## ASCE 7 Wind Loads on Rooftop Structures

## ASCE 7 Wind Loads on Rooftop Structures

(OP)

Hey,

Thanks in advance for the help. Is uplift insignificant for rooftop structures greater than 60 ft? ASCE 7-10 requires uplift forces of 1.5x the lateral wind pressure applied as an uplift force on rooftop structures for buildings less than 60 ft, but does not require the uplift for rooftop structures on buildings greater than 60 ft. This seems like an arbitrary cutoff. I'm assuming structures up to 60 ft had test data and greater than 60 ft did not. So as an engineer, am I suppose to use my judgment in assigning uplift forces for these structures?

Thanks in advance for the help. Is uplift insignificant for rooftop structures greater than 60 ft? ASCE 7-10 requires uplift forces of 1.5x the lateral wind pressure applied as an uplift force on rooftop structures for buildings less than 60 ft, but does not require the uplift for rooftop structures on buildings greater than 60 ft. This seems like an arbitrary cutoff. I'm assuming structures up to 60 ft had test data and greater than 60 ft did not. So as an engineer, am I suppose to use my judgment in assigning uplift forces for these structures?

## RE: ASCE 7 Wind Loads on Rooftop Structures

The newest copy of ASCE-7 I have is 05 but can you say where the 1.5X requirement appears? I don't remember anything like this. Normally the MWFRS pressures come from Fig 6-6.

## RE: ASCE 7 Wind Loads on Rooftop Structures

The 1.5 can be reduced to 1 as a linear function of the equipment area. I'm not sure why it is limited to H<60ft though. They do say that the research is limited, but reference a couple of studies in the commentary.

EIT

www.HowToEngineer.com

## RE: ASCE 7 Wind Loads on Rooftop Structures

C.A.B., I don't believe the 1.5x uplift multiplier is in ASCE 7-05. It is in ASCE 7-10. However, both ASCE 7-05 and 7-10 require a multiplier of up to 1.9x the wind load on the face of rooftop structures for h < 60 feet. This has a huge impact on the design of these structures!

## RE: ASCE 7 Wind Loads on Rooftop Structures

I know I'm speaking in extremes and the typical design of structures for wind loads consider uplift on the net roof and its components, but I'm trying to dig deeper into the bones of the wind provisions. I design manufacturing and industrial structures, so I operate in this gray area of structural engineering where I have to really understand the codes and their intent in order to apply them.

In the end, maybe I'll just figure out how to do wind tunnel tests in my garage and figure it out. You don't suppose there are any starter kits out there? ~

## RE: ASCE 7 Wind Loads on Rooftop Structures

EIT

www.HowToEngineer.com

## RE: ASCE 7 Wind Loads on Rooftop Structures

Mike McCann

MMC Engineering

## RE: ASCE 7 Wind Loads on Rooftop Structures

## RE: ASCE 7 Wind Loads on Rooftop Structures

Must be the gator factor.

Mike McCann

MMC Engineering

## RE: ASCE 7 Wind Loads on Rooftop Structures

## RE: ASCE 7 Wind Loads on Rooftop Structures

Section 1609.8

http://www.ecodes.biz/ecodes_support/free_resource...

## RE: ASCE 7 Wind Loads on Rooftop Structures

Thanks for pointing out that section Triangled in the FBC. I don't do a lot of rooftop wind design anymore and was not aware of this.

To the original post, wouldn't wind pressures increase with height on rooftop components the same way they do with exposure factors?

There is a table here (FWIW) with values up to 400ft:

http://www.academia.edu/2451278/WIND_LOAD_ANALYSIS...

## RE: ASCE 7 Wind Loads on Rooftop Structures

## RE: ASCE 7 Wind Loads on Rooftop Structures

Greater pressures with increasing height are covered in the tables and formulae.

Michael.

"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin