Problems in the design of portal steel frame structure

With the rapid development of the national economy, China's steel production has increased significantly. Welding H -shaped steel is used in large quantities, and the application of portal steel frame structure in industrial or commercial buildings is becoming more and more widely used. The SAFS steel structure discusses the problems in the design of the portal steel frame structure industrial plant through the practice and exploration of many projects, and gives corresponding solutions and suggestions on related issues.

1 Overview

With the rapid development of the economy, portal steel frame structure houses have emerged quickly in my country due to their processing system, easy installation, and fast. However, due to the late starting research on light steel structure in my country, the relevant design specifications of the "Technical Regulations for Steel Structure of Light Housing Housing Housing" in the relevant design specifications are also relatively lagging. Prior to this, you can only design the "Steel Structure Design Specifications" (GBJ17-88) and "Technical Procedures for Cold Bend Thin Wall-Wall Steel Structure" (GBJ18-87) and relevant foreign regulations. Therefore, there is a large gap with Western developed countries in terms of design level, design experience and rationality. In recent years, domestic scholars have conducted a lot of exploration and research on the design of portal frame steel structure, and have achieved fruitful results. With the implementation of the "Technical Regulations for the Steel Structure of the Steel Light House" (CECS102: 2002), the corresponding practical design software has been continuously developed. Software such as portal frame steel structure light housing design system PFCAD, steel frame light housing design CAD system PS2000, PKPM, and 3D3S developed by Tongji University can analyze and calculate the portal frame steel structure. Because the design specifications are not the same as foreign abroad, we cannot copy foreign design specifications when we design, and apply foreign design software. Therefore, it is particularly important to explore the optimization design calculation method that is in line with the domestic steel frame cross -section optimization design and reduce the construction cost of the portal frame steel structure.

In recent years, a large number of portal frame steel structure have been adopted in factory design practice. Through the practice and exploration of these projects, they have also accumulated some experience and understanding. This article discusses some problems encountered during the design of the portal frame steel structure.

2. The main problems and solutions existing in the design of the current portal frame steel structure plant

2.1 The problems and solutions existing in the structure model

In the design of light portal frame steel structure, the intermediate column is often designed as the upper and lower nodes in the form of a hinge. At this time, the middle column only plays the role of the middle support in the beam. Regardless of the bending moment, the calculation length coefficient is 1, and the cross -section is greatly reduced compared with the rigid connection. At the same time, the hinge connection structure of the column and the beam is greatly simplified compared with the rigid connection structure, and it also saves a lot of steel. If the column is high, the pillar is shifted under the influence of the wind load. The pillar's foot should be rigid, and the connection between the middle column and the beam should also be used. When the span of the beam is large, it is advisable to use a broken beam. The height of the beam should not be less than 1/35-1/40 of the span. The height of the middle section of the beam should not be less than 1/60 of the full span. The length of the cross section calculated from the end of the beam can generally be 1/5 to 1/6 of the span, and it should be coordinated with the pitch.

The anti -wind column is the main component that supports the gables in the portal frame steel structure and resist the horizontal wind load. The upper end of the anti -wind column is connected to the rigid beam, and the lower end has set the foundation separately. The design methods and structural measures of the wind column not only affect the stress characteristics of the windy column itself, but also affect the rigid shelf and basic design and force connected to it. There are two ways to connect the wind column and the foundation. When hinged, the foundation only bear a small axis and horizontal shear power. The design and structure are very simple, and the amount of engineering is small. If it is just connected, the shaft force and bending moment passed to the base are much larger. The eccentric distance is also very large, which is not conducive to basic design; therefore, the windy column should be hinged.

2.2 The problems and treatment of irregular buildings

The size of the building mainly includes the span, column distance, eaves height, and roof slope of the rigid frame. For portal frame housing steel structures, unreasonable building size often leads to a sharp rise in steel volume and increased costs. In addition, due to the flexibility of the production of steel structure components and the construction of light houses (wall) surface materials, the production and construction of portal frame steel structure houses can basically be tailored.

The "CECS102: 2002: 2002) (CECS102: 2002) (hereinafter referred to as" door -type steel frame regulations ") is recommended to use the pillar distance of 6 ~ 9m. Vertical loads (such as roof loads, hanging loads, crane loads, etc.) are the main factor affecting the pillar distance of the economic column. When the load is large, the pillar distance of the economic pillar will decrease, and the economic column distance of the load will increase. When the load conditions are the same, the economic column is not obvious by the span, that is, the economic column distance of the various span -rigid systems is basically the same. However, the larger the span, the more sensitive the amount of steel is used to the column, and the range of fluctuations is increased. The better the good economic benefits presented by the economic column distance.

The portal frame steel structure system also has economic spans, so it is not advisable to blindly pursue large spans. The main factor affecting the economic span is load. The larger the load, the more sensitive the amount of steel is used to the span. The more you should pay attention to the reasonable span. This is because the large -load -large column section is large; the economic span of the portal frame steel structure is 18-30m, the economic span is 24-30m when the tonnage of the crane is large, the tonnage without a crane or a crane is small, and the economic span is 18 ～ 21m. Therefore, the use of reasonable spans can also save steel, reduce the total cost, and economic benefits are considerable.

2.3 Solution of deformation problem

Table 3.4.2-1 from the "Portal Frame Regulations" can be found in the limit of the design value of the rigid columns. Top allows a lot of displacement. This is the difference between light steel structure and ordinary steel structure. However, among the crane factories, especially in the large tonnage crane factory building of more than 20T, when the pillar top allows deformation, the pillar height affects this factor. The absolute value of controlling its horizontal displacement is within a reasonable range to ensure the normal use of the plant.

2.4 Discussion on issues related to node design

The connection node of the portal frame steel structure beam and the rigid column, according to the "portal frame steel structure regulations", can be divided into three methods: end plate vertical, end plates, and oblique end plates. Each form can be divided into two methods: end plate flat and end plate extension. In order to reduce the thickness of the end plate, the rib should be set up between the end plate to connect the bolt, so that the support boundary form of the end plate is on both sides or three sides, thereby increasing the intensity and stiffness of the connection node. In the portal frame steel structure with cranes, its structure should conform to the principle of the beams and columns in the process of use, that is, the so -called rigid connection node. If the construction conditions permit, the beam and column nodes are best to use the bolt -welded connection node, that is, the wings are connected to the welding seam, and the web plate is connected with a high -strength bolt.

It is important to note that although the pillar and the beam are envisaged as a rigid, in fact, due to various factors, the calculation assumptions may not match the actual situation. For example, the connection between the step -shaped upper columns of the crane plant and the roof beam. Compared with the section of the beam end, the cross -section height is often smaller. Although the high -strength bolt is used to connect the node design according to the calculation of a rigid connection, it seems to be just connected, but because the cross section of the beam is far greater than the connected column section height, the two rigidity ratio is very different. The pillar rigidity is small, and the beam cannot be well -embedded, and it cannot have the ideal stiffness. This makes this node similar to the state between the fixed connection and the hinge, and the embedded solid at the end of the beam at the top of the column must be guaranteed with a sufficient stiffness of the column itself.

In addition to the connection node of the rigid beam and the rigid column, the stitching nodes of the rigid beam are selected in the small parts of the bending momentaries, and the manufacturing and transportation unit often takes 8-12m. The results of practice and experts show that the connection method of external extension and rib end plates is more reasonable. In order to reduce the difficulty of bolt arrangement during the design of the end plate, the 10.9 -level friction -type high -strength bolt should be preferred. The steel number of the bolt can also be selected with 20mntib, or No. 40 steel and 35VB steel are selected.

3. Conclusion

The portal frame steel structure houses are widely used in various buildings with large span, light weight, fast construction speed, low comprehensive economic indicators, and wide scope of application. With the extensive application, there is a certain accumulation of experience. However, there are many problems worth discussing, such as the impact of welding form on the performance of components; these problems require engineering and technical personnel and researchers to work together. The above is the summary of some design experience in the design process. I hope to get the correction of experts.