Analysis of natural vibration characteristics of pre-stressed apace truss

Vibration characteristics of the seismic analysis of structures are a prerequisite. The natural vibration characteristics is the precondition of aseismic analysis .This paper uses the block Lanczos method to calculate the evacuation of prestressed truss natural frequencies and formation, prestressed value analysis, the impact of grid height, mesh size and prestressed cable strut height of the vibration characteristics of the structure, and summed up the relevant laws for structural design. Introduction Along with social economy development, the construction sector in the emergence of many new forms of spatial structure , spatial structure typically includes a shell structure , grid structure , lattice shell structure, cable structure , membrane structure, and by the two or more hybrid structures. Among them, the development on the fast, the most widely used is the grid mesh shell structure[1]. Vibration characteristics of a dynamic analysis of the basic dynamic characteristics. Features include natural vibration frequencies and mode shapes structure, the natural frequencies can be learned from the case of structural rigidity, has a decisive effect on the dynamic response of the structure [2] . By calculating natural frequency calculation structure can reduce harm resonance structures under dynamic loads generated by impact of structural vibration characteristics since there are many factors, each affecting different parameters affect the vibration characteristics of the structure is not the same cause. Analysis of dynamic characteristics of prestressed truss Computing model and calculation assumes When conducting evacuation prestressed grid computing power, take the following simplified model and assumptions A. grid structure into a plurality of discrete lumped mass elastic system, grid nodes are hinged node space , each node has three degrees of freedom B. belong to a small range of structural vibration , that structure belongs to a small deformation areas C. structural damping is very small , which can affect the structure ignored coupled between the various modes D. rod only bear axial force , the cable unit only tensile stress E. structure to meet the conditions of displacement and strain conditions Grid structure vibration equation According to D'Alembert principle , acting on particle system active force and constraint forces and inertia force vector is zero , when the effects of structural damping is ignored , but this time the external force is zero , then the grid structure represented by the matrix free vibration equation can be expressed as[3] [ ]{ } [ ]{ } 0 M K δ δ + =  [ ] M --Mass matrix, is a matrix in which the grid nodes; International Conference on Information Sciences, Machinery, Materials and Energy (ICISMME 2015) © 2015. The authors Published by Atlantis Press 74 [ ] K -The overall stiffness matrix { } δ -Displacement array { } δ ={ } 1 1 1 T i i i n u v w u v w w   ; { } δ -Acceleration Array { } δ ={ } 1 1 1 T i i i n u v w u v w w          Attributed to [ ] [ ] 2 | | K M ω − =0 { } [ ] 1 2 T m w w w ω =  In this paper, we use the block Lanczos method to solve the vibration frequency structure. Parametric analysis of prestressed composite truss vibration characteristics Examples In this paper, taking the time to type diagonal square pyramid truss bottom chord as the basic model pit tendon disposition.The structure modal analysis using finite element software ANSYS. Grid infrastructure to take the winding 11 × 11 grid (46.67m × 46.67m), grid basic parameters: truss top chord lx = ly = 3m, the distance between the upper and lower chords of Z = 3m, prestressed cable strut h = 1m, pretensioned P = 100KN. Factors evacuated the vibration characteristics of prestressed truss To evacuate diagonal square pyramid truss bottom chord Pit Tendon Disposition for example, adjusting the various parameters investigated various parameters on the natural frequencies of the grid[4]. Impact on the structure of the different values of prestressed. Prestressed truss structure, cable tensioning process will at certain stiffness in a certain margin to increase the stiffness of the structure. Cable stiffness and prestress exerted on the cable -related , according to the semiparallel wire cable tension range , were taken prestressed value P = 0KN, 100KN, 200KN, 400KN, 600KN for analysis, view different prestressing degree By taking the time to value the role of prestressed grid of diagonal square pyramid vibration frequency . Under the effect of different values of prestressed truss bottom chord Pit evacuated tendon disposition frequency plot. Shown in Figure 1-1 by can be seen taking the time to apply different degrees of prestressed diagonal square pyramid grid model , the grid value changed little since the vibration frequency , the conclusion in line with the situation . In taking the time to diagonal square pyramid grid model conclusion, we can see the same value the role of prestressed structural natural frequency with increasing order increases[5]. Different heights natural frequency grid Rack height affects the appearance of the nature of the grid architecture. Grid height is too high, affecting the appearance, the lower the value would cause insecurity visual. Meanwhile, a different