The main problem addressed in this paper is to evaluate robustness of a linear elastic structure with an uncertain static external load. We consider the compliance constraint as a performance requirement and use the robustness function as a qualitative measure of robustness. The robustness function is defined as the largest level of uncertainty in the external load, up to which the compliance constraint is satisfied. We show that the robustness function can be computed by solving a semidefinite programming problem. Numerical examples illustrate that robust preference between two given structural designs depends on the critical performance.