Seismic Design for helipad on roof top

[dougseason]

I am designing a rooftop helipad in a high seismic region in the USA (California). I have the gravity design loads figured out but I can't seem to find a suitable lateral system to determine the seismic coefficient. The helipad is on a rooftop and I am only responsible to design the helipad. The building superstructure is being designed by another structural engineer. The tricky part is that the helipad platform needs to be supported by vibration isolators then attached to the roof structure. I need to figure out the seismic force of the helipad platform and provide reactions forces at the isolators to the building engineer. I think the helipad seismic coefficient can be determined either from chapter 13: Non-Structural components or chapter 15: non-building structure of ASCE 7-16 but can't seem to find a system that fits a helipad. The only system with a vibration isolator is from chapter 13 table 13.6-1: Vibration-Isolated components and systems but that is under the mechanical and electrical components section which the helipad is not.

Anyone has done a similar design like this before?

Any input will be greatly appreciated.

Thanks

D

 

[r13]

Are you talking about the helipad only, or include the helicopter? Can you post a sketch for the helipad?

 

[HTURKAK]

ASCE 7-16 , 4.11 defines the helipad loads. Table 4.3-1 Minimum Uniformly Distributed Live Loads, Lo , and Minimum Concentrated Live Loads are applicable for the design loading.

You should design the helipad ( considering a separate penthouse) for gravity loading together with impact and provide the necessary data to the building superstructure designer. The data should include, gravity loading ,reactions of penthouse frame, seismic weight of the penthouse together with helicopter .(effective seismic weight could be taken as the dead load and half the reduced life load).

The main structure of the building SHALL BE analyzed together with roof top helipad penthouse and the proposed sections for the penthouse shall be revised accordingly..

The seismic loading combinations should not include impact loading of helipad..

Pls look to the worked example 15.2 at FEMA P-1051/July 2016 .

PS. Will you pls. provide the detail of vibration isolators ?

 

[r13]

I guess the helipad is easily incorporate into the building design as a load, but who is responsible for the connection design, gravity and seismic?