Reinforced concrete is a combination of concrete and reinforcement. There are different types of concrete that do not contain reinforcement.
Gravity structures such as retaining walls, solid concrete dams, etc. are constructed without reinforcement. They are designed in such a way that no tensile stress develops in the cross section.
If there are no stresses in the concrete, no reinforcement is required for such structures. However, this does not mean that this applies to all structural elements.
For example, concrete columns are subjected to pure compressive load when the tensile stresses caused by bending moments are less than the axial compressive load. Although the section is fully pressurized, we at least added reinforcements to prevent buckling.
This decides whether the structure should consist of reinforced concrete or unreinforced concrete.
The most commonly used construction material is reinforced concrete compared to other materials such as steel and wood.
The combination of reinforcement and concrete provides the necessary resistance. Element sizes are adjusted based on applied loads such as axial force, bending moments, shear forces, torsional moments, etc.
Both in-situ concrete and precast concrete can be reinforced.
Why do we need reinforcements?
As we all know, concrete is both compressive and elastic. Generally, the tensile strength of concrete is about 1/10 of its compressive strength.
Therefore, we need something that can withstand tensile stresses when they occur in a section with loading effects. In this context, the compressive stress can be absorbed by the concrete and the tensile stress is transferred to the reinforcement, since concrete cannot absorb such large stresses without cracking.
There are generally two categories of reinforced concrete, depending on the reinforcement required. They are
- Simply reinforced
- Double reinforced
The type of load and amount of load determine whether compression reinforcement is necessary or not. The articles Designing a Simply Reinforced Beam AND Double Reinforced Version could be used as a method for designing a section.
This should be noted Shelf Life Requirements AND Durability of Concrete in Reinforced Concrete Construction.
Concrete can deteriorate due to several factors such as carbonation, chlorination, etc. Therefore, it is necessary to have adequate reinforcement coverage, concrete quality and water-cement ratio, suitable construction material, etc. Before construction begins, the property must be selected according to the technical requirements.
Let's discuss some important facts about reinforced concrete
- Reinforcement cover
This is selected depending on the exposure class and fire resistance of the concrete.
- Concrete quality
Selection is based on exposure class and durability requirements. BS 8500 standards provide comprehensive guidance on concrete selection.
- Reinforcement
Reinforcement must be tested in accordance with relevant standards before use. The order of installation and sampling must be in accordance with the relevant specification or code.
- Characteristic resistance of concrete
The characteristic strength of concrete is the parameter/resistance we use to design the structure.
- Factors affecting the strength of concrete
The article Factors Affecting the Strength of Concrete For more information, you can refer to the following.
- Usability limit state
All structures are tested for their usability limit state. This is the state in which the structure is checked for factor loadings.
The dimensioning of foundations, deflections, crack limits, etc. are checked for their usability limit state.
- Ultimate limit state
All structures are designed for load capacity. Load factors depend on the type of load and relevant standards.
- Reinforced concrete reinforcement
The usual reinforcement is used in reinforced concrete structures. Additionally, other types of reinforcement, such as fiber reinforcement, are also used in construction to absorb tensile stresses in concrete.
- Water resistance
All reinforced concrete structures built underground or below the water table are subject to attenuation and when this reinforced concrete is exposed to oxygen, corrosion can occur.
Depending on the importance of the structure, the structures are sealed.
This can be considered a durability requirement.
The article Advantages and disadvantages of reinforced concrete could be forwarded for subsequent inspection of its use.
