Pin Plate Supports

[ILL_INI]

Hey group,

I am a very green structural engineer(great timing). I am designing a base plate with a pin to connect to another pin plate that could have axial loads as high as 300 kips. I am not sure what method is best to size and detail the plates around the pin. I was considering idealizing the 300 kip force as an equivalent force at the point of the pin that connects to the top of the gusset plates. I would then idealize the plates as struts and then make sure all the forces cancel out like a truss node. I think this is pretty conservative and I'm not sure if it is the standard way of doing things. I don't have access to much design software. If anyone has any tips or resources that may be helpful, I would greatly appreciate it.

Thanks!

 

[JLNJ]

Speaking of load path, I'm not a fan of the stiffener plate being right in line with bolt holes. You will have some very large forces in those plates (especially on the tension side where the middle plate in line with the force won't do much of anything).

Where the stiffener plates are in tension, the stresses at the end near the bolts will be off the charts and the weld might want to "unzip". So, 300 kips between 6 bolts is 60 kips of shear per bolt (or more since you can't guarantee the distribution will be equal). Add in the 60 kips per bolt in tension and those welds are doing real work.

It seems to be that the traditional arrangement of stiffeners either side of the bolt is a much better way to predictably distribute the forces. As it is, I'm having a hard time seeing the flow of force from bolt to base plate to stiffener.

 

[dhengr]

ILL_INI:
Slow down a little bit and think about what you are doing. You get to take part in the orientation, sizing, spacing discussion on the A.B’s, or they make your job really tough. Right now, your load orientation would dictate that the A.B’s. should be on the left and right edges of the base pl. to be most effective, not the top and bot. edges as your detail shows. Alternatively, rotate the base pl. 90°so the six A.B’s. are more effective. Furthermore, you can’t have a 10” long pin sticking up 10.25” from the slab, without its butt end being down in the base pl. by 1,” can you? And, that is a better detail, so keep it. The detail needed is enough (should be enough) to start generating a meaningful discussion of your real problem, and describe it sufficiently for that discussion, not some imaginary textbook problem which you don’t fully understand, in the first place. You’ll be surprised how much an experienced engineer can glean from more engineering detail and well proportioned, well thought out sketches. You have to ask yourself, what info is needed so others understand my problem in enough detail so we are talking about the same thing. Remember, we can’t see what you are looking at from here, and we shouldn’t have to waste a bunch of time guessing what you want and need.

I’ve got some other thoughts too, but firstly…, you say “Lastly, the bolting pattern and the relative footprint of the base plate are predetermined by the company this is being designed for.” Why are they controlling that part of the design? If that is truly their position, and you are not misunderstanding them, then I would want them to complete the base pl. design which they seem to know so much about. Let them fix their own self inflicted bulls. Let them provide the adjustability for their misplaced, cast in place A.B. holes, or you’ll be blamed for them too. Are they trying to reuse some existing base pls. from a previous job? Do they have some special slab rebar spacing issues they are trying to deal with? You may not be asking the right questions of them, but if they want you to design the bracing struts and connections to the bldg., they should let you do it.

 

[r13]

As sketch is as important as speech, you should have do that before posting. Also, as others pointed out, you shall be more clear on your scope on the design, and an explanation for any part that you were not involved, or have no control of.

 

[r13]

Don't shy away from criticism, all pointing to the work shown only. Here is something to get you start to think about, which is the way I'll do without computer. After you understand the logic, you shall be able to modify the model, if necessary, and refine my numbers.

Object - Distribute the applied load to the rod and the stiffeners, and sizing the plates.
- A36 steel, use allowable stress design method.
- Assume all components are rigidly attached to the base plate, and all are inter connected.

A_rod = pi*4.5²/4 = 15.9 in², assume 15 in²
Assume allowable shear = 10 ksi
Capacity of the rod, P_rod = 10*15 = 150 kips
Forces to be carried by the stiffeners = 300 - 150 = 150 kips
Assume the pair stiffeners in Y direction ineffective,
and approx. assume Δ1 = 2*Δ2 (see Fig 1), thus Ps1 = 2*Ps2, or Ps2 = 0.5*Ps1, by proportion
P_st = 2*Ps1 + 4*(0.5*Ps1) = 4*Ps1 = 150 kips ---> Ps1 = 37.5 kips, Ps2 = 18.75 kips
Determine plate thickness - again assume allowable stress = 10 kai ----> As1 = 3.75 in²
Assume plate length L1 = 10", ---->t_s1 = 0.375" (3/8"), conservatively use 1/2" for all plates
I think you are able to pick up the calculation from here to check the stresses in the rod and the stiffeners, and design the weld. Have fun.

 

[ILL_INI]

Thank you all that commented and helped me understand not only the design, but also the way I need to present the questions. I welcome the critiques because I want to be better.

I think I have a solid idea of what I need to do and will now be able to present my ideas in a coherent way to my seniors.

I will also make sure I am clear on what my limitations are and why I have been given constraints on the base plates.

Sometimes when you're very green you don't know what you don't know. Thank you all for helping in that regard.