Engineering guide
The WIND module calculates wind loads on free-standing process equipment and plant structures — typically columns, vertical vessels, stacks and pipe bridges. From the wind speed or velocity pressure, the structure geometry and the aerodynamic force coefficients, the module determines the wind forces distributed over the height as well as the resulting shear forces and bending moments, which enter the strength and stability verifications of shell, courses and anchorage as external loads.
The national wind load standard underlying the module (DIN 1055-4, a German wind load code, and its predecessor rules) has been withdrawn. Wind loads are nowadays determined per Eurocode 1, DIN EN 1991-1-4 together with the applicable national annex; wind zones, terrain categories, gust velocity pressure and force coefficients are regulated anew there. For existing plants, reassessments and the evaluation of older design documentation, however, the calculation per the withdrawn code remains relevant — for example when an existing apparatus is to be checked against its original design basis.
Scope
- Wind loads
Typical workflow
Define site and wind parameters
From the wind zone or reference wind speed and the height above grade, the height-dependent velocity pressure is determined; the increase of wind speed with height is captured via a height profile.
Geometry and force coefficient of the structure
For the cylindrical apparatus, the diameter (including insulation and attachments), height and slenderness are recorded; from these follows the aerodynamic force coefficient, which for circular cylinders depends on the Reynolds number and the surface roughness.
Calculate the wind forces over the height
The wind load per height segment results from velocity pressure, force coefficient and projected area exposed to the wind; attachments such as ladders, platforms and piping increase the effective area.
Section forces for the stability verification
By summing the segment-wise wind forces, the shear force and bending moment over the height of the apparatus are built up — in particular the fixing moment at the base, which governs the shell cross-section, the base ring and the foundation anchorage.
Frequently asked questions
May new designs still be calculated to the withdrawn wind load standard?
No. For new equipment and structures, DIN EN 1991-1-4 (Eurocode 1, Part 1-4) with the national annex must be applied. The withdrawn code is only used for reassessments of existing plants when the original design basis has to be reconstructed or evaluated. In the case of significant modifications to an existing plant, inspection bodies generally require verification per the current code.
What distinguishes the wind load on a cylinder from that on a sharp-edged structure?
For a circular cylinder, the force coefficient depends strongly on the Reynolds number and the surface roughness: in the supercritical range, where large process equipment practically always operates, it drops well below 1. Attachments, insulation cladding with seams and mounted piping increase the effective roughness and thus the coefficient — they must not be neglected when determining the loads.
Do slender columns additionally require a check for cross-wind vibrations?
Yes. Slender, lightly damped columns and stacks can be excited into vortex-induced vibrations transverse to the wind direction (Kármán vortex shedding) when the vortex shedding frequency approaches the natural frequency. This verification is carried out separately from the static wind load calculation and may require constructive measures such as helical strakes (Scruton spirals) or dampers.
Technical content source: LV-Solved-Problems-Content 628d313247e7