Posted by B.J. Novitski on March 11, 2003 at 10:33:46:
In Reply to: ArchWeek - New Curve in System Ceilings posted by Kevin Matthews on February 05, 2003 at 00:45:19:
ArchitectureWeek received a question from a reader about the seismic implications of using this system. Although the question did not appear in this forum, USG has formulated an answer and asked me to post it. They wrote:
The CURVATURA 3-D Suspension System from USG Interiors is utilized as a decorative accent in building projects. Consequently, the system will not carry any lay-in light fixtures or mechanical items, and should, therefore, be considered a decorative display as opposed to a suspended ceiling membrane. Seismic bracing would be a matter of interpretation.
It should be noted that the grid members themselves are manufactured (prior to curving) in accordance with ASTM C635, meet the requirements set forth in UBC Standard 25-2, and are listed in ICBO Report #2244, as well as LA RR #22179, as DX26 Heavy Duty Main and DX224 Cross Tees. The basic installation should be in accordance with ASTM C636, with vertical wires at strategic locations along the main tees (vault tops or valley lows) for proper support of the vertical curves, not to exceed 4 feet 0 inches o.c.
It is also the uniqueness of this inventive system that helps separate it from similar, so-called ceiling systems. The curved main tees defy testing for loads, vertical or axial, and only contain lightweight panel loads in a typical application.
USG Interiors offers suggestions for seismic bracing, which are outlined below, based on our structural engineering and extensive ceiling experience. We believe these to be sensible ideas for review by the architect and local building department prior to installation of the actual CURVATURA system.
The CURVATURA system consists of rolled formed metal tees, known as main and cross tees, 1-1/2 inches high and 15/16 or 9/16 inches face width, with the heavy-duty (per ASTM C635, prior to curving) main tees being factory curved to repeatable specified radii (valley or vault directions), supported by hanger wires at 4 feet 0 inches o.c., and generally spaced at 24 inches o.c. This spacing is accurately maintained, and lateral restraint provided to the mains by nominal 24 inch by 1-1/2 inches by 15/16 or 9/16 inches face DX224 Cross Tees, installed 24 inches o.c. perpendicular to the main tees. DX intersections are as listed with DSA and exceed all tension and compression requirements. A variety of nominal 2 by 2 foot flexible panels (expanded metal, wire mesh, flat aluminum and FRP) are available for lay-in application into the 2 by 2 foot tee modules. The tee members included integral hold-down tabs that trap these panels to the tees. Other system accessories include edge trim, wall molding and fiberglass back panels.
The system application may fall into one of the following three categories:
1. A “decorative” system consists of the tees and panels in a floating (island) mode, within these guidelines:
A. Not supporting any heavy objects, such as light fixtures or air diffusers,
B. Less than 1,000 square feet per island,
C. Not connected at the perimeters (systems in this category will not require any seismic restrains, such as splay wires, compression posts, etc.).
2. Areas over 1,000 square feet, floating or with perimeter attachments, with curved main tees of a 7 foot 0 inch radius or larger, require use of the standard Uniform Building Code Standards seismic restraint methods.
3. Areas over 1,000 square feet, with curved main tees of a 7 foot 0 inch radius or less, will require bridging, such as DXW Main Tees, spanning across the CURVATURA Main Tees, parallel to them at 12 feet o.c. The bridging tees are screw fastened to the “hard” points of the CURVATURA system, such as the tops of the vaults. Seismic restraint as prescribed in UBCS, is then attached to these straight bridging runners.
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