| The ancient masonry pagoda has a unique architectural form and a high historical and artistic value.It is not only an outstanding representative of religious architecture,but also a valuable historical.It not only retains historical production techniques,construction techniques and materials production,but is also a microcosm of culture,politics,economy etc.Most of the ancient tower structures have experienced some natural disasters and human damage.The ability of the ancient tower structure to withstand various natural disasters,especially earthquake disasters,has been declining.The ancient tower structure is in urgent need of earthquake and disaster prevention protection research.However,considered the particularity of the structure of ancient brick and rock pagoda,scholars' research on its seismic performance and seismic protection methods is still not perfect.In this paper,the following contents are studied on the seismic performance,seismic risk and seismic protection methods of Xiaoyan Tower and Guangta which is the typical representative of the ancient masonry pagoda:(1)This paper takes the structure of Xiaoyan pagoda as the main research object.we have mastered the geometric parameters,material properties,structural forms and tower defects of the Xiaoyan pagoda structure by consulting historical documents and on-site field investigations and actual measurements.The surveied and measured results show that the main structure of the Xiaoyan pagoda has many cracks and serious weathering.Through the simulation analysis of the test results,and referring to the expression form of the constitutive equation of the existing uniaxial compression masonry material,combined with a large number of field test results,A stress-strain constitutive equation for the material of Xiaoyan pagoda was established,which can be used for seismic performance and seismic risk analysis of Xiaoyan pagoda was established.(2)According to the results of the field investigation and test,four model specimens simulating the Xiaoyan pagoda structure wall were designed and fabricated,and the corresponding low-cycle repeated load test was carried out to study the failure mode and layer inter-displacement angle of the Xiaoyan tower structure wall.According to the test results and considering the particularity of the protection of the masonry tower structure,the recommended interval of the displacement angle limit of the Xiaoyan tower structure is given Xiaoyan tower.Then,taking the data corresponding to the mean quantile as an example,the quantified index limits corresponding to the performance benchmarks on the curve are obtained,and the seismic response of the ancient brick and rock pagoda structure(Xiaoyan tower)under different ground motion strengths is different.The variation law of the displacement angle between layers is analyzed under the performance level,and the weak parts of the small goose pagoda structure are analyzed.In addition,the structure of the Xiaoyan pagoda is seriously damaged in most floors under the 8 degree earthquake,and the upper part of the tower body collapses,which should be paid attention to by the relevant departments.(3)Based on the results of IDA analysis,the maximum interlayer displacement angle was selected as the structural damage index.We carried out the seismic vulnerability analysis of the Xiaoyan pagoda structure,obtained the corresponding seismic vulnerability curve that was used to carry out the surpass probability analysis.From the normal use state to the final collapse state,the over-probability of the normal use level of the structure is 31.21%,98.55% and 99.99%,respectively.The probability of surpassing the temporary use level is 10.93%,96.46% and 98.61%,respectively.The probability of surpassing safety level points is 1.29%,94.55%,and 96.65%,respectively.The probability of surpassing the collapse level is 0%,33.46%,and 92.07%,respectively.It can be seen that the Xiaoyan pagoda structure has a high probability of collapse under the 8 degree rare earthquake,and it is recommended to take effective measures for seismic protection.(4)The seismic hazard of the Xiaoyan pagoda structure is analyzed by probabilistic analysis method,and the seismic hazard curve with seismic intensity and seismic peak acceleration as parameters is obtained.Seismic hazard curves for different years,which takes into account the particularity of the protection of the ancient tower structure,are obtained through analysis.On the basis of structural vulnerability analysis,site hazard analysis and probability damage analysis,the probability curve of the Xiaoyan pagoda structure under different failure states is obtained.The earthquake loss analysis of the Xiaoyan pagoda structure was carried out,and the corresponding earthquake risk assessment model was obtained,which can provide reference for seismic risk assessment of similar masonry tower structures.(5)Considering the particularity of the protection of the ancient tower structure,the principle of “safety first” and “minimum intervention” is taken as the basic criterion,and the modified epoxy resin impregnation method which has less influence on the ancient tower structure is proposed and adopted.Through the mechanical properties enhancement test and constitutive model study of 4 groups of 12 ancient tower masonry model structures,the constitutive equation of the ancient tower masonry with enhanced mechanical properties was established.The results show that the compressive strength of the specimens strengthened by the "modified epoxy resin impregnation method" is about 40.5% higher than the substrate,the shear strength is increased by about 11%,and the elastic modulus is increased by about 26.7%,which shows that the modified epoxy resin has good performance enhancement effect on the ancient tower structure.In addition,this paper also analyzes the structure of Guangzhou light tower which is similar to the structure of Xiaoyan Tower but has completely different structural shapes.The results show that the seismic vulnerability surpassing probability of Xiaoyan pagoda and Guangzhou light tower structures is significantly reduced after performance enhancement.It shows that the proposed method can effectively improve the seismic reliability of masonry tower structure,which can be used for practical application. |
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