The Transient Response Analysis Of Bolt Anchorage System Under Different Load

The purpose of nondestructive testing of anchor is in order to ensure the safetyand reliability of the anchor structure, which provide important basis for the ultimateload, the stress distribution and the degree of defect of bolt。As we all know, anchorusually works under a certain load, but the current research is mostly not consideringthe influence of load and the understanding of load is insufficient, which affect thejudgment of the anchoring quality.This article make indoor model with differentquality of anchor bolt to solve the problem that not considering the load when selectthe parameters for the anchor quality evaluation on the basis of careful analysis andsummarizes the predecessors’ research results. Then discussed the effect of load onthe bolt stress distribution based on the stress wave reflection method and extract theoriginal dynamic signal with the method of wavelet analysis, and carrying on morecomprehensive in-depth research for the key parameters such as velocity, fundamentalfrequency, dynamic stiffness and damping that affect the quality of anchor, mainlycome to the following conclusions:(1) With the strain analysis for each measuring point of integrity bolts, it showsthat when the differential stress of steel with medium interface is greater than the limitshear stress, the anchor stress will redistribute as the increasing load and cause theload sliding down, and the threshold is the bone force between reinforced andmedium interface. When the limit shear stress is small, the performance is not obviousat the top section with larger load, however, the change process is obvious in thebottom part with small stress. As for the anchor with single air plasma and differentcompactness, its stress have obvious difference that characterized by stress is moreeven, but the value of strain is bigger than the integrity bolts at the same status, andthe redistribution process is not obvious.(2) Through the test of section wave velocity for different anchor withmulti-point testing, results indicate that the effect on wave velocity of the anchor with mainly in the previous and air plasma section, but it is not obvious after the air plasmasection. The wave velocity of the anchor that has an air plasma section changed withobvious leap as different load. By contrast, it has not obvious in integrity bolt. Inaddition, the wave velocity in single air plasma anchor is smaller than the integritybolts, which value of the bolt with single air plasma and different compactness fall inbetween. In conclusion, the wave velocity can be used as important parameters toevaluate the quality of anchor.(3) The vibration amplitude increased with the increasing of load, and thesmooth of original signal is affected, but the signal to noise ratio is reduced. The loadhas great influence on the analysis result when evaluate the anchor quality onlythrough original signal. However, on the basis of the theory of wavelet analysis, thede-noising effect is obvious, having smoothness curve and good readability. Whichshow load has a great influence on the original dynamic signal.(4) The frequency diagram in each of the bolt, the smallest is the single airplasma bolt but the fundamental frequency of integrity bolt is the largest. In the initialstage the fundamental frequency increase with the increased load, but the integritybolt increase with the slowest speed, on the contrary, the worst anchor with defectsincreased fastest, and the speed of single air plasma different compactness anchor fallin between. As load increases, the frequency come to stability, integrity bolt still is thelargest. Although after the fundamental frequency stability, the load is not theimportant factor, the frequency band energy distribution has obvious changes. so it isimportant in the bolt anchorage quality and the analysis of working status.(5) Dynamic stiffness analysis shows that dynamic stiffness of the integrity boltand the single air plasma different compactness anchor is relatively close, but theanchor with single air plasma is smallest, which all increase with the increasing ofload. Therefore, it is sensitive to bolt stress.(6) The amplitude ratio analysis for different anchorage quality of anchorindicates that the damping of different quality of anchor bolt decrease by the increaseof load under the compression state. For the integrity bolt, the damping changeposition focused on the air plasma section; but it mainly concentrated in the end pressure section and air plasma for the bolt with a single air plasma; yet it has evidentchange between the compression face and air plasma for the single air plasmadifferent compactness anchor. The defects influenced the damping of bolt mainlyfocus some distance in front of the defect and has little influence on the defects andsubsequent measurement section.