Engineering guide
This module determines the live loads on a vertical cylindrical structure with attachments to DIN 4133 (the German standard for steel stacks, 1991-11 edition) for heights up to 50 m. Typical applications in vessel and plant engineering are columns, reactors and steel stacks on which ladders, platforms, piping or insulation act as attachments that enlarge the wind exposure area. The calculation delivers the bending moment at the restraint point, i.e. at the base fixity of the cylinder.
This restraint moment is the central internal force for all subsequent verifications: it enters the strength and stability check of the vessel wall under supplementary loads (for example per AD 2000-Merkblatt S 3/0 or B 9 of the German AD 2000 code) and sizes the foundation, anchor bolts and support skirt. Anyone who wants to calculate wind loads on a vessel needs, besides the velocity-pressure profile, above all a correct treatment of the attachments, because they can significantly increase the force coefficient and the projected area.
DIN 4133 has been withdrawn. New designs today follow DIN EN 1993-3-2 (Eurocode 3, steel chimneys) with wind loads per DIN EN 1991-1-4. For existing plants erected to DIN 4133, and for re-rating and comparison calculations, the old load level remains of practical importance — that is what this module is provided for.
Scope
- Live loads on a cylindrical body with attachments
Typical workflow
Record geometry and attachments
The cylindrical structure is described by its diameter and height (h ≤ 50 m). Attachments such as ladders, platforms and external piping are recorded with their wind exposure areas and elevations, since they change the resulting wind load and its lever arm.
Apply the velocity pressure over the height
Per DIN 4133 the velocity pressure is applied as a function of height. For each height segment this yields the area load acting on the cylinder and the attachments.
Determine the force coefficients
For the cylinder, the aerodynamic force coefficient is determined taking slenderness and surface condition into account; separate coefficients are applied for the attachments. From these follow the segment-wise wind forces.
Sum the internal forces at the restraint point
The wind forces of all segments and attachments are integrated with their lever arms into the bending moment at the restraint point. This moment is the module's result and serves as input for wall thickness, stability and anchorage verifications.
Frequently asked questions
Why must attachments be considered separately?
Ladders, platforms, cable trays and tracing pipes not only enlarge the projected area, they also disturb the flow around the cylinder. A smooth circular cylinder has a comparatively favorable force coefficient; with attachments, the effective coefficient rises noticeably. Anyone who neglects attachments systematically underestimates the restraint moment — often by double-digit percentages.
Does the calculation also apply to guyed structures or structures held at the top?
No. The model assumes a freely cantilevering structure fixed at its base (cantilever). Guy wires, intermediate supports or coupling to a supporting structure fundamentally change the static system and require a dedicated structural analysis.
What is the difference between DIN 4133 and today's Eurocode rules?
DIN 4133 worked with the old German velocity-pressure concept and generic coefficients. DIN EN 1991-1-4 uses wind zones, terrain categories and a gust velocity pressure, and DIN EN 1993-3-2 governs the chimney-specific verifications including vortex-induced cross-wind vibrations. The load levels can differ; a reassessment to the Eurocode may therefore lead to restraint moments that differ from the original structural analysis.
What is the bending moment at the restraint point used for afterwards?
It provides the additional longitudinal stress in the vessel wall (verification against yielding and against buckling on the compression side), sizes the support skirt and enters the design of the anchor bolts and the foundation against overturning. Combined with dead weight and internal pressure, it forms the governing load case at the vessel base.
Technical content source: LV-Solved-Problems-Content 628d313247e7