Abstract: As a cultural relic protection facility, the first site (Peking Man Cave) protection shield at Zhoukoudian Site is built to protect the main archaeological site from further weathering. The shield over the Peking Man Cave simulates the shape of the surrounding mountains and presents itself as irregular spatial surface. On the main long-span single-layer steel structure, double-layers blades are set. Sprawling herbs are planted in the grooves on the upper blades, and the lower blades are made by GFRP (glass fiber reinforced plastics) to model the rock texture. The structure will blend into the surrounding natural scenery from both inside and outside view angles when the plants thrive, and the design concepts for harmony and reconstruction of remote antiquity are realized.
In order to minimize the disturbance to the site and the surrounding environment, the main structure adopts a long-span single-layer special-shaped steel shell structure to control its volume. Due to the thinness, the single-layer grid structure provides more convenience for the double-layers blades installation. The global projection distance of the shield is 79 m in its longitudinal direction and 55 m in the transverse direction. The maximum oblique span is 83 m and the foundation height difference is 33 m. The shield is fixed by the hinge supports at the top and foot of the mountain. The safety of single-layer grid structure is often controlled by stability, which can be influenced by structural defects and boundary conditions. Three-dimensional and non-linear finite element methods are used to analyze and estimate the overall stability of the long-span single-layer special-shaped steel shell.
The stability ultimate capacity of the structure is analyzed by ANSYS software, and the influence factors of the stability ultimate capacity including the degree and distribution of overall structure defects as well as the stiffness of hinge support are investigated. According to the complete load-displacement curve, the stability ultimate capacity is confirmed. Analysis shows that the degree and distribution of overall structure defects have no obvious effect on the overall stability ultimate capacity as the shield is a complex spatial structure not an ideal shell, therefore, only the initial defect is taken into consideration for convenience of calculation. When initial defect of 1/300 of the oblique span is applied to the structure, and follow the first buckling modal shape distribution, the overall stability safety factor of the special-shaped shell is 3. 58, and the performance of the structure meets the requirements of Technical Code for Space Grid Structures (JGJ 7-2010). Analysis suggests hinge supports considering the significant effect of the boundary conditions on the stability ultimate capacity. The foundation anti-push resistance should be paid due attention to in design by the research.
The dynamic stability performance of the shield is analyzed by ANSYS software. Result shows that the special-shaped shell has satisfactory dynamic stability, and the damage seismic amplitude to cause dynamic instability can reach 0. 8g. The elastic buckling load of typical member of the special-shaped shell is obtained by applying unit force and eigenvalue analysis. The out-of-plane calculated length coefficient of members is determined as 1. 6 by inverse calculation of Euler formula, which meet the structural design requirements well and can be adopted for further reference.