Hairpin Design 2

[hdp321]

Has anyone else utilized more than one hairpin to resist large thrust loading? Most examples use one hairpin and this is fine for smaller buildings, but if the thrust is very high can two or three hairpins per column be utilized?

Tie rods cannot be used for this scenario.

 

[KootK]

...apologies, Koot...

No sweat. In my heart, I've always felt as you do really. Sure, mechanical splices are a reliability improvement. But, then, what makes that reliability improvement more important in a tension tie than in the bottom steel of some giant transfer girder? There must be some fundamental difference but I've yet to put my finger on it. Maybe the code provision is really intended for things that "hang" which we tend to be more skittish about in general.

 

[phamENG]

There must be some fundamental difference but I've yet to put my finger on it. Maybe the code provision is really intended for things that "hang" which we tend to be more skittish about in general.

I don't do a ton of concrete anymore, but if I remember correctly that's exactly what it's about. Tension members have that restriction. For flexural tension, you can generally detail your way out of it, putting splices in areas of typically lower tension. So if the the member is designed to see pure tension (like, well, a tension-tie), it has to be mechanically spliced because there is no place to put the splice that will reasonably see less tension.

 

[KootK]

@phamENG: I'm grateful for the feedback.

For flexural tension, you can generally detail your way out of it, putting splices in areas of typically lower tension.

Rationally, one probably can detail their way out of it. However, to my knowledge, there is no requirement for designers to do that. As far as I know, we can put our splices anywhere we like.

 

[dik]

I've never treated them as structural slabs, even when specially reinforced for local items... I was just wondering if others did... I've always use hairpins to take the horizontal load from PEMBs into the temperature steel... it's there... you may as well use it for something.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

Here's the commentary on lap splices and mechanical splices from ACI 318-14. You're right, KootK - it is up to the designer and there's no prohibition on splices in high moment regions. But the commentary does suggest that the intent of the splice requirements is to "encourage" the designer to keep them in lower demand regions.