Rebar as bolts in base plate connections 3

[LJ_]

As you can see the following details, the base plate is connected to the concrete through rebars instead of J/L bolts. I am wondering if I can assume it is a L/J bolt in my calculation with the same diameter. The rebar strength is 60ksi. Welding is a more widespread practice in my city but I am concerned about brittleness in that area. But maybe I am overthinking this. What are your thoughts? Thank you!

Edit: typo

 

[Agent666]

I personally don't have any issues with this type of approach provided it is treated appropriately.

If welding is it really any different to casting in a plate with welded bars, so no issue there in my mind. You'd obviously need an appropriate welding procedure for the site welding.

If threading the reinforcing, then you need to consider this in the area used for shear and tension calculations like what you might do for a bolt. You also want to make sure you have sufficient threaded length so that the bars/bolts have sufficient length to stretch over, without concentrating any inelastic strains in a small length of threads.

If welding or threading bars you also need to be mindful of not using quenched and tempered bars, only use microalloy bars.

 

[Agent666]

I'd also design for the yield strength of the bars, not the ultimate strength of the bars (like you might do for a bolt, where bolt design is typically based on f_u instead of f_y)

 

[LJ_]

Hello Agent666 thank you for your answer.
What are the disadvantages though? Why is that this type of connection is not more widespread in codes and there are many other types of cast in situ bolts?. Would this work even for a seismic area ?

 

[phamENG]

Cost. Anchor bolts are cheaper to make. For this, you have to first make the rebar, and then turn it into a bolt.

 

[r13]

I believe numerous pull out tests by ACI and many researchers in the past have shown the poor pull out performance of L bars in direct tension.

 

[dik]

Used to be quite common... I've often used Dywidag threadbars for anchor rods with 'real' loads. Only problem is the cost of the specialised 'nuts' are expensive.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[phamENG]

r13 - those tests applied to the smooth anchors that rely on the out turned leg to bear on the concrete above in direct tension. In the OP's example, you'd be doing development length calculations for hooked bars in tension. Certainly a reliable and widely trusted means of resisting tension in concrete, but again - expensive for fabrication. Portland Bolt has a decent Q&A on the subject and they direct most of the answer toward the difficulty of cutting or rolling the threads. First, you have to smooth out the threaded length plus some, then do your cutting and rolling.

The welded option is also more expensive. A guy with a wrench is cheaper than a field welder every time. Throw on top of that the fact that A615 bars are not necessarily weldable. For that, you need A615 with a supplemental specification stating that it can be welded or A706 bars.

 

[phamENG]

dik - Wow. Those are some serious anchors. Are we talking column base plate anchors, or other more "exotic" applications?

 

[STrctPono]

What are the disadvantages though? Why is that this type of connection is not more widespread in codes and there are many other types of cast in situ bolts?. Would this work even for a seismic area ?

I guess the better question is why would you want to use this connection over a CIP anchor bolt? You are introducing so many variables that you do not know and cannot control. F1554 anchor bolts have been thoroughly tested to perform as such for static loading, cyclic loading, cold weather environments, ductility, etc. Using rebar in an application that it was not intended might be fine for 90% of the applications but why risk it when headed anchor bolts are so widespread and available?

In the OP's example, you'd be doing development length calculations for hooked bars in tension.

Everything about this element is an anchor bolt despite the fact that it is made from rebar. I would still perform all the standard ACI checks that we normally make for anchor bolts.

 

[dik]

Serious loads... else I would have used A307

Predated F1554... now I like Grade 55 S1... and nearly always use it...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
-Dik

 

[dhengr]

I suspect that those rebar substitutes for A.B’s. are free in the supplier’s minds, not to their customers, of course, in many countries. They are cut-offs, out of the scrap pile, who’s ever going to check the mat’l. spec., or if it is weldable? If you have the right dia. and length, the bending is cheap, done in the rebar shop or on site, with the rest of the rebar. Bolts and nuts are a specialty import. If it’s going to be welded, I’ll bet they’ll even cheat a couple mm on dia., over or under, who’s ever going to know? On site welding is probably not prohibitive in cost either; a cheap welding machine, some wire, no welding procedure req’d., make some bright, flashing light and you are done. And, they are really fairly unlikely to be overloaded or pulled out if the designer applied any FoS to his/her design. If someone wants to thread those bars, that’s their problem and expense, at a later time.

 

[hokie66]

I think it would vary by location. In Australia, I have used grade 60 bars many times as holding down bolts (that's what they call anchor bolts here). The reinforcing bar rolling mills publish design data for threaded rebars. They take into account that the outer, deformed skin of bars is harder and stronger than the core, so when you thread that part, it reduces the tensile capacity of the bar more than it would with a smooth bar.

 

[moments]

I specify these regularly. More frequently in vertical surfaces, but that’s a minor point. They’re genetically known as “deformed bar anchors,” and for non-seismic loading, look into “D2L bars,” for seismic “D6L bars.”