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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...

Hello All, I am working on replacing rooftop equipment on an existing single-story building. The new RTUs are located along the column line in the middle of the building with supports on either side of the column, attached to the glulam member, increasing the negative moment. In 2010, a...

I am curious why there is no 'quick calc' or any checklist item that relates to the capacity of the diaphragm. I am currently looking at type C2/C2a checklist. They do have checks for openings and irregularities, but not capacity checks. If the irregularity checks are compliant, you could...

I am using ASCE41-17. Table 10-13 is more clear on what m-factor to use based on the failure mode. I agree with that. The equivalent table in ASCE41-13 for columns is 10-9. Interestingly enough - the table in ASCE41-13 is pretty clear with Condition i, ii, iii, and is clearly defined in...

Thanks retired13. I should clarify a bit - "actions" in asce41 lingo means the capacity check of various failure modes (shear, axial, flexure, etc.). In a typical table, they will have sub-sections for each action; so for a braced frame, they will have separate m-factors for tension and...

Hi Everyone, I am a little confused by the language in ASCE41 (surprise surprise) regarding the checking of an existing concrete moment frame and what actions are considered to be deformation or force-controlled. Per Section 10.3.2.1: "Deformation-controlled actions are defined by the...

Thanks, chris3eb. We discussed this today - just using ASCE7 w/ R factor reduction since it puts us in between eq 7-5 and eq 7-6. I think that is a reasonable and defendable approach to the situation we have.