| The space truss is the structure type that is used most in space structure. In engineering pratice, with richness and variety of architectural styles or with the needs for light and air, the space truss with inclined plane can be adopted. Because the space truss is placed inclined and the supporting columns have large elevation difference, the mass and stiffness of holistic structure is evidently asymmetric. Under earthquake action, the low-side and high-side supporting columns interact through space truss, so the holistic structure has generality of space truss as well as individuality of space truss with inclined plane. The analysis should be based on the holistic structure.The paper carries on different analyses of statics, natural vibration characteristics, elasto-plastic time-history analyses for inclined space trusses of different substructure stiffness, and compares with plane space truss in respect of stress features. The analyses show:the whole stress features of inclined space trusses have large distinguish between x, y direstions. When inclined space trusses vibrate in direction of y(direction of second or third vibration mode), the high-side and low-side supporting columns and space truss constitute a solid lateral resistant system, so the shear forces is distributed according to lateral stiffness of supporting columns under earthquake action in direction of y; When inclined space trusses vibrate in direction of x(direction of first vibration mode), the low-side columns don't constrain high-side columns powerfully, shear forces in direction of x are determinated by loads that every column bear based on D'Alembert Principle; Because the axial forces that are passed from high-side and low-side columns to top chords and web members have much difference, the internal force distribution of inclined space truss has this unique character under earthquake action; When the supporting stiffness of space truss of inclined plane changes, it mainly has influence on lateral vibration of holistic structure and vertical vibration of superstructure of space truss.The paper considers and realizes the initial influence of static loads in elasto-plastic time-history analyses also. The analyses show:Under rare earthquake ANSYS elasto-plastic time-history analysis should consider the initial influence of static loads. That superposition principle is applied in elasto-plastic stage will cause dynamic displacement of space truss relatively smaller, dynamic internal forces of unyielded bars relatively smaller and dynamic internal forces of yielded bars relatively larger.Lastly, aiming at dynamic response characteristics of space truss of inclined plane, the paper takes measures that buckling-restrained braces are added between high-side supporting columns to control the displacement of high-side columns in direction of first vibration mode, and makes comprehensive comparison with conventional braces. The comparison show:buckling-restrained braces can control horizontal dynamic-displacement of holistic structure and shear forces distribution at the column bases more reasonably that conventional braces. |
