How to use alpha ( thermal expansion coefficient) as piecewise function.

Hello evrybody,

I m using a time dependent problem of a beam restricted at both ends. When we use alpha ( thermal expansion coefficient) as a piecewise function, then they give error as "Failed to evaluate variable Jacobian for alpha". Can anyone help me how to use alpha as piecewise function. if possible give the path of some model library or documentation.

Thank you.