As part of the fitting of the mooring lines to a wave energy device, the pin-jointed structure shown in Figure Q is to be subjected to a small degree of plastic deformation by applying a force, F, in the direction shown.

The structure is made from two members, each of cross-sectional area 50mm², using a high strength steel whose elastic-plastic stress-strain relationship is:

(a) Calculate the load, F, required to cause first yield in members AC and BC.

(b) Find the deflection, u, for a load, F, of 35kN and determine the residual plastic strain in the members after removal of the load.