Tendong grouting cause changes in stress in AQB, but it doesn't in CSM?

[netsonic_Sofistik]

We know that for post-tensioned members, before tendon grouting, the net section is used; while after grouting, the transformed section is used.
So the section properties before and after grouting are different, therefore the stresses are different too.

But in CSM manual $2.4,

All construction stages that cause changes of stresses have to be considered. Therefore
construction stage grouting / extrusion (CS: x2) is not necessarily to be computed, due to the
fact that the grouting mortar causes no changes in stresses.

Is it correct?

[mico]

I guess it is noticed there that grouting itself does not case any loads, so if cs:x2 stage is not calulcated it is no problem, but after cs:x2 stage brutto section properties are used.

[netsonic_Sofistik]

This is the official Sofistik Verification Example:
DCE-EN17: Stress Calculation at a Rectangular Pre-stressed Concrete CS
verification.dat\dcbenchmarks.dat\dce-en17\stress_prestress.dat
I add “CSM” in it.

At mid-span of the beam:

1. Hand calculation & AQB:
   dead load moment = 1250 kNm
   prestressing moment on net section (before grouting)= -1435.91 kNm
   prestressing moment on transformed section (after grouting) = -1406.11 kNm
   on net section, moment = 1250-1435.91 = -185.88 kNm, the bottom stress = -4.82 MPa
   

   
   
   on transformed section, moment = 1250-1406.11 = -156.08 kNm, the bottom stress = -4.51 MPa
   
   

2. CSM
   on net section, moment = -185.88 kNm, the bottom stress = -4.82 MPa
   Both are the same as those in AQB
   

   
   
   on transformed section, moment = 1250-1406.11 = -156.08 kNm, the bottom stress = -4.82 MPa
   
   
   
   The moment is the same as that in AQB’s transformed section. But the stress is the same as that in AQB’s net section.
   Why???

dat is attached
stress_prestress - CSM.dat (2.9 KB)

[netsonic_Sofistik]

replied to my self
The stress in transformed section in CSM is correct, because the stress before grouting is “locked in” the structure, it won’t change after grouting.

[netsonic_Sofistik]

Hi mico,

but after cs:x2 stage brutto section properties are used.

I think so.
In Sofistik official verification example:
C:\Program Files\SOFiSTiK\2025\SOFiSTiK 2025\verification.dat\dcbenchmarks.dat\dce-en17\stress_prestress.dat

I made 2 changes:

1. set ECC in Tendon from 9.9 to 0
2. add CSM as shown below

!#!Chapter	CSM
head
CTRL	DL	NO
CS	NO	TYPE
	11	P
	12	-
	20	-
GRP	NO	ICS1
	10	11
END
'+apply $(NAME)_csm.dat

In the original dat file, CS11 is prestressing, CS12 is grouting. I add CS20 in the CSM, I hope brutto (transformed) section properties used in CS20 according to “but after cs:x2 stage brutto section properties are used.”.

This is the stress results
The left is AQB load case 100 (CS11), the right is CSM CS11, both use net section, the stresses are the same

The left is AQB load case 102 (CS12), it use brutto section properties, the right is CSM CS20, it still use net section.

Teddy file is attached
stress_prestress.dat (5.2 KB)