Problems with design result 'decompression cover check'?

What is it and how does PRE-Stress take it into account?


In EN1992-1-1 7.3.1 (5), (Crack Control - General considerations) states that a maximum crack limit should be set, depending on the function of the structure. A good definition of the function is the exposure class.


Figure 1. Default value for EN 1992-1-1 (Standard/No annex)


It basically states what maximum crack widths are allowed depending on the exposure class. For normal reinforcement and post tension strands the left column should be considered, while for prestressing strands the right column should be used. So depending on what type of reinforcement and load combinations are considered the values for a maximum crack could be different.


For prestressing strands in XD1, XD2, XS1, XS2 and XS3 for frequent load combinations the field "Decompression" comes into play. PRE-Stress assumes XD3 are part of this group too, as it is missing from the table.


But since this is a national parameter each EuroCode country might select to use this table or use their own tables and values.


So for the national annexes that are implemented in PRE-Stress this means that there might be differences from the Standard:


Finland:


Source: NATIONAL BUILDING CODE OF FINLAND, Strength and stability of structures Concrete structures, 2016


United Kingdom:



Source: UK National Annex to Eurocode 2: Design of concrete structures - Part 1-1: General rules and rules for buildings - 2009


Norway:

Source: NS-EN 1992-1-1:2004+A1:2014+NA:2018


Denmark:

Source. DS/EN 1992-1-1 DK NA:2017


Sweden:

Source: Boverket BFS 2019:1, EKS 11


So, how does it work in PRE-Stress?

The decompression check is not part of any utilization curve. The condition of the prestressing wires are either OK and well within concrete in compression or placed in concrete in tension, or close to it (and in that case in need of a modification if the exposure class and load combinations so require). Then it will give a warning about strands in tension and a code reference. Then the user has to check if it is ok or not to have the strands in a region with tension in the concrete or close to it.



Here follows a complete chart of all requirements within PRE-Stress. Decompression check will only be performed for requirements shown with red border: 

Decompression


Here follows a complete chart of all requirements.

National annex
Exposure class
EuroCode (wmax)
Quasi-permanentFrequent
Normal reinforcementPrestressed reinf.
Normal reinforcementPrestressed reinf.
Standard
X0
0,40
No value given
No value given
0,20
Standard
XC1
0,40No value given
No value given
0,20
Standard
XC2
0,30DecompressionNo value given
0,20
Standard
XC3
0,30DecompressionNo value given
0,20
Standard
XC4
0,30DecompressionNo value given
0,20
Standard
XD1
0,30No value givenNo value given
0,20
Standard
XD2
0,30No value givenNo value given
0,20
Standard
XD3
No value givenNo value givenNo value givenNo value given
Standard
XS1
0,30No value givenNo value given
Decompression
Standard
XS2
0,30No value givenNo value given
Decompression
Standard
XS3
0,30No value givenNo value givenDecompression
Standard
XA1
No value given
No value givenNo value given
No value given
Standard
XA2
No value given
No value givenNo value given
No value given
Standard
XA3
No value given
No value given
No value given
No value given
National annex
Exposure class

Quasi-permanent
Frequent
Normal reinforcement
Prestressed reinf.
Normal reinforcement
Prestressed reinf.
Finland
X0
0,40
-No value given
0,20
Finland
XC1

0,40-No value given
0,20
Finland
XC2

0,30Decompression
No value given
0,20
Finland
XC3

0,30Decompression
No value given
0,20
Finland
XC4

0,30Decompression
No value given
0,20
Finland
XD1

0,30Decompression
No value given
0,20
Finland
XD2

0,20-No value given
Decompression
Finland
XD3

0,20-No value given
Decompression
Finland
XS1

0,30Decompression
No value given
0,20
Finland
XS2

0,20-No value given
Decompression
Finland
XS3

0,20-No value given
Decompression
Finland
XA1
No value given
No value given
No value given
No value given
Finland
XA2
No value given
No value given
No value given
No value given
Finland
XA3
No value given
No value given
No value givenNo value given


National annex


Exposure class

Quasi-permanent
Frequent
Normal reinforcement
Prestressed reinf.
Normal reinforcement
Prestressed reinf.
UKX0
0,30
No value given
No value given0,20
UK
XC1
0,30
No value given
No value given0,20
UK
XC2
0,30
Decompression
No value given0,20
UK
XC3
0,30
Decompression
No value given0,20
UK
XC4
0,30
Decompression
No value given0,20
UK
XD1
0,30
No value given
No value givenDecompression
UK
XD2
0,30
No value given
No value givenDecompression
UK
XD3
0,30
No value given
No value givenDecompression
UK
XS1
0,30
No value given
No value givenDecompression
UK
XS2
0,30
No value given
No value given
Decompression
UK
XS3
0,30
No value given
No value given
Decompression
UK
XA1
No value givenNo value givenNo value given
No value given
UK
XA2
No value given
No value givenNo value given
No value given
UK
XA3
No value given
No value given
No value given
No value given
National annex
Exposure class
Environmental classQuasi-permanent
Frequent
Normal reinforcement
Prestressed reinf.
Normal reinforcement
Prestressed reinf.
Denmark
X0PassiveNo value given
No value given
No value given
No value given
Denmark
XC1PassiveNo value given
No value given
No value given
No value given
Denmark
XC2Moderate0,400,300,400,30
Denmark
XC3Moderate0,400,300,400,30
Denmark
XC4Moderate0,400,300,400,30
Denmark
XD1Aggressive0,300,200,300,20
DenmarkXD2Extra aggressive
0,200,100,200,10
Denmark
XD3Extra aggressive
0,200,100,200,10
Denmark
XS1Aggressive
0,300,200,300,20
Denmark
XS2Aggressive
0,300,200,300,20
Denmark
XS3Extra aggressive
0,200,100,200,10
Denmark
XA1Moderate
0,400,300,400,30
Denmark
XA2Aggressive
0,300,200,300,20
Denmark
XA3Extra aggressive
0,200,100,200,10
National annex
Exposure class

Quasi-permanent
