huangyhg

allowable defelction for spandrel beam bracing masonry
does anyone know a reference stating what the allowable deflection is for a spandrel beam bracing the top of a masonry wall?
application is for a metal building. the owner wants a 13'-4" high masonry wall. i told them the metal building must brace the wall.
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i am assuming you mean weak axis deflection of the spandrel?
i would probably use l/600. that is what we would typically use for metal stud back-up for brick. while the deflection is for the vertical spanning studs/brick, i imagine it would be similar to the horizontally spanning spandrel.
i am interested to hear from others.
i think the ibc gives the l/600 limit for
see chapter 4 of aisc steel design guide 3. if i'm reading this correctly, for reinforced masonry, it limits deflections for girts and columns to the span/240 under a ten year wind.
l/600 is the minimum per code, but i'm a little more stringent - i use l/1000. i don't like cracked brick.
mike mccann
mmc engineering
been down this road several times with cmu 'wainscot' walls around pre-engineered metal buildings.
imho, if the top of the masonry wall is supported by the girt, it is the movement of the building frame (@ the girt elevation) plus the girt deflection that must be limited to h/600.
if the girt deflects a 1/2" but the metal building frames are deflecting 1" (at an elevation of 13'-4"), the deflection that a piece of masonry located 1/2 way between building columns would experience is 1 1/2".
in reality, it is often difficult to get the mb supplier to limit the deflection of his building frame to accomadate masonry. for 8' or 10' high walls in similiar situations we look at just cantilevering the masonry off of the footing becasue this problem. at a masonry height of 13'-4", this is getting a bit difficult.

from structure magazine: may 2008.
agree with lkjh345 about the way the deflection should be calculated, but if the wall is reinforced concrete masonry, i think the h/600 limit is much too stringent. think of this as half of a simple span, where l/600 may be appropriate, and you get h/300 for the top deflection limit.
i have been using a deflection criteria of length/300 for a 20yr wind return when doing header design. this value is company policy. i'm interested to see some people on this thread using very stringent limits.
keep in mind that the l/600 limit is only required when supporting unreinforced masonry and brick. i've had great success using something less stringent for supporting reinforced masonry.

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