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Problems that should be paid attention to in space frame structure design (Part 2)

3.4 Calculation program of space frame structure

At present, the commonly used space frame structure calculation software in China includes: 1) MSTCAD; 2) SFCAD; 3) MSGS, etc. These three calculation software can meet the space frame structure design of general engineering. The current space frame structure software usually consists of three parts: pre-processing, analysis and calculation, and post-processing. However, it is best to use one software for trial calculation and then use another software for checking calculation.

Member design and node construction of 4 space frame structure

In general engineering, most space frame structures are made of steel, mostly Q235 and Q355 steel, which have good mechanical properties and welding performance, and the material is relatively stable.

(1) There are many cross-sectional forms of rods, but the empty stomach loading surface is the best, such as rounded steel pipes, square steel pipes, etc., and the moments of inertia of these two cross-sections are large. It is beneficial to the force. In addition, after the fasting section is closed, the interior is not easy to corrode, and the surface is also difficult to accumulate dust and water. It has good anti-corrosion performance.

(2) Section selection and construction requirements of the member. There should not be too many specifications for the cross-section of the member selected for a space frame. Generally, 2 to 3 types of space frames with a small span are suitable, and it is not suitable to exceed 6 to 7 types of space frames with a large span. The supplied specifications and the length of the rod are related to the grid size of the space frame. In addition to considering the production of the roof panel, the commonly used fixed length should also be considered to avoid waste caused by excessive length. If the section of the bar is too small, it is easy to produce initial bending that is unfavorable to the force, so there is a minimum section requirement for the bar of the space frame. When designing rods, it is advisable to avoid dead corners that are difficult to inspect, maintain, and accumulate moisture or dust. For tubular sections, both ends should be closed. Tension rods generally should not have joints, and compression rods should not have joints. If it must be provided, only one joint is allowed for compression rods, and this joint should be located in the area of less stress and avoid excessive concentration of joints.

(3) Node construction and design of the space frame structure.

The nodes of the space frame structure play the role of connecting the cross members and transferring the load. Therefore, the node design of the space frame structure is an important content in the design of the space frame structure.

Reasonable node design has a direct impact on the safety performance, fabrication and installation, project progress and project cost of the space frame structure. The nodes of the space frame structure are divided into two types: internal nodes and support nodes. Their design and structure should follow the requirements of reasonable force, clear and reliable force transmission, simple structure, and convenient fabrication and installation. The space frame structure nodes include welded steel plate nodes, Welded hollow ball joints, bolted ball joints, direct intersecting joints and welded steel pipe joints.

Welded hollow ball joints are one of the earlier joints used in my country. It can be a hollow ball without ribs or a hollow ball with ribs. The welding of two hemispheres and the welding structure of two hemispheres and ribbed rings, the hollow The size of the ball diameter should be able to arrange all the connected steel pipes on the surface of the ball and ensure that the gap between the rods meets the relevant requirements. The steel pipe is connected with the hollow ball, and the steel pipe should be cut open, and a certain gap should be left between the two for penetration.

The bolted ball joint is the most widely used joint form in my country. It is composed of bolts, steel balls, pins, sleeves and cone heads or sealing plates, and is suitable for steel pipe connections. The design and construction of bolt ball joints include the selection of part materials, determination of steel pipe diameter, calculation of high-strength bolt bearing capacity, calculation of rod sleeves, determination of outer dimensions of sleeves, construction of cones or sealing plates, and construction of pins wait.

The size of the steel ball depends on factors such as the diameter of the bolt, the angle between adjacent rods and the length of the bolt extending into the sphere, and it is required that the adjacent bolts extending into the sphere do not collide. The high-strength bolts are determined according to the calculation of the tensile bearing capacity. For the compression rods, the pressure is mainly borne by the sleeve, and the diameter of the high-strength bolts can be appropriately reduced. Come pull the pressure. When the pipe diameter of the rod is > Φ76mm, it is advisable to use the conical head connection, otherwise the sealing plate connection can be used. The pin is not stressed after the space frame is installed, and it bears the shear force when the sleeve is rotated, and the magnitude of the shear force is related to the frictional resistance of the bolt extending into the steel ball.

The support node is the connection piece through which the space frame transmits the load to the substructure. It is the space frame node on the supporting structure. When analyzing the internal force of the space frame, certain constraints must be added to the support node. These constraints are generally Movable hinge support, fixed spherical hinge support and fixed cylindrical hinge support. In actual construction, the design of support nodes should be clear and reliable in force transmission, simple in structure, and consistent with its calculation model.