Essay On Deflection

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DEFLECTION
Deflection is the distortion or movement of a structure and its elements, such as trusses and beams, from their original positions. It is as significant for a designer to regulate deflections and strains as it is to recognize the stresses due to loads.
The practice of the ACI Code requirements, taking into account the non-linear relationship between stress and strain in concrete, has resulted in significantly smaller sections than those by the elastic theory. The ACI Code, also recognizes the use of steel up to a yield strength of 80 ksi and the use of high-strength concrete for structures. The practice of high-strength concrete and steel results in relatively smaller sections and a decrease in the toughness of the flexural member …show more content…

1. Instantaneous Deflection
The deflection of structural elements is mainly due to the dead load combined with a fraction of or whole of the live load. The deflection that happens immediately upon the application of the load is called the instantaneous or immediate deflection.
Its calculations are based primarily on the elastic behavior of the flexural members. The deflection ∆, is a function of the span, L, load, W, modulus of elasticity of the material, E and moment of inertia, I:

∆= f (WL/EI) = α (WL³/EI) = K (ML²/EI) …show more content…

Long-Time Deflection
Deflection of RC members continues to increase under the action of constant load, though very slowly with respect to time. Creep and Shrinkage are the major causes of this additional deflection, known as long-time deflection. This type of deflection is mainly influenced by humidity, temperature, curing time period, quantity of compression steel, and degree of the load. The ACI Code, Section 9.5.2.5, recommends that the long-term deflection for both lightweight and normal type of concrete flexural members can be found by λ= ζ

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