Exterior Suspended Ceilings

[jim57]

Looking at a 2' x 4' suspended ceiling panel system placed as a soffit on the exterior of a building. Ceiling failed in high winds. It was obvious there were no uplift struts. Going to court and need to cite all codes discussing the requirements. I found ASTM c-635. i have the 2003 version. Has this changed? Also, need additional codes if any as well as manufacturer's requirements.
Thanks

 

[ajk1]

I investigated this type of exterior ceiling failure due to high winds in a very open level site where the building was located, and came to somewhat similar conclusion that they failed to design properly (or at all) for the wind uplift forces on the ceiling; the lack of compressive struts was one of the main deficiencies, but not the only thing wrong. The architect of record relied on his inadequate spec, which among other deficiencies did not recognize that the uplift pressure in such situations is in fact not covered by the Code. In his mind, all he had to say in his specification was design to the Code. This is good for structural engineers because it creates work for them to devise remedial measures, but the situation was dangerous because the ceiling panels were periodically flying thru the air and it was only by the grace of God no one was struck. Unfortunately I cannot be of help as to where this might be covered in Codes...I don't think it is covered in North American Codes, but I am not an expert on that.

 

[dhengr]

Jim57:
The codes do say/imply that the structure should be designed for all the loads that will be imposed upon it. ASCE 7 has pages and pages of wind loading criteria, for all areas and surfaces of structures, building corners, roof edges vs. distance from the edge, leeward and windward surfaces, uplifts and suctions on every imaginable surface. We’ve seen dozens of papers, articles, our text books on Fluid Mechanics, fluid flow, that show wind hitting a wall and then diverging outward, in the plane of the wall, or being rammed into a semi-enclosed space and pressurizing it, or flowing over a surface or edge and causing a negative pressure. What more do you want, or need? Things seldom fail becuase the load you used was 15psf as opposed the 15.3psf that some test or code says to use. The problem isn’t that the designer missed the max. load by 2psf, it is that he didn’t even account for its existence, and you shouldn’t need a code to tell you that. In good part the reason codes have become so complex, full of meaningless verbiage and unmanageable these days is that engineers can’t take basic concepts and apply them with experience and good engineering judgement. They want a separate code paragraph for every possible condition in the universe. And, then get upset and unsure because their color of ceiling material isn’t specifically listed in that para.

If you’re going to court, keep it simple, or the judge’s and juror’s eyes just start to glaze over. The code says you should design for all loads imposed on the structure. These loads are common engineering knowledge, assuming the designer had some/any of that, and he didn’t account for this load condition. If the Arch. is dumb enough to ignore that possibility or delegates that design responsibility, the installer had better be on his toes, because the code is pretty clear about accounting for all loads imposed. We can argue at some length about the exact magnitude of this uplifting load on the ceiling panel system, with a fair degree of uncertainty as to the exact magnitude, but there should be little disagreement, by people reasonably well versed on the matter, that they exist. And, they made no effort to account for them, period. The more you try to tie this up by citing many different codes and code paragraphs, the more you just tend to tie your own hands. There should be no argument that the load must be accounted for in our design, just look at what’s happening here; but you can argue all day about the validity of a few psf +/-.

 

[hokie66]

Exterior ceilings/soffits are subject to the same wind pressure as the walls which they abut.

 

[wannabeSE]

ASTM C635 has more to do with the bits and pieces of the lay in ceiling system (e.g. the load and deflection requirements for the runners). ASTM C636 covers the installation (e.g. hanger spacing, hanger wire requirements). Neither standard provide specific requirements for exterior installation. See section 1.3 of scope for

http://www.astm.org/Standards/C635.htm.

And, section 1.5 for

http://www.astm.org/Standards/C636.htm.