Research On Secondary Stress Of Pipe Truss

Steel tube arch truss, which has merits of definite load condition, concise calculation model, convenient construction, economical use of steel, etc, is a popular structural form in large-span structure system at present. In recent years, this modern structure presents in hallways, airports, gymnasiums, meeting exhibition centers and other designs with its concision, fluency, and beautiful visual effect.At present, in ordinary steel structure design of truss, the method that we adopt generally is to calculate according to ideal pin-connected model, thus draw the sectional stress of each pole, and we can choose the type of suitable pole according to these sectional stresses. While calculating the internal of the truss, generally the basical assumptions are adopted as follows:(l)the nodes are pin-connected; (2) the axises of the poles are straight and intersect at the center of node;(3) the action line of the load passes the node of truss .All axises of the poles and the action line of load in the planar truss must be in the same plane. If the truss accords with the above-mentioned assumptions totally, its internal force is axial force only, and the stress caused by axial internal force of the pole is called direct stress. But in the factual structure, these assumptions aren't correct absolutely. Generally speaking, the poles intersecting at the joint of the truss are connected whether directly or by nodal board, the joint is difficult to be deemed to pure "pin-joint", and the tip of the pole has certain rotating restriction more or less. Apart from axial force, the actual truss structure also have secondary stress: bending moments and shear forces, the secondary internal force generated by the secondary stress. The secondary stress generally caused by truss structure's rigid nodes, eccentric nodes, lateral load, and so on.In this paper, using large-scale finite element analysis software ansys9.0, the distribution of the secondary internal force of flat plane truss under the load is analyzed, the relative displacement of bar ends which cause the secondary internal force are given, the factors of its distribution which are explored are structural load, linear stiffness, the length of the bar; the distribution status and distinction of the secondary internal force of the several common truss forms is discussed , the relationship between the truss shape and the secondary internal force is revealed; the distribution of the secondary internal force of space truss is discussed in the basis of the plane truss, according to a actual monitoring of a large-span stadium, three simplified space models for the calculation of space steel truss are recommended, and some ideas on calculation and design of steel truss are proposed .