Roof Steel Structures of Long-span Public Buildings

In the process of building construction, many new architectural structures have emerged, which can fully meet people’s diverse needs for buildings, but in this process, higher requirements have been put forward for architectural design and construction. This also makes the design and selection of buildings more complicated, so under such circumstances, great attention must be paid to the selection and design of steel structures for long-span public buildings.

1 Project overview

The airport terminal building of a certain project has a novel and unique shape, which is divided into four parts: the main building, the street crossing building on the north and south sides, the two corridors on the south side, the connection building, and the north connection building; there are 29 aircraft seats on the station apron, and the air traffic volume is predicted as the design target year In 2020, it will meet the annual passenger throughput of 31 million person-times, and can obtain the C-level service level recognized by the International Air Transport Association during typical peak hours.

2 key factors for large-span selection

2.1 Beautiful appearance is first of all to fully reflect the large-scale structure in the shape. In ancient times, there were also some large-span buildings. For example, the Pantheon dome in ancient Rome is a typical structure of this kind However, at that time, long-span structures were built on the inside, so visually speaking, the characteristics of this long-span were not fully reflected, but at that time, people had already realized that in Among the long-span buildings, the large-span place and the external shape are not the visual effect produced by the simple combination of the external shape and the internal shape. In front of span buildings, people will feel very small and humble, because these buildings are made by human beings, so they will also feel the greatness of human wisdom.

2.2 Practical and durable structure Practicability and durability are the most basic requirements for buildings, and the requirements for durability are very high. First, the shape of the building must reflect a very strong rationality, and those unnecessary structures cannot be designed . Different use functions have very different requirements for architectural space design. Therefore, in this process, only by taking effective measures to fully handle the relationship between architectural functions and architectural space can it fully demonstrate its practicality. The second is to have a very strong resistance to some adverse natural factors, such as typhoons and earthquakes, etc. Only in this way can the safety and stability of the structure be better guaranteed.

  2.3 Lightweight structure The weight of the structure itself is relatively small because of its own structural characteristics and selected materials. New technologies and materials make the weight of the structure smaller and more practical. If you look at it from the appearance From a perspective, the membrane structure is the lightest of all structures, and many buildings built with the membrane structure have a light and flying visual experience. The rotary hook structure is usually used on bridges, so from the most intuitive feeling, it will also give people a sense of elegance. If compared with other methods, the reticulated shell shell structure will appear old-fashioned and old , and from the material point of view, they are basically steel structures, and they will be very light if the amount of steel is small.

2.4 Structural forms with reasonable force and large span are very common, and the composition materials of this structure are also relatively diverse. This structure will show great advantages in the process of application. The rationality of the structure is the first advantage. The composition The strength of this structure can fully play its positive role. The current engineering mechanics theory and building materials are constantly developing and improving, and the form of the structure has also undergone many changes. The least material can be used to obtain the most Good effect is also a main goal that people pursue, so in the design process, the material and form of the structure should also be reasonably selected, and the force should be more scientific and reasonable. In the design, we should use those structures with complex shapes but simple force structural form.

3 Roof steel scheme selection

3.1 The structure is light in weight and the steel has high strength. Although the bulk density of steel is about 3 times that of reinforced concrete, the strength of steel is very high. When the load and conditions are the same, the steel structure has light weight and is easier to build long-span structures. When all are the same, the weight of the steel roof is only 1/3-1/4 of the reinforced concrete roof.

3.2 The steel pipe truss has high rigidity and good geometric characteristics. The steel pipe truss has a thinner pipe wall, but a large section radius of gyration, so it has good compressive and tensile properties.

3.3 The appearance is beautiful. The steel pipe truss has the characteristics of simple, beautiful and light appearance, which is suitable for the architectural shape, internal space and visual effect requirements of this project. In addition, according to the layout and requirements of the building, combined with the rationality of the structure, the roof structure support system of the main building adopts the steel tube concrete column + tree support steel column system. The steel tube concrete frame column network in the departure hall on the top floor of the main building has a column spacing of 36m in both the vertical and horizontal directions of the terminal building. The four tree-shaped supporting steel columns on the top of the column convert the 36m steel tube concrete column network into a space frame of 18m in the middle. The two-way inverted triangular space steel pipe truss system is supported on the top of the vertical support column (that is, the two-way distance between the truss fulcrums is 18m).

4 Steel structure design calculation

The project structure adopts Tongji University’s “Space Steel Structure System CAD Software 3D3s” and MI-DAS/GEN two programs to carry out the overall calculation (modeling and internal force calculation and analysis) at the same time, and compare the calculation results generated by the two software with judgment. The load and main parameter values ​​of this project: The load calculated by the structure is composed of dead load, live load and wind load, and the temperature effect and earthquake action are considered at the same time.

(1) Dead load. In addition to the self-weight of the steel structure components is automatically calculated by the program, the roof dead load is taken as 1.0kN/m2: (the dead load above the main purlin).

(2) live load. The live load of the roof is taken as 0.5kN/m².

(3) Wind load. The basic wind pressure is 0.4kN/m2 (according to the 100-year wind pressure value). The shape coefficient of the wind carrier is selected according to the results of the wind tunnel experiment, and after comprehensive classification, unfavorable combinations are made. The minimum value is 0.2 in the mid-span, and the maximum value is 3 at the top of the edge of the overhanging eaves.

(4) Temperature effect. Since this project belongs to the long-span steel structure, the value of the temperature difference is according to the note in Article 210.2 of the “Code for Design of Steel Structures”, and the temperature difference At=~15~C is taken.

(5) Earthquake action. According to 8 degrees, class II site calculation. In addition to considering the horizontal seismic action, the vertical seismic action should also be considered.

(6) Structural importance coefficient: 1.1. The steel used in this project is Q355B seamless steel pipe. According to calculations, the minimum pipe diameter is 146~6, the maximum is 273~16, and the theoretical steel consumption is about 63kg/m2, which is more economical than ordinary steel structures. Under various load combinations, the maximum deflection is at the cantilever end of the truss, and the deflection value is 60mm (about 1/383), so the arching of 50mm was considered in the production and processing, which meets the specification requirements. Through the practice of this project, it can be seen that the steel pipe tree column + space steel pipe truss system can achieve a large span, meet the requirements of construction and use, and have good integrity and small steel consumption.

5 main node design

There are three main types of truss nodes in this project: one is directly welded intersecting nodes. Since there is no gusset plate in this kind of joint, steel is saved. In order to ensure the cutting accuracy and welding quality of the end of the branch pipe, it is required to use a space automatic parabolic cutting machine for cutting and processing. The upper chord of the truss is a “K” joint, and the lower chord is a double “K”. secondly, hemispherical nodes are adopted for tree-shaped column supports. The conventional hollow spherical joints are used for the support joints of the concrete-filled steel tube columns, so that many members meet on the spherical surface, and the welding seam overlap between the members is avoided. The finished anti-seismic fixed hinge support is used between the lower part of the ball and the top of the column. The advantage of this support is that it allows the node to have a certain rotation angle in any direction, so as to reduce the horizontal thrust of the tree-shaped column on the steel tube concrete column; the third is The main trusses supported by the tree-shaped columns are connected by pins. Its processing is relatively simple, and it is more consistent with the calculation diagram, and it is an extremely important node of this project.

The selection and design of long-span structures is a very systematic and complex problem. In the design and construction of architectural projects, such structures are usually special in shape, but they are unique in function. It is relatively complicated, so effective measures must be taken in the design to design it reasonably. Only in this way can better design effects be reflected, thereby promoting the wide application of this structural form.