Anchor Rods with Very High Tension & Limited Pier Depth

[AJC3636]

I am inheriting a project where a column has a max tension load of 1095 kips due to side-thrust of a very large crane. The main failure limit is anchor tension reinforcement group. The pier that this column is going on currently has a max depth of 5'-6" due to an existing spread footing under the pier and it can not go any deeper. I was hoping for some directional suggestions and thoughts. I attached some sketches of the current base plate and anchor rods.

I have six anchor bolts currently trying to take that tensile load. Even with using hairpin reinforcing I am still coming up short and it is not close.(400K short)

Another question I have: Appendix D says that you need development length of tensile reinforcing rebar overlapping the anchor rod depth and also below the anchor rod. A peer thinks that we should turn the bar once it reaches the bottom of the pier and will be able to use the now horizontal length as part of the development length. I am skeptical though.

Looking at a similar building in this area, previous design welded a plate at the bottom of the anchor rods just above the nut, but I have never seen this before. If there is a design material on that method, perhaps that would be the best case but I do not understand how that helps much. I am really struggling with a path to pursue.

 

[JoshPlumSE]

Early in my career (at a company that did heavy industrial engineering) it was relatively common to use fairly large plates on the ends of our anchor bolts to increase pull out area. The one caveat is that you had to be careful during construction so that you didn't get air pockets under the plates.

You might want to take a look at this thread (which discusses ACI punching shear strength vs anchor pullout strength).

https://www.eng-tips.com/viewthread.cfm?qid=428273

One thing is discussed is the tendency of some engineers to use through bolting to embed plate on the other side of the slab to justify using the punching shear strengths instead.

Also discussed are some potential reasons for the discrepancy in strengths using the two different calculations.

 

[ldeem]

My interpretation of Appendix D is based on visualizing the shear cone formed by the AB's. The point of tension rebar is to hold the cone in place. So you need sufficient development length on BOTH sides of the shear cone. Hooking the bar will shorten the development length as compared to a straight bar - so your colleague is sort of correct but only if he means to hook the bar and shorten the development length.

You will basically have two shear cones, the three bolts close to each other are going to basically be one shear cone at the embedment depth you are using. The two shear cones formed by ABs on each column flange will probably overlap - so watch that.

Are the uplift forces from bending at the column base? In that case only one side will be in tension.

What about shear? A shear key will help a lot.