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Plumber meets Electrician
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Joined: Mar 2011
Posts: 28
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...coffee on me then!!!

I am sorry and and I am glad that you learned it on hard way. If you understand what I mean.

...for the old topics...I will ocationally respond some of them when I see something picking my eye. I feel better here than reading newspaper.

While I am saying this, are they any free electrical magazines what you can recomend. I know http://www.electricalline.com/ with nice virtual view ( check at the bottom ).


“If you don't know where you are going, any road will get you there”.
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Joined: Dec 2012
Posts: 2
C
New Member
In CA, an inspector red tagging the equipment or plan checker would call out IBC or CaBC Chapter 16, or:

"1613.1 Scope. Every structure, and portion thereof, including nonstructural components that are permanently attached to structures and their supports and attachments, shall be designed and constructed to resist the effects of earthquake motions in accordance with ASCE 7, excluding Chapter 14 and Appendix l1A."

CaBC points to the IBC, which points to the ASCE 7, which then might point to ACI 318 for concrete, AISC 360/341 for Steel Bldgs, NDS for wood or timber construction, and ASCE 5 for CMU/Masonry structures.

It isn't as simple as calling out a particular sized bolt or screw to anchor the equipment. If enforced it requires some design.

A simple skid mtd boiler weighing about 7000lbs, requiring 8 - 5/8dia anchor bolts drilled into a concrete slab, required a 34 page structural calculation report to generate a simple note calling out 8 bolts on center in predrilled holes.

Unlike many other load problems, seismic loads are based upon the inertia generated by a mass being accelerated during a seismic event. The lateral force generated then has to be traced to the structure, to the foundation, to the soils around the structure.

For Mechanical and Electrical equipment, the lateral forces resisted are coded to be less than the bldg.

As a rule of thumb, anything over 400 lbs or above the floor by 4 ft, needs specific design calculations and detailing during design for anchorage. Technically anything weighing over 20 lbs attached to the bldg (even wall partitions) should be considered.

The codes and difficult to understand until one designs a few bldgs, and ALL structural members, but there have been some recent FEMA pubs freely available, which help in a practical fashion.

FEMA 454
FEMA e74

The explicit calculations Elec/Mech nonstructural components is generally F= [(0.4)(a)(Sds)W/(R/I)](1+2z/h), where a = 1.5, Sds is found from the USGS website for the location ,..it's the design spectral acceleration, short term, and usually ranges from 0.5 to 2.0g. W is the operating seismic weight of the equipment. R is a Response coefficient, I is an Importance factor, z is the height off the floor and h is the roof height. (each defn in the code is more explicit)

This calc provides and lateral force for a design seismic event for a piece of equipment applied at the centroid of the equipment. That lateral force will induce a moment and force upon the structure, which must be resisted along the bldg's structural path to the floor to the walls, to the columns, to the foundation, to the soil around the bldg.

There are additional detailing requirements. For example brackets holding the equipment in place need be designed so that when things fail, they do so in a fashion so people can live and the bldg doesn't suffer catastrophic failure ,...or so is the intent.

Rule of thumb, bolt one bolt to the equipment and 2 bolts to the floor at each bracket, in both directions for any 360 degree seismic motion. This way if the bolts fail, they are designed either keep the brackets attached to the equipment or to the structure.

There are a litany of other minutia,...generally, don't use powder actuated fasteners when the anchor is in tension,..violates the seismic codes.

Hospitals and schools probably have the best seismic designs in general practice, but look at the FEMA e74 for some typical examples of how to anchor equipment and examples of their failures.

Joined: Dec 2012
Posts: 2
C
New Member
PS

The only facilities really requiring such extreme design documentation are Class IV facilities,..ESSENTIAL facilities, such as hospitals, fire stations, etc.

Read the Exemptions section in Chapter 16 of the ASCE 7 if in doubt.

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