Force characteristics and calculation analysis of tube truss structures

The spatial triangular steel tube truss embodies the stress-bearing mechanism of web members for shear resistance and chord members for bending resistance under vertical uniform load. The main influencing factor of the chord axial force is the section height, while the main influencing factor of the vertical diagonal web member axial force is The inclination angle of the vertical web bar to the vertical line. The force on the horizontal web bar under the action of vertical load is small, but when it is affected by significant torque, appropriate consideration should be given to increasing the cross-sectional size.

Calculation
1. Static calculation
The tube truss structure should be designed with member sections after displacement and internal force calculations. If the rod section needs to be adjusted, it should be redesigned to meet the design requirements. After the design is completed, the rods should not be replaced. If a member needs to be replaced due to difficulties in material preparation, it should be done in accordance with the principles of equivalent section and stiffness. The replaced member should not be the main load-bearing member of the structure, and its number should not be too much (usually no more than 5% of all members), otherwise it needs to be re-checked. By analyzing the internal force caused by the temperature change of the tube truss structure, the reaction force at the fixed end caused by the temperature difference acts on the nodes at both ends of the bar as an equivalent load, and then the finite element method is used for analysis.
2. Seismic calculation
Under single-dimensional earthquake action, when calculating the effect under frequent earthquake action, the revitalization decomposition response spectrum method can be used. For complex or important long-span structures, time-history analysis should be used for supplementary calculation. When using the time history analysis method, no less than two groups of actual strong motion records and a group of artificially simulated acceleration time history curves should be selected according to the type of building site and the design earthquake grouping. The seismic influence coefficient curve used in the method is statistically consistent, and the peak value of the acceleration curve should be adjusted according to the maximum value of the acceleration time-history curve of frequent earthquakes corresponding to the seismic fortification intensity, and a sufficiently long duration of ground motion should be selected.

When using the mode decomposition response spectrum method to analyze the seismic effects of a tube truss structure, at least the first 25 to 30 vibration shapes should be taken. For particularly complex or important structures, more vibration shapes need to be taken for effect combination. In the seismic analysis, the first 25 to 30 vibration shapes should be taken. Consider the impact of the support system on its force. At this time, the truss structure and the support system can be considered at the same time and calculated according to the overall analysis model. The support system can also be simplified as an elastic support of the tube truss structure and calculated according to the elastic support model. When analyzing the structural seismic effects, for For pipe truss structures with peripheral landings, the damping ratio can be 0.02. For pipe truss structures supported by concrete structures, the damping ratio is 0.03. For pipe truss structures with complex shapes or large spans, multi-dimensional random vibration analysis methods and multi-dimensional response spectrum methods should be carried out. or time course analysis.

Calculation Software
At present, STS, STCAD, MST 2006 and 3D3S are software that can perform preprocessing analysis on truss structures and process joint design drawings. The STS truss module can easily establish a plane truss model, but it cannot establish a space truss model. STCAD's modeling and model editing functions are powerful, but it is inconvenient to operate, the section definition and grouping are cumbersome, and the node design parameters are rich. The truss model of MST2006 basically uses the network Calculation function of the frame model. 3D3S can easily input element, node and local element loads. The loads of various working conditions can be converted from surface loads to node loads by means of guided loads. Wind load can automatically take into account changes in wind pressure, height and wind vibration coefficient. The most commonly used calculation software in engineering is 3D3S.