girt deflection limits
girt deflection limits
(OP)
I am curious as to what some of you hold the deflection to an exterior wall girt using the IBC2000 code if the girt was supporting a brittle masonry wall?
Also, those familiar with the SBC97, are you allowed to reduce your wind load on said girt above by 0.75?
Thanks
Also, those familiar with the SBC97, are you allowed to reduce your wind load on said girt above by 0.75?
Thanks






RE: girt deflection limits
I'd spec/design for a maximum deflection of about L/600 or L/720 or whatever the SBC or IBC requires for masonry...
RE: girt deflection limits
Definitely use at least L/600 as the deflection limit for a masonry wall. Brick Industry Association Technical Note #28b (http://www.brickinfo.org/pdfs/28b.pdf) discusses brick deflection limits for a steel stud supporting wall. I would think the same logic would apply to your case. That is the best definitive reference I have been able to find on the web after a lot of searching.
I am not familiar with the SBC, but the allowable wind load reduction (if still valid) should only be applicable to stress calcs, not deflection. However, given that most general building codes still had an allowable 75% wind load factor ca 1996/97, the SBC may also allow it, provided that code governs for your project.
RE: girt deflection limits
The SBC does allow for the 75% reduction of wind load. I guess my question was misleading. I was really needing to know if that could be applied to the deflection too. Some of the Code requirments seem to be vague and can be interpretted different ways. I am an EIT and have caught PE's who were interpetting the particular code on that project wrong. They corrected their way but it made me realize how easy it is to do. I am sure I am doing it on other areas of the code.
Thanks again.
RE: girt deflection limits
RE: girt deflection limits
RE: girt deflection limits
Section 1605.3.2 of the IBC 2000 states that " ...combinations that include wind or seismic loads, allowable stresses are permitted to be increased or load combinations reduced, ..."
I take that to mean that IBC does permit the .75 reduction contrary to what you stated in your reply. Please help me clarify your assertion, it's possible that I may be interpreting the code the wrong way.
For Masonry Deflection limits, I typically refer to Table 1617.3 of IBC 2000 and use that as a guideline to determine allowable girt deflection. These requirements are usually more strict even than the L/240 requirement.
JS.
RE: girt deflection limits
Table 1617.3 is for limiting seismic drift. I don't think it is appropriate for a serviceability check. Generally the Codes don't address serviceability.
RE: girt deflection limits
MikeE55, I am currently designing wind to a girt with .75x for deflection and 1.0x for stress. I have been designing wind girts to L/360 in the past because a brick manufacturer suggested that to resist cracking. Above some of the replys to my initial question recommend L/720 for girts supporting masonry or brittle finishes. That seems excessive and not cost effective. I am trying to find out what everyone else is using for wind girts supporting masonry. I didn't know that the L/240 was supposed to work with a crack at the base for rotation I assume. The brick manufacturer I had talked with said that L/240 was not enough to prevent cracks.
Thanks for you replys
RE: girt deflection limits
MikeE55, I am currently designing wind to a girt with .75x for deflection and 1.0x for stress. I have been designing wind girts to L/360 in the past because a brick manufacturer suggested that to resist cracking. Above some of the replys to my initial question recommend L/720 for girts supporting masonry or brittle finishes. That seems excessive and not cost effective. I am trying to find out what everyone else is using for wind girts supporting masonry. I didn't know that the L/240 was supposed to work with a crack at the base for rotation I assume. The brick manufacturer I had talked with said that L/240 was not enough to prevent cracks.
Thanks for you replys
RE: girt deflection limits
f. The wind load is permitted to be taken as 0.7 times the "component and cladding" loads for the purpose of determining deflection limits herein.
Would a girt be considered a 'component'? If it can be, then frames would be designed to 0.75x and girts to 0.7x
RE: girt deflection limits
Anyone else have any thoughts on this?