friction or anchor?
friction or anchor?
(OP)
I am designing a footing for a heavy transformer (177 kips). My seismic force is approximately 20% of the dead load. Do I need to anchor the transformer to the concrete or will the friction between the transformer and concrete be sufficient to resist lateral force?






RE: friction or anchor?
First check that the resisting moment is at least 1.5 times the overturning moment. This ensures that you have no net tension at the base.
Second check that the sliding resistance is greater than the lateral force acting on the transformer.
RE: friction or anchor?
RE: friction or anchor?
RE: friction or anchor?
RE: friction or anchor?
RE: friction or anchor?
Sometimes, when dealing with mechanical/electrical installations, there are situations where a piece of equipment is so "dense" that it just doesn't need to be anchored to resist normal "building" wind and seismic loads.
However, that being said, if you are going to anchor it anyway then make sure you consider the effects of thermal expansion and contraction on the anchor bolts. Often a combination of oversize and slotted holes in the base plates are used to allow some movement.
RE: friction or anchor?
What seismic performance category are you in? Have you figured out the Ip of this piece of equipment? I ask because IBC (at least NJ version of it) allows you to forego Section 1621 analysis if you are in cat C bldg or less, with Ip=1.0. In other words, mechanical anchors are not required in that situation.
You will need to determine if the transformer is vital to life/safety operations of your building after an earthquake to determine the Ip (See IBC sect 1621.1.7). Would also take into consideration if this transformer is inside or outside the building. If its inside I might design anchors even if they aren't required by the code. Who wants a giant cannonball dancing around loose during a seismic event?
Having said all that, I agree with above posts that one should not rely on friction of any kind to resist seismic loads. In an earthquake, anchors for a building or piece of equipment can get loaded by both vertical and horizontal movements in the subgrade, and it seems quite possible that frictional resistance could be marginal or nil due to elastic movements of the anchors. A "gray back from way back" that I thoroughly respect taught me such, a long time ago.
Let us know what you decide. Regards.