The Dynamic Analysis And Security Assessment Of An Old Brick Tower Excited By Explosive Vibration

Brick towers are with great cultural and research value. However, because of their non-reinforced structure, ages of weathering and man-made sabotage, their vibration resistant capacity is relatively poor compared to modern buildings. On the engineering background of the vibration monitoring and control of Shahe Tower against the influence of tunnel blast working, dynamic testing system is utilized in the on-site testing of vibrational excitation and response, which includes ambient vibration, response of tower body excited by trial blasts with increasing explosive charge. The result shows positive correlation between the maximum response amplitude of each measuring point and single charge weight, and the influence of changes in single charge weight is relatively smaller on the upper measuring point, indication that the dynamic characteristics of the structure decrease the effects of the changes in features of vibrational excitation on the response of the structure. By comparing the frequency components of the upper and lower measuring points, the research proves that the tower body absorbs high-frequency components of vibrational excitation, so is insensitive to high-frequency vibration. According to the propagation law of explosive vibration shown in on-site testing, the research evaluate and make suggestions on the value range of parameters in attenuation formula provided by current specification, and proposes the estimation of safe explosive charge for the project.A three-dimensional simulation model is put forward to calculate the dynamic characteristics of the structure, internal forces and deformations under gravity and wind load, and response of structure excited by ambient and explosive vibration, with the results showing that under the condition that the single charge weight is5.6kg, the compressive strength of the first floor doesn’t meet the safety criteria, with little risk of crushing failure. Meanwhile, as the results show really high compressive stress caused by traffic load compared with that led by explosive vibration, traffic load ought to be considered with significance as one of the major factors in existing damages such as cracking. Because of its fatigue effect form long-term repeated action, it would be necessary that the tower be monitored regularly in the development of its tilt and cracks, with proper maintenance and reinforcement.