With the rapid development of national economy, industrial buildings should constantly meet the requirements of modern large-scale industrial production and process renewal. In the past, a single function and a single architectural form can no longer meet the needs of the transformation of production methods, so multi-functional workshops such as joint workshops, flexible workshops and industrial buildings came into being. In addition, due to the shortage of construction land and the need of technological process, more and more multi-storey factories and even high-rise factories appear. Multi-storey factory buildings are characterized by large span, large load, many openings and multi-storey cranes. In the design process, some problems are worth summarizing and discussing.
Second, the main points of structural design of multi-storey industrial workshop
Due to the requirements of process layout, multi-storey factory buildings generally need large space, and the structure usually adopts frame structure. If there are more floors and process conditions permit, frame-shear structure can also be adopted. The principle of structural layout is: make the column network symmetrically and evenly arranged as far as possible, and make the stiffness center of the house close to the center of mass, so as to reduce the spatial torsion of the house. The structural system requires simplicity, regularity and clear force transmission. Avoid stress concentration and sudden deformation of concave corners and contraction, as well as excessive vertical extension and adduction, and strive to keep the stiffness in the vertical direction unchanged or not too sudden.
1. Controls the period of horizontal and vertical frames. Due to the large span direction and size, the multi-storey factory building has fewer columns; However, the direction of column spacing is smaller and the number of columns is more. Generally, it is horizontal control, so that the seismic capacity in vertical and horizontal directions is roughly the same, which is not only beneficial to earthquake resistance, but also makes the design more economical and reasonable.
2. Reasonably arrange the position of the elevator room. Due to the heavy equipment and goods and the need of vertical transportation, elevators should be set up in multi-storey factories. The rigidity of reinforced concrete elevator shaft is very large, so the eccentric influence of elevator shaft on the building should be fully considered, and the elevator shaft should be avoided at the corner and end of the building as far as possible in structural layout. When process layout is necessary and inevitable, measures should be taken to strengthen the surrounding floors and frames.
3. Multi-storey factory buildings in earthquake areas should be provided with few or no seismic joints. The expansion joints of buildings in earthquake areas are integrated. When the building is long, the following structural and structural measures should be taken to reduce the number of expansion joints and seismic joints. During construction, an 800mm wide 1400mm post-cast strip is set every 40m, and the position of post-cast strip is located in the section with the least impact on the structure; In the top floor, bottom floor, gables and walls with internal longitudinal walls which are greatly affected by temperature, the reinforcement ratio should be appropriately increased; Thicken the roof insulation layer or set the overhead layer to form a ventilated roof.
Third, the commonly used structural system
1. Frame support system. In other words, it is designed as a rigid frame in the horizontal direction, a column support system in the vertical direction, and the support between columns is used to resist horizontal load. This system is economical, but the support between columns may affect its use. This form is especially suitable for factories with long longitudinal direction and short transverse direction.
2. Pure frame system. The workshop is designed as a rigid frame vertically and horizontally, and there is no support between columns. Its advantage is that it does not affect the use space, but the disadvantage is that I-shaped columns are not suitable for columns, but are cross-sectional forms with little difference in inertia moments in two directions (such as box columns), and the steel consumption increases.
3. Steel frame-braced hybrid system. The difference between this form and the first form is that the longitudinal design is a mixed type of steel frame and support, and the horizontal force is resisted by both. This form can effectively reduce the longitudinal bending moment of columns, but it requires high floor stiffness, otherwise the deformation between columns will be uncoordinated and the support between columns will not be fully exerted.
Fourth, problems that should be paid attention to in structural design
1. Coordination of structural design and process design. Workshops are all for production. As a supporting specialty, the structural specialty in plant design must first meet the technological requirements, and the structural design can only obey the technological conditions. However, process designers often conflict with structural design when arranging processes. The place where the hole is opened is the frame beam, but the equipment could have been arranged along the beam, but it was arranged in the middle of the span. The proposed load is often too large, and sometimes even the load of equipment is proposed as uniform load. Especially in the scheme stage, structural designers should cooperate with the process well, try to understand the process layout and reduce many unnecessary troubles in design and construction.
