suspended transformer

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iwire

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Location
Massachusetts
Depends on the zone
but at an actual say 10:1 probably not
even a severe zone will impose a 1 g force laterally
the resultant still << 10:1

attachment to the wall is always preferred
I also use vibration isolators on the clg strut if not braced to wall, otherwise on xfmr base
I also prefer angle > threaded rod and limit length

weight factors in
200 lbs requires a different approach than 1000
F = ma
a is a resultant of g gravity (basically the weight) and external, usually siesmic
m is mass or weight, ie, proportion to the net force

OK. lets try this, forget the rods forget the angle iron.

I have a thousand pound transformer that I will hang with four 1" wire ropes that have a minimum breaking strength of 83,600 lbs and safe working load of 16,700 lbs.

Is that over design sufficient for seismic bracing?

IMO, and I am willing to be shown I am wrong, it is not.

It is my understanding that seismic bracing is not just about keeping things from dropping to the floor but to keep things still relative to the building so that conduits, wires etc are not damaged by the swinging transformer.
 

iwire

Moderator
Staff member
Location
Massachusetts
Good luck with that
my obligation is to my client, not covering your butt

Yes, it is too your client and I am not asking you to cover my butt I requesting you do your job. Now if your contract with your client puts this beyond your scope perhaps you will need to get an extra to do it.

I have no idea how things work where you are, but I am pretty clear on the realities here and often the engineering firms client is our client as well and even when there is a GC between us we have a relationship with the client. They look to us as installers and they look to the engineer / designer to do the design.


I would say don't hang it, I'll get someone to do it and back-charge deductive CO
All in writing with notice from the solicitor
it would be hung one way or the other

And that would be the last time you worked for the clients we work with.:p
 

Ingenieur

Senior Member
Location
Earth
OK. lets try this, forget the rods forget the angle iron.

I have a thousand pound transformer that I will hang with four 1" wire ropes that have a minimum breaking strength of 83,600 lbs and safe working load of 16,700 lbs.

Is that over design sufficient for seismic bracing?

IMO, and I am willing to be shown I am wrong, it is not.

It is my understanding that seismic bracing is not just about keeping things from dropping to the floor but to keep things still relative to the building so that conduits, wires etc are not damaged by the swinging transformer.

depends
is there freedom of movement?
are joints articulated
can it strike anything within a radius of 1/2 x l suspended
flex conduit connection(s)

F = ma
if we can keep a ~ 0 no net force
prevent initial movement is one way
the other is to allow some controlled movement
 

GoldDigger

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Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
depends
is there freedom of movement?
are joints articulated
can it strike anything within a radius of 1/2 x l suspended
flex conduit connection(s)
And some folks thought the flex was just there to block vibration! :)
Flex long enough to cover suspension movement is a different issue.
 

Ingenieur

Senior Member
Location
Earth
Yes, it is too your client and I am not asking you to cover my butt I requesting you do your job. Now if your contract with your client puts this beyond your scope perhaps you will need to get an extra to do it.

I have no idea how things work where you are, but I am pretty clear on the realities here and often the engineering firms client is our client as well and even when there is a GC between us we have a relationship with the client. They look to us as installers and they look to the engineer / designer to do the design.

And that would be the last time you worked for the clients we work with.:p

it is YOUR job to establish construction means/methods
mine is to spec and size, establish quality level
keep you honest
if we had say 8 elecs bidding
and only 1 asked about something like this we would hope he was not low lol
and assume the others knew the work

We seldom issue a gc contract that includes elec/mech/plumb
in fact law requires 4 contracts for any public money
prevent collusion
gives us more control
lowers cost, no gc mark-up
we still lay project facilities, scheduling and some coord on the gc

And that is why my clients always come back
had a rep with contractors essy to work with
but yet very low co percentage
always came in at/below engineers estimate/budget

I lkked negotiated work where I could pick the contractors
not alot of it though in public work
so every once in a while you'ld get a bum who could not hang a 350 lb xfmr
:happyyes:
 

Ingenieur

Senior Member
Location
Earth
1/2" wire rope, swivels both ends 10' long
x 4 each
1000 lb suspended, 3' x 3' x 3'
how much force to displace it 1' horiz?
how much does it move vert?
state force in g
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
1/2" wire rope, swivels both ends 10' long
x 4 each
1000 lb suspended, 3' x 3' x 3'
how much force to displace it 1' horiz?
how much does it move vert?
state force in g

State earthquake acceleration in multiples of G.
To stay in same position relative to building would require applying that much force just to keep the suspension from moving relative to building.
If you can discount resonance of suspension at earthquake frequency, relative motion could still be up to twice the earthquake motion amplitude.
The (fictitious) force will be whatever it needs to be.
 

iwire

Moderator
Staff member
Location
Massachusetts
it is YOUR job to establish construction means/methods
mine is to spec and size, establish quality level

No, it is not at least not here.

