With the increase in my country's steel production, steel structure workshops have been widely developed due to the advantages of high steel structure strength, good plastic toughness, lightweight and fast construction speed. This article discusses the issues that should be paid attention to in the design and construction of steel structure workshops and provides a reference for more and better construction of steel structure workshops.
Because of its high strength, lightweight and fast construction speed, steel structure has always been a favorite structure. In the past hundred years, it has developed rapidly, especially in the second half of the last century. As the world's steel production has increased significantly, the steel structure has also expanded its application field, especially in large spans, high towers, super high-rises, heavy-duty, power A large number of steel structures are used within the load structure. With the rapid development of the national economy, light steel structure construction has also developed rapidly in the field of construction in China. Steel structure construction is the new development and application of the most revolutionary architecture after reinforced concrete construction. The characteristics of light steel structure buildings are outstanding: good overall rigidity and seismic performance, fast construction speed, small space occupied by the structure, and high bearing capacity. In industrial plants, steel structures have gradually replaced more reinforced concrete structures, with their large spans The performance of the large space is quite outstanding on the scale of the building.
Several aspects needing attention in the design of steel structure workshop
1. The setting of temperature expansion joint
The temperature change will cause the deformation of the steel structure factory building, causing the structure to produce temperature stress, its size is related to the column stiffness, crane rail top elevation, and temperature difference. When the scale of the plant is very large, in order to avoid excessive temperature stress, temperature slits should be set in the horizontal or vertical direction of the plant to divide the plant with large plane size into several temperature sections (also called structural units). The length of the temperature section can be implemented according to the design specifications of the steel structure. The temperature expansion joint is generally treated by setting a double-column method or a single-column method.For longitudinal temperature expansion joints, rolling supports can be installed at the roof truss support, and transverse temperature expansion joints can be used at the connection between the frame beam and purlin Sliding method of the elliptical hole or sliding method of channel steel plywood.
2. Insulation and fire protection design
Steel is quite sensitive to temperature, but the increase and decrease in temperature will change the properties of steel. Steel has very good thermal conductivity, and its thermal conductivity reaches 50W / (m・ ℃ ). For steel structure buildings, if thermal insulation is not carried out, it will inevitably cause a lot of energy waste and consumption, while also meeting technological requirements and Comfort requirements. In contrast, low-temperature performance is more important. The figure below shows the relationship between the mechanical properties of steel and temperature.
Therefore, when the surface temperature of the steel structure is above 150 ℃, heat insulation and fire protection design must be done. There are generally two methods:
The ratio of high-temperature yield strength to room temperature yield strength
The ratio of high-temperature elastic modulus to room temperature elastic modulus
(1) Refractory bricks, concrete, or hard fireproof plates are encased in steel components.
(2) Thick coating fireproof coating is adopted, and the thickness is in accordance with "Technical Application of Steel Structure Fireproof Coating".
3. Roof support system and roof design
The layout of the roof support system should be determined according to the conditions of the plant span, height, column grid layout, roof structure, crane settings and tonnage size, vibration equipment conditions, and other conditions. In general, the roof structure of purlin or no purlin system should be provided with vertical support.In the no purlin system, the large roof panel has three points and roof truss welding, which can play the role of upper chord support. Installation needs, no matter purlin or no purlin system roof should be set on the roof string and skylight frame string chord to provide a string of lateral support. Longitudinal horizontal support shall be provided for the factory buildings with a roof frame spacing of not less than 12 m or those with heavy bridge cranes or large vibration equipment in the factory buildings. The focal point of roof design is waterproofing. Roof waterproof design involves factors such as roof slope, gutter form, single-slope roof length, and so on.
According to the "Technical Specifications for Roofing Engineering", the minimum roof slope is 5%. However, in actual projects, the roof slope of some foreign-funded steel companies often reaches 3% or even 2%. Considering that the current domestic steel structure manufacturers have uneven technical strength, node processing, and material performance, people control the roof slope to 5%. In areas with large snow cover, the slope should be increased appropriately. The length of a single-slope roof mainly depends on the maximum temperature difference in the area where the project is located and the height of the maximum head formed by rainfall. According to the collected data and engineering design experience, the length of the single-slope roof should be controlled within 70 m. If it exceeds 70 m, special research and special treatment are required.
