Analysis And Study On The Influence Of Microvibration On Ancient City Wall Of Dajingmen

Traffic vibration is a slight vibration,which will continue to have a long-term impact on sensitive buildings and ancient buildings.Although the energy generated in a short period of time is small,in the long term,it will lead to dynamic response of neighboring buildings,wall structure cracking,loosening,foundation subsidence,damage accumulation and strength reduction.Dajingmen ancient city wall is close to the road,and vehicles pass by continuously every day.Under the increasing traffic vibration,the structural performance of the city wall will be greatly affected.On the other hand,the number of tourists on the ancient city wall of Dajingmen is also increasing gradually.The activities of tourists on the city wall are also of slight vibration,which has exerted adverse effects on the city wall for a long time.This paper first monitors the vibration of the ancient city wall when vehicles pass through Dajingmen,then organizes the field test for tourists and monitors the vibration of the city wall,and finally establishes the three-dimensional finite element model of pavement,foundation and city wall for simulation and comparative analysis.The main content of the article is as follows:On the other hand,the ancient city wall of Dajingmen has gradually increased the number of tourists.The activities of tourists on the city wall also belong to the micro-vibration,which affects the city wall for a long time.In this paper,the vibration of the ancient city wall of Dajingmen in Zhangjiakou is monitored when vehicles pass by.And the site organization of visitors to test,monitoring the vibration of the wall.At the same time,a three-dimensional finite element model of pavement,foundation and wall was established for simulation analysis and comparison as the theoretical basis for the protection of ancient wall.The main content is as follows:（1）Using 3D laser scanner and total station instrument to collect appearance data of Dajingmen ancient city wall;using GPS-RTK instrument to collect real-time coordinate data of city wall;combined with manual measurement method to record detailed structure parts of ancient building.Record the damage location and damage degree of the ancient city wall of the Dajingmen to be studied;record the repaired position and repair effect;record the material information and strength information of the structural members and the foundation.（2）The Weikende vibration sensor is used to collect the vibration speed of the city wall during the peak traffic hours of the morning,afternoon and night,and the different activities of the tourists.At the same time,the recorders are recorded together to record the number of vehicles,the arrival time of large vehicles and 100m.The time used by the road.Then,through the Weikende dynamic test software and MATLAB,the vibration velocity data collected by the test is analyzed and processed,the effective data is intercepted and the vibration acceleration data is transformed,and transformed into the frequency domain for analysis.The analysis shows that the maximum vibration speed caused by vehicle driving and tourist activities is2.3×10^-3mm/s and 1.1×10^-3mm/s;the maximum vibration acceleration is0.3 mm/s²and 0.14 mm/s².They are all within the limits allowed by the specification.（3）Establish the finite element model of Dajingmen ancient city wall,and obtain the natural vibration frequency and period of the structure through modal analysis;The influence of different types of road amplitude curves was simulated through dynamic analysis,including road amplitude curves of small cars,medium cars and large cars driving for 30 days,and road amplitude curves of small cars and large cars operating for 30 months.On the one hand,observe the response of the ancient city wall of Dajingmen when the load is close to the actual situation;on the other hand,verify the fatigue condition of the city wall under the long vibration time of vehicles,analyze the influence on crack propagation,and calculate the vibration intensity of vehicles that cause damage to the city wall.The maximum speed and acceleration response of the wall at different operating conditions is 6.7×10^-3mm/s and 0.75mm/s²,which are consistent with the requirements of the regulations.The stress at the most unfavorable position of the wall under long time load is 0.12MPa,which is lower than the bearing capacity of the wall brick,but still needs attention.The mass of the car that made the wall respond beyond the specification limit was about 7.5t.