Question:

How can I Model Compression only Spring Support

Ans: 

We find that “springs” tend to be modelled in 2 ways in Microstran. Both of these are described below, the 2^nd method satisfies the spring being “compression only”. 

1. Designating Spring Supports at Point Supports, per the manual

Spring supports are used to model external elastic supports provided by the foundation or other structures. They are defined by specifying up to six spring stiffnesses at each node where there is an elastic connection between the structure and a point of rigid support. All spring stiffnesses act in the global axis directions and must be specified in consistent units. Spring supports may be applied to any DOF that has not been suppressed because of the structure type. If a fixed support and a non-zero spring stiffness are specified at any DOF, the spring support will take precedence. At each node where one or more spring supports exist, the following data is required:

KX       X translation spring stiffness.
KY       Y translation spring stiffness.
KZ       Z translation spring stiffness.
KRX     X rotation spring stiffness.
KRY     Y rotation spring stiffness.
KRZ     Z rotation spring stiffness.

Translational spring stiffnesses are defined in units of force per unit displacement. Rotational spring stiffnesses are defined in units of moment per radian (i.e. the moment required to produce an elastic rotation of one radian). All stiffness values must be zero or positive – a zero value indicates that there is no spring in the corresponding direction.

Nodes with spring supports are identified graphically by a spring symbol.

Use the Structure > Attributes > Spring Supports command to input spring supports at one or more nodes.

2. Model the Springs as actual members in Microstran, adjust member type as necessary. If you have Microstran, an example of this in action is per below:

Structure à Standard Structures à Beam on Elastic Foundation

Have a look at the resulting structure generated, the springs themselves are actually members in Microstran, with one end connected to the structure and the other as fixed support.

Since the springs themselves are actual members, you can modify the member properties to be “compression only”.