Seismic Damage Evaluation Indexes and Classification Criteria of Spatial Structures

Large-span space structures are widely used in large public buildings such as terminal buildings, high-speed railway stations and exhibition centers, which have intensive population and enormous investment. It is necessary not only to ensure their seismic safety under earthquakes, but also to consider their potential seismic damage and economic losses, that is, to carry out performance-based seismic design. The basic principles of seismic performance design in China′s Code for Seismic Design of Buildings(GB 50011-2010) are mainly based on concrete structures and not suitable for large-span space structures. Therefore, in this paper, taking single-layer spherical reticulated shells, single-layer cylindrical reticulated shells and trusses as examples, the finite element method is used to analyze their seismic response characteristics and failure modes, determine suitable seismic damage evaluation indexes, classify their seismic damage levels, and provide support for performance-based seismic design of large-span space structures. According to the Technical Specification of Space Frame Structures(JGJ 7-2010), 15 single-layer spherical reticulated shells, 9 single-layer cylindrical reticulated shells and 16 tubular trusses with different spans and rise-to-span ratios were designed by using the design software 3D3S. The finite element software ABAQUS was used to establish the finite element models of these structures. According to the Code for Seismic Design of Buildings, 34 ground motions conforming to the target response spectra of structures were selected from the ground motion database of Pacific Earthquake Engineering Research Center, and the ground motions were three-directionally scaled in a 1∶0.85∶0.65 ratio. The responses of the structures under different ground motions with different intensities are analyzed, and the seismic response characteristics and failure modes of the structures are summarized.
The results show that for single-layer spherical reticulated shells, the maximum displacement of nodes changes significantly with the seismic intensity, and the plastic strain energy can fully reflect the damage levels of the structure. Therefore, two parameters, the maximum displacement of nodes and the plastic strain energy reflecting the earthquake damage degree, are used as the seismic damage evaluation indexes of the structure, based on which the damage index is formed using different weights, and the seismic damage classification criteria are proposed for single-layer spherical reticulated shell structures according to the damage index. For single-layer cylindrical reticulated shells, the structural deformations of the structures in the secondary static analysis are similar to the seismic displacement responses, indicating that the damage of the structure under static loads is the further development on the basis of the seismic damage. Therefore, the static ultimate bearing capacities of the structure before and after earthquakes are used as the evaluation indexes of structural seismic damage. Based on the damage index considering the change of the static ultimate bearing capacity, the classification criteria of seismic damage for single-layer cylindrical reticulated shells are proposed. For the tubular trusses, large plastic deformations occur in the mid-span and near-support areas of the main truss, and the structural stiffness is significantly reduced. The plastic strain is used as the seismic damage evaluation index of the rods with large plastic deformation, and the damage levels of the rods are classified. According to the proportions of the rods with different damage levels, the seismic damage classification criteria for the tubular trusses is proposed. For both the single-layer spherical reticulated shell and single-layer cylindrical reticulated shell, the ratios of the maximum displacement to span are positively correlated with the damage indexes. Therefore, the seismic damage levels of these two types of structures can be classified according to the ratio of the maximum displacement to span, which is simpler and faster.