P/S box beam end reinfocement
P/S box beam end reinfocement
(OP)
Hi,
I have a p/s spread box (BII-48x33, 48 strands) bridge, simple span. AASHTO 9.22.1 requires vertical stirrups at anchorage zone. Can someone explain why they are needed? My calculation requires 4 sq.in. steel within 6 in. of the end of the beam. It seems to me that it's difficult to fit in this much steel unless go to much larger bars than #4. (I also have #4 stirrups at 6in. in the end zone.) How does this anchorage thing work?
I have a Penn Standard drawing also shows a rebar grid at the end of the beam. Is this for spalling/bursting? AASHTO doesn't say anything of this issue for prestressed beams though. What is it?
Thanks for answering.
I have a p/s spread box (BII-48x33, 48 strands) bridge, simple span. AASHTO 9.22.1 requires vertical stirrups at anchorage zone. Can someone explain why they are needed? My calculation requires 4 sq.in. steel within 6 in. of the end of the beam. It seems to me that it's difficult to fit in this much steel unless go to much larger bars than #4. (I also have #4 stirrups at 6in. in the end zone.) How does this anchorage thing work?
I have a Penn Standard drawing also shows a rebar grid at the end of the beam. Is this for spalling/bursting? AASHTO doesn't say anything of this issue for prestressed beams though. What is it?
Thanks for answering.





RE: P/S box beam end reinfocement
I usually spec #5 stirrups in the anchorage zone.
Anyway, the rebar grillage from PennDOT is probably for post-tensioned girders to meet the anchorage zone requirements. Normally, this is designed using a strut-and-tie model. Maybe they pulled the detail from PT Girders and are using for PS Girders?
MikeD
RE: P/S box beam end reinfocement
I think I have a relatively large prestress force in the section (48 0.6in. strands in 48x33 box beam). This makes the anchorage steel req't difficult to meet. Is there any way to get around AASHTO? I do have a 12 in. end block though (from bearing center to the end of the beam).
RE: P/S box beam end reinfocement
PennDOT probably just adds this grillage and doesn't give it a second thought.
In a way it is easier to fit the added rebar in a PT girder since the strands are in ducts. In a PS Girder they are spread out and you'll have trouble fitting the stirrups in between.
Two options: 1)You can call this a disturbed region and check it as a strut-and-tie model. 2)Call a local fabricator and ask them how the detail is usually handled.
Last word: You might check with local fabricators anyway because if you have too many strands their beds might not be able to handle it. They also may have a slightly different pattern in their beds. In past experience the PCI max number of strands cannot be reached by the fabricators. The available locations and number of strand is pretty much theoretical in my opinion. Your software may say 48 strands works but sometimes they cannot hold down that much.
Good Luck
MikeD
RE: P/S box beam end reinfocement
Koo