Ad Hoc Construction Joint in Waffle Slab?
Ad Hoc Construction Joint in Waffle Slab?
(OP)
Hi,
I'm not sure if this is going to sound a bit stupid but here's the situation:
I work at an 8-story parking garage building project, we already completed the first waffle slab and now the second slab is on its way, awaiting confirmation for the time to pour concrete,
but one of the management has decided (NOW!!) that this building is too big and needs a construction Joint to split the slab in half to prevent shrinkage, etc.
I'm not sure this is possible now, and I came here for help.
this is an EXTREMELY rough sketch and I will post the structural and other CADs later, : https://www.dropbox.com/s/gqwb9xwqwd75383/waffle%2...
PDF if you dont have ACAD at the moment: https://www.dropbox.com/s/t7s9t1urlkrsr3h/waffle%2...
not sure if this is possible for my case http://www.concretenetwork.com/concrete-joints/con...
http://www.sefindia.org/forum/files/construction_j...
Much appreciated!
I'm not sure if this is going to sound a bit stupid but here's the situation:
I work at an 8-story parking garage building project, we already completed the first waffle slab and now the second slab is on its way, awaiting confirmation for the time to pour concrete,
but one of the management has decided (NOW!!) that this building is too big and needs a construction Joint to split the slab in half to prevent shrinkage, etc.
I'm not sure this is possible now, and I came here for help.
this is an EXTREMELY rough sketch and I will post the structural and other CADs later, : https://www.dropbox.com/s/gqwb9xwqwd75383/waffle%2...
PDF if you dont have ACAD at the moment: https://www.dropbox.com/s/t7s9t1urlkrsr3h/waffle%2...
not sure if this is possible for my case http://www.concretenetwork.com/concrete-joints/con...
http://www.sefindia.org/forum/files/construction_j...
Much appreciated!






RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
I'll get the CADs soon by email, will upload them as soon as possible,
but 40+ meters by 60+ meters, spans between 7m and 10m , slab thickness 50cm , topping 7cm
Thanks for the reply!
RE: Ad Hoc Construction Joint in Waffle Slab?
A construction joint is common for constructability reasons. Just place it near centre span, where shear is minimal.
RE: Ad Hoc Construction Joint in Waffle Slab?
sorry for not being so clear, English is not my first language,
the slab reinforcement steel is already built , and I want a section or a detailing of the construction joint, esp. that the primary beams' reinforcement is already built with no consideration for construction joints
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
And make sure it is ALL propped until the second pour has reached stripping strength.
RE: Ad Hoc Construction Joint in Waffle Slab?
Kindest regards,
T. K.
RE: Ad Hoc Construction Joint in Waffle Slab?
Shear is transferred by added rebar dowels as hokie suggests, or forming a shear key with wood nailed to the bulkhead in each waffle rib perpendicular to the span. I think dowels are easier for the slab since it's so thin. Pick whichever is easiest to build, and send RFI asking if it is OK along with the location (I recc third-span of your center bay). Owner sounds very capable of alerting the A/E of its urgency.
Also---waffle slab, cool! Figured those were out of style these days but guess not.
RE: Ad Hoc Construction Joint in Waffle Slab?
These are the CADs : https://drive.google.com/file/d/0B3Q6BZ33FuxBMU9Hb...
it would be really helpful if you could illustrate your answer calvin on this whiteboard https://whiteboardfox.com/66238-7956-7446 since I am not as familiar with some of the terminology you used, I work in an Arab country and technical English terminology isn't widely used.
Kindest regards,
T. K.
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
I may get back here for more help if that's ok..
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
Thanks again.
T. K.
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
placed perpendicular to the main reinforcement are at points
of minimum shear or points of contraflexure. Joints are usually
located at midspan or in the middle third of the span, but
locations should be verified by the engineer before placement
is shown on the drawings. Where a beam intersects a
girder, ACI 318 requires that the construction joint in the
girder should be offset a distance equal to twice the width of
the incident beam."
I understand that the point of contraflexure is the zero moment where moment changes sign, but does this point also coincide with the points of minimum shear?
Kindest regards,
T. K.
RE: Ad Hoc Construction Joint in Waffle Slab?
In your case, with a waffle slab, I don't think the part about a beam intersecting a girder is applicable.
The most important part of the clause you quoted is the need to verify with the engineer. You have stated that you have limited experience, so these decisions should not be made by you alone.
RE: Ad Hoc Construction Joint in Waffle Slab?
I would tend to do the same with RC slabs. As long as the short end is poured first, it allows the builder to "accidently" remove the formwork before the second section is poured without problems.
Remember that even though the full load shear diagram is 0 at midspan (in a symmetric internal span), once you consider partial loadings it could be anywhere in about the middle 1/3 of the span.
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
I assume you meant NOT PT.
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
Kindest regards,
T. K.
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
The 1 meter strip they will pour later is at third of span in the middle span of the slab
Reference sketch : http://s19.postimg.org/ogsh5p0n7/screenshot_41.jpg
do you think this will help with thermal expansion at all?
Kindest regards,
T. K.
RE: Ad Hoc Construction Joint in Waffle Slab?
It won't help with thermal but it will help with shrinkage which is probably the primary concern. In my neck of the woods, we'd call this a "pour strip" and I think that it's an excellent solution here. If I were the contractor here, I think that I'd want to create the construction joint by removing a line of waffle slab forming pans anyhow. That way you'd make the joint in solid (not ribbed) concrete and, I think, have a much easier time installing the bulkheads and creating a shear key(s).
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: Ad Hoc Construction Joint in Waffle Slab?
Hard to tell from your plan how much restraint to shrinkage you have. Are there perimeter walls, or are the shaded parts just balustrades?
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
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: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
There will also be restraint cracking perpendicular to the shorter end wall.
RE: Ad Hoc Construction Joint in Waffle Slab?
https://goo.gl/photos/o6Nno2Q8D1Q8xNeE9
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
not sure, but maybe people with more expertise than mine can say their opinion?
Kindest regards,
T. K.
RE: Ad Hoc Construction Joint in Waffle Slab?
RE: Ad Hoc Construction Joint in Waffle Slab?
Follow up question, waffle slab formwork removal is 28 or 14 days ?
RE: Ad Hoc Construction Joint in Waffle Slab?