Solution to Problem 237 Statically Indeterminate

Use σ_co = 70 MPa and σ_st = 140 MPa
$\delta_{co} = \delta_{st}$

$\left( \dfrac{\sigma L}{E} \right)_{co} = \left( \dfrac{\sigma L}{E} \right)_{st}$

$\dfrac{70 L_{co}}{120\,000} = \dfrac{140(240)}{200\,000}$

$L_{co} = 288 \, \text{ mm }$ answer