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The curved surfaces of the upper and lower layers of the double-layer cylindrical space frame are mostly three-centered circles, and the primary forms are triangular pyramid system, quadrangular pyramid system, cross truss system, etc. The triangular pyramid system is divided into a triangular pyramid space frame and an evacuated triangular pyramid space frame. The cross truss system mainly includes a two-way orthogonal positive space frame, a two-way orthogonal oblique space frame, and a three-way space frame. The quadrangular pyramid system is mainly divided into positive placement quadrangular pyramid space frame (Fig. 1-1), evacuation positive placement quadrangular pyramid space frame (Fig. 1-2), etc.
Figure 1-1 Upright quadrangular pyramid space frame
Figure 1-2 Evacuation and positive placement of quadrangular pyramid space frame
Among them, the upright quadrangular pyramid space frame is arched by the positive quadrangular pyramid space frame to form a cylindrical space frame structure with a certain curvature. It takes the quadrangular pyramid as the structural unit, the connecting rod at the top of the cone is the lower chord, the cone edge is the web rod, and the four sides of the cone bottom are the structural upper chord. The cylindrical space frame structure is mainly subjected to one-way force, and the load is transmitted to the longitudinal support along the span direction, and the force transmission path is clear and clear. The positive quadrangular pyramid space frame is uniformly stressed. Compared with other quadrangular pyramid space frames, the space rigidity is large, the layout is uniform, the standardization of components is high, the types of rods are few, and the joint structure is relatively simple. It is a commonly used space frame structure form.
The evacuated positive-placed quadrangular pyramid space frame is based on the positive-placed quadrangular pyramid space frame, usually, along the span and length direction, every 1 quadrangular pyramid unit is separated by evacuating the cone edges and lower chords of one unit. The upper chord is not evacuated due to the need to lay the roof purlin structure. It is still a stable structural system, and its overall rigidity is slightly weaker than that of the square pyramid. This form of evacuated quadrangular pyramid space frame has fewer rods, a simple structure, and shortens the installation period, but the rigidity is reduced compared to the positive quadrangular pyramid double-layer space frame.
Most of the existing evacuation methods are along the span and length directions, and every four pyramidal units are separated from each other to evacuate the cone edge and lower chord of a unit. We will establish a variety of structural models of different evacuation forms through the steel space structure design software 3D3S for comparison, and expect to obtain a better evacuation plan. The double-layer cylindrical space frame steel structure is subjected to relatively large forces near the support, at the intersection of the cylindrical space frame and the gable, and at the mid-span top of the space frame. In order to ensure the stability and rigidity of the structure, the above three local rods are not evacuated.