Shade Canopy on Existing Parking Garage
Shade Canopy on Existing Parking Garage
(OP)
Hi, question about a steel shade canopy (with solar panels) being put on top of an existing concrete parking garage (4-story SMF). The canopy is an ordinary cantilever column system but the plan reviewer is requiring that I design the canopy under section 13 of the ASCE for seismic purposes. He is classifying the addition as a non-building structure thus requiring that I generate the seismic forces per ASCE section 13.3.1. I'm questioning why the steel canopy is being classified as a non-building structure when it's being given a use occupancy of S-2.
My opinion is that the canopy should be designed under Chapter 12 for seismic and also the existing parking garage checked for additional seismic loads under chapter 12. This is located in CA.
My opinion is that the canopy should be designed under Chapter 12 for seismic and also the existing parking garage checked for additional seismic loads under chapter 12. This is located in CA.






RE: Shade Canopy on Existing Parking Garage
Equation 13.3-1 gives a z/h multiplying factor to account for whipping effect at higher levels of structure - it will greatly increase the seismic forces.
RE: Shade Canopy on Existing Parking Garage
RE: Shade Canopy on Existing Parking Garage
I'm kind of visualizing the canopies too as like a penthouse but not quite though. I'm being told since it does not match any of the non-building types under chapter 13 or 15 tables for classification, it should be under "all other self-supporting structures" type classification. Due to the over-strength factor for this classification, the shear force would be almost 4 times for designing the base plate connections. Going into an existing concrete parking garage columns with limited concrete area, the bolt capacities would be the limiting factor. Whether they realize it or not, this would have the inadvertent effect of almost not allowing certain canopy structures to be installed on existing parking garages.
Would a more rational approach would be to design the canopy members under chapter 12 then when it's time to check the existing parking garage for the additional seismic load, this is where you'll consider chapter 13 to amplify the vertical distribution of seismic forces?
RE: Shade Canopy on Existing Parking Garage
RE: Shade Canopy on Existing Parking Garage
1) Based on the mass differential, I assume that the concrete garage shakes as though the canopy were not there.
2) I feel that the canopy will vibrate as a cantilevered column excited by a base acceleration equivalent to the acceleration of the garage roof level. This is consistent with Dekers two-stage recommendation.
3) We should be able to estimate the acceleration of the garage roof as the diaphragm seismic load there divided by the mass.
4) I'd expect this to yield some pretty high forces still so this may not be any better than the non-structural component route. Rather, it may justify the non-structural component route.
In terms of building code classification, I feel that it's essentially roof top mechanical. The fact that it supplies some shade doesn't change all that much in my estimation.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.