×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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!
  • Students Click Here

*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

Jobs

Large Concrete Anchorage Forces
4

Large Concrete Anchorage Forces

Large Concrete Anchorage Forces

(OP)
I have a beam that frames into a concrete wall, parallel to the length of the wall. This beam will need to transfer about 1200kN (270 kips) axial tension force to the concrete wall. I initially envisioned an embedded plate with weldable rebar (2 vertical rows, 14 bars per row) that are 1200mm long (4') welded to the embedded plate to develop the full strength of the bar. Even with that, I am not getting the concrete break-out capacity that I require. Now I am thinking of welding plate washers to the end of the bars (this should give me the capacity that I require, but I am in the process of confirming it). I am using Appendix D in the code for anchorage design. Do embedded bars with welded plate washers seem like an odd solution to you? Any suggestions or alternatives? Your advice is appreciated.

RE: Large Concrete Anchorage Forces

I guess once I use welded rebar to a plate - and lap spliced to rebar in the wall - I'm not using Appendix D at all.

RE: Large Concrete Anchorage Forces

If I remember correctly- if you embed bars (or anchor bolts) into the concrete- neglect tension in the concrete behind bars/bolts- and check shear on the surface around the bolts, you pretty much get the concrete breakout strength design from Appendix D.

Regardless, for the original post, are you looking at breakout strength or pullout strength? Pullout will be increased with the welded washers, breakout would be more dependent on the depth and distribution of the anchors. If you satisfy pullout, but not breakout- add reinforcement through the breakout cone, then design for shear beyond that area. If you're adding welded washer plates, you can design them as bolts, and don't need deformed bar.

RE: Large Concrete Anchorage Forces

If you develop a bar into concrete, why is there a requirement to mess with Ap. D?

RE: Large Concrete Anchorage Forces

That's my point too, ztengguy.

RE: Large Concrete Anchorage Forces

Appendix D only applies to younger concrete that is not fully developed yet.

I have used the welded plate option many times, even with the full development length achieved. It just feels better to me, is easy to do, and cheap extra capacity in anchorage design.

Mike McCann
MMC Engineering

RE: Large Concrete Anchorage Forces

Quote:

Appendix D only applies to younger concrete that is not fully developed yet.

Mike, can you clarify where you got this idea? I thought App D was for anchors in all concrete. Not just younger concrete.

RE: Large Concrete Anchorage Forces

rofl2 Gotcha...

Mike McCann
MMC Engineering

RE: Large Concrete Anchorage Forces

OK I'm gotten.

RE: Large Concrete Anchorage Forces

Why mess with App. D: If the rebar going into the slab goes more or less all the way through the slab, then checking for concrete breakout is just a punching-shear check at that location. But, if the rebar only goes partway into the slab, the punching-shear check assumes shear through the entire slab, whereas you could actually have the concrete break-out failure as in App. D instead of a shear failure through the whole slab.

RE: Large Concrete Anchorage Forces

At Galileo-
Yes, don't mess with Appendix D with this high of forces. Fully develop the rebar by welding to the plate. Then lap to the rebar for the full length of wall. In high seismic zone when detailing for overstrength, the chance of getting a "headed anchor bolt" to work for anything but the smallest loads is zilch to none.

RE: Large Concrete Anchorage Forces

2
I often (almost always) see embed plates like this detailed with weldable rebar extending from the embedded plate into the concrete approximately the anchorage length of the specified rebar. Usually it's insufficient and indicative of confusion regarding what anchorage length actually is.

Anchorage length is simply the embedment length required to prevent rebar from pulling out of concrete via bond stress failure. Providing anchorage length rebar embedment doesn't mean that you can actually develop the tensile strength of the embedded rebar. To develop the tensile strength of the rebar, you also need to do one of two things:

1) Deal with concrete breakout using some form of diagonal tension check (Appendix D, simplified shear check, etc.)
2) Pass the tensile force to rebar elsewhere in the concrete (laps, strut & tie, etc.)

I apologize to anyone who may find this condescending. I've encountered enough confusion about this that I really do feel that it warrants detailed explanation.

As for the case at hand, I recommend using a simplified strut and tie model to pass the tension force from the concentrated rebar coming off of the embedded plate to the - usually not so concentrated - horizontal rebar in the wall. This takes the form of a suite of compression struts originating at the end of the embedded rebar and fanning back to an equivalent area of horizontal wall steel. All the while, you need to be cognisant of the need to develop the ties and keep your strut angles reasonable. You'll also need a vertical tie in your wall adjacent to the embed plate. Usually, nominal detailing rebar does the trick for that.

When I do this, I usually do a very abbreviated analysis. I don't check node stresses or any of the fancy suff. I just set out the rebar such that I feel confident that I've effectively lapped my embedded rebar with an equivalent area of wall rebar and generally paid homage to STM concepts. Usually, the end result ends up being exactly what TDIengineer suggested: the embedded bars are lapped to matching horizontals and those are carried deeeeep into the wall.

With regard to anchorage plates and lenton couplers, all those do is shorten the tie development length required at the end of the embedded rebar. I usually omit them as they cause some congestion and don't decrease the overall embedment length all that much. For an extra fun version of this problem, tie an axially loaded beam into a wall up near the top. I find this requires even longer embedded rebar lengths and a serious vertical tie at the end of those bars, usually involving U-bars lapped to the vertical ties.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

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!


Resources