The choice of whether a structure should be constructed from concrete, steel, masonry or wood depends on the availability of materials and many value judgments.
Often, the most important consideration is the overall cost of the structure. This is, of course, a function of the cost of materials and labor and the time required to erect them. Concrete floor systems are thinner than structural steel systems because the girder and beams or joists all fit to the same depth, or the floors are flat plate. This produces an overall reduction in the height of a building compared to a steel building, which leads to a
- Wind load is less because there is less area in contact with air
- and savings in cladding and mechanical and electrical risers
Often, however, the overall cost is more or less affected by the overall construction time because the contractor and owner must allocate funds to build and receive any return on their investment until the building is ready for occupancy. Will not done. As a result, the financial savings due to faster construction can more than compensate for the increased materials and making costs. Materials for reinforced concrete structures are widely available and can be produced according to their requirement in construction, as opposed to structural steel, which must be ordered in advance to schedule a job at a steel fabricating yard and Must be paid partly.
The designer can take any measures to standardize the design and will generally pay a lower overall cost. For example, column sizes can be kept the same for multiple floors to save money on form costs, while changing the strength of the concrete or the percentage of reinforcement to allow for changes in column load.
2. Material suitability for architectural and structural works
A reinforced concrete system often allows the designer to combine architectural and structural functions. Concrete has the advantage that it is held in a plastic state and given the desired shape and texture through forms and finishing techniques. This allows elements such as flat plates or other types of slabs to serve as load bearing elements while providing a finished floor and ceiling surface. Similarly, reinforced concrete walls can provide an architecturally attractive surface in addition to having the ability to resist gravity, wind or seismic loads. Ultimately, the choice of size or shape is governed by the designer and not by the availability of standard manufactured members.
The structure in a building must withstand the effects of fire and must remain standing while the building is evacuated and extinguished. A concrete building naturally has a fire rating of 1 to 3 hours without special fire proofing or other details. Structural steel or timber buildings must be fireproof to achieve the same fire rating,
The occupants of a building may be disturbed if their building shakes in the wind or the floors vibrate as people walk by. Vibration is rarely a problem due to the greater rigidity and mass of the concrete structure.
5. low maintenance
Concrete members inherently require less maintenance than structural steel or wood members. This is especially true if dense, air-repellent concrete has been used for surfaces exposed to the atmosphere, and if care has been taken in the design to provide adequate drainage on and off the structure.
6. material availability
Sand, gravel, cement and concrete mixing facilities are very widely available, and reinforcing steel can be transported to most job sites more easily than structural steel. As a result, reinforced concrete is often used in remote areas.
On the other hand, there are many factors that can cause one to choose a material other than reinforced concrete. This includes:
1. low tensile strength
As stated earlier, the tensile strength of concrete is much less than its compressive strength and hence concrete is subject to cracking. In structural uses this is overcome by using reinforcement, carrying tensile forces and limiting the crack width to within acceptable values. Unless taken care of in design and construction, these cracks can become unsightly or allow water to enter.
2. Form and shoring
The construction of a cast in place structure does not involve the three phases encountered in the construction of a steel or wooden structure. these
- form creation,
- removing these forms, and
- Support or edge the new concrete until its strength is sufficient to support its weight.
Each of these steps involves labor and/or materials that are not required with other forms of construction.
3. relatively low power per unit of weight or volume
The compressive strength of concrete is roughly 5 to 10% of steel, while its unit density is about 30% that of steel. As a result, a concrete structure requires greater volume and greater weight of the material than a comparable steel structure. As a result, long span structures are often made from steel.
4. quantity change over time
Concrete and steel both undergo approximately equal amounts of thermal expansion and contraction. Because steel has less mass to be heated or cooled, and because steel is a better conductor than concrete, a steel structure is generally more affected by temperature changes than a concrete structure. Concrete, on the other hand, undergoes drying shrinkage which, if prevented, can lead to deflection or cracking. Furthermore, the deflection will tend to increase over time, possibly doubling, due to creep under constant load.