Carport loading 1

[ag89]

I am doing an analysis of a carport that is already constructed. The allowable loading needs to be determined for permit purposes. I can't find any reference to live load for carport roofs in UBC. The closest I can find is the 12 psf for standard roof loading. The trouble is that the carport will need to be modified to bring it up to code. I am trying to back into the live load on the roof. The critical case is DL + LL + WL on the columns. The wind load and the dead load being the only knowns. Any help would be appreciated

 

[ishvaaag]

There must be a determinant code saying this. What is the LL made of, exclusively cars or other more heavy are permitted? In any case see how nonchalantly the spanish code deals with the vehicle live loads in buildings: if only cars allowed, 400 kgf/m2; otherwise, trucks included 1000 kgf/m2. Try to make the division of 1250 kgf weight of a car, multiply per 1.25 impast factor and divide 2.5x5 m2 its parking allocation to see that impact factored load under cars is about...125 kgf/m2.

Look your code.

 

[ag89]

This is a standard carport to protect cars from the elements, i.e. no cars etc. to be supported.

 

[Ron]

Under UBC, look at the "canopy" requirements. In general you are looking at DL+Lr, which for a canopy as you have described is about 22 to 24 psf. For wind load, the load case is DL+W, which will range from more than the DL+Lr to significantly less than DL+Lr for just about anything less than a 110 mph wind speed.

If the carport roof is flat or only nominally sloped, live load reductions are not appropriate so you get no help there.

If using ASCE 7 (allowed under UBC), then this would be considered an "other structure", and generally computed by F=qCfA, with Cf coefficient from monoslope roof table.

 

[daski]

I don't know where you live, but in most parts of the US, the main "live load" on a roof is snow and snow drifting. If you don't get snow, is it possible for rain water to accumulate on the roof due to clogged drainpipes? Otherwise, just use the code live load (12 psf as you say).

mdaskilewicz@cuh2a.com

 

[Polecat]

If this carport is an open frame attached to a building (or even free-standing), you are going to encounter a fierce uplift load which will entail a close look at your roof framing, columns, foundation and connections thereto.

See ASCE 7-95 or 98 for further details.
The Polecat

http://www.spiraleng.com

I invite people to visit my website if you wish to discuss these issues further.

 

[StructuralDzine]

You don't generally need to combine roof live load with wind load. Roof live load is basically a construction or maintenance load. It is assumed that no-one will be on the roof during the design wind speed event.

 

[haynewp]

From cleaning off carport roofs in my childhood, I can tell you that there are often a lot of trees planted nearby the house that will clog the gutters (especially pine trees).If it is also a very small roof slope (as Ron stated), I would be tempted not to use a live load reduction at all and also check a D+L+W case.