Structural form of quadrangular cone system

The upper and lower chords of the quadrangular cone grid are square (or rectangular near square) grid, staggered by half a grid, so that the corner of the lower chord grid is aligned with the upper chord grid of the form of the centre, and then in the upper and lower chords of the nodes are connected with the web, that is, the formation of the quadrangular cone system grid. There are five forms of quadrangular cone system grid:

(1) positively placed quadrangular cone space frame consists of inverted quadrangular cone, cone bottom of the four sides of the space frame for the upper chord rod, the cone rib for the web rod, the top of the cone connected to the lower chord rod. Its chords are orthogonal to the boundary, so it is called the orthogonal four-angle cone space frame. This kind of space frame rod force uniformity, spatial stiffness than other types of quadrangular cone space frame and two-way space frame, roof panel specifications, easy to arch, roof drainage is also easier to deal with, but the number of rods is more, the amount of steel is slightly higher.

Positively put the quadrangular cone space frame is suitable for building plane close to the square peripheral support, also applies to the roof load is large, large column distance point support and has a hanging crane industrial plant situation. Typical examples are Shanghai Jing’an District Gymnasium (40m×40m) and Hangzhou Opera House (31.5m×36m).

(2) Positively placed evacuated quadrangular cone space frame: positively placed evacuated quadrangular cone space frame is based on positively placed quadrangular cone space frame, in addition to the periphery of the grid does not move, appropriate to draw off some of the quadrangular cone unit in the web and chord rods, so that the chord space size is doubled. The number of rods is less, reducing the amount of steel, the evacuated part can be used as a light skylight, the internal force of the lower chord is about doubled compared with the positively placed quadrangular cone, the internal force uniformity, stiffness has decreased, but still meet the engineering requirements. Positively put the evacuation of quadrangular cone space frame is suitable for the roof load is light in the middle and small span space frame.

Shijiazhuang railway hub south station shed (132m×132m, column spacework 24m×24m, multi-point support) and Tangshan gear factory joint plant (84m×156.9m, column spacework 12m×12m, peripheral support and multi-point support combination) is the use of this form of spacework frame earlier typical examples.

(3) Obliquely placed quadrangular cone space frame: Obliquely placed quadrangular cone space frame of the upper chord at an angle of 45 ° with the boundary, the lower chord is placed, the web and the lower chord in the same vertical plane, the upper chord length of the lower chord is about 0.707 times the length of the lower chord. In the case of peripheral support, the top chord is generally under compression and the bottom chord is under tension. Fewer bars converge at the nodes (6 at the top chord nodes and 8 at the bottom chord nodes), and the amount of steel used is more economical, but due to the diagonal placing of the top chord grid, there are more types of roof panels, and it is more difficult to form the roof drainage slope.

When the plane aspect ratio is between 1~2.25, the lower chord internal force in the long span is larger than that in the short span; when the plane aspect ratio is larger than 2.5, the lower chord internal force in the long span is smaller than that in the short span. When the plane aspect ratio is between 1~1.5, the maximum internal force of the top chord is not in the middle of the span, but in the middle of the 1/4 plane of the frame. These internal force distribution laws are different from those of ordinary simply supported flat slabs.

When the diagonally placed quadrangular cone space frame is peripherally supported and there is no rigid connection around the periphery, an unstable situation will occur in which the quadrangular cone rotates around the axis, so it is necessary to arrange rigid side beams around the periphery of the space frame. When it is point-supported, closed side trusses can be arranged in the periphery, which is suitable for square or rectangular planes with medium or small span peripheral support or combination of peripheral support and point-support.

Shanghai Stadium practice hall (35m×35m, peripheral support) and a hangar in Beijing (48m×54m, three-side support, opening) adopt this kind of space frame structure form.

(4) Star-shaped quadrangular cone space frame: the unit of this kind of space frame is shaped like a star, and the star unit consists of two inverted triangular small trusses crossing each other. The bottom edge of two small trusses constitutes the upper chord of the space frame, and they make 45°angle with the boundary. There is a vertical rod at the intersection of two small trusses, and the vertices of each unit are connected as the bottom chord. Therefore, its upper chord is orthogonal diagonally placed and lower chord is orthogonal orthogonal placed, and the diagonal belly bar is in the same vertical plane with the upper chord bar. The top chord is shorter than the bottom chord and is reasonably stressed, but the top chord at the corners may be in tension, and the support there may be in tension. The force situation of the space frame is close to that of the cross beam system, and the stiffness is slightly inferior to that of the orthotropic quadrangular cone space frame.

Star-shaped quadrangular cone space frame is suitable for medium and small span peripheral support of the space frame. Hangzhou lifting machinery factory canteen (28m × 36m) and China Academy of Metrology wind and rain playground (27m × 36m) used in this form of space frame structure.