concrete group silos is a general engineering structure widely used in food,energy,building and other engineering.For such structure,the rigidity of the support column is designed to be much smaller than that of the upper silo body,and thus there is a sudden change at the connection part of the column and the upper silo.This is not beneficial to prevent earthquake damage caused by stress concentration at the joint region.Therefore,it is necessary to study its seismic behavior in practice.However,due to the structural complexity of the group silos,the corresponding dynamic response of it is not included in the current design code,in which only the seismic design of the independent single silo is involved.The improper application of the single silo result to the group silos can cause wrong design.Therefore,the seismic performance of column-supported group silos is a scientific problem to be solved.The result will be useful to the engineering applications.Supported by the project of National Science Foundation of China "Study on the dynamic interaction mechanism of reinforced concrete group silos based on environmental incentives",the column-supported group silos is investigated and compared to the single silo.To do this,the group silo with 3×3 silo pattern and the single silo samples are designed with the scale ratio 1:25 and made of plexiglass.The test of the column-supported group silos and the independent single silo model under different horizontal earthquakes in the three storage states of empty,semi-storage and full silo was carried out,using the combination of shaking table test,finite element analysis and theoretical calculation.The main work and conclusions are as follows:(1)The dynamic characteristics of the column-supported group silo and the independent single silo are obtained,including acceleration,displacement and strain.The results show that:1)With the increase of the storage quality,the natural vibration frequency decreases.The overall frequency of the group silo is about 11.33%higher than that of the independent single silo under the three storage conditions.2)The amplification factor of the group silos and the independent single silo is distributed along the height line,and the acceleration response of the group silos is larger than that of the independent single silo;the acceleration response in the group silos is changed as the position of silo changes,and the acceleration response of the corner silo is about 10%higher than that of the central silo;3)the group silos under the same working condition has smaller displacement than the independent single silo;4)the strain of support column at the connection region to the silo body in the group silos is smaller than that of the symmetrical counterpart.Under the same working condition,the strain at the bottom of column for the group silos is larger than that of the independent single silo.Therefore,it is not safe when the results of single silo are directly applied to guide the design of group silos.It is recommended to carry out the seismic design of the support column according to the position of each silo in the group silos.(2)The finite element models of column-supported group silos and independent single silo are established.The finite element calculations under different seismic conditions were carried out.The results show that:1)The finite element results of self-vibration frequency are very close to the experimental results,and thus the established finite element model is reasonable;2)the finite element results of acceleration and displacement response for the group silos agree well with the experimental results;3)although there is clear discrepancy between the finite element results and the experimental results of the group silo support column,they show similar tendency;4)The dynamic pressure on the silo wall shows good consistence between finite element results and the test results along the height of the silo wall,but the finite element results are greater than the test results.So the D-P model is used to simulate the storage material with limitations.(3)The distribution rule and overpressure coefficient of the dynamic side pressure along the wall height of the group silos and independent single silo under the action of earthquake are obtained,and the important issues in the dynamic side pressure calculation is discussed.The results show that:1)The maximum value of the overpressure coefficient of the corner silo,side silo,central silo in the group silos and independent single silo occurs in approximate 1/3 range of the silo to the top;2)their values are 3.4,3.4,3.0 and 2.5,respectively,all of which are greater than the comprehensive coefficient of 2.0 specified in the specification.This means that the standard value is unsafe for group silos design.It is recommended to consider the earthquake effect for each silo in the group silos.The present research results fill the blank of the influencing factors of the seismic action in the horizontal pressure calculation of the silo storage.(4)The dynamic models of the column-supported group silos and the independent single silo are established.Based on the vibration mode decomposition response spectrum method and the shaking table test,the results of shear force at the base of the group silos and the independent single silo are evaluated under different working conditions.The results show that:1)The first-order natural vibration frequency of the model is close to the experimental results and the finite element results,and the established model is reasonable;2)the shear force at the base of each silo in the group silos under earthquake is almost uniform and independent of the storage condition,the type of seismic wave and the peak value of the table top acceleration;3)the ratios of shear force at the base of each silo in group silos and the independent single silo are 1.5,1.3,and 1.2 for the three-stock states.(5)A simplified calculation method for seismic action of column-supported group silos structure is developed by commonly considering the independent single silo and the practical shear ratio coefficient,which provides a basis for seismic design of column-supported group silos. |
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