1. Structural stiffness and quality issues
One major advantage of steel structure is its high strength and lightweight, which is an advantage in conventional construction. But in some structures, this may become a disadvantage.
Steel has a higher density than concrete, but why is it said to be lightweight? It is because steel has high strength and requires less steel under the same load conditions. Overall, the quality is lighter than concrete. This is a major advantage of steel structure.
Due to the low usage of steel structures, it can lead to a lack of stiffness. When it comes to power issues together, small quality may not necessarily be a good thing.
The wind and earthquake resistance of high-rise and super high-rise buildings is a major issue, and the wind and earthquake resistance mentioned here is not a strength issue, but a stiffness issue.
That is to say, in the case of strong winds and earthquakes, one is not afraid of the building falling, but rather afraid of shaking too much, or rather, afraid of shaking with too much acceleration.
Imagine a building that has been shaking all the time. Do you dare to live there?
A building without proper functionality is undoubtedly a time bomb.
At this point, the strength advantage is difficult to fully utilize, and although stiffness issues can be addressed through structural means, their lightweight may be a fatal problem.
In large-span bridges, especially suspension bridges, due to the lightweight steel structure, we even need to add counterweights to the steel box to improve its dynamic characteristics.
Steel structure and concrete core tube should be used in the corresponding building structure to handle stiffness issues.
The Empire State Building, Twin Towers, and Sears Tower are indeed super high-rise steel structures, but they are all running towards world records. The key issues they deal with are the wind resistance of steel high-rise structures, and they are too expensive to be used for residential purposes.
In addition, it should be noted that the power problem is very complex, and low stiffness may not be suitable, while high stiffness may not be good. Only a suitable range is reasonable.
2. Corrosion protection issues
Corrosion prevention of steel structures is a major issue, especially in coastal areas. The following picture shows a bay bridge that was opened to traffic in 1991.
20 years later, the steel pipes have rusted into leaf patterns.
3. Fire prevention issues in steel structures
Steel structures usually lose their load-bearing capacity and undergo significant deformation at temperatures ranging from 450 to 650 ℃, resulting in bending of steel columns and beams. As a result, they cannot continue to be used due to excessive deformation. Generally, unprotected steel structures have a fire resistance limit of about 15 minutes. The length of this time is also related to the speed at which the component absorbs heat.
From a construction perspective, the steel structure may be more difficult to construct.
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