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Mechanism of Load Transferred in Plain & Reinforced Concrete

Function of structure is to transfer all the loads safely to ground. A particular structural member transfers load to other structural member.

Merits of Concrete Construction

  • Good Control over cross sectional dimensions and shape: One of the major advantage of concrete structures is the full control over the dimensions and structural shape. Any size and shape  can be obtained by preparing the formwork accordingly.
  • Availability of  Materials: All the constituent materials are earthen materials (cement, sand, crush) and easily available in abundance.
  • Economic Structures: All the materials are easily available so structures are economical.
  • Good Insulation: Concrete is a good insulator of Noise & heat and does not allow them to transmit completely.
  • Good Binding between Steel and Concrete: There is a very good  development of bond between steel and concrete.
  • Stable Structure: Concrete is  strong in comparison but week in tension and steel as strong in tension so their combination give a strong stable structure.
  • Less Chances of Buckling: Concrete members are not slim like steel members so chances of buckling are much less.
  • Aesthetics: Concrete structures are aesthetically good and cladding is not required.
  • Lesser Chances of Rusting: Steel reinforcement is enclosed in concrete so chances of rusting are reduced.

Demerits of Concrete Construction

  • Week in Tension: Concrete is week in tension so large amount of steel is required.
  • Increased Self Weight: Concrete structures have more self weight compared with steel structures so large cross-section is required only to resist self weight, making structures costly.
  • Cracking: Unlike steel structures concrete structures can have cracks. More cracks with smaller width are better than one crack of larger width.
  • Unpredictable Behaviour: If same conditions are provided for mixing, placing and curing even then properties can differ for the concrete prepared at two different times.
  • Inelastic Behaviour: Concrete is an inelastic material, its stress-strains curve is not straight so its behaviour is more difficult to understand.
  • Shrinkage and Creep: Shrinkage is reduction in volume. It takes place due to loss of water even when no load is acting over it. Creep is reduction in volume due to sustained loading when it acts for long duration. This problem is not in steel structures.
  • Limited Industrial Behaviour: Most of the time concrete is  cast-in-situ so it has limited industrial behaviour.

Codes

These are rules given by various organizations in order to guide the designers for safe and economical design of structures.

  • ACI 318-08 by American Concrete Institute. For general concrete constructions (buildings).
  • AASHTO specifications for Concrete Bridges. By American Association of State Highway and Transportation Officials.
  • ASTM (American Standards for Testing and Materials)for testing of materials.

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