Dogbone Design 4

[Althalus]

I'm getting further and further into seismic design lately. Most of the methods described in AISC 341 are straight forward and easy to understand.

I became aware of the use of dogbones to combat oversized connections. The principle seemed simple enough. But when I brought it up to another consultant, he raised his eyebrows and warned that this was a very complex design methodology and you really need to know your stuff. This came from the manager of this company's structural group who has a guy whose master thesis was on seismic design.

So, I'm wondering if I'm missing something. Here's what I understand. Tell me what I'm missing.

1) One requirement of joint design requires that it be designed for the "maximum load that can be transmitted through the joint".
a) This means that theoretically, the full strength of the member (including the factor for material being stronger than the nominal strength) being loaded to full load capacity at the connection.
b) Assuming maximum moment controls. I'm still unclear on whether that allows for combinations of axial, bending, and shear. But it seems that (at the very least) it does not take into account variables like unbraced length, k value, etc. (correct me if I'm wrong.)

2) One way of combating that is to weaken the beam at a location where the load is rather low.
a) Since the maximum moment being transmitted through the weakened point is much lower than the maximum beam capacity, the resulting moment at the connection is also lower.

3) Placing a "dogbone" near the end of a beam is a common method.
a) The dogbone must be formed using smooth shapes such as circles and elipses, such that no load concentration occurs due to the shape of the hole.
b) It must be placed in a location that takes advantage of the low loads at a particular location, but still close enough to the ends such that the additional moment built up in the intervening distance
does not overload the connection.

So, what is the complex part of the design I'm missing?
And if anyone knows of a good online source (or possibly a publication) that goes over the steps, I'd really appreciate a reference.

 

[TLHS]

On the column base issue, I actually saw an interesting detail last week in an Australian document about tank foundations. They have a seat that extends several inches up and gives you a stretch length, which is normal. Then they also neck down the anchor rod that's in that seat length for the length they are considering as stretch length to make good and sure that the failure point is in the stretch length. I know I'd get crazy looks if I did something like that on normal construction, but it's the best solution I've seen to the problem. It's a really straightforward way of forcing the exact behaviour you want and it seems like it would be pretty easy to implement if it were common practice.