allowable deflection for horizontal aluminum mullion
 

allowable deflection for horizontal aluminum mullion
does anyone know what is the delfection limit for deadload( gravity only) for the horizontal members in aluminum curtainwalls or storefront.
i have been using l/175, but some manufacturers use min of l/360 or 1/8". where does the 1/8" limit come form. is it in the code?
thnaks,
sutki

it is likely just the deflection limit that their particular system can handle. the code may impose some limits, but individual manufacturers may have additional requirements based on their system performance.
the 1/8" limit can also come from the amount of space in the glazing track and the movement it can handle before loading the glass panel below it.
the more stringent limit is because you are talking about the deflection being in the plane of the glass. the glass is stiffer and therefore will need stiffer supports if the supports are to take the load (similar to brick supports).
l/175 is an out of plane limit.