Study of the Xi’an Xiao Yan pagoda’s dynamic characteristics

Finite element software ABAQUS was used to calculate the dynamic characteristics of Xi’an Xiao Yan pagoda by a three-dimensional entity model, and a variety of factors were simulated on its dynamic characteristics. Results show that it is feasible to calculate the structural dynamic characteristics by a finite element three-dimensional entity model. Through model comparison process, it was found that tilted wall is favorable to the seismic performance. And the elastic-plastic time-history analysis was carried out to simulate the tower under the big earthquake damage, and the corresponding reinforcement measures were discussed according to the simulation results. Introduction Xi’an Xiao Yan pagoda located in Jianfu temple, is a dense canopy tower in the Tang dynasty. and it had 15 original layers formerly, and now it exists 13 layers with 43.4 meters in height[1][2]. The Xi’an Xiao Yan pagoda has experienced many times of earthquake and received damages in history. As a precious historical and cultural heritage, its seismic performance research is particularly important. It is shown in figure 1. Fig.1 Xi’an Xiao Yan pagoda In the recent years, the domestic scholars have a lot of researches in the view of old tower’s seismic performance, such as Chen Ping’ discussion on the Xi’an Xiao Yan pagoda. Chen put forward that the weakness of the perforated brick pagodas was that the axis of shear capacity in tower body was low, so the seismic reinforcement should be paid attention to[3][4]. Yuan Jianli concluded the modeling methods, and analyzed the main factors that influenced the model. At last, he put forward the classic theory and the modeling methods which combines test data and the computer simulation[5][6]. However, the research of the influence of tower structure on the dynamic characteristics is still insufficient. This paper calculates the dynamic characteristics of the Xi’an Xiao Yan pagoda’s three-dimensional entity finite element model by the finite element software ABAQUS, studies the feasibility of ABAQUS’ simulation on the dynamic characteristics of masonry pagodas structures, simulates the door opening, the form of wall, and the roof overhang three factors’ influence on its dynamic characteristics, summarizes the influence of several factors on the simulation results. Then the finite element model of tower was put into elastic-plastic time-history analysis, which attempted to simulate the tower’s collapse state under earthquakes. Finally, several methods of reinforcement 2nd International Conference on Machinery, Materials Engineering, Chemical Engineering and Biotechnology (MMECEB 2015) © 2016. The authors Published by Atlantis Press 408 were presented according to the results of finite element simulation, which was seen as some references for the reinforcement of Xi’an Xiao Yan pagoda. Basic parameters Due to the several earthquakes, Xi’an Xiao Yan pagoda suffered severe damages, and it didn’t have initial bricks in the subsequent reparation, so the strength of the blocks were large discreted, which was verified through our site springback experiment. The value of Young's modulus was based on the literature[1], and it was reduce to E=1500Mpa, Poisson ratio was μ=0.15, density was ρ=1900kg/m3. Tower body geometry sizes (table 1) were measured at actual field. Table 1 Xi’an Xiao Yan pagoda real geometry size (unit: m) level length Floor height Wall thickness Hole height Outer hole Width 13 6.50 1.45 1.82 0.37 0.37 12 7.15 1.54 1.94 0.37 0.40 11 7.72 1.60 2.20 0.40 0.49 10 8.00 1.98 2.26 0.60 0.54 9 8.56 2.28 2.50 0.80 0.59 8 9.13 2.47 2.78 0.80 0.62 7 9.44 2.62 2.85 0.85 0.66 6 9.87 2.82 3.00 1.20 0.74 5 10.10 3.18 3.10 1.22 0.76 4 10.30 3.34 3.20 1.36 0.88 3 10.50 3.45 3.28 1.40 0.94 2 10.86 3.75 3.38 1.45 0.97 1 11.40 6.84 3.57 2.68 1.77 The establishment of the finite element model This paper adopted finite element analysis software ABAQUS, and employed the method of three-dimensional entity modeling (as shown in figure 2) and element type C3D10H, and the automatic mesh generation method was employed, and it produced 72158 units (as shown in figure 3). The Xi’an Xiao Yan pagoda’s former six ranks natural vibration period and frequency is shown in table 2, which indicated the model has good agreement with experimental data. Figure 4 is the former six figure vibration modes. The first two ranks translated along the north-south, east-west respectively, because its symmetrical structure, natural frequency difference was little, and the third rank vibration mode was a reverse along the vertical direction. The ratio of the first cycle, which took torsion as its main movement, and the first cycle, which took translation as its main movement, shows that the bearing layout is reasonable, and the structure will be better controlled under severe sensation of torsion effect. The sixth rank vibration mode was structural vibration along the vertical, and the top part of the tower had the biggest vertical deformation. Moreover, the top part was at the most unfavorable position except torsional vibration, and structural section size decreases along the height direction from the bottom to the top. The minimum cross section is at the top of the tower, and the shear and tensile strength are all minimum here, so there should be paid attention to the reinforcement. Table 2 Natural vibration period and frequency of the vibration model Number Natural frequency of vibration(Hz) Natural vibration period(s) Number Natural frequency of vibration(Hz) Natural vibration period(s) 1 1.3182 0.759 4 5.0598 0.198 2 1.3557 0.738 5 5.1637 0.194 3 4.1432 0.241 6 6.4060 0.156