document
Types of mixed material building frames
The materials used in the skeletal frameworks of buildings fall into 2 main categories. They must all be strong, but the two types are strong in different ways:
1. Materials that withstand compression. They can be squeezed or carry enormous weight without bending or crushing:
concrete
stone
brick
ice
2. Materials with high tensile strength. They can span long distances, or carry large weights as narrow upright beams without snapping:
steel
iron
wood
bamboo
Many buildings combine materials from groups 1 and 2 to capture the advantages of both. Large buildings typically use concrete and steel, which are heavy-duty materials suitable for massive construction.
Under mixed materials, there are 4 categories of steel-concrete combinations:
1. concrete-steel tandem
In a tandem construction, concrete walls and steel beams remain distinct from each other but are joined together. Most commonly a concrete core is surrounded by a grid of steel beams (a tree trunk with scaffolding around it).
2. steel-in-concrete composite
This resembles reinforced concrete, but instead of small bendable reinforcing bars laced into the concrete column, there is a solid steel beam wrapped in concrete. Common in Asia, especially in very tall skyscrapers.
3. concrete-in-steel composite
Less common than the above types, this is the reverse of number 2. A hollow steel beam is filled with poured concrete for added strength.
4. concrete and steel stacked
Some floors are steel and others are concrete. The two materials do not interact much; they are stacked in layers. Normally concrete is used for the lower floors and steel for the top section, with the order reversed on rare occasions.