Difference in PSC check and envelop load value.


The model show PSC check for Shear. When i compare the PSC shear value and the shear value from my envelop, it is very different. For example, element 17 PSC show this 
V_ed range is from 21582kN to 25474kN (i notice the Type is FX min/max, not the FZ ???)

But the envelop of shear load for member 17 is 
shear -Z show max value is 36986kN, which is much biger than 25474kN.

I attach the model in here for your review.



Kindly let us know the exact version of the software being used at your end for further assistance.

Technical Manager, MIDAS


I'll try to elaborate on what is exactly happening here.  As you already know, prestress had 2 components, Tendon Primary and Tendon Secondary.  For SLS cases we consider both tendon primary and secondary while for ULS we just consider tendon secondary.
However, particularly for design shear force only, practically engineers reduce the acting force in accordance to the acting tendon primary.  If this isn't done, the sections are very conservative for shear design.  Now, we do not select tendon primary for ULS load combination.  Hence, when checking the shear force from the result table, the effect of tendon primary wouldn't be reflected in the combination.  But, when checking from design result tables, the acting shear force is reduced in accordance to component of the tendon primary and hence this would be lesser.  For verification purpose, kindly check a simple model with a straight tendon.  In this case, since prestress wouldn't have any vertical component, the shear forces would be comparable.
A sample model is attached herewith for your quick review.  Kindly let us know if further assistance would be required.

Technical Manager, MIDAS

Thank you Nandeep for your explanation. It is extremely helpful.

Sincere thank,

Creation date: 10/17/2018 9:02 PM (dklee@midasit.com)      Updated: 10/18/2018 6:32 AM (dklee@midasit.com)
Uniform spring.mcb