Leg supports consist of individual structural members welded or bolted to the vessel shell or bottom head, extending to a foundation. They are widely used for small to medium vertical vessels, spherical storage tanks, and horizontal vessels where saddles are impractical. PSI supports two leg configurations: standard (unbraced) legs and braced (arriostrada) legs.Documentation Index
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Unbraced legs
Simple structural sections (rectangular plate, angle, or tube) welded to the vessel. Suitable for short vessels or locations with low lateral loads.
Braced legs
Structural sections interconnected with horizontal or diagonal bracing. Required when leg slenderness or lateral loading demands additional stiffness.
Parameters
Leg Configuration
Number of legs supporting the vessel. Options: 3, 4, 6, or 8.
Cross-section shape of the structural leg member. Available options depend on the leg configuration:
- Unbraced legs:
Rectangular,Angle,Tube - Braced legs:
Angle (L),Beam (W/I),Pipe (Sch 40/80),Square Tube (HSS)
Designation of the brace member cross-section, using standard structural notation (e.g.,
L2x2x1/4 for a 2×2×¼ angle). Only shown for braced leg configurations. The brace profile is used to calculate the brace axial capacity and connection forces.Unsupported length of each leg from the vessel shell attachment to the base plate. For braced legs, this is the total leg height; bracing tier positions are determined by
bracingTier.Number of horizontal bracing levels distributed along the leg height. Options: 1, 2, 3, or 4. More tiers reduce the effective buckling length of each leg segment. Only shown for braced leg configurations.
Base Plate (Vertical and Spherical Vessels)
Base plate parameters are shown only for vertical (columna vertical) and spherical (Esférico) vessel types. Horizontal vessel legs use longitudinal and transverse spacing instead.
Width of the base plate at the bottom of each leg. The base plate must be sized to limit bearing pressure on the foundation grout.
Length of the base plate at the bottom of each leg. Together with
legBasePlateWidth, defines the bearing area and bolt hole layout.Spacing (Horizontal Vessels)
Spacing parameters are only shown when the vessel type is Horizontal.
Centre-to-centre distance between the two leg pairs measured along the vessel axis (longitudinal direction). This dimension governs the bending moment in the vessel shell between supports.
Centre-to-centre distance between the two legs within each pair, measured perpendicular to the vessel axis (transverse direction). This dimension affects the stability of each pair under lateral loads.
Bolt Circle (Non-Horizontal Vessels)
Diameter of the bolt circle (Dbc) on which the anchor bolts at the leg base plates are positioned. Shown for all vessel types except horizontal.
Under-Slung Configuration (Spherical Vessels)
Indicates whether the legs are attached below the sphere equator in an under-slung arrangement. Options: Yes or No. When enabled, the bolt circle warning for small Dbc values is suppressed, as the geometry is intentionally inverted.
Under-slung leg arrangements are geometrically possible but are generally considered unstable for free-standing spherical vessels. Consult your structural engineer before selecting this option.