Vertical Deviation Angle

A hanging support holds the pipe from above on a rod. When the pipe moves horizontally, the rod swings out of plumb. The deviation angle measures how far.

Why it matters

A rod hanging vertically applies a purely vertical force. A rod hanging at an angle does not: it applies a vertical component and a horizontal one, and the vertical component is smaller than the load the support was sized for.

Two consequences follow. The pipe receives a horizontal force nobody designed for, and it receives less vertical support than intended. At small angles both effects are negligible. At larger angles they stop being negligible, and the progression is not linear — the horizontal component grows much faster than the first few degrees suggest.

How the software calculates it

The angle is derived from two quantities:

The horizontal displacement — the resultant of the lateral and axial movements combined, not either one alone. A support with movement in both directions deviates more than either figure taken separately implies.

The effective hanging height — the installation height, adjusted for the components in the assembly. Two-bolt and three-bolt clamps reduce it by their own height, because the rod does not extend all the way to the pipe centreline. Some spring types adjust it in the other direction.

The angle is then the arctangent of the displacement over the height, expressed in degrees.

The practical reading: a longer hanger deviates less for the same movement. Where the geometry allows it, raising the attachment point is the simplest fix.

The warning thresholds

These are advisory, not blocking. The software does not prevent you continuing, and it does not modify the design. They exist so the condition is visible and gets a decision.

What to do about a warning

Lengthen the hanger. The angle falls as the height rises. Often available where the steelwork permits.

Offset the installed position. Standard practice: install the hanger deliberately out of plumb, in the opposite direction to the movement, so it passes through vertical mid-travel. This halves the maximum deviation. It is a site instruction, not a software setting, and belongs on the drawing.

Change the support type. If the horizontal movement is large enough that no hanger geometry works, the pipe probably needs guiding or a different support concept.

Accept and document. Below 8° this is frequently the right answer, particularly where the horizontal movement is small in absolute terms even if the hanger is short.

Where the angle is not calculated

The angle is meaningless for supports that do not hang, and the software sets it to zero for:

• Clamp bases and U-bolts — nothing hangs
• Struts and snubbers — different geometry entirely
• Sliding plates — nothing hangs
• Certain spring types where the movement refers to the pipe rather than to the support

It is also skipped when the structure elevation has not been entered, or when no horizontal movement has been defined. In both cases the absence of a warning means the check did not run, not that the geometry is fine.