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What is a shear key in steel structures?

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 In steel structure engineering , the column base connection serves as the pivotal interface linking the superstructure to the concrete foundation below. It must safely and reliably transmit various loads from the upper structure: vertical pressure , uplift forces , bending moments , and horizontal shear forces . When horizontal shear forces become substantial, the friction alone between the column base plate and the concrete foundation surface proves insufficient to resist them. At this juncture, a critical small component becomes indispensable—the shear key . Shear keys, as the name suggests, are structural steel connection components specifically designed to resist and transmit horizontal shear forces. Essentially, they are short steel members. Installation location: Typically welded or anchored to the base plate of a steel column (or other load-bearing components such as equipment supports ), with its lower end embedded in the concrete foundation or concrete structure cast ...
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What are the design difficulties of steel large-span roofs?

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 The design difficulties of steel large-span roofs are mainly reflected in the following aspects:


I. Structural stability and deformation control
Stiffness and stability: Due to the light weight of steel structure, its stiffness is relatively small and the structure is not stable enough. In the case of large span, once the force exceeds the maximum range that the structure can bear, the steel structure may be bent, deformed, shifted, twisted, etc., which seriously affects the stability of the whole structure. Therefore, the design needs to ensure that the structure has sufficient stiffness and stability to meet the use requirements.
Deformation design: In order to ensure that the structure can still maintain a good shape after being stressed, the design needs to focus on deformation design. This includes analysing the system components of the steel structure as a whole to ensure that the forces in each component meet the criteria and avoid exceeding the bearing capacity of the bars. At the same time, the stability of the structure can be enhanced by applying prestressing to prevent the occurrence of destructive deformation.
II. Load design
Permanent load: the permanent load of large-span steel structure mainly includes the quality of roof and roof cover. If there are coverings on the upper part of the roof and other facilities, such as pipes and equipment, they also need to be calculated. Designers need to carry out synthetic simulation through calculation software to find out the optimal load calculation and the maximum load carrying capacity, taking into account the actual situation of the whole steel structure building.
Live load: The live load borne by large-span steel structure varies greatly due to the differences in the system mechanism. Common live loads include roof live loads and roof snow loads. The design of roof live load should be carried out in accordance with relevant codes, while the design of roof snow load should consider the reproduction period of snow pressure.


III. structure and node design
Complex structure: large-span steel roofs often have complex shapes, such as shaped roofs, super-high rack columns and high wind-resistant curtain walls in a civic centre project in Nanjing, which increase the difficulty of design. The design needs to fully consider the reasonableness of the structure to ensure that the structure can meet the use requirements.
Node processing: node is the key part of large-span steel structure, and its design directly affects the stability and safety of the whole structure. In the design of large-span steel roof, it is necessary to pay special attention to the processing of nodes to ensure that the connection of nodes is reliable and the force is reasonable.
IV.Construction and installation difficulty
Risk of working at high altitude: the construction of large-span steel roof often needs to be carried out at high altitude, which increases the risk and difficulty of construction. Construction personnel need to take safety measures to ensure safety during construction.
High component precision: The components of large-span steel roofs require high precision to ensure construction quality and structural stability. This requires strict control of the precision and quality of the components during production, transport and installation.

In summary, the design difficulties of steel large-span roofs mainly include structural stability and deformation control, load design, structure and node design, as well as construction and installation difficulties. In order to solve these difficulties, designers need to fully consider various factors and adopt scientific and reasonable design methods and construction techniques to ensure the safety and stability of the structure.

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