Thanks, HTURKAK. Could you expand what you mean by 'accidental case'. We are reducing the site design values based on ASCE 37-14, using a 0.2 reduction factor.
My question was more about the concept of including the inertial forces of the blocks themselves in the analysis - which based on...
Unfortunately not, they have already set the equipment down on a steel plate and lifting it to put everything on a sled would likely cost more than just getting a few more blocks to hold it in place as it sits. Interesting idea though for sure.
Yes, this is a very large transformer. We looked at screw anchors as one option, but the proximity of the transformer to an existing building foundation system makes it difficult to install.
Burying the blocks would be a good option as well if the client is ok with patching and repairing...
Hello -
A client has a piece of equipment that is going to be stored on site for about 1 year before installation. They would like it to be temporarily anchored until then. We are exploring using concrete blocks (deadman block, eco block, etc) with weights around 3-4kips per block. The...
I agree, for this type of structure, we would detail to AISC360 (Table 15.4-1, OCBF w/ unlimited height). But for sake of argument, say we did detail to OCBF, R = 3.25. I think the correct approach is to utilize Ch15 for the frame design, since it is responding like an OCBF system, and not a...
Thanks for the response. Good thought with the rigid nonbuilding structure, I had not thought about that provision. I suppose my question is more general though where the supporting structure of a nonstructural component is not at all like the component - where the ap/Rp values in Ch13 don't...
Hello All -
I am interested to see how other folks approach nonstructural component support design when the support system is more analogous to a structural system than a component.
Consider a 500lb sheet metal box transformer (ap = 1.0; Rp = 2.5), and the following two cases:
A sheet...
Hello,
I'm working on some equipment support/anchorage designs that are supported by steel platforms. We calculated the Fp forces based on ASCE7 Ch13 to determine the anchorage forces between the equipment and platform and then used Chapter 15 to analyze the platform structure itself (OCBF...
Hello,
A client is relocating a PEMB canopy about 100 yards from its current location. No change in seismic/wind conditions (SDC D). After reading Ch14 of the 2022 CEBC, our understanding is that since we are not modifying the structure at all (e.g. not adding seismic mass, not removing any...
Thank you for the responses.
Yes, I was just reading the commentary and found this bit that answers my question about when it is composite (which aligns with BridgeSmith's response):
It also appears there are restrictions on %composite action but still reading into it.
Hello All -
I have a question about the limitations of composite action. The general understanding is that when your stud anchor capacity (∑Qn) < 0.85*f'c*beff (Cs,max), your section is partially composite because you can't transfer the full load into the concrete.
[ol 1]
What happens if...
right, and that is sort of where I get hung up. At what point does the Fp force end, and the 'lumped mass' begin?
Obviously, I design the anchors and transfer of load into the plywood using the Fp force. And the units are not directly over an existing wall, so I would imagine I can still...
I guess the way I think about it is like this...
Case 1:
The total diaphragm weight is around 300k. If you do a ch. 12 building analysis, with a Cs = 0.33, your total diaphragm force is 100k. If you add your Fp forces directly to this, (about 20k each unit), this is nearly a 50% increase...
Thanks, phamENG. This is how I understood it but wanted to make sure I wasn't missing something.
The building is a single story, ~20,000sf office/lab and I have 2x 9000lb units on the roof. The units result in about a ~6% increase in the overall diaphragm weight. I've added columns below the...
Thanks, driftlimiter.
I guess the question is more conceptual than the actual weight of the unit.
Basically, you have an Fp force that is 2x the weight of the unit. So if you just lump the weight of the unit into the diaphragm mass, are you underestimating the true load that the diaphragm...
Hello,
I have a question about rooftop unit nonstructural component forces and how they relate to building diaphragm forces.
Say I have an RTU that weighs 1000lb. It is spring isolated, resulting in an Fp ~= 2500lbs. I design the connections to the roof utilizing the Fp force (ASCE7 Ch...
Thanks,phanENG. Your approach makes sense if not considering a transform section. I am using SAP so I did a quick model following your approach. My D/C for the glulam is 0.85 and my D/C for the channels is 0.32. This makes me feel a little better knowing that I am still under capacity on the...
Thanks for the input, KootK. I will try to address each of your points..
1) We had planned on adding regularly spaced anchors to create a better composite action.
2) I see your point here, but wondering how to actually calculate/determine this? When we looked at the stresses of each...
The glulam is a 24F-V8, so it is a balanced layup. Since we are looking at the extreme fiber for the glulam, I believe the Fbx+ and Fbx- (they are the same in this case) are appropriate to use? Or should I compare the stress demand against Ft and Fc since I am looking at tension/compression in...
Thanks, driftlimiter. This makes sense and is what I was missing.
So, I can basically take Mc/I (with 'c' to the steel flanges) and compare against steel stress and then Mc/I (with 'c' to the wood extreme fiber) and compare against allowable wood stress (modified by modular ratio).
As far as...
