Applies To
	Product(s):	STAAD.Pro
	Version(s):	All
	Environment:	N/A
	Area:	Modeling Solutions
	Subarea:	Supports
	Original Author:	Bentley Technical Support Group

How does STAAD "direct" a spring to determine if it is in compression or tension?

In view of the above, how should one specify radially directed springs located around a circular tunnel or pipe and designate them as "compression" only in the physical sense of the term?

For the purpose of defining the sense of the force in the SPRING TENSION/SPRING COMPRESSION facility, the following rules are adopted in STAAD :

A support reaction force is considered TENSILE if it is opposite to the positive direction of the axis under consideration. Another way of putting it is that, for this condition, the displacement along that axis of the support node is in the same direction as the positive direction of that axis.

A support reaction force is considered COMPRESSIVE if it is along the positive direction of the axis under consideration. Another way of putting it is that, for this condition, the displacement along that axis of the support node is in the direction opposite to the positive direction of that axis.

These rules are applicable for global axis supports, as well as inclined axis supports.

Hence, use the center of the circular pipe as the REFERENCE POINT for the INCLINED supports. The local X axis for the inclined supports will then point from the perimeter towards the center of the circle. The supports around the circumference can then be assigned COMPRESSION only springs. .