Precast TT's 1

[PrecastDroopy]

This is about reinforcement in twin T's

First, is the web steel based on a deep beam member?

Second, are the flange members considered continous over the stems? or are they cantilevered off of the stems. This is considering that they have vector connectors every 4'-0".

I ask this because many differing designs have come accross my desk and I want a general opinion of others.


Thanks

 

[KarlT]

I'm not sure what you mean by your first question??
In lightly loaded double tees, you can actually get away with some very minimal web reinforcing at each end, as per a report done in the PCI Journal.

I would consider the flange to be continuous over the double tee legs, but not across a flange to flange joint.

I'm not sure how helpful this has been, but if you could expand on your questions maybe I can give you more input.

KarlT

 

[PrecastDroopy]

I am just curious how to determine what is required by code. I did see that article. I am estimating a job and just curious if any "quick" way is available.

 

[haynewp]

Usually the spans are out of the deep member range or I wouldn't be using a double T member.

If you have a PCI handbook you could find the size of double T required and call some precasters for an estimate. If you don't have the book, you could still call a Metromont engineer and he could give you good info for what you are looking for.

 

[KarlT]

I agree with haynewp - you only need to consider the member as a "deep" member for shear if the clear span is less than or equal to twice the member depth, which for say a typical 24" deep DT would result in a 4'-0" long member.

I believe the PCI handbook has a design example for sizing the steel in the double tee deck.

There are also numerous prestressed design programs such as Concise Beam, or LEC Press that can give you an answer really quickly.