Insert a spring on the end of the beam. It can be a Body-Ground spring or a Body-Body spring connection depending on your application.

Insert a Command Object under that spring to convert it from a simple linear elastic spring to a COMBIN39 nonlinear spring or a COMBIN40 nonlinear spring, depending one what type of nonlinearity you need.

Read the ANSYS Help on COMBIN39 by copy and paste the URL below into an open ANSYS Help browser. Don't paste it into any Browser or you will be delivered to the Customer Portal.  Here are more instructions if you fail to open this link.