Wind load for a gable roof on an open structure

[CENAEN]

I'm reviewing some shop drawings for wind load compliance and noticed a gray area in ASCE 7-98. I'm curious to know how everyone else would approach this situation.

The structure is an open structure with a gable roof. The designer used the MWFRS coeff. for an enclosed, partially enclosed building (Fig. 6-3) for their analysis. But the building is not enclosed; it's open. For an open building it only provides MWFRS coeff. for a monoslope roof (Table 6-9). Should I interpret each side of the gable roof as a monoslope roof or is their interpretation correct?

Thanks,
Juan

 

[cnprabhakar]

Cenaen,

I think u r right, we can take the co-eff of monoslope roof

Prabhakar

 

[carlputnam]

This is a big gray area because eq 6-20 in (ASCE7 6.5.13) is only for horizontal wind loading, not uplift. "Af" is defined as the projected area normal to the wind direction. I am dealing with light aluminum structures and want to find out how to resist the uplift. The rest of section 6 deals with partial and fully enclosed buildings. Only in Table 6-7 does it mention anything about open building (GCpi = 0) but does not give the GCp in any table. Does anybody have an idea about how to calcualte uplift for open buildings????

 

[sc]

Have a look at thread507-56833 for a discussion on wind loads.

In Australia the design code AS1170.2 indicates that free a standing roof is treated depending on whether they are; mono slope, pitched or troughed, clear under or blocked under (truck storage, hay shed, etc).

I would imagine that the US codes have some similar form of requirements.

AS1170.2 indicates that monoslope a roof is not the same as one side of a gable roof. Although having said that for slopes <15deg they are essentially the same, for slopes near 30deg they are very different.

regards
sc

 

[CENAEN]

Thanks for the help. I called Kishor Mehta at Texas Tech University (one of the authors of ASCE 7-98 and Guide to the Use of Wind Load Provisions for ASCE 7-98). He was gracious enough to take the time to speak with me about the situation. He agreed that the code lacks direction in this area and suggested using Figure 6-3 with a GCpi=+/-0.55. He said this is a good approximation that will approach the actual wind pressures for the structure.

Juan

 

[steve111]

Try ASCE Paper No. 3269 'Wind Forces on Structures', a Swiss Paper, much referenced (See SEI/ASCE 7-02 C6-36 the english interpretation in ASCE paper above)and still to this day in the codes, is used. In the swiss paper 1956, are open walled roof only structures and their pressure co-efficients are listed in Fig 4(d)-Wind Pressure Coefficients for Shelter Roofs. Train stations actually because they reference what effect a train sitting beside the structure has on the pressure co-efficients. Sorry i don't have a more complete title for the ASCE paper but i'm sure a little digging and you could find it...