Architectural design of large span steel structure workshop

The overall lifting of the large span structure means that the structure is assembled and formed on the ground as a whole, relying on the top of the vertical structure as the lifting bearing point, using the flexible steel strand as the lifting bearing cable, and using a special hydraulic jack as the power device to lift the lifting structure into place at high altitude. Construction molding method. Since the length of the lifting steel strand is not limited, the super-altitude and long-distance lifting construction of the structure can be realized. The introduction of hydraulic jacks also makes the lifting equipment not only has strong lifting capacity but also can achieve continuous and uninterrupted lifting. Because the assembly of the structure is carried out on the ground or at a low altitude, large-scale hoisting equipment is not required, high-altitude operations are avoided, and the amount of support can be significantly reduced, so the construction efficiency is high and the construction cost is reduced. It is a green construction technology.

1.Classification of large span building steel structures

Large span building steel structures are divided into three categories according to the difference in rigidity and their different combinations: rigid structure, flexible structure and hybrid rigid-flexible hybrid system structure. This paper mainly introduces the following two types of large span building steel structures.

Rigid long span building steel structure

The rigid long span building steel structure is composed of a large number of steel members, such as space trusses, space frame, etc., which can be divided into the following two types according to the different forms of structural units, one is called space grid structure, and the other is called space frame structure.

Flexible long span building steel structure

Flexible long span structures can be divided into the following three categories by their different force systems: vertical plane structure, horizontal plane structure and space structure. In the flexible steel structure, its force is relatively uniform, and the structural force is mainly concentrated in vertical, horizontal and spatially symmetrical positions, such as suspension cable structure, membrane structure and so on.

2.Problems existing in the design of large span steel structure buildings

2.1 Overall stability and local stability

In the stability design of steel structures, there are situations in which the overall stability and local stability of large span steel structures are not properly calculated. Although its stability calculation draws on past experience to determine the safety factor between the overall stability and local stability, it does not calculate a more scientific safety factor based on specific engineering conditions, so it cannot truly reflect The relationship between global stability and local stability cannot guarantee the stability of steel structure design

2.2 Uncertainty factors

In the design of steel structure systems, there are many uncertain factors that will affect the stability of the design, such as physical and geometric uncertainties, including materials (elastic modulus, yield stress, etc.), member size, cross-sectional area, residual stress and initial deformation, etc. When determining the geometric and physical quantities related to stability, most of the problems will be analyzed based on past experience, without considering the actual situation. In addition, when the designers analyze the steel structure, the assumptions, mathematical models and boundary conditions proposed are inconsistent with the current technological development level, and it is difficult to reflect them in the calculation, resulting in the difference between the theoretical value and the actual bearing capacity. At present, most of the problems dealt with by structural random influence analysis are limited to the range of determined structural parameters and random load input. In practical engineering, due to the uncertainty of parameters, there will be obvious differences in structural response.

2.3 Incomplete pretensioning system

The pretensioned steel structure system is another important component system in the stability design of the steel structure. In the past, the theory of pretensioning system was not very perfect. There was no complete and reasonable theoretical system to analyze the stability of pretensioned structures. Therefore, it was difficult to ensure the stability of the project. Therefore, it was necessary to establish a scientific and perfect pretensioning structure. Tension System Theory.

2.4 Beam-column stability design

In the stability design of reticulated shell structures, beam-column element theory has become the main design method. However, beam-column theory cannot fully reflect the stress state of reticulated shell structures, such as the coupling effect of axial force and bending moment. Beam-column is the most basic part in the stability design of the entire steel structure. Therefore, in the stability design of the steel structure, full attention should be paid to the stability of the beam and the column and the mechanical effect between them.

3.The main points of large-span steel structure building design

3.1 Reasonable selection of domestic high-quality steel

In recent years, my country has achieved obvious results in the construction of typical large span steel structures in buildings. Experience has also been accumulated in the attempt to use steel structures in the construction of major international competition venues. Nowadays, the number of high-rise residential or commercial buildings in my country’s urban construction has increased significantly. With the test of practice, it has been proved that the quality of my country’s steel is no less than that of foreign steel. In my country, the variety of high-quality steel is increasing, and the country has also promulgated industry standards in terms of steel quality and performance. With the development of economic construction, it is a development trend to gradually replace imported steel with domestic high-quality steel in the construction of steel structures in my country. There will be a large number of domestic high-quality steel enterprises to provide high-quality steel for my country’s construction industry.

3.2 Control of the safety level of steel components

With the gradual improvement of construction industry standards, there is also a theoretical basis for the reliability design of steel structures in the standards. In the process of steel structure construction, the safety level of steel components can be adjusted according to the actual situation. When it is necessary to change the safety level, make necessary adjustments. When the main components have hidden dangers, the safety level must be increased; when the secondary components are selected, the safety level can be slightly reduced. The general requirement is that the safety of the entire steel structure and the bearing capacity of the building must be guaranteed. In the event of earthquake force majeure damage, the overall structure of the entire building must be guaranteed to ensure the safety of people’s lives and property to the greatest extent. Under the premise of the safety of the steel structure, there is no need to excessively require the safety level of the steel structure.

3.3 Variable loads

In the large span building steel structure, it mainly includes the following variable loads

(1)Building live load. In general, the uniformly distributed live load of the building is calculated based on the horizontal projected area. For different building structures, the value of the uniformly distributed live load of the building is different. The standard value of the uniformly distributed live load of the building is 0.5, and the standard value of the uniformly distributed live load of the building is 2.0KN/m2. Considering the actual situation, the value of building live load is revised.

(2)Snow load. Large span structures are relatively sensitive to snow loads, and building snow loads account for a certain percentage of variable loads. Buildings with different structural forms have different snow load values, which are also related to the orientation of the building and the perennial wind direction. Under normal circumstances, the value of building snow load is less than the plane snow pressure, because the building has a certain slope, when the snow falls on the building, some have already slipped along the sloped building. However, some special structural forms of buildings will generate snow, which will increase the snow load. Therefore, when determining the snow load, the actual situation should be fully considered.

(3)Wind load. Under the action of wind load, the building will generate a certain pressure or suction, and the wind load has the dual characteristics of static force and dynamic action. Calculate the wind load value. The wind carrier coefficients of long-span structures are generally obtained through wind tunnel tests.

(4) Temperature effect. Different from concrete structures, steel structures have large thermal expansion and cold shrinkage properties. In some areas with large temperature differences, steel structures will deform due to temperature differences, forming a large internal load, called temperature stress. When acting, it should be considered according to different climatic conditions.      

(5) Displacement of the support. In the large span steel structure, the additional stress inside the rod caused by the displacement of the bearing cannot be ignored, and when the bearing has a large uneven settlement, it may cause local damage to the structure, and even endanger the safety of the entire structure. In the live load calculation, the additional internal force caused by the displacement of the support should be fully considered.

3.4 Accidental loads

When carrying out the mechanical analysis of the structure, the accidental load action should be fully considered, and the earthquake action is mainly considered in this paper. Seismic action is a kind of inertial action of buildings due to ground motion, which belongs to dynamic action. Differential equations are established through D’Alembert’s principle. Its size is related to both the natural vibration characteristics of the structure and the characteristics of ground motion. Large-span building steel structures are greatly affected by earthquakes. When designing the building structure, it is necessary to ensure that the rigidity of the roof structure and the supporting structure are uniformly distributed and have a clear force transmission route, so that under the action of the earthquake, the load on the structure can be passed through. The support is transmitted downward to avoid large torsion or other deformation of the steel structure, and to ensure the safety and reliability of the structure. In addition, seismic analysis should be carried out for the weak parts of the building, and reinforcement should be carried out to ensure that the force meets the requirements and is coordinated with the entire structure. Due to the large plane projection size of long-span structures, seismic traveling wave effects and local site effects should also be considered. Therefore, for large span space structures, it is a better way to set up certain seismic joints. According to the specific project scale and seismic requirements, the seismic check is carried out, and the seismic joints are set at suitable positions to resist the earthquake.

When designing the structure, the weight of the structure should be strictly controlled, and the natural vibration period should be fully considered in the selection of steel, and the natural vibration period of the structure should be as long as possible, so that the structure can release the energy input by the earthquake through deformation, In this way, damage to the structure due to seismic action can be reduced.