Cf for Cable Tray waterfalling

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I have a quick question. In general wind loads on cable trays we use Cf = 2.0 for all wind loadings going laterally against.

When we get a transition portion say from a pipe bridge to pipe rack at a lower elevation when the cable tray is vertical and we want to model the wind loads normal to the tray for the "waterfall" portion F = qz*G*Cf*A is Cf of 2.0 still used? In the "Wind Loads for Petrochemical and Industrial Facilities" publication they give a design example however only use Cf = 1.0.

Any thoughts are welcomed.

Thanks,

 

[HTURKAK]

This is true for lateral load calc. for the rack .. But for longitudinal load calculation on pipe bridge, the cable trays jumps to EL 36.0 from 30.0 .

And the trays are sloped say 30 degr. ( pls look Figure 6.1.3 Pipe Bridge Example )

The vertical prjection area of cable trays = 0.9 x 20 ft x 6 ft = 108.0 ft2 ( assuming the solidity ratio 0.9)

Cf may be estimated from

- Table 5.3 ( with assumption a/b=0.25 , c/b= 3.2) Cf=1.2
- ASCE 7 Figure 30.8-2 ( Pitched free roof )

Probably Cf=1.0 is selected considering the cable trays are perforated and for simplicity..

 

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Thank you for the detailed response. Our cable trays will be going at a 90 deg angle and thus could ASCE 7 Figure 29.4-1 "Solid Freestanding Sign" be used as well?

 

[HTURKAK]

I would prefer ASCE 7-16 ( FIGURE 29.3-1 Design Wind Loads (All Heights): Force Coefficients, Cf, for Other Structures— Solid
Freestanding Signs )

Cf varies betw 1.30-1.95 . I would reduce the figure as per solidity ratio .

 

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