Adjoint aerodynamic optimisation has recently gained increased popularity for turbomachinery applications due to the large number of parameters that can be used without incurring additional major computational costs. This work presents an adjoint based aero-structural optimisation method having efficiency as the objective function and maximum von Mises stress set as a constraint. The full optimisation loop was set up with free-form deformation for geometry parametrisation. A response surface was created beforehand for computing the maximum von Mises stress using a meshless method. A discrete adjoint approach was used to obtain the gradients of the objective function with respect to each design parameter, while the constraint gradients were computed using finite differences. A sequential least squares programming algorithm was used as the optimizer. Tests carried out on a highly loaded compressor blade showed that the method successfully increases the efficiency by more than 3% while maintaining the maximum stress under the imposed value. The results also showed that the constrained optimisation loses about 1% in potential efficiency gain compared to the same optimisation process without stress constraint. Overall, the work provides a methodology for conducting structurally constrained adjoint aerodynamic optimisation that can be applied for large number of design parameters while maintaining low computational costs. It also provides reference for constructing and selecting a response surface to be used in the optimisation process.