×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Anchor Bolt Shear Reinforcing Stirrup Development
5

Anchor Bolt Shear Reinforcing Stirrup Development

Anchor Bolt Shear Reinforcing Stirrup Development

(OP)
Detail below is drawn to scale but I can provide specific dimensions if needed. My question is, would you consider the top stirrup in this condition adequately developed to provide shear reinforcing for the loading condition shown? Anchors fail without some form of shear reinforcing. Thank you!



RE: Anchor Bolt Shear Reinforcing Stirrup Development

It's not the most ideal scenario. Is there anything in the way of moving the anchor to the right? Is this a anchor bolt scenario and then covered by a tube steel post over the 4 anchor rods? That said, you could consider at least the first stirrup to be developed. PCI did research on stirrups in thin toppings.
https://www.pci.org/PCI_Docs/Publications/PCI%20Jo...

RE: Anchor Bolt Shear Reinforcing Stirrup Development

I would use a Strut-and-Tie model, Widianto et. al (CSA Today, Vol. III, No. 12) is a common reference for these situations.


RE: Anchor Bolt Shear Reinforcing Stirrup Development

This is common is industrial design. Try googling Design of Anchor Reinforcement in Concrete Pedestals or PIP STE05121 Anchor Bolt Design Guide or Design of Headed Anchor Bolts

RE: Anchor Bolt Shear Reinforcing Stirrup Development

Anchor bolt for petrochemical facilities is also a good reference



RE: Anchor Bolt Shear Reinforcing Stirrup Development

You can also conservatively calculate the pullout capacity of the hooked leg of the tie as a J-bolt anchor. I consider the other leg to be fully developed since it wraps around the pier. This strategy is implemented in this spreadsheet: http://www.civilbay.com/Tech-Writing/Design-of-Anc...

RE: Anchor Bolt Shear Reinforcing Stirrup Development

I think that you're good if you consider your shear load delivered to your rear anchors, as your sketch would imply. In that case, I'd just lean on the provision that allows beam stirrups to be considered instantaneously developed when #5 or less and hooked around a longitudinal bar. Granted, your claim to the longitudinal bar is a bit dubious in this scenario for the uppermost stirrup.

If you don't have weld washers on the other hand, then I think that your shear needs to be assigned to the front anchors. Then none of this stuff will save you.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

Quote (bones206)

You can also conservatively calculate the pullout capacity of the hooked leg of the tie as a J-bolt anchor.

Can you elaborate on that a bit? What I'm imagining sounds like a J-bolt with near zero embedment which would be sketchy.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

On a pedestal with small plan dimensions, the hooked leg of the tie might not be long enough to be considered fully developed for Fy, so I may assign it a lower pullout capacity instead. So in the OP's example I would take this approach with the circled leg of the tie.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

(OP)
Thank you for the all the responses. This is all very helpful.

Quote (KootK)

If you don't have weld washers on the other hand, then I think that your shear needs to be assigned to the front anchors. Then none of this stuff will save you.

Yes, I am calling out weld washers. Otherwise as you alluded I wouldn't have a prayer of making this work.

Quote (bones206)

On a pedestal with small plan dimensions, the hooked leg of the tie might not be long enough to be considered fully developed for Fy

Good point. According to my layout the hook is a little over 8" past the failure plane.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

I'll sometimes try to dictate location of the tie hooks in the pier detail. Or if the loads can reverse, I'll call out alternating hook locations in each layer of ties. But the chances of this actually happening when they assemble the pier cage is slim to none.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

The fitment that is hooked around the vertical bar would develop its strength basically immediately beyond the hook. The codes imply that this is the case for small diameter fitments that are hooked around a transverse bar of the same or greater diameter. I believe KootK mentioned this already.

As for alternating the hook position, I have never seen a need to do this. As long as the hooks turn inwards and are anchored in the core, these bars are considered to be fully anchored.

My only concern, if I am ever relying on a bar developing its strength immediately at the hook, is whether the cage is assembled so that the hook and transverse bar are in intimate contact to begin with, which is rarely the case. There is one particular study that showed that the hook alone, without the presence of an anchoring bar in the corner, can be enough to develop the full strength of a small diameter bar.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

Quote (bones206)

On a pedestal with small plan dimensions, the hooked leg of the tie might not be long enough to be considered fully developed for Fy, so I may assign it a lower pullout capacity instead. So in the OP's example I would take this approach with the circled leg of the tie.

