Steel structure has the following advantages and disadvantages:
High strength, light weight, density to strength ratio than concrete and wood smaller.
Good wood property, high reliability. Steel has good uniformity and can be regarded as isotropic elastoplastic material. Concrete needless to say, mixing and pouring will inevitably have fine particles not uniform distribution; Wood has different compression resistance to grain and cross grain.
High degree of industrialization, short construction period. Concrete has demoulding strength requirements: for concrete structural engineering components, the concrete strength to design a certain amount of concrete cube compressive strength standard value, can carry out the dismantling of the template.
Good sealing. If the pipeline is basically steel structure.
Good seismic performance. Light weight, flexible structure, the earthquake can effectively consume energy.
Good heat resistance to heating: less than 250 °C, little change in strength.
The production of steel is large, but the cost is not high.
Poor corrosion resistance. Need to brush paint regularly, high maintenance costs.
Poor fire resistance. Above 300 °C, the strength of steel gradually decreased, to 600 °C strength less than the design strength 1 / 3; And the unprotected steel structure in fire can only last about 20 minutes.
Poor sound insulation, strong transmission. To take an extreme example, partition walls must have ears, and walking upstairs will cause you to notice, so undesigned steel structures are not suitable for living.
Steel concrete structure has the following advantages and disadvantages:
Good durability. The strength of the concrete increases with time and the concrete cover protects the internal reinforcement.
Good fire resistance. Unprotected steel concrete structure can maintain 1-3 hours in fire.
Good integrity. On-site whole pouring, each component is closely connected. (Note: Prefab construction may not satisfy this clause.)
Good modularity. Everything can be modeled, such as the Sydney Opera House.
(Historical advantages) can be local + save steel. Now concrete is unified configuration, steel production is large enough, so it is a historical advantage.
Since the major earthquake weak.
Easy to crack, and do not deal with the words of reinforcement to play a role must work with cracks, so poor sealing.
Templates are basically one-time, and a few can be repeated several times.
Construction is affected by seasonality.
There are many structural types of housing, such as common steel (steel), reinforced concrete structure, steel structure, brick concrete, brick wood, wood structure and so on.
Now commercial residential, residential, commercial buildings, such as reinforced concrete structures, the reasons are as follows:
1, the material is convenient, many iron and steel plants, steel prices are relatively cheap; Commercial concrete mixing station mainly with cement, sand, stone, water to a certain proportion, doping other additives or admixtures, raw materials to obtain convenient cheap, processing difficulty is relatively small.
2, steel and concrete have an approximate coefficient of expansion, There is a good adhesion between each other, the response to external stress will not be too large, and concrete can protect steel from corrosion, the overall performance is good, and has a strong robustness, durability.
3, reinforced concrete due to its own material reasons, with good fire performance, residential use is relatively safe.
4, the workability of concrete to ensure its completion of a variety of architectural shapes, wide applicability.
5, reinforced concrete structure from the foundation to the top part of the whole, with better seismic function.
6, the process is mature, the cost is controllable.
Are timber buildings necessarily worse than reinforced concrete buildings?
There are two common types of timber structures. One is the wooden frame, which is commonly used in ancient China, and is the form of the palace hall and so on. The other is the wood shear wall, the movie or TV show in North America to see a large number of one to two residential buildings are wood shear walls.
Wood as a structural material has many advantages, specific to the seismic effect, The tensile strength and compressive strength of wood are close to, there is a certain ductility, and the weight is light, corresponding to the “light high strength” of steel, wood can be called “light medium strength,” mechanical properties are equivalent to the weakened steel. Modern wood structures use a large number of reliable metal joints, the wood used are also factory production of composite materials, the design theory is relatively perfect. It can be said that the design and construction of reasonable timber structure, fully able to achieve the design of good seismic performance. This is illustrated by numerous engineering practices in North America and Japan.
And reinforced concrete this structural material, the overall weight is very large, which is very unfavorable to seismic. The performance of reinforced concrete depends heavily on the design level and construction quality, this disadvantage will be magnified in China. Wenchuan earthquake in a large number of reinforced concrete frame column core area damage, strong beam and weak column damage, and even the overall collapse, is an example.
Conclusion: Under the premise of reasonable design and construction, for low-rise buildings, wood structure and concrete structure can also obtain good seismic performance. Domestic rare wooden structure, not because of earthquake is not good, but because of economic, policy and other factors. For high-rise buildings, the mechanical properties of natural wood is limited, coupled with the fire performance constraints, and not suitable for high-rise building needs.