Combined Thermal Conductivity of I Beam with different k values

Hi There

Hope you can help me. I need to calculate a thermal conductivity of a 3 piece constructed I Beam.

The flanges are in a different material to the web. Flanges are 0.029m x 0.029m with k value of 0.075 W/m⋅K and the web is 0.009m x 0.05m with k value of 0.12 W/m⋅K

The 3 materials are in series, and at this stage can ignore any join between the 3 of them. I have tried various methods but nothing looks correct.

Many thanks in advance

David