Vertical Parking Stacker - Story Shear from Vehicle

[renzasaurus]

I am designing post-installed anchors for a pre-engineered parking stacker system in a high seismic area. Though the car is a live load, I feel it's necessary to include the full operational weight of the system in my seismic analysis. The stacker is on an existing flat plate slab, so I am considering this to be a non-building structure supported by other structures (7-16 sec. 15.3.2). Vertical distribution of seismic forces is ELF method.

My question: Would you determine the vertical distribution factor, Cvx (eq. 12.8-12), with the car's center of mass elevation but apply the resulting shear at the platform level? or would you apply a fictitious story shear above the parking platform structure (at the car's center of mass) just to increase the overturning moment? I understand the difference may be negligible, but am interested in other opinions. Thanks.

 

[atrizzy]

Does your question pertain to the design of your stacker, or for the global impact on the building as a whole?

 

[renzasaurus]

atrizzy, stacker is pre-engineered but connection to supporting structure is my scope. I also need to give forces imposed on the building to the SEOR.

 

[atrizzy]

It's been a while since I've used US codes, but for this situation I'd use what's known in Canada as seismic design for 'Elements of Structures, Non Structural Components and Equipment'. It provides a force level to consider for your element (in your case your frame/vehicle(s)) based on rigidity, vertical positioning in the structure, weight, etc. I imagine there's a similar procedure in US codes.

I'd consider the worst case position for your vehicle, either at the top if the frame is cantilevered, or in the middle if it's connected at the ceiling and base. For the SEOR, provide the method used for your force calculation, as well as the actual forces (shear & moment) on the floor/floors affected.

 

[EngineeringEric]

If there is an EOR of the stacker, shouldn't they be providing you with the loads? they know their reactions and rigidity not you? i would anticipate this to be similar to a Pre-Engineered Metal Building.

Technically, you aren't imposing any loads onto the building as much as resisting the loads 'IT' imposes onto the foundation. Or i am totally misunderstanding your scope

to your question, id say that the building sees the force at the actual platform level, now the force it sees will be a lateral shear with a little moment since the Center of Mass is transfered trough the car-to-wheels, but a vehicles center of mass is probably only 2-3feet above the platform if even that high.

 

[KootK]

Clearly I've been playing too much Mario Kart.

or would you apply a fictitious story shear above the parking platform structure (at the car's center of mass) just to increase the overturning moment?

That one is the most technically correct in my opinion if we're assuming that the vehicles will travel laterally in unison with the deck which I feel is prudent.

I understand the difference may be negligible, but am interested in other opinions.

I agree that the impact of this would be modest. That said, and because the effect would be modest, I might just shift all of my vehicle masses up to the nearest deck above to ensure that the effect is captured. Probably short story heights anyhow.