So, in the sketch below, is the hook of your faux J-bolt on the left side of that leg, or the right?

RE: Anchor Bolt Shear Reinforcing Stirrup Development

Quote (gusmurr)

There is one particular study that showed that the hook alone, without the presence of an anchoring bar in the corner, can be enough to develop the full strength of a small diameter bar.

Any chance you could point me to that? I'm not surprised really. It's tempting to thing that the transverse bar is providing some kind of mechanical anchorage for the hook but that's not the case. The transverse bars just prevent splitting. Pish posh... how big of a deal can splitting really be in the grand scheme of things?? Just get stickier concrete or something.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

The J-bolt is the highlighted part, with embedment depth starting at the breakout plane. I'm not saying that this approach is the only correct way to look at it, just that it's a conservative approach. If you look at Example 1 (pg. 139) of ASCE Anchorage Design for Petrochemical Facilities, they do something similar where they limit the allowable stress of the hooked leg at 20 ksi.



Here is some more background:

Quote (ASCE Anchorage Design for Petrochemical Facilities)


3. For tie reinforcement, and with reference to Figure 3.18, the following assumptions are suggested:

a. Only the uppermost two layers of ties (assume two #4 ties within 5 in. (127 mm) of the top of the pedestal as required by ACI 318 Section 7.10.5.6) are effective.

b. Tie reinforcement should consist of ties with seismic hooks. If internal ties are required, hairpins could be used. As an alternative, diamond-shaped ties can also be used.

c. The location of hooks and the direction of hairpins should be alternated as shown.

d. If the available development length of hairpin, ldha, is shorter than the required straight development length for a fully developed hairpin, ldh, the maximum yield strength that can be developed in a hairpin is: Fy x ldha/ldh

where Fy is the yield strength of the hairpin. If ldha is shorter than 12 in.(304.8 mm), (that is, the minimum development length based on ACI 318 Section 12.2.1), then a hairpin should not be used.

e. Away from the hook, the tie is assumed to be fully developed. For example, under the shear force Vua, the tie on layer A can develop Fy at nodes 1 and 6

f. At the node where the hook is located, the tie cannot develop Fy. For example, under the shear force Vua, while the tie on layer A can develop F[sub]y[/sub at node 6, the tie on layer B cannot, because the hook of the tie on layer B is located at node 6. In order to calculate the contribution of the tie on layer B to the tension tie at node 6, and with reference to Figure 3.19, the stiffness of a hooked bar bearing on concrete (Case 1 - smooth rebar with 180° hook bearing in concrete [Fabbrocino et al., 2005]) is compared to the stiffness of a hooked bar bearing on rebar (Case 2 - the conventional single-leg stirrup with reinforcing bars inside the bends [Leonhardt and Walther, 1965 as cited in Ghali and Youakim, 2005]).

Even though the capacity of Case 2 may be higher than that of Case 1 because of bearing on rebar of a larger size than the stirrup, contact may not always be present because of common imprecise workmanship. When the contact is not present, Case 2 is assumed to behave as Case 1. Leonhardt and Walther (1965) found that in order to develop fy on the bends of 90°, 135°, and 180° hooks when engaging bars located inside the bends (Case 2), there was a slip of about 0.2 mm (0.0079 in.). Based on the test results of Fabbrocino et al. (2005), the stress that was developed at the hook of the smooth rebar with a 180° hook bearing in concrete when it slipped 0.2 mm was about 20 ksi (138 MPa). Therefore, it is assumed that the tie can only develop 20 ksi (138 MPa) at the node where the hook is located.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

Quote (Bones206)

The J-bolt is the highlighted part, with embedment depth starting at the breakout plane. I'm not saying that this approach is the only correct way to look at it, just that it's a conservative approach.

Thanks for the clarification. I thought that you were doing the J-bolt thing on the other side of the crack. I agree that's a conservative approach where you're using it. I'll check out the Petrochemical stuff. That's clearly advanced the Widianto method some from when I last looked at it.

RE: Anchor Bolt Shear Reinforcing Stirrup Development

Thank you very much gusmurr.

Gotta love academics always botching the fundamental detailing.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close