Hello
The difference in the values is due to shear deformation.
When STAAD computes the displacement at a node it considers the :
1. flexural deformation
2. shear distortion
Hence, the joint displacements consist of the pure bending component plus the shear deformation component. When you did a manual calculation , you did not consider the shear deformation part, also , in the standard textbooks , this shear deformation is not considered for displacement calculation .
This is the reason why text book result does not match with Staad output .
You may instruct the program not to consider this Shear Deformation by using the SET SHEAR command .
Using this command, Staad will only take in the flexural deformation and displacement will match with the standard manual calculations .
I hope this helps .
Cheerzz