Request diagnosis about applying pretension to cables in Karamba

Dear all the experts with Karamba,

I am doing my graduation work with a cable-strut system. With Karamba I thought things could be easier as for further optimisation.

However, I met some problems which need some kind support and help:

1) The pretension in the cables was not fully transferred.

eg: In the model I applied pretension - elongation 5mm/m, but the resultant beam axial force ranges from (-3.79,158)kN, far less than the expected 500kN.

2) To model cables, I  gave no bending to the curved elements, at the same time added joints to both ends. I 'm not sure if this is proper or not. Anyway, results says there is no bending in the cables.

Best,

Zhengyu