CRACKING IN POST TENSIONED BEAMS
CRACKING IN POST TENSIONED BEAMS
(OP)
Fellow structural engineers, do you know of a good reference for guidance in classifying crack types for several types of construction? I recently made a site visit for a cast in place post tensioned parking garage that we designed. The only cracking I noticed were a few beams have 1 to 3 vertical hairline cracks a couple of feet away from the beam column intersection. The crack is very small in width, you would be hard pressed to fit a hair into the crack. I have attached a picture of one such location. My initial thought is that it is a crack related to temperature expansion. Your thoughts, as always is appreciated. Thank you.






RE: CRACKING IN POST TENSIONED BEAMS
The cracks appear vertical on the left and then sloped like a shear crack pattern towards the right.
Any other input you can provide? How many days between pour and tension?
RE: CRACKING IN POST TENSIONED BEAMS
RE: CRACKING IN POST TENSIONED BEAMS
RE: CRACKING IN POST TENSIONED BEAMS
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RE: CRACKING IN POST TENSIONED BEAMS
RE: CRACKING IN POST TENSIONED BEAMS
The beams are 36 inches total depth. There are top, bottom, and each face bars continuous end to end with both the top and bottom bars hooked into the column and fully developed. The stirrup spacing at the column face is 2 legs of #4 bars, 5 @ 2", 5 @ 6".
The loading is uniformly distributed dead and live loads, but to this point the deck should only have been subjected to full dead load and construction live load, not full live load.
The cracks appear to run from near the bottom of the slab to the bottom of the beam.
The construction is 1 and 2 62 ft span beams. 7 inch slab, 16 inch wide and 36 inch total beam depth.
I hope this provides for a better picture.
RE: CRACKING IN POST TENSIONED BEAMS
BA
RE: CRACKING IN POST TENSIONED BEAMS
RE: CRACKING IN POST TENSIONED BEAMS
RE: CRACKING IN POST TENSIONED BEAMS
1. the drape of the tendon at the continuous end is putting the bottom of the beam in tension allowing the shrinkage cracks to open up.
2. Cracks occurred prior to tensioning and aren't being closed.
In the photo, is the column to the right?
In any case, the reinforcement seems appropriate and cracking on the underside of a slab shouldn't be a concern regarding maintenance. The cracks should close even further once live load is placed on the slab.
RE: CRACKING IN POST TENSIONED BEAMS
RE: CRACKING IN POST TENSIONED BEAMS
I am assuming that the prestressing at this end of the beam is in the centroid of the shape (discontinuous end). Is it possible that the PT duct is eccentric to the centerline of the beam? Do the cracks appear on both sides of the beam or just one face? Short of that, I am at a loss.
RE: CRACKING IN POST TENSIONED BEAMS
BA
RE: CRACKING IN POST TENSIONED BEAMS
BAretired, typically 4 in2 top reinforcing continuous and fully developed into the columns, and 3 in2 bottom reinforcing midspan with 2 in2 at each end fully developed into the columns. Usually minimum reinforcing controlled (As = 0.004 Act).
RE: CRACKING IN POST TENSIONED BEAMS
RE: CRACKING IN POST TENSIONED BEAMS