Applies To
	Product(s):	Microstran
	Version(s):	V8i
	Environment:	N/A
	Area:	Modeling; Analysis
	Original Author:	Richard Collins

What's the Difference Between Restraints and Releases?

A restraint may be applied to a node to create a fixed support while a release may be inserted at either end of a member to create an internal hinge. The default condition for a node is unrestrained and the default condition for a member is without releases. Thus, as you draw new members with graphical input, the nodes initially are not supports and the members initially have no releases (unless you change the default condition for new members). This is just what you would expect because, usually, most nodes are unrestrained and most members don't have releases.

At each node there are six potential degrees of freedom (DOF), each corresponding to a global axis translational or rotational direction. Each DOF may be either free (the DOF exists) or fixed (a "restrained DOF", i.e. the DOF does not exist). Strictly speaking, the term "release" is not used in connection with nodes.

At each end of a member, there are six potential releases (but they can't all exist together). When they do not exist, the member end is rigidly connected to the adjacent node. This condition is sometimes described as "fixed" but we prefer not to use "fixed" in connection with members because it is imprecise - if the member end is fixed, is it fixed absolutely (as in "fixed-end moment") or is it merely "fixed" to the node? We may refer to "releases" being present or not, or we may describe the member end as being continuous with the adjacent node or not. When a release exists, the corresponding member force component is "released" (i.e. it becomes zero).

Why Are There Different Conventions for Restraints and Releases?

The short answer is that they are the same.

This question refers to the fact that Microstran uses a "1" in the restraint code to denote fixity at a support and a "0" in the release code to denote the absence of a release. There is a superficial similarity between these two conditions and the confusion arises because Microstran describes one with a "1" and the other with a "0". The superficial similarity, however, is caused by the imprecise use of the term "fixity" in connection with member end releases (see What's the Difference Between Restraints and Releases?, above). Microstran's use of "1" and "0" for restraint codes and release codes is explained in terms of simple English - "1" means "yes" and "0" means "no" - if a restraint or release exists, use a "1"; if it does not exist, use "0". Note also that the default condition for nodes and members is zero, i.e. no node restraints, and no member releases.

Similarly, Microstran uses a "0" to denote the absence of fixity at a node while "1" denotes the presence of a release at the end of a member. In this case, the similarity between the two conditions is more than superficial because you could create the same pinned support with either (but not both together). Perhaps you should not be asking why a similar outcome can be produced by a "1" in one place or a "0" in another, when "restraint" and "release" are almost opposites in plain English!

Why Are "1" and "0" Used Instead of "F" and "R" for Restraints and Releases?

To avoid ambiguity - for instance, does "F" mean "Free" or "Fixed", and does "R" mean "Restrained" or "Released". Microstran uses the simple convention that "1" means "yes" and "0" means "no". For example, if a restraint or a release exists, we use "1"; if it does not exist, we use "0". This means that the default, or usual, situation for node restraints and member releases is indicated by zeros.