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In my class notes I have the following: If we consider a 1D beam of lenght L wich is fixed at x=0 and subject to an effort F at x=0 we have the following boundary condition depending if the effort is a compression or a traction effort:

[itex] u(0)=0 ; SE(L) \frac{du}{dx}(L)=F [/itex] if F is a traction effort

[itex] u(0)=0 ; SE(L) \frac{du}{dx}(L)=-F [/itex] if F is a traction effort

Where S is the beam section and E is the Young constant.

My question is the following: what happens with boundary conditions if the beam is fixed not in x=0 but in x=L? In my opinion it would be the following:

[itex] u(L)=0 ; SE(0) \frac{du}{dx}(0)=-F [/itex] if F is a traction effort

[itex] u(L)=0 ; SE(0) \frac{du}{dx}(0)=F [/itex] if F is a traction effort

What I did was simply put "0" instead of "L" and change the F sign: in this situation F would be positive if we have a compression effort and negative if we have a traction one. Is this correct?

Thank you very much and sorry for my English...