Analysis Of The Influence Of Site Conditions On The Dynamic Interaction Between Masonry Pagodas And Foundations

The ancient masonry pagoda is a model of ancient high-rise architecture in China.However,due to frequent earthquakes,the ancient pagodas in the earthquake zone are severely damaged,and the seismic protection of the existing masonry pagodas is urgent.The seismic response and damage of ancient pagodas are a significant basis for their earthquake-resistant protection.The results of the seismic response analysis of the pagoda based on the rigid foundation conditions differ significantly from the real state,and the dynamic interaction relationship between the masonry ancient pagoda and the foundation in the earthquake has a significant effect on the seismic response of the pagoda.The dynamic interaction relationship between the foundation and the structure is different under different site conditions.In this article,the dynamic characteristics and seismic response of the interaction system between the ancient pagoda and the foundation are studied by shaking table tests,and the seismic response of the pagoda is compared with the seismic response of the pagoda under the action of stiff foundation to study the effect of the interaction between the ancient pagoda and the foundation on structural seismic response under different site conditions.The main contents and conclusions are as follows:(1)Shaking table test of masonry pagoda and foundation interaction systemA 1/8 scale model of Xuanzang Pagoda and a three-way deformation laminated shear model container were designed and fabricated,white noise and three seismic waves were input to obtain the dynamic properties of the structural model,acceleration and displacement responses of the foundation surface and each floor of pagoda,and the damage phenomena of the pagoda under earthquake of different intensities were observed and recorded.It is found that the pagoda is firstly cracked along the masonry joints at the top of the pagoda under the excitation of seismic waves,and some blocks fall off when the intensity is higher,and then with the increase of intensity,the cracking damage develops to the bottom structure.The main damage pattern of the foundation soil is the cracking of the soil around the pagoda,and the crack width grows with the increase of intensity and gradually extends to the edge of the foundation.(2)Numerical simulation analysis of masonry pagodas under consideration of soilstructure interaction systemBased on the results of shaking table tests and in-situ dynamic tests,finite element models of masonry pagodas under rigid foundation conditions and consideration of soil-structure interactions were established respectively.Three seismic waves with different intensity conditions are input to calculate the seismic response of the pagoda and the foundation.The acceleration,displacement response and principal tensile stresses of the structure are extracted,the results show that the top of the pagoda is the weak part of the structure under the action of a rigid foundation,and the tensile damage area of the pagoda is mainly concentrated at the first floor and the eaves of the pagoda.Considering the soil-structure interaction conditions,the section from the fifth floor to the top of the pagoda is the weak point of the structure.The tensile injury area of the structure is mainly concentrated on the second-floor pagoda and the eaves of the first to second floors.The damaged cracking area spreads from the first floor to the superstructure layer by layer.(3)Analysis of the influence of soil-structure interaction on the dynamic response of structuresThe comparison between the shaker test results and the numerical simulation results shows that the time of acceleration generating peak on the time course curve is the same.Due to the pagoda exists damaged accumulation in the test,the acceleration of the superstructure in the test is greater than the simulated value.The damaged areas are also the same.In contrast to the dynamic response of the structure under rigid foundation conditions,the soil-structure interaction attenuates the acceleration response of the structure,increases the displacement response of the structure,and aggravates the degree of damage at the base of the pagoda.(4)The effect of site conditions on the seismic response of structures under a foundationmasonry pagoda interaction systemVarying the calculation parameters of foundation soil to simulate the change of dynamic properties for four classes of site.Establish numerical calculation models of masonry ancient pagodas and foundations under different venue conditions,respectively.Import seismic waves for seismic response calculation,comparing the variation characteristics of the structural dynamic response of the pagoda under four types of site conditions and rigid foundation conditions,the results show the class Ⅰ site soil has no significant amplification effect on the elastic horizontal displacement of the ancient pagoda.However,the displacement increases with the increase of site soil category under the action of class Ⅱ to class Ⅳ site soils and reaches the maximum value at the base of the pagoda.In addition,the dynamic response of the structure under consideration of soil-structure interaction is influenced by the frequency as well as the amplitude characteristics of the seismic wave,and the matching of the seismic wave with the resonant frequency of the site soil increases the amplified response of the corresponding site soil under the action of that seismic wave.As the site category increases,the interlayer displacement angle value of the pagoda gradually increases,indicating that the seismic resistance of the structure is unfavourable for the class Ⅳ site soil.