Let us consider the following truss structure:

 

 

In calculation we assume that P1 = P2= P3 = 10 [kN] and L=1[m].

 

Now let’s assume that the forces changes in the 5% i.e

 

P1= P1 ± 2.5%

P2= P2 ± 2.5%

P3= P3 ± 2.5%

 

If we calculate the relative error of axial forces

 

 

then we will get the following results:

 

 

 

 

 

 

 

We can see that in some cases the relative error

of calculation is equal to 60%.