Masonry Wind Loads
Masonry Wind Loads
(OP)
I know I have seen this question on this forum before but I can't seem to find it at this time.
I have a masonry wall that is 20' high x 30' long (no openings), when sizing the wall reinforcing for wind loads (I am using the Components and Cladding requirements) do you use the full area of the wall (600 ft^2) or do you use the tributary area to each bar (say @40 in oc or 66ft^2). I have had some pretty lively discussions with other engineers in the office and was wondering what other people think.
I have a masonry wall that is 20' high x 30' long (no openings), when sizing the wall reinforcing for wind loads (I am using the Components and Cladding requirements) do you use the full area of the wall (600 ft^2) or do you use the tributary area to each bar (say @40 in oc or 66ft^2). I have had some pretty lively discussions with other engineers in the office and was wondering what other people think.






RE: Masonry Wind Loads
Dik
RE: Masonry Wind Loads
RE: Masonry Wind Loads
DaveAtkins
RE: Masonry Wind Loads
BA
RE: Masonry Wind Loads
RE: Masonry Wind Loads
The question was about determining area for calculating components & cladding wind loads. dik did not address that at all, so I don't know what you're agreeing with.
The codes I work with in the US all reference back to ASCE7. That was the basis for my suggestion. I would think other codes have similar provisions for determining area for c&c wind loads.
As far as lively discussions... I can definitely see that. The same thing goes for designing tilt-up walls. Is the area the area of the entire panel, or is it the span times the spacing of the reinforcement?
RE: Masonry Wind Loads
DaveAtkins
RE: Masonry Wind Loads
It send you to Fig. 6-20 to find Cf
RE: Masonry Wind Loads
There was no reference to ASCE7.
Dik
RE: Masonry Wind Loads
In the National Building Code of Canada, pressure coefficients are given for walls and roofs of varying slopes. A wall would be designed for a pressure derived from the algebraic sum of the internal and external pressure. These in turn would be determined in accordance with the code, taking into account q, the reference velocity pressure which is listed for many locations in Canada, Ce the exposure factor, Cg the gust factor and Cp the external pressure coefficient.
These various factors are all tabulated in the Structural Commentaries to the NBC. The area affected would be the entire wall area, although factors in the corner regions are greater than the central area. I believe that is why dik indicated he would design the wall for a uniform pressure with increased pressure in the corner regions.
There is no mention in our code of "effective area" and in fact, I still do not understand what you mean by the term. DaveAtkins says it is height squared divided by three which does not help in my understanding. Please elucidate.
BA
RE: Masonry Wind Loads
I have missed the original question as strength (reinf) rather than component concern, though the OP has indicated he was using such pressure.
RE: Masonry Wind Loads
Under ASCE7, the external pressure coefficient GCp varies, based on the wind zone and effective wind area that the component supports. Wind area for a girt, for instance, would be the girt span x tributary load width (spacing between girts). ASCE7, however, adds the "effective" description by stating that the tributary load width (effective width) does not need to be taken as less than span/3. That is why DaveAtkins says height (span) squared, divided by three.
I thought all codes required that components supporting smaller wind areas had to be designed for higher winds. This relates to the principles of probability... the smaller an area the member supports, the more likely the member is to be fully loaded over it's entire area.
RE: Masonry Wind Loads
Just so that I am clear. This question refers to the sizing of the reinforcing in a masonry wall due to wind normal to the wall. If you have bars spaced at 32 in o.c. what area do you use when entering the Components and Cladding charts of ASCE 7? Is the area based off the entire wall? Or is the area based off the bar spacing times the height of the wall?
Spats has cleared it up.
Sorry for the confusing question.
RE: Masonry Wind Loads
RE: Masonry Wind Loads
-strucguy
RE: Masonry Wind Loads
In your original post you mentioned two things; use of Components & Cladding (C&C) loads and the width to use in designing a masonry freestanding wall.
I pointed you toward Section 6.5.14 & Fig. 6-20 because I think that you are designing the Main Wind Force Resisting System,MWFRS and not C&C.
The Freestanding Walls section will ask you to investigate three load cases, A,B,& C and the resultant F value is the total wind load on the wall. How you proportion that total load to the wall and the reinforcing is up to you.
I hope that this clears up my initial response.
RE: Masonry Wind Loads