Wind Loads per IS 875 Part 3
For plant structures designed under Indian codes, the program calculates the wind load per IS 875 Part 3 Wind Load on Buildings and Structures, Fourth Revision (2002). A static wind pressure is applied to the structure by the program using the following general procedure.
- Calculate Basic Wind Speed, Vb, based on mapped values (Figure 1 in Section 5) or the table supplied in Appendix A of IS 875.
- Calculate Probability Factor (risk coefficient), k1, from Table 1 in Section 5 of IS 875.
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Calculate the k2 Factor (Table 2 in IS 875) based on structure height and terrain category. Separate k2 values are determined at different height intervals for vertical vessels as well as for each horizontal vessel in a stacked configuration.
- Calculate the Topography Factor, k3 per Appendix C in IS 875.
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Calculate the Design Wind speed for each height considered (IS 875, Clause 5.3) as:
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Calculate the wind pressure for each height considered (IS 875, Clause 5.4) as:
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Calculate the design wind pressure for each height as:
Kd = wind directionality factor, as determined in Cl. 5.4.1.
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For each height, the exposure area, A, is consider. This area is calculated differently for vertical and horizontal vessels.
Exposure areas for vertical and horizontal vessels
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Calculate Force coefficient, Cf, which is considered for structures without openings.
Note: For vertical vessel, the equipment is symmetric and thus the wind load need only be evaluated from only one direction. Therefore, only one set of Cf is calculated. For a horizontal vessel, the wind is considered from both the longitudinal (x) and transverse (z) directions. So, two sets of Cfn are calculated. -
Calculate the Wind force, Fn, from Clause 6.3.3.2 of IS 875 for each wind height considered as: