Penetration in Hybrid RC-Post-Tensioned Beam 1

[waytsh]

I have a hybrid rc-post-tensioned beam 14" wide by 34" deep with a 14" diameter penetration. I have the flexibility to locate the penetration anywhere on the beam however I need to hold it to a particular elevation in the depth of the beam.

Obviously my problem is figuring out how to correctly analyze the beam for this penetration. I would welcome any input on how to handle this or any suggestions on reference material which addresses this type of analysis.

I know PCA has an example of a beam with a web penetration, however, it is not a hybrid and it is a little unclear how they arrive at the compression and tension forces in the legs.

Hope someone can help.

Thanks,

 

[MikeT14]

waytsh,

I've got a standard detail from ADAPT that deals with stem penetrations. It limits the hole size to H/4 (your penetration seems to exceed this recommendation) and shows 2-#6 above and below each hole and 3-#4 stirrups @3" o.c. each side of the hole. Spacing for multiple holes is limited to greater than or equal to 1.5 times the largest hole diameter. Location is shown as a minimum 2H from the face of the support and positioned at midheight of the beam.

As for analysis, I'd try a strut-and-tie method to account for the tension and compression forces around the reduced section. Or possibly an analysis using the reduced section properties of the beam.

Is this new construction or renovation? If a renovation, make sure you know where your tendons are located! If it's new, perhaps a smaller penetration or series of smaller penetrations using the spacing guideline above?

Hope this helps . . .

 

[waytsh]

MikeT14,

Thanks for the response. This is new construction so I will be able to miss the strand locations. I have some standard details from ADAPT as well I guess I will have to look through them. I didn't realize they addressed this situation. Do you know the detail and drawing number?

Also, I just found an ACI reference Title no. 98-S39 "Design of Reinforced Concrete Beams with Circular Openings". It looks like it has some good information although it does not address the prestressing in my beam.

Thanks again!

-waytsh

 

[MikeT14]

waytsh,

Sure, the detail is a part of the "ADAPT - Details; Post-Tensioning Details & Notes" sold by ADAPT. Its a set of recommended details and notes. My firm purchased it and received the spiral bound set of details (about 120), a set of typical plans, and actual set of plans from a Bijan Aalami job in 1989, and a cd containing electronic copies of everything. The drawing number I'm referring to is detail10.dwg.

Mike

 

[waytsh]

Mike,

We had just won the ADAPT details package in a raffle at the PTI conference, but I had not had a chance to look through them. So you do not need to forward it on to me. Thanks for letting me know the number and for your willingness to help.