edemarcos,

Refer to the ASCE Publication:  Wind Loads and Anchor Bolt Design for Petrochemical Facilities.  This publication is dated 1997 and references ASCE 7-95 (the first one to use the 3-second gust as a basis).  In Appendix 5.A. is an example of wind loads on a pipe rack with pipes and cable trays on it.  

For the pipes, they use G = 0.85 and Cf = 0.7.  They recommend using an effective area for the pipe as follows:

Ae = Largest pipe diameter + 10% of rack width  (per foot of pipe rack length).

regards,


chichuck

Thanks for the answer.
This value for G is valid for ASCE 7-02 also ?

edemarcos,

Yes, the gust factor is also applicable to the 7-02 code.  In the newer code, the proscriptive value of 0.85 is applicable to all exposures, not just to exposure C as was true for the 95 code.  There were some changes between the two codes as regards gust factor, (ref. section 6.5.8 in 7-02 and  section 6.6 of 7-95), but the proscriptive value is still valid.

Regards,

chichuck

edemarcos/chichuck,
                    Remember that the loading calculated as given above is for the total load onto the piperack. If you are talking about an individual pipe that is to be stress analysed for wind loading then this is different and far less loading.

Regards

DSB123

We use the following formula for pipe racks, based on equating a pipe group to a single equivalent pipe.  Unfortunately I'm not sure of the original source/reference.

F_w = C_d*p*(d_max + d_ave*a)

where:
  'F_w' is the unit wind load [kN/m]
  'C_d' is the drag coefficient for the largest pipe in the group
  'p' is the wind pressure [kPa]
  'd_max' is the largest diamter in the pipe group [m]
  'd_ave' is the average diamter of the pipe group [m]
  'a' is a factor for the number of pipes in the group
     1 pipe, a = 0; 2, 0.70; 3, 1.19; 4, 1.53; 5, 1.77; 6, 1.94; 7, 2.06; 8, 2.14; 9, 2.20; 10, 2.24; >10, 2.30