2. Structural calculation. With the rapid development of computer software and hardware, complex structural calculation problems have been solved, and structural engineers have been freed from heavy and trivial calculation work. They can put a lot of energy into the selection and comparison of structural schemes, and reasonably determine the structural scheme and structural layout, thus improving the design level and quality and reducing the project cost.
Calculation of equivalent load of (1) layer. Load calculation is the condition of structural calculation, and the accuracy of load value is directly related to the accuracy of calculation results. For example, an engineering process puts forward that the floor uniform load is 15 kN/m2. According to the equipment layout and equipment weight of the process, the calculation method of floor equivalent load is given according to the specifications, and the calculated floor uniform load can be considered as 10 kN/m2. Because there are many differences between multi-storey industrial buildings and general multi-storey civil buildings in structural form and floor live load, the floor live load of multi-storey industrial buildings is greater than that of multi-storey civil buildings. Some small and medium-sized machine tools also have crane loads on floors, columns and beams. Its cross-column network is generally larger than civil buildings, and the story height is also relatively high. The biggest feature is that there is almost no internal partition wall in the whole plane. Multi-storey industrial buildings generally adopt cast-in-place reinforced concrete slab beam-column structure, the thickness of which is thicker than that of ordinary civil buildings, and the plane stiffness of the floor can be regarded as infinite. If the shear wall is not used between the elevator and the freight elevator, the whole stiffness center of gravity moves to the shear wall, and the elevator or the freight elevator is generally located at the end, so the structural stiffness arrangement is unreasonable, so the frame infilled wall structure is used between the elevator and the freight elevator.
(2) Shear checking calculation of the joint core area. The design of frame joints should follow the principle of "strong columns and weak beams are strong joints", and the shear capacity of joints with seismic grade I and II should also be calculated. Because the center lines of beams and columns in multi-storey factory buildings often cannot coincide, and the cross section of columns is relatively large, the eccentricity of joints is also relatively large, which has a great adverse impact on the structure and stress of the core area of column joints. Therefore, for multi-storey factory buildings with large span, large space and large load, the shear checking calculation of the joint core area is more important.
(3) Checking calculation of crack width and rare earthquake. The checking calculation of crack width is to meet the requirements of normal use. The code stipulates that the crack width of concrete beams should not be greater than 0.3 mm, and if it is exceeded in calculation, it can be adjusted by reducing the section of steel bars and increasing the number of steel bars. If it does not meet the requirements, the section of column beam should be modified and recalculated. The principle of seismic design is "three inaccuracies", that is, "a small earthquake is not bad, a moderate earthquake can be repaired, and a big earthquake cannot collapse". Seismic checking calculation only meets the requirements of "small earthquake is not bad", structural reinforcement meets the requirements of "moderate earthquake can be repaired", and checking calculation of rare earthquake meets the requirements of "big earthquake can not collapse". According to the code, the seismic deformation of weak layers (parts) should be calculated for frame structures with floor yield strength coefficient less than 0.5 at 79 degrees, and the elastic-plastic displacement angle between weak layers (parts) should be less than 1/50. The equipment investment of multi-storey factory buildings is often much larger than that of civil engineering, so it is necessary to check the rare earthquake.
(4) Consider the connection between the frame and the elevator shaft. In the past, the design was based on pure frame calculation, and the elevator shaft wall was reinforced according to the structure, which was unsafe. The frame part is reinforced according to the calculated value of the wall frame, and the elevator shaft wall is reinforced according to the shear wall.
In addition, multi-storey factories generally have multiple cranes. In the design, the crane on the first floor is used as the crane load input, and the crane load on other floors is considered as the live load.
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