Friction in lieu of anchorage for slab-on-grade?

[161km]

I'm working on a slab-on-grade to support a battery energy storage system cabinet for solar energy. The specified product is manufactured in China, and product's technical specifications state that "due to the large weight and size of the container itself, it is generally not necessary to fix it." I've run sliding calcs using a coefficient of friction of 0.20 for the interaction of concrete and steel, and I'm getting a factor of safety greater than 1.5 (as well as a FS of 7 for overturning).

My question is: is this allowed in the States? I've done a bit of digging and found a Eng-Tips thread from 2005 that references a "Component Force Transfer" section of an IBC code that disallows considering friction. However, I can't the source of that reference. The best I've been able to find is a reference in the 2002 Wisconsin Enrolled Commercial Building Code. As far as I can tell, it's no longer in modern code. Do you believe this provision still applies?

 

[human909]

If you slab is literally a slab on grade as opposed to a slab AT grade then your slab is relying on friction to remain in place. I've installed heavy equipment (17T, ~2m x 3.5m) that rely soley on friction to stay in place. If something is heavy and squat then friction will keep it in place in seismic conditions unless you are in an extreme location.

But I can't comment on the IBC code.

 

[XR250]

Isn't there some nominal vertical seismic component that may unweight it a bit?

 

[Tomfh]

Peak seismic horizontal ground accelerations often surpass the design-level earthquake forces we apply to the building.

In a decent earthquake you will see peak horizontal accelerations well in excess of your 0.2G friction, ie expect some slip in a big one.

Mightn’t be an issue. Maybe you’re happy for it to slip around. It’s just something to consider.

 

[HTURKAK]

I'm getting a factor of safety greater than 1.5 (as well as a FS of 7 for overturning).

These FS's seems to be for seismic only. If you can satisfy a reasonable FS against sliding and OT , for WIND and SEISMIC cases , my vote would be OK.
I would like to remind that the seismic sliding would be around max. several cm but sliding due to wind loading is totally different story.

 

[Tomfh]

HTURKAK,

I disagree that a normal coefficient of friction is sufficient to resist any significant seismic forces. During large earthquakes, the ground can move horizontally with accelerations exceeding 1G, far surpassing the typical static coefficient of friction of 0.2–0.3G that holds an object laterally in place. In this context, the friction acts as a “fuse”—a limited mechanism that will inevitably fail if the ground accelerates more quickly than 0.2-0.3G, which it does in big earthquakes.

That said, you are correct in pointing out that we are often dealing with small back-and-forth displacements rather than a dramatic lateral movement, like being swept away by the wind. If a slight shift of a few centimeters won’t create significant problems, then the consequences are indeed much less critical.

 

[HTURKAK]

I disagree that a normal coefficient of friction is sufficient to resist any significant seismic forces. During large earthquakes, the ground can move horizontally with accelerations exceeding 1G, far surpassing the typical static coefficient of friction of 0.2–0.3G that holds an object laterally in place.

My experience based on observations that during large earthquakes , this kind of equipments can change location in the range of several cms, provided that a min friction coeff. is satisfed btw skid and supporting concrete . I would like to remind the reason is reversal of acceleration during EQ.
EDIT : A limited sliding during large EQ, which will not disturb any connection and endanger service of the equipment could be assumed reasonable . The following excerpt from API 650 ;

...When tanks are lower profile, i.e., H/D < 0.8 and are either self- anchored or have
long anchor bolt projections, the tanks can slide at the high impulsive accelerations. This sliding effectively limits the
amount of force transferred into the tank. This limitation should not apply if the tank is prevented from sliding.

 

[Tomfh]

Yes the limited change in position is because the motion is cyclic, not because friction has kept it stuck to the floor. Even things on casters (with zero friction) dont move far.