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Re: SCBF Compressible Material?

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J. Lin,
 
        I can not answer your question directly but I have seen styrofoam used for similar purposes where it does not work as intended.  I have seen it used under grade beams supported on piles to prevent uplift due to frost action or swelling soil where it does not perform as expected.  The structurally weakest (white) styrofoam type of insulation generally resists about 10 p.s.i (1440 p.s.f.) before significant yielding takes place; and stronger (structurally) grades, such as Styrofoam HI, can resist from four to eight times as much or more.
 
        These are very small stress levels compared to structural building materials; but if you have large enough contact (and here, I am not familiar with your geometry) areas the resulting forces may not be irrelevant.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
From: SE3949
Sent: Thursday, May 10, 2007 10:58 AM
Subject: SCBF Compressible Material?

For Steel Special Concentrically Braced Frame (SCBF), I always saw the Contractor using Styrofoams at both sides of the embedded gusset plate as the compressible material to eliminate the lateral restraint. 
 
Recently there is a project that the Contractor using the "JOINT FILLER" (Fibre Expansion Joint by W. R. Meadows, Inc.; similar to the one you saw on your concrete driveway as the concrete divider but harder) instead of the Styrofoam. The Contractor and the Design professionals claimed that this FILLER were used for MANY projects in the past several years in SCBF design/construction.
 
Can you let me know your opinion regarding those rigid-like filler for SCBF?
 
My opinion: That filler will provide excessive lateral restraint and will prevent the brace to buckle in pin-pin shape. If the brace did not buckle at the designated force level (lost the function as the FUSE system), then other portion of the frames (columns, beams, joints, connections) might fail before the actual brace buckling. The designer's nightmare of sudden building collapse might occur since the brace wouldn't buckle (dispatchs the energy and also acts as the warning sign) at that designated seismic force.
 
J. Lin, SE
Los Angeles



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