Building

Reinforcement in building construction

Introduction

Reinforced concrete (RC) or reinforced cement concrete (RCC) is a composite material (A structural material that gains its strength from a combination of complementary materials) in which concrete’s relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength or ductility. Reinforced concrete is concrete with the addition of a material such as steel to overcome the tensile weakness.
Reinforced concrete may also be permanently stressed (concrete in compression, reinforcement in tension), so as to improve the behaviour of the final structure under working loads. wikipedia

The concrete is strong only in compression but when it comes to tension it is a very weak material, also the nature of concrete is brittle so sudden failure occurs at ultimate loads that is why reinforcement is needed in a concrete.

Reinforcement in concrete could be materials made of steel, polymers or alternate materials in connection with reinforcing bars (rebar).
Reinforcing schemes are generally designed to resist tensile
stresses in particular regions of the concrete that might cause unacceptable cracking and/or structural failure.

Pre-tensioning and post-tensioning reinforced concrete

Pre-tensioning and post-tensioning is the method in which reinforced concrete may be permanently stressed (concrete in compression, reinforcement in tension), so as to improve the behaviour of the final structure under working loads. These methods are commonly use in the United States.

Precast concrete is a construction product produced by casting concrete in a reusable mold or “form” which is then cured in a controlled environment, transported to the construction site and lifted into place (” tilt up “). In contrast,
standard concrete is poured into site-specific forms and cured on site. Precast stone is distinguished from precast concrete using a fine aggregate in the mixture, so the final product approaches the appearance of naturally occurring rock or stone. More recently expanded polystyrene is being used as the cores to precast wall panels. This is lightweight and has better thermal insulation. Precast can be used within exterior and interior walls. Wikipedia

Reinforced concrete are use in part of building structures and components of structures including beams, columns, wall, slabs, foundations, frames etc.

Properties of good reinforced concrete

For a strong, ductile and durable construction the reinforcement needs to have the following properties:

  1. High relative strength
  2. High toleration of tensile strain
  3. Good bond to the concrete, irrespective of pH, moisture, and similar factors
  4. Thermal compatibility, not causing unacceptable stresses (such as expansion or contraction) in response to changing temperatures.
  5. Durability in the concrete environment, irrespective of corrosion or sustained stress

Reinforcing materials

Steel is one of the most commonly use material in reinforcing concrete due to it high tensile strength. I will be discussing about steel as reinforcing materials and it properties.

Steel is a metallic materials of an Iron-Carbon alloy having a carbon content less than 2.0 percent and generally below 1.5 percent. It usually contain substantial quantity of manganese.
It good physical properties important to engineers are:

  • Strength
  • Elasticity
  • Stiffness
  • Ductility
  • Malleability
  • Brittleness


Advantages and Disadvantages of using reinforced concrete in building construction

Advantages:

  • Reinforced concrete may be the most cost-efficient solution for building large and moderately large structures (buildings and bridges). For small buildings like houses, I think it’s safe to say that timber is always the cheapest option (however, it’s not a widely used material in many coutries);
  • It doesn’t demand the most qualified workers on site. Steel structures have components which require specialized workers (for example, to execute weldings). With reinforced concrete, you kind of follow a recipe;
  • If the structure is properly designed and executed, it can go well past its designed project lifespan without needing, or needing only minor, structural interventions (reinforcement/rehabilitation);
  • It’s a robust type of construction. It withstands extreme weather events and (once again, if properly designed) even extreme events like earthquakes;
  • If not thermal, they certainly have a better acoustic performance than other types of buildings.

Disadvantages:

  • It takes much longer to build, when compared to steel, and especially, timber contructions;
  • Concrete doesn’t dry out in cold weather;
  • Measures have to be taken to reduce shrinkage. Nevertheless, concrete structures will always have cracks, even if only small ones.

Reference:
Filipe Pereira, MSc Civil Engineering & Structures, IST – Instituto Superior Técnico (2016) on advantage and Disadvantage of using reinforced concrete

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