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Control of deflection and ensuring lateral stability in beams as per Clause23.2 &23.3 of IS-456.
Clause23.2 of IS456 stipulates the limiting deflections under two heads as given below:
(a) The maximum final deflection should not normally exceed span/250 due to all loads including the effects of temperatures, creep and shrinkage and measured from the as-cast level of the supports of floors, roof and all other horizontal members.
(b) The maximum deflection should not normally exceed the lesser of span/350 or20 mm including the effects of temperature, creep and shrinkage occurring after erection of partitions and the application of finishes.
It is essential that both the requirements are to be fulfilled for every structure.
This depends the loading type, structural behavior, structural boundary conditions.
For example, L/360 can be used for Live Load of the Structure but when it is a dead load and live load combination then L/260. This typically applies for floor load or vertical load spans horizontally. However, you may want to consider stringent limits for horizontal load on vertically spanned structure. For example, wall with cantilever free end may need a different limit.
lesser of span /350 or2-20 mm
it depends on what the structure will be used for
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