Study On Propagation Law And Shock Absorption Mechanism Of Collapse Vibration In Demolition Blasting

With the acceleration of urbanization in our country, demolition blasting is used in building demolition more and more because it’s security,fast and economic,but its harmful effect is also growing.Because the buildings’weight and volume is moer and more big, people pay more attention to the damage of the surrounding buildings and other facilities by the collapse vibration. At present domestic research on collapse vibration is lack of high repeatable experimental.So this article mainly research buildings’collapse vibration caused by blasting demolition.In this paper, the research on collapse vibration is divided into three parts.Firstly, mathematics and mechanics method is used to analyzes the toppling stage of buildings, collapsing touchdown impact load and the propagation and character of collapse seismic wave. Then using the method of dynamic compaction in construction engineering to make the experiment scheme. And then analyzing the data of the measured under different conditions to reseach the factors that affect collapse vibration. Using the differential method to gain the collapse vibration acceleration time history curveand and using dimensional analysis to gain the equation of the collapse vibration velocity.After that,the article researches the propagation and attenuation rule of collapse seismic wave with test methods. gaining the data of the collapse vibration wave along different directions and when it passed through a damping ditch.,the data are analyzed using the HHT method.It is found that the height and weight of the collapse,the strength of the shock platform,the shock surface state of the collapse and the distance between the measurement point and the collapsing point distance affect collapse vibration velocity when analysising of the experimental results.The vertical direction maximum vibration velocity appeares later than radial direction. As the impact strength decreases, the time of maximum vibration velocity appearss is delayed,it is shown that the seismic wave spreads in the medium is concerned with the material of medium, the release velocity is more fast when the seismic wave spreads in the soft medium. The same area of the rectangular planar impact, the velocity which its long/short edge directs is not the same, it is ignored in previous studies. The study has shown that collapse vibration wave in the low frequency part contains more energy, the propagation of collapse seismic wave along the different directions is different,it also proved that the lenth and the depth of damping ditch are the critical factors which influences its vibration absorbing effect, the wave energy decreases in damping ditch.Because of the incident wave and reflected wave superpose on damping ditch walls,it makes the vibration velocity of damping ditch wall which near the cave point increases.The research also found that the collapse vibration wave’s energy is not reached the maximum at the outset, but suddenly began to increase at a time, in a very short period of time to peak next, then in a short period of rapid attenuation.