250kg is a force of about 2,500N due to gravity.

Do a hand calculation of the force created in the bottom half of the beam due to a 10C temperature increase.

For a beam that is fixed at both ends with cross-sectional area of A in m^2, a Modulus of Elasticity of E in N/m^2, a CTE in units of /C, you can compute the axial Force in N in the beam as A*E*CTE*10