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Re: Precast Panel Cracking[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: Re: Precast Panel Cracking
- From: mludvik(--nospam--at)hardesty-hanover.com
- Date: Wed, 26 May 2004 18:06:59 -0400
It would make sense to me that you get a very small crack down the reveal - you have effectively restrained the panel perpendicular to the span, so any shrinkage strain at all would translate to a crack. This is not helped by the lack of transverse rebar, and the reason it occured at the reveal is that it is the weak point of a section in tension. It should be a small crack though. If you have 0.02% shrinkage strain, and the panel is 48" wide, the crack would be a maximum of about 0.01". Do you know how big the crack actually is? That might be enough to cause a leak, I don't know. If they are talking about structural failure and panels falling off, I can only imagine the anxiety levels around your friend's place. I should also add as a caveat to the above that I am not a super expert on precast - I am a bridge engineer and I worked at a precast factory during summer break at college. Michael "Chad Van Kampen" <Chad@GeraceConst ruction.com> To <seaint(--nospam--at)seaint.org> 05/26/2004 09:02 cc AM Subject Precast Panel Cracking Please respond to <seaint(--nospam--at)seaint.or g> Michael, Jim, and others, The panels were supposed to be Spancrete but were changes after crushing became and issue. The panels are horizontal in direction stacked 110’ up and bearing on each other. The lower few panels have insulation, and the upper ones (above the lower roof) are solid un-insulated panels. There is significant bow difference between these two panels, about 2” so there is a ledge for the water to sit on here. I am no longer working at this precaster but I am good friends with the project manager and he is struggling to figure out what is going on, with no help from the current engineer. He has told me that the mix for this particular panel was the “Spancrete” mix wetted down, and it was not extruded, but formed and poured on the Spancrete beds. The structural is only cracked at the embeds. This building is welded everywhere in every corner to everything else, so cracking at the embeds is not a big surprise. My guess is these welds cracked during erection while dead load was still being applied. The face cracks however, are a bit more puzzling. They are all cracked 2’-0” in from the end and down the center at a reveal. The cracks at the ends run perpendicular to the stand, the reveal crack runs with the strand, there is no other mild steel in the panel, and this was the first time they have used this procedure. As for the truss system it is running perpendicular to the strand, and span. It is the Meadow Burke Single Girder Truss system at 4-’0” oc in every panel, but is running in the short direction, not with the span. I appreciate your help because the P.M. is afraid that the face will fall off punching the lower roof, the only thing holding on the face is these trusses. This is not a composite panel the face is not acting to resist any loads. I was on SMA (The Spancrete Manufacturing Association) and issues like this were discussed but not in great detail. Have any of you ever “designed” the face? The P.M. is asking how we engineers take into account issues like this. I typically ignored the face since it was just for looks. Thanks again, Chad Van Kampen P.E.
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