Cracked And Uncracked Concrete Differences
I am still unclear on this issue. I am working on a metal stud job where I am using epoxy anchors in various situations. Many are for a cantilevered sill, so I have one bolt at each stud (16' O.C.) and it acts in tension only (about 1400 lbs ASD). This is an existing building with 9' PT slabs.
They are going to x-ray it to make sure we don't hit anything.If I assume cracked concrete, my anchor fails unless we go with a deeper embedment. If I assume un-cracked, it passes.I have asked a few former collegues and they say they would assume un-cracked.What are the rules? RE: Cracked Versus Uncracked (Structural) 1 Nov 16 18:08. How to demonstrate? I've seen several definitions of uncracked concrete that name shrinkage restraint as a source of fastener compromising cracks. With that on the table, even a PT slab might not qualify as uncracked locally. I wish that they'd ditch the untracked option altogether so that we could just all play by the same rules.
I feel more comfortable with uncracked when there is some redundancy and, by virtue of probability, not all of the fasteners will land in cracks. You situation would qualify in my opinion.I like to debate structural engineering theory - a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it. RE: Cracked Versus Uncracked (Structural). For the PT case, using same DL+LL and simple-span beam as above: The pre-compression (P/A) provided by the post-tensioning may create a situation where, during service level loading, the expected tension stresses at the bottom of the beam may never/rarely be realized during service because P/A is large enough such that it overcomes any tension by My/I. This is an idealized scenario though. A cantilever, for example, may have different states of stress depending on backspan geometry, deflection requirements, etc.I am only fastening into the slab and there is no cantilever.
Cracked And Uncracked Moment Of Inertia
They really make this stuff complicated nowadays. I can't wait to retire!Thanks for your advice RE: Cracked Versus Uncracked (Structural).
If this is in the top of a floor slab, is it near an area of negative moment? If not you may be ok. However in SDC C or higher you have to assume cracked concrete.This is what I don't get.
Cracked And Uncracked Concrete Differences Chart
These bolts are not for major structural components - just some light exterior metal stud walls. An earthquake big enough to crack the slab will still have no effect on these walls as they weigh nothing. Yea, i can see if it was the Big Dig, but there is no safety issue here.
RE: Cracked Versus Uncracked (Structural) 1 Nov 16 18:56. The AEFAC technical note had a list of references that I started digging through.
I found this.It is amazingly specific and clear. It has areas that can be considered uncracked by inspection, and also clarifies that minor cracking is acceptable at time of installation as long as it is not expected that further cracks will form or that existing cracks will expand. That would take shrinkage cracks out of the equation, for most applications.Note that this is a british opinion, so their recommendations for areas that remain uncracked don't appear to account for seismic load reversal.
I'd never consider a potentially life safety seismic application as uncracked, personally. Even if analysis level loads show that a member stays in compression, the true deformations are going to be higher and part of the assumed ductility mechanism involves concrete cracking. RE: Cracked Versus Uncracked (Structural) 1 Nov 16 21:54. And a bit more.Hilti's non-north american technical information is significantly more in-depth. I have a european manual hanging around somewhere and it goes significantly further into how they've come up with their capacities.That page goes a bit into cracking and makes it clear that the major concern is that when cracks propagate after an anchor is installed they have the propensity to intersect with the anchor hole itself due to the stress concentration at that point.
If a wide enough crack forms, it basically bisects the pullout cone into two pieces.Presumably, small width random cracking that would existing in almost any concrete beforehand has a significantly smaller effect on the breakout characteristics. RE: Cracked Versus Uncracked (Civil/Environmental) 1 Nov 16 22:17. It is amazingly specific and clear. It has areas that can be considered uncracked by inspection, and also clarifies that minor cracking is acceptable at time of installation as long as it is not expected that further cracks will form or that existing cracks will expand.
That would take shrinkage cracks out of the equation, for most applications.Shrinkage cracks don't expand? That's news to me.I'm all in favour of following engineering judgement and keeping it simple, but that means adopting the more conservative option if there is any reasonable doubt.What are the potential consequences of designing for cracked when uncracked would have been ok?What are the potential consequences of designing for uncracked if at any stage of the life of the structure it may become cracked, and subsequently be subject to maximum possible loads?Doug JenkinsInteractive Design Services.
The American Concrete InstituteFounded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete. Title: Differences between FRP Bond Behavior in Cracked and Uncracked RegionsAuthor(s): M. Taher Khorramabadi and C.J. BurgoynePublication: Special PublicationVolume: 275Issue:Appears on pages(s): 1-18Keywords: anchorage region, average bond stress-slip model, bond behavior, cracked region, local bond stress-slip modelDate: 3/1/2011Abstract:Based on an analysis of the experimental results of a proposed bond test method, significant differences are shown to exist between the local FRP bond stress-slip relationships in the uncracked anchorage regions and in the regions between cracks. The proposed method simulates the bond behavior between the flexural cracks and anchorage regions of a flexurally FRP-strengthened RC beam.
The boundary conditions, including the presence of cracks and steel, are shown to have significant effects on the local bond stress-slip models. The results showed that, at the same force, the bond stresses in the regions between cracks were lower than in regions outside the cracks, so the debonding formed in the anchorage regions. The local bond stress-slip models in the anchorage regions can be obtained from the conventional bond test methods but these do not mimic the conditions between the cracks.