Fire resistance duration of concrete wall panels with flexural cracking
Fire resistance duration of concrete wall panels with flexural cracking
(OP)
Does anyone have experience with fire resistance of concrete tilt-up wall panels (that are intended to serve as a 3 hour duration separation wall) with FLEXURAL cracking?
40'H x 12'W panel with 18'H x 8'W door opening, central about bottom of panel - so a inverted U-panel.
The EoR has stated that the 'cracking is cosmetic and not structurally significant'. However, the architect is rejecting the GC's panel due to compromising of fire resistance due to the local flexural cracking.
I found a few technical papers on the subject, although most are in relation to post-earthquake damaged concrete elements that are then subjected to fire. The flexural cracking for our project is due to erection/handling stresses.
I did find this ASCE Journal of Materials paper that seems appropriate:
We are assisting the GC in repair options, however, I am interested if other engineers have encountered the argument above put forward by the architect and how you resolved it.
40'H x 12'W panel with 18'H x 8'W door opening, central about bottom of panel - so a inverted U-panel.
The EoR has stated that the 'cracking is cosmetic and not structurally significant'. However, the architect is rejecting the GC's panel due to compromising of fire resistance due to the local flexural cracking.
I found a few technical papers on the subject, although most are in relation to post-earthquake damaged concrete elements that are then subjected to fire. The flexural cracking for our project is due to erection/handling stresses.
I did find this ASCE Journal of Materials paper that seems appropriate:
"Thermal Propagation through Tensile Cracks in Reinforced Concrete." by Ervine, A., Gillie, M., Stratford, T., and Pankaj, P. (2012).
Quote (ASCE paper)
"Consequently, it is concluded that the effects of tensile cracking on the thermal propagation through concrete can be ignored in structural analyses."
We are assisting the GC in repair options, however, I am interested if other engineers have encountered the argument above put forward by the architect and how you resolved it.






RE: Fire resistance duration of concrete wall panels with flexural cracking
RE: Fire resistance duration of concrete wall panels with flexural cracking
Something tells me though that if the architect wants to reject these panels I'm sure he or she will find a way. That much flexural cracking doesn't seem appropriate for a new structure.
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Fire resistance duration of concrete wall panels with flexural cracking
RE: Fire resistance duration of concrete wall panels with flexural cracking
The flexural cracking was caused by erection/handling of the panel - the lift points were incorrectly located on site so the center of lift was out of alignment to CG. Cracking is very localized at the re-entrant corner.
GC intends to epoxy inject the cracks via pressure injection, BUT, the architect then said that the epoxy-resin will not meet the fire resistance required. We have assumed he is referring to the glass transition temp (Tg) of epoxy being only about 150°F. Damn architects!
RE: Fire resistance duration of concrete wall panels with flexural cracking
ACI 224R-01 says that the the allowable loading in ACI 318-95 corresponded to a probable crack width of 0.41mm for interior exposures and that the co-efficient of variation is about 40% with isolated cracks sometimes in excess of twice the computed value occurring on occasion.
I suspect you won't find any real fire testing on cracks in the 1mm+ range. I suspect it probably doesn't seriously affect the fire-resistance but couldn't prove it.
Could you toss them a bone on the big cracks and use ACI 224R to show that the small cracks are industry typical? Do a patch job on the larger ones.
RE: Fire resistance duration of concrete wall panels with flexural cracking
The facility is a storage warehouse, and the wall gets cement washed then painted anyway. Seems wrong to reject a panel due to such a relatively small/localized defect.
RE: Fire resistance duration of concrete wall panels with flexural cracking
I found a PhD dissertation that tested beams with upto 0.7mm crack widths - with similar conclusions to the ASCE paper I quoted above.
See my comments above that the GC intends to inject the cracks except the architect is rejecting that proposal as the epoxy will not meet the fire endurance.
RE: Fire resistance duration of concrete wall panels with flexural cracking
There's a pdf download link on this page for the thesis. His 'major damage' crack width was in the order of 5mm +/- 0.7mm and showed no difference in temperature inside the concrete. There could be convective effects that weren't captured, but I think this probably should show that minor cracks aren't significant risks to fire protection.
RE: Fire resistance duration of concrete wall panels with flexural cracking
RE: Fire resistance duration of concrete wall panels with flexural cracking
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
www.americanconcrete.com
RE: Fire resistance duration of concrete wall panels with flexural cracking
Yep, that's the one...and he is one of the co-authors of the ASCE paper too. I misread the 'major damage' crack width of 5 mm +/- 0.7mm - I read it as 0.7 mm total crack width in error.
5mm is a BIG crack width:
Thanks TLHS.
RE: Fire resistance duration of concrete wall panels with flexural cracking
RE: Fire resistance duration of concrete wall panels with flexural cracking
RE: Fire resistance duration of concrete wall panels with flexural cracking
We were informed by the GC that they attempted to re-erect the cracked tilt-up panel (with some 'strong-backs' installed) and the panel cracked further, so they decided to recast/replace the panel.