If the engineer designer says hang the transformer from ceiling it is up to them to tell us how.

You can go on and on but that is how it is here.
 

iwire

Moderator
Staff member
Location
Massachusetts
depends
is there freedom of movement?
are joints articulated
can it strike anything within a radius of 1/2 x l suspended
flex conduit connection(s)

F = ma
if we can keep a ~ 0 no net force
prevent initial movement is one way
the other is to allow some controlled movement

It does not depend.
 

mgookin

Senior Member
Location
Fort Myers, FL
I think there's a disagreement on what means & methods is.

A PE can't draw a rectangle and say "Big building goes here" and expect everyone else to do all the design work.

Likewise, you don't have to tell the trades how to erect their scaffolding, tell them to fully engage a nut before applying a load, fix someone else's errors, etc. If they want help with that stuff, it would be extra or they could find another PE if they want one.
 

big john

Senior Member
Location
Portland, ME
This thread has been very valuable.

I have learned that if I ever have to submit an RFI to an engineer about hanging a transformer, instead I'm just gonna bolt the darn thing to the floor.
 

iwire

Moderator
Staff member
Location
Massachusetts
This thread has been very valuable.

I have learned that if I ever have to submit an RFI to an engineer about hanging a transformer, instead I'm just gonna bolt the darn thing to the floor.

:thumbsup:

When the company I work for does design build the transformers stay on the floor or on racks that are on the floor.
 

Ingenieur

Senior Member
Location
Earth
seismic map US
https://en.wikipedia.org/wiki/File:2014_pga2pct50yrs_(vector).svg

san andreas fault 0.8 g
LA 0.4 g

E/W = tan a
E/W = earthquake force/weight of object in g's
if E/W = 0.4 then a = 22 deg
this assumes enough velocity for mgh = 1/2mv^2 (potential = kinetic energy)
and on rope
on rod/angle much would be absorbed by the material
1000 load 400 lb lateral force in 4 x 1/2" x 10' rods
0.78 sq in steel, even if cheap/soft 15 kip bending
it might not move

if sf = 4:1 vert and 2:1 horiz you are covered almost anywhere in the country

since F = ma a small mass is not the problem (and 1000 is small compared to a building)

where I practice 0.05 g, absorbed into any design with a reasonable sf
 

iwire

Moderator
Staff member
Location
Massachusetts
sure it does
no difference between the reaction of a pinned or rigid joint?
:lol:

In my example is 1,000 pounds hanging from wire ropes, the only thing stoping it from horizontal movement would be the conduits and conductors. :)




I must be blessed as this sort of design is always found in the prints as I posted. Perhaps engineers around here are just more proactive.
 

Ingenieur

Senior Member
Location
Earth
In my example is 1,000 pounds hanging from wire ropes, the only thing stoping it from horizontal movement would be the conduits and conductors. :)


I must be blessed as this sort of design is always found in the prints as I posted. Perhaps engineers around here are just more proactive.

OK
or contractors not as competent?
j/k ;)
 

iwire

Moderator
Staff member
Location
Massachusetts
OK
or contractors not as competent?
j/k ;)

Could be. :D

At the least not qualified to do structural design.

The PV systems we do preset this issue and when we are design build we have to hire a designer to make sure we don't overload the roof. MA allows us to do the electrical design, not the structural.
 

mgookin

Senior Member
Location
Fort Myers, FL
Could be. :D

At the least not qualified to do structural design.

The PV systems we do preset this issue and when we are design build we have to hire a designer to make sure we don't overload the roof. MA allows us to do the electrical design, not the structural.

Just curious: What structural do they let you do? The racks for the equipment but not any building structural retrofit?
 
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