Progressive Collapse - Alternate Path Method in UFC
Progressive Collapse - Alternate Path Method in UFC
(OP)
Anyone familiar with UFC 4-023-03 (2009), particularly the Alternate Path Method as it applies to Structural Steel framing?
A couple questions:
1. The load combination is listed as (1.2 OR 0.9) * Dead Load. Typically a 0.9 factor is used when you have load acting opposite of dead (wind uplift), but with progressive collapse, its all gravity loads. Still, using a 1.2 factor on such an extreme event seems like too much of a penalty.
2. Do you include the floor diaphragm in the building model? The diaphragm tends to take some in-plane forces while still allowing the frame members to be in flexure. It seems unreasonable to neglect the diaphragm, as the slab will be there in the event of a collapse.
3. Any idea what "Gn" is in Figure 3-13 ?
Thanks in advance,
Pete
A couple questions:
1. The load combination is listed as (1.2 OR 0.9) * Dead Load. Typically a 0.9 factor is used when you have load acting opposite of dead (wind uplift), but with progressive collapse, its all gravity loads. Still, using a 1.2 factor on such an extreme event seems like too much of a penalty.
2. Do you include the floor diaphragm in the building model? The diaphragm tends to take some in-plane forces while still allowing the frame members to be in flexure. It seems unreasonable to neglect the diaphragm, as the slab will be there in the event of a collapse.
3. Any idea what "Gn" is in Figure 3-13 ?
Thanks in advance,
Pete






RE: Progressive Collapse - Alternate Path Method in UFC
Well, respect 1.2 D they just want to be conservative. These installations are manytimes overseas and the verification of the dead weights are not always stricts. I can say you that in Spain there is a customary unconservative weight evaluation of terrazzo floors, well above the 20% excess (but only for that part of the dead weight).
Respect the second I would include anything that is able to restrain the progressive collapse that is not expressly forbidden by the code. Make a seart for the word "diaphragm" in the pdf, will make you clear that the intent of the check wants the diaphragm action retained if available.
3-2.12.4.1 Loads.
GN = Increased gravity loads for Nonlinear Static Analysis
Use always the find tool in pdfs for these questions, use to help.
RE: Progressive Collapse - Alternate Path Method in UFC
RE: Progressive Collapse - Alternate Path Method in UFC
RE: Progressive Collapse - Alternate Path Method in UFC
RE: Progressive Collapse - Alternate Path Method in UFC
You may find it by word search on "Alternate Path Method".
Title of the paper "UFC 4-023-03: Design of Buildings to Resist Progressive Collapse", by K. A. Marchand, D. J. Stevens, B. Growder & T. Campbell. It was published on April 2006, Structure Magazine.
RE: Progressive Collapse - Alternate Path Method in UFC
2. The examples in the UFC have diaphragms modeled as rigid.