After investigation and research, there are two common steel structure roofing practices on the market at present: 1) Double-layer color profiled steel plate with thermal insulation cotton inside, a large amount of use, but the color steel plate thermal expansion and contraction caused by large temperature difference and single slope length The problem is difficult to solve. 2) The composite flexible steel roofing system is composed of a roof color steel plate inner panel, a vapor barrier, an insulation layer, and a coiled material waterproof layer. Because the outermost layer is laid with flexible coiled material, the entire roof is a closed system, and the problems of thermal expansion and contraction are not prominent, and the cost is slightly higher than that of domestic general steel structure manufacturers.
4. The main components of the steel structure workshop
4.1 Steel roof system: First, the steel roof load-bearing member is composed of thin and thin rods, the cross-sectional shape is complex, and the node stress concentration is eccentric; secondly, when the roof system is designed, the calculated load and calculation sketch is more correct. And close to the calculation limit state, the structural member's load-bearing safety reserve is minimum, it is very sensitive to overload, temperature, and corrosion, and it is easy to fail due to accidental factors, plus various effects that occur during manufacturing, installation and use, steel structure The roof has become the most serious part of the steel structure factory damage. The failure of the steel roof includes roof collapse, truss member breakage (including disconnection from the joint plate), roof deflection exceeding the standard, bending of the member, bending or cracking of the joint plate, roof support buckling, and other types.
4.2 Crane beam system: The crane beam system is an important part of the steel structure workshop, including the crane beam, brake structure, crane track, and connection. The crane beam is complicated, and the vertical force and lateral force of the crane have dynamic characteristics, impact, and fatigue effects. Compared with the roof system crane beam calculation diagram, the calculation method is more different from the actual situation, the uncertainty is more, the structure is more The durability and reliability are the lowest.
4.3 Column system: the column designed according to the most unfavorable load combination, because the probability of simultaneous load is very low, under normal working conditions, the actual stress is much lower than the design stress, the safety reserve of the column is quite large, and the possibility of damage is very small There are very few cases of damage caused by insufficient overall bearing capacity of the column. The columns of industrial plants are often damaged as follows (column limb deformation, column limbs have incisions, lattice pillars are bent and twisted, the welds at the column head and crane beam support corbels are cracked, the pillars are tilted vertically, and the enclosing structure connects the nodes Damage, the crane track is off-set), which will affect production.
4.4 Foundation foundation: The strength problems of foundation mainly include: the insufficient bearing capacity of foundation or foundation lose stability, slope lose stability. The problem of foundation deformation mainly refers to excessive deformation and uneven settlement of soft soil, collapsible loess, expansive soil, seasonally frozen soil, and other regions. There are three types of foundation damage: overall shear failure, punching shear failure, and local shear failure.
5. Common construction problems and solutions of steel structure workshop
5.1 Construction problems that should be paid attention to during the construction of steel structure workshops
It is tied to the quality of the entire steel structure project. The operating temperature of the coating should be between 5 and 38℃. When the weather temperature is lower than 5℃, the corresponding low-temperature coating material should be selected for the application. When the temperature is higher than 40 ℃, the coating operation should be stopped. When the temperature of the component exceeds 40°C, the application of paint on the surface of the steel structure will generate air bubbles and reduce the adhesion of the paint film. When the air humidity is greater than 85%, or there is condensation on the surface of the component, the steel structure coating operation should not be carried out. Before the steel components are produced, the hidden parts of the components and the parts where the structural interlayer is difficult to remove rust should be removed in advance and painted in advance.
5.2 There are some problems that cannot be ignored in the steel structure system.
In the current research on the stability of reticulated shells, the main problem is how to reflect the coupling effect of axial force and bending moment. The relationship between global stability and local stability in long-span structural design is also a question worthy of discussion. At present, a unified stability safety factor is adopted in large-span structural design, which does not reflect the correlation between global stability and local stability. There are many random factors in the study of the stability of the steel structure system. At present, most of the problems dealt with by the random impact analysis of the structure are limited to such a pattern range as the determined structural parameters and random load input. In actual engineering, due to the structural parameters Uncertainty will cause significant differences in structural response. Therefore, we should focus on the study of structural extreme value instability, interference buckling, and jump-type instability considering random parameters. We have conducted useful research on the stability of dome reticulated shells considering random parameters.