Study On The Blasting Vibration Characteristics And Safety Standards Of The Large-span Steel Structure

When digging by the blasting way between the subways,the blasting vibration effect usually affects the safety of the upper structures.In order to ensure the safety of the upper structures,it is necessary to monitor and control the blasting vibration effect.The existed control standard can not be used in construction of large-span steel structure for the upper structure directly because whatever in the aspect of building structure or in terms of seismic design are different from other buildings.This paper took the subway tunnel under through the train station project in Xiamen as an example,through on-site monitoring the speed of blasting vibration,and combined the numerical simulation of the ANSYS/LS-DYNA finite element software,studied the vibration characteristics of the main structure of the upper part of the train station by blasting construction,and put forward the safety standard through the analysis of stress curve line.The main conclusions are as follows:(1)Tunnel blasting has cavity effect.At the distance 10m away from the tunnel face in the floor,the vibration velocity is greater than that in the tunnel face.The amplification coefficient of each floor is different,and the cavity effect of the first floor is most significant.Elevation has a significant amplification effect on the blasting vibration velocity.As the floor increases,the vibration velocity does not show the characteristic of decreasing gradually:the vibration velocity of the second floor is obviously greater than that of the first floor,and the vibration velocity of the third floor has not continued to amplify,in contrast,it decreases rapidly.(2)The distribution of the peak vibration velocity on the floor shows the characteristic of whiplash effect:from inside to outside,the peak vibration velocity of each particle firstly increases and then decreases,later increases and finally decreases.Through the comparative analysis,we found that the vibration velocity distribution rule on the second floor is quite similar with that on the first floor,while the vibration velocity distribution rule on the third floor is fuzzy.(3)According to the three relationships of vibration velocity,charge mass,distance of blasting center to combine with the least square fit Sadov's formula,the fitted formula coefficient is suited for the condition of construction field.But the particle vibration velocity of the rocks surface around the main structure does not obey the distribution rule of Sadov's formula,the vibration velocity is greater than the vibration speed calculated from the Sadov's formula,and is close to the particle vibration speed of the edges on second floors.(4)Start from the three relationships among the energy of blasting earthquake,vibration velocity and stress,through the stress obtained the conclusion of the description of blasting vibration.On this basis,through the analysis of the stress curve proposed the standard of safety decision:according to the relationship between the maximum vibration speed and the dosage,obtained maximum allowable vibration speed;there is a difference between numerical simulation results and on-site monitoring results,the difference between 10%-25%.(5)Considering the frequent blasting make the construction and rock mass occurred cumulative damage,it will on a certain to reduce the seismic performance of upper buildings,It is recommended that the actual blasting should be reduced on the basis of the maximum blasting vibration velocity.Through a series of measures for reduction vibration,to reduce the vibration effect,can reach the purpose of protecting the main structure.