Modal modification based analysis of seismic performance of the Jiufeng Temple Ancient Masonry Pagoda

Based on detailed data collected on-site, including structural construction, cross-sectional dimensions, and material properties, this paper establishes a refined three-dimensional solid initial numerical model (INM) of the Jiufeng Temple Ancient Masonry Pagoda using the ABAQUS finite element software. On the basis of the measured modal characteristics (frequency, vibration mode, and damping ratio) of the ancient masonry pagoda, a modified numerical model (MNM) was obtained by adjusting the key parameters (damping ratio, Rayleigh damping coefficients, elastic modulus, and material density) of the initial numerical model. Based on the modified numerical model, five actual strong earthquake records were input to calculate the seismic response of the ancient masonry pagoda. The seismic failure mechanism of the ancient masonry pagoda, as well as the distribution characteristics of the principal tensile stress and seismic weak-layers were analyzed. The results indicate that the stiffness and mass distribution of the ancient masonry pagoda are consistent along its height, and the deformation at the top of the ancient masonry pagoda is significant under seismic action. The results obtained from the initial numerical model are more conservative, with the maximum storey drift being 19 %, 40 %, and 27 % larger than those of the modified numerical model under minor earthquakes (with a 63 % probability of exceedance in 50 years, also called frequently occurring earthquakes), moderate earthquakes (with a 10 % probability of exceedance in 50 years), and major earthquakes (with a 2 % probability of exceedance in 50 years, also called rarely occurring earthquakes), respectively. Under the action of major earthquakes, the upper portion of the Jiufeng Temple ancient masonry Pagoda, particularly above the 9th floor, may suffer severe damage. The 10th, 11th, and 12th floors are identified as the weak-layers of the ancient masonry pagoda, and the weak-layers determination from the modified numerical model are consistent with the results of standard calculations. The method proposed in this paper can provide technical support for the seismic protection of ancient masonry pagodas.