I am performing concrete design for a beam per the ACI code. At the start as well as the end nodes of the member, the value "Vu" which is reported in the shear design output does not match the shear force Fy from the member end force output. Why is that?
STAAD performs concrete design for shear and torsion at locations defined by (d + SFACE) from the start of the member and (d+EFACE) from the end of the member respectively. In case you are not familiar with the parameters SFACE and EFACE, you will see in Chapter 3 of the STAAD.Pro Technical Reference Manual in Table 3.1 that these are values which the user may specify to convey to STAAD how far the face of the member is from the nodes of the member. The default value for SFACE and EFACE is 0.0. "d" is the effective depth of the member. The basis for this assumption can be found in Section 184.108.40.206 of ACI 318-95.
If you want the shear & torsion design to be performed using the member end forces (the nodal values) and not those at the location mentioned in the previous paragraph, you can set the values for SFACE and EFACE to be negative quantities equal in magnitude to "d". That will result in (d+SFACE) and (d+EFACE) becoming zero, which means that the design will be performed at the nodal points of the member.
So, in your input file, under the START CONCRETE DESIGN command, specify these parameters along the following lines :
START CONCRETE DESIGNCODE ACISFACE -d MEMB 110EFACE -d MEMB 110DESIGN BEAM 110END CONCRETE DESIGN
where "d" is the effective depth of the member.