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Maximum ratios of computed deflection to span L for beams and slabs as per ACI 318: The Building Code:

Types of memberDeflection to be consideredDeflection Limit
Flat roofs not supporting or attached to non-structural elements likely to be damaged by large deflection.Immediate deflection due to the live load.L/180*
Floors not supporting or attached to non-structural elements likely to be damaged by large deflections.Immediate deflection due to the live load.L/360.
Roof or floor construction supporting or attached to non-structural elements likely to be damaged by large deflections.That part of the total deflection that occurs after attachment of the non-structural elements (the sum of the long-term deflection due to all sustained loads and the immediate deflection due to any additional live load.***L/480**
Roof or floor construction supporting or attached to non-structural elements not likely to be damaged by large deflections.L/240 $

beams-slabs

* This limit is not intended to safeguard against ponding. Ponding should be checked by suitable calculations of deflection, including the added deflections due to ponded water, and considering long-term effects of all sustained loads, camber, construction, tolerances and reliability of provisions for damage.

** this limit may be exceeded if adequate measures are taken to prevent damage due to supported or attached elements.

*** the long term deflection may be reduced by the amount of deflection that occurs before attachment of the non-structural elements.

$ but not greater than the tolerance provided for the non-structural elements. This limit may be exceeded if camber is provided so that the total deflection minus the camber does not exceed the limitation.

Read More:

Causes of Excessive Deflections in Reinforced Concrete Slabs

Factors Affecting Deflections of Reinforced Concrete Beams and Slabs

How to Control Deflection of Reinforced Concrete Beams and Slabs?

Construction Measures & Materials to Reduce Deflection of Concrete Beams and Slabs

About Gopal MishraVerified

Gopal Mishra is a Civil Engineer from NIT Calicut and has more than 10 years of experience in Civil Engineering and Construction. He is the founder of The Constructor.