In study and work, everyone will inevitably come into contact with papers. Thesis is a tool for the exchange of academic achievements. I believe many friends are very upset about writing papers. The following are the design points of the long-span portal frame structure workshop I collected for your reference, hoping to help friends in need.
abstract:
With the continuous development of modern society, the construction technology of factory buildings is also improving. Many enterprises use long-span portal frames when building factories. Because of its low cost, beautiful appearance and simple installation process, this kind of building structure has been highly valued by many construction enterprises, even in many high-rise buildings, warehouses and exhibition halls. Based on this, this paper mainly discusses the design and application of long-span portal frame light steel factory building, studies its design points from two aspects of structure and application, and makes a comprehensive study on some problems needing attention in the design of light steel factory building with rigid frame, and puts forward corresponding suggestions.
Key words:
Portal rigid frame; Workshop design; Application; Suggestions;
1, Introduction
Compared with the traditional workshop, the long-span portal frame workshop has the advantages of less workload, high comprehensive benefit and convenient disassembly, which can save a lot of costs for enterprises, is suitable for all kinds of enterprises and has a shorter construction period. If the enterprise wants to build a factory building quickly, the long-span portal frame light steel factory building is a very good choice. In recent years, many enterprises have begun to design long-span portal frame light steel factory buildings, but there are still some quality problems in the current engineering construction. This paper expounds the technical points of portal frame design in detail, hoping to bring some thinking and inspiration to all enterprises.
2. Characteristics and application scope of long-span portal frame structure.
In recent years, the industrial production level has been improved year by year, the manufacturing and processing conditions have been effectively improved, and the overall industrialization process has entered a new era. The technical content and application value of the construction industry have been improved by leaps and bounds. The long-span portal frame light steel factory building is a color steel plate structure. Because of its light weight and good seismic effect, it meets the requirements of vigorously developing green buildings in China and is favored by many architects. In particular, this kind of building structure has unique advantages, which brings higher safety performance and economic benefits to enterprises. At present, all walks of life in China have begun to increase the application of long-span portal frame light steel factory buildings, adopting mature steel structure technology, combining information, intelligence and humanization, making the development prospect of long-span portal frame light steel factory buildings more clear. At present, the code applicable to long-span light steel factory buildings with portal frames is Technical Code for Steel Structures of Light Buildings with Portal Frames, which specifies in detail that the span of portal frames should not exceed 36m, and the height of the whole building should be 4 ~ 9m, and the rigid structural equipment of the whole building should be further strengthened.
3. Design points of long-span portal frame workshop
3. 1, saving cost and reasonable layout structure.
Under normal circumstances, the long-span portal frame factory building is generally determined according to the actual use and technological requirements of the building, generally 9 ~ 35 m, with a span of 20 ~ 30 m, with the highest cost performance. Generally, the steel consumption of rigid frame depends on its spacing, but the steel consumption of crane beam will increase with the increase of rigid frame spacing. Compared with the previous construction experience, it can be found that 5 ~ 8m span is used without bridge crane, and large column spacing is often used for large span, and 3 ~ 5m is the most suitable. If a crane with a height of 10t or a heavy suspension load is used, the column spacing is about 6m.
The average height of portal frame is 4 ~ 9m, and the overhead crane shall not exceed 12m. The roof slope is1/8 ~ 211,and the roof drainage meets the production requirements. Taking the smallest slope as far as possible can effectively reduce wind load and save building materials. If the wind load is not very large, the rigid frame can be appropriately reduced under the condition of low building height.
If the design span of the factory building is not very large, the form of single ridge and double slope can be adopted. In other cases, a purlin is needed on both sides of the roof, and an extra purlin is needed for an extra roof. At the same time, it is necessary to increase indoor drainage materials to avoid wind and rain, which will lead to water accumulation and snow accumulation in the workshop and increase the load of the workshop. If the load is too large, it will leak to the workshop and affect the enterprise. Therefore, from the perspective of saving costs and increasing economic benefits, the method of multi-ridge and multi-slope can be adopted.
3.2, component section design
In order to give full play to the role of materials, according to the structural design of long-span portal frame, steel is saved. Generally, beams and columns with variable cross-sections are used, and the cross-section height and web thickness are changed when necessary. When there is a bridge crane, the column adopts equal section members, the roof load is light, the steel beam span is large, and the I-section is mainly shear in the flexural members. For portal frames, the buckling strength of the plate should be fully utilized. When the cross section does not meet the requirements, the flange plate should be thickened first, which can achieve better economic results. The design can also simplify the column foot structure of portal frame, reduce the foundation requirements and further reduce the project cost. If there is a bridge crane, the lateral stiffness is strictly required, and the column foot should be designed as a steel joint.
3.3, the layout and structure of the supporting structure
The support system of long-span portal frame includes rigid tie bars, inter-column supports and lateral supports. The whole knowledge system can ensure the overall stability of the rigid frame and transfer the longitudinal horizontal load to the foundation. When setting the bracing between columns, the transverse bracing of the roof can be set at the same time to form a geometrically invariant system, and rigid tie rods can be set at the corner of the rigid frame. If the columns of the workshop are high and there is no crane, double-layer supports between columns can be set according to the included angle of the supports, and the included angle between the supports and the water surface should be kept at 30 ~ 60. As a longitudinal tie rod, the crane has no lower support for the upper and lower columns to reduce the temperature stress of the crane beam. Once the angle of cross support between columns is less than 30, the upper column support can be herringbone or W-shaped. In the workshop without crane, the cross round steel support of tensioner can be used. When there are cranes over 5t, cross round steel supports should be adopted, and longitudinal roof supports should be set to improve the lateral rigidity of crane beams.
3.4, Angle brace Settings
During construction, it is necessary to consider that the rigid frame beam may be compressed, and bearings must be set on both sides of the compressed beam as lateral support. In the actual construction process, corner braces are often used as out-of-plane fulcrums of steel beams to reduce the stress of steel beams, improve the stability of the whole building structure, appropriately reduce the supporting length and increase the internal force. Angle braces shall be set during construction to ensure the installation accuracy. Generally, every 1 purlin is provided with 1 gusset, and the spacing is 2 ~ 4m. When designing angle braces, we should also pay attention to the following issues:
First, if the section of the steel beam is large, the strength of the gusset should be accurately calculated according to fixed rules.
Secondly, the purlin thickness of the gusset connection is not easy to be too thin. If it is less than 2mm, the steel beam cannot be supported. Therefore, it is necessary to calculate the local bearing capacity of purlins in advance.
Thirdly, whether the calculated length of steel columns with angle braces can be measured by spacing is still controversial. Without experience, it is suggested to take 1. 1 double brace spacing [1].
3.5, long-span portal frame end plate connection design
In order to improve the convenience of construction, the commonly used rigid frame span is 15 ~ 36m, and it is assembled and installed on site by means of transportation and processing. In the installation process, the connection characteristics of end-plate structure are involved, in which end-plate connection is the most cost-effective way in the whole node connection design, and it is widely used in long-span light portal frames. Compared with flange splicing and common web splicing, end-plate connection can reduce the material cost and increase the overall structure. There are three forms of end plate splicing, namely vertical, inclined and horizontal. The end-plate connection also tests the bending moment and shear force it bears. According to the maximum stress design, high-strength bolts shall be adopted, and the connecting bolts of end plates shall be symmetrically arranged, with no less than two rows. The thickness of the end plate should not be less than 1cm. The welding of flange and end plate adopts full penetration butt welding technology to ensure the welding quality.
3.6, roof live load value
At present, the design structure of long-span portal frames used in the market is mainly formulated according to relevant design specifications. Through investigation, it is found that the live load in the steel structure design code is 0.5kN/m2, but if the load area of the member is large, the multiplier reduction factor is 0.6. The long-span portal frame meets this condition, and the live load is 0.3kN/m2.
This data is very different at home and abroad. The design of this kind of house abroad needs to consider the additional load of 0. 15 ~ 0.5 kn/m2, but there is no such description in the design content of our country. Therefore, the column beams of some factory buildings are too thin, so the load is deducted. If you encounter bad weather such as strong wind, it may exceed the load quota, which may easily cause workshop safety problems. Therefore, when building a long-span portal frame, we must pay attention to the value of the live load of the house, and we can't deduct the load blindly to ensure the stability of the factory building.
3.7, need to calculate the reasonable span.
Span problem affects the stability of factory building structure to a great extent. Because there may be a big gap in the use of different production processes, some enterprises even hope to rationally allocate the form and size of the factory building according to their own use requirements. In this case, it is necessary to calculate in advance which span can help enterprises save costs and meet the production process requirements as much as possible. To determine a reasonable span according to the height of the house, the beam height and load should be calculated first. After the two values are determined, the steel consumption of long-span rigid frame will increase appropriately, but the overall cost will be lower, which can further save space, so the comprehensive effect is good. Through calculation, it is found that if the cornice is too high and the span is too large, setting the pendulum column in the middle can save about 20% of the steel consumption compared with the single-span rigid frame, and a more economical span should be chosen in the design [2].
3.8, the determination of the rigid frame spacing
The interval between house prices is related to factors such as the load span of the house. Choosing a larger spacing will find that the amount of steel used in purlins is not economical. In order to meet the specification requirements, the spacing of rigid frame columns is 6 ~ 9m.
3.9. Wind-resistant measures for column foot
In practical engineering, it is occasionally heard that rigid frame columns are uprooted in strong winds. In fact, the main reason is not that the load is calculated incorrectly, but that the force transmitted to the column foot is forgotten when supporting the column. Especially, the vertical dimension of the building is small, and only a few columns are involved to resist wind load, so the support will bring great tension to the column foot. Without reliable fixing measures, the column foot is likely to be uprooted. Therefore, in areas prone to strong winds, special attention should be paid to the wind-resistant measures of the column foot, such as setting tracing bolts at the end of the column foot and setting tracing plates [3].
3. 10, fire protection design
As we all know, although long-span portal frames have many advantages, their fire resistance is poor, especially when the workshop temperature changes greatly, the internal buckling strength and elastic modulus will decrease with the increase of temperature. In the case of sudden fire, the steel structure of the factory building will lose its bearing capacity because of the rapid temperature rise, which will lead to the collapse of the factory building. In order to improve the stability of steel structure at high temperature, it is necessary to take protective measures for steel structure. It is necessary to classify the fire risk, and all designers should determine the fire protection grade of portal frame and light steel factory building. At the same time, according to China's norms and protection requirements, ensure the quality of steel members and avoid the negative impact of high temperature on steel structures to the maximum extent. At the same time, the measures of coating fireproof materials on the surface of steel structure can also be adopted to improve the fireproof performance of steel structure workshop. In addition, the design of steel structure should proceed from the overall situation and consider the design work from multiple angles, such as setting emergency exits of evacuation elevators according to the requirements of national codes, so that employees in the factory can be evacuated in the shortest time in case of sudden fire, avoiding the economic losses of enterprises and ensuring the personal safety of employees.
3. 1 1, waterproof design.
The material required for long-span portal frame workshop is metal color steel plate. Although it is beautiful, the waterproof problem has always existed. It is very necessary to build a long-span portal frame factory building and do a good job in waterproof design. Because of the large thermal conductivity of metal color steel plate itself, when the external environment in contact with it changes greatly, it will produce a certain temperature difference change, which will cause the color steel plate to shrink, thus generating displacement errors at the interface, so it is very easy to have water leakage problems, and the interface of color steel plate is a high-incidence area for water leakage problems. In the steel structure system, the steel structure itself is prone to temperature change, deformation due to external forces such as wind load, and water leakage at the fulcrum joint. Due to the different connection of materials, the stress caused by temperature change in special parts is not synchronous, so it is necessary to repair the hidden water leakage in time. For the waterproof design of metal color steel plate, we should take the way of leading first and then blocking, attach importance to the whole design and construction process, and take the waterproof project as a systematic project. In the design stage, many factors such as slope, slope length and components should be considered, and the specification of color steel plate should be adopted scientifically. Design a reasonable section and enough water drop points, and introduce detailed waterproof structural measures to reduce the possibility of water leakage theoretically. In the construction process, the construction personnel should also improve the design and supervise the construction links during the construction process. Once the problem is found, it should be rectified in time, checked and accepted, recorded in the house watering test, and the construction quality should be strictly controlled. Even after acceptance, it should be overhauled regularly to ensure that there is no hidden danger of water leakage before it can be put into use [4].
3. 12, calculate the lateral internal force of the rigid frame.
At present, there are many methods to choose from in the process of calculating internal forces. Elastic analysis method is usually used to calculate the internal force of portal variable cross-section rigid frame structure. Although the required parameters can be obtained by other calculation methods, the basic accuracy of calculation is not as high as that of elastic analysis method. In addition, plastic analysis is also a common method, but this method is only used to calculate the internal forces of all steel columns with equal section in rigid frames. In the concrete calculation process, the finite element method of element bar system is usually used, and the parameters needed for calculation are relatively complicated, so the effects produced in the earthquake process can be determined by this method. At the same time, the internal force results are determined according to different load conditions. In the process of concrete analysis, it is necessary to determine the specific combination of different loads, and the internal force results caused by different combinations are also very different. In the calculation process, try to find out the internal force combination of the control section, and control the cross section position of the top of the bottom connecting column and the cross section of the beam. Finally, there are relatively many influencing factors of lateral internal force. Therefore, it is necessary to determine which factors are the main influencing factors and which are the secondary influencing factors in the calculation process. Because elastic analysis method is usually used to determine them in the calculation process, only the value of standard load needs to be obtained in the specific calculation process. Although some other data will also have some influence on the final result, such as the coefficient of partial load, the complexity of this coefficient is relatively high, so the calculation and analysis results of lateral internal force of rigid frame are very important for the construction of rigid frame structure in the calculation process. In the later construction process, it is necessary to choose the corresponding construction location according to the specific value of displacement measurement, so we must pay attention to this process.
4. Conclusion
In short, due to the late development of steel structure enterprises in China, many construction details may have to be determined after many calculations in actual design, and many workers are not rich in construction experience, which leads to unsatisfactory construction effect and low overall structural stability. Therefore, designers need to further learn the knowledge of steel structure, change the design concept, improve the existing problems, ensure the improvement of engineering design quality, and promote the further development of new portal frame steel structure in China.
refer to
[1] applied research on plastic bearing capacity of long-span [J-shaped frame inclined beam] in Liang Huixi [D] Shenyang: Shenyang University, 20 17.
Jaco. Design and analysis of long-span portal frame structure [D] Handan Hebei University of Engineering, 20 14.
[3] Research on wind-resistant optimization design of Dong Chao super-long-span [J-shaped rigid frame]. Guangzhou: Guangzhou University, 20 12.
Structural design of Pan Zhelin's long-span light steel workshop [J]. Zhejiang architecture, 20 1 1, 28 (03): 19-2 1.
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