Plotting combined functions (the sum of two functions)

Hello!

I want to plot a total deformation diagram such that it is a sum of two deformations caused by two different forces. 

While plotting I get the following error message: There are too many range variables. I think that it is strange since I use three sets of traces, where each trace set corresponds to one deformation only.

May somebody, please, assist me with the proper construction of described diagram?

Best regards,

Sergey