Fp=2.16 Wp, but Wp=1.3Fp? WTF?!?!?

September 5, 2008 12:12 PM

How do you figure seismic sway bracing?

I've been tasked with figuring out the sway bracing on a Class E soil medical facility. I've got a binder from a manufacturer, and some values off the structural engineering plans for the site.

However, as I read through the manual, they effectively say, "here's some car parts"...some formulas, no explanations. Then they give examples using different variables, and get conclusions that mean nothing..."here, make an airplane spanner wrench out of them." The results are numbers - %wp, which I can't seem to figure out what to do with from there.

The structural plans give an entirely *different* set of variables, none of which coincide with the manual's variables. It's like they started talking about railroads for all it's worth.

Anyone have any references to recommend?

I've tried googling, but can't find anything.

posted by notsnot to science & nature (5 comments total)

Contact a seismic engineer in your local yellow pages.
posted by felix at 12:33 PM on September 5, 2008

Shouldn't this kind of thing be covered by your structural engineer to begin with? Is this for new construction or for a retrofit?

Basically, felix has it. If you're trying to figure out seismic stuff for a building, there's some liability involved, and it might have to be planchecked by your local building department, and unless you're a structural/civil engineer yourself, they won't accept your stuff anyway.
posted by LionIndex at 4:12 PM on September 5, 2008

I guess I mis-explained. I"m the plumbing contractor. Each of the plumbing, HVAC, electrical take care of their own sway bracing for their pipes, ducts, and conduits, respectively. I'm just trying to figure out *what* I need to figure out on bracing my pipes - they flat-out say every 40 ft laterally, 80 longitudinally for ductile materials, and half that for non-ductile (cast-iron and pvc pipe), and we've got cable and supports based on the maximum load for our largest pipe. I'm not sure what all the other calculations are for!

The one time our sister company tried to use an outside engineer, our draftsman was running circles around the engineer with respect to seismic, so (even as a degreed engineer myself) I'm doubtful outside help will, well, help.
posted by notsnot at 4:53 PM on September 5, 2008

Ask the draftsman then?

Not to be snarky but you may have hit one of the few dead ends at ask.mefi. This is a very specialized field.
posted by amanda at 5:37 PM on September 5, 2008

A plumbing engineer should not personally be designing seismic restraints for anything. Hire a PE.

Each of the plumbing, HVAC, electrical take care of their own sway bracing for their pipes, ducts, and conduits, respectively.

Every MEP set of drawings I have ever seen (produced by the MEP consultant) has a typical detail for seismic restraints, which basically describes spacing, anchorage, min/max brace angles. Typically the engineer has hired (I assume) a PE as sub-consultant to develop these typical details, and then they proceed to use them on every project until new building codes are published. Our structural engineer (I'm the architect in this scenario) will occasionally review these types of details for MEP consultants, but NEVER for the sub-contractor. If you are the sub-contractor, you are on the hook to hire whoever you need to hire to install per design documents, contract, and all applicable building codes.
posted by misterbrandt at 7:45 PM on September 5, 2008