What should I consider when designing Post Tensioned beam with pour strip in it? Can anyone provide typical detail or design info? Do I design it just like a regular beam as id there is no break but provide pour strip where the tendons stop at CGC of concrete section and call it a day? How do I handle mild reinforcement?
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Pour Strip through PT neams
- Thread starter priya15
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I've never done a pour strip with a PT beam, but I don't see why it would be any different than for a slab.
I design the entire span that has the pour strips as mild only, making sure that the rebar lapped in the pour strip can be take the moment. The cables don't HAVE to terminate at the neutral axis of the beam, but it's good practice unless you have a specific reason to do otherwise.
I design the entire span that has the pour strips as mild only, making sure that the rebar lapped in the pour strip can be take the moment. The cables don't HAVE to terminate at the neutral axis of the beam, but it's good practice unless you have a specific reason to do otherwise.
First off, if the pour strip is through a single span beam then I don't design it as a p.t. beam. If the pour strip is through the end span of a continuous beam then I don't put tendons in the short length of beam beyond the pour strip.
I locate the pour strips at mid-span. (Some engineers put pour strips at the point of inflection of tendon drape. I never do that. That seems to be an awkward design - and if the shores are accidentally pulled then you will have a problem. Better to put the pour strip at midspan and design the beam to cantilever and support it's own weight + some construction live load in the event that the shores are prematurely removed. I have been doing it this way for 25 years.)
Keep the tendon drape at the pour strip high enough that you can arrange all of the anchors properly and avoid interference between the tendon anchors and the bottom reinforcing steel (which has to be designed to resist all of the positive moment. (Leave room for shear friction horizontal each face bars to pass through the pour strip within the depth where the tendon anchors are occuring. (In other words, don't have a wall of tendon anchors across the full width of the beam at teh pour strip.)
I usually put 2x4 keys at 4" o.c. or 2x6 keys at 6" o.c. (depends on beam depth), and I put shear friction horizontal bars at 4" or 6" o.c. (with as many rows as needed to transfer shear across the joint. (True, there is not much shear at mid-span of a uniformly loaded beam, but I like to have a good amount of shear strength anyway.)
I add a couple of extra stirrups at 3" o.c. on each side of of the pour strip joint. (Again, this is probably conservative, but I want redundancy and ductility at this joint.
I locate the pour strips at mid-span. (Some engineers put pour strips at the point of inflection of tendon drape. I never do that. That seems to be an awkward design - and if the shores are accidentally pulled then you will have a problem. Better to put the pour strip at midspan and design the beam to cantilever and support it's own weight + some construction live load in the event that the shores are prematurely removed. I have been doing it this way for 25 years.)
Keep the tendon drape at the pour strip high enough that you can arrange all of the anchors properly and avoid interference between the tendon anchors and the bottom reinforcing steel (which has to be designed to resist all of the positive moment. (Leave room for shear friction horizontal each face bars to pass through the pour strip within the depth where the tendon anchors are occuring. (In other words, don't have a wall of tendon anchors across the full width of the beam at teh pour strip.)
I usually put 2x4 keys at 4" o.c. or 2x6 keys at 6" o.c. (depends on beam depth), and I put shear friction horizontal bars at 4" or 6" o.c. (with as many rows as needed to transfer shear across the joint. (True, there is not much shear at mid-span of a uniformly loaded beam, but I like to have a good amount of shear strength anyway.)
I add a couple of extra stirrups at 3" o.c. on each side of of the pour strip joint. (Again, this is probably conservative, but I want redundancy and ductility at this joint.
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