Numerous examples in nature show the excellent structural properties of circular tubular shapes under compression, torsion, and multidirectional bending. It inspires people to break through the traditional steel structure design concept and combine the circular tube structure with the building appearance to form an attractive steel tube structure.
Large-space and large-span buildings such as gymnasiums, exhibition halls, airport terminals, subway stations, and large-scale industrial plants continue to emerge. Traditional reinforced concrete structures, masonry structures, wood structures, etc., are difficult to achieve such a large-span spatial structure.
1) Classification and characteristics of steel pipes
Seamless steel pipe (SMLS): The wall thickness can be thicker and the diameter and thickness are relatively small, which is its advantage, but the pipe diameter is limited, and the cost of large-diameter seamless steel pipes is relatively high.
High-frequency welded steel pipe (
ERW pipe): High-frequency welded pipe has good pipe shape, uniform wall thickness, high degree of automation, and low production cost, but the wall thickness is relatively thin and the pipe diameter is relatively small. It is especially suitable for making pipe truss structures in steel structures.
Straight seam welded pipe (LSAW) adopts double-sided submerged arc welding technology and is welded under static conditions. The quality of the weld is high, the weld is short, and the probability of defects is small. The steel pipe is expanded through the whole length, the pipe shape is good, the size is accurate, the steel pipe wall thickness range and the pipe diameter range are wide, the degree of automation is high, and the production cost is lower than that of the seamless steel pipe. It has broad prospects in steel structure bearing columns such as bridges, dams, and offshore platforms, super-span building structures, and pole tower mast structures.
Spiral submerged arc welded pipe (SSAW): The welding seam is distributed in a spiral line, and the welding seam is long, especially under dynamic conditions. It forms a certain angle with the axis of the steel pipe, generally between 30-70°. This angle is exactly the same as the shear failure angle, so its bending, tensile, compressive and torsional performance is far inferior to that of the straight seam submerged arc welded pipe. At the same time, due to the limitation of the welding position, the saddle-shaped and fish-ridge-shaped welds produced will affect the appearance. In addition, during the construction process, the intersecting line welds at the joints of the spiral welded parent pipe split the spiral seam, resulting in a large welding stress, thus greatly weakening the safety performance of the components, and the spiral submerged arc welded pipe should not be used in important steel structures.
2) Features of steel pipe structure
1. The section has biaxial symmetry, the section centroid and shear center coincide, etc. The moment of inertia of the section is the same for each axis, which has outstanding advantages as a bending and compression member.
2. The section is closed, the torsional rigidity is large, and the local stability of the plate is good. Especially the round pipe section is particularly effective against torsion.
3. The appearance is simple and smooth, the rods can be directly welded at the same point, and the gusset plate can be omitted to save steel.
4. Compared with the open section, the section has the characteristics of smooth surface, no dead angle and small external surface area, which is conducive to saving anti-corrosion and fire-resistant coatings, and is also convenient for dust removal.
5. The wind resistance coefficient of the steel pipe section is small, which has significant advantages when exposed to fluids (such as wind and water flow).
6. The inner space of the steel pipe structure is available. Filling the steel pipe with concrete (concrete steel pipe structure) can not only improve the bearing capacity of the component, but also prolong the fire resistance limit of the component (up to 2h on average); water injection in the pipe can use the internal water circulation for fire prevention; transmission of liquids, such as oil pipelines, Drainage pipes, etc.; prestressing cables can also be placed in the pipes to apply prestressing in the body.
3) Application status and prospect of straight seam welded pipe (LSAW) in steel structure
Status quo at home and abroad:
1. In 1947, the first modern steel tube structure offshore platform was built in the Gulf of Mexico, which opened the prelude to the application of steel tube structure;
2. The waiting hall of Stuttgart Airport in Germany adopts the tree-shaped support structure of steel pipe members and cast steel nodes, which has the characteristics of unique shape, simplicity and clarity;
3. The roof structure of the terminal building of Kansai Airport in Osaka, Japan adopts a curved triangular truss with a circular tube section;
4. In Bushleyn Palace, London, England, the exposed circular tube section truss transmits the facade load to the column, and water is injected into the tube section for fire prevention, which just makes up for the weak fire resistance of steel structure buildings;
5. The opening and closing roof of Skydome in Toronto, Canada and the high-speed railway station at Charles de Gaulle Airport in France are all famous steel pipe structure buildings.
6. China's Olympic venues represented by the Bird's Nest were completed, establishing a unique historic landmark building for the 2008 Olympic Games. The project used low-alloy high-strength steel Q460 for the first time. In addition, the hall columns of the National Grand Theater of China are made of fire-resistant and weather-resistant submerged arc welded steel pipes for the first time, which can not deform or soften at temperatures above 600°C, and can be protected from corrosion for a long time without any anti-corrosion operations outdoors.
Application prospects:
As a new type of structure, the steel tube structure has been developed rapidly in the world in recent years. In the last five years, the use of steel pipes in Europe has increased by 25%. Statistics from the North American Iron and Steel Institute confirm that as the U.S. steel industry targets the underlying commercial building market, the demand for steel pipe structures is also on the rise. Consumption is increasing at a rate of 5% to 10% every year.
In recent years, with the continuous growth of my country's steel production, steel structures, with their own advantages, account for an increasing proportion of buildings, and steel pipe structures have also made great breakthroughs. The pipe truss structure in the steel pipe structure is favored by people because of its unique advantages, and it is mainly used in some large public buildings at present;
It has great application potential in industrial plant columns and roof trusses, light steel structures and residential steel structures;
It has broad prospects in steel structure bearing columns such as bridges, dams, and offshore platforms, super-span building structures, and pole tower mast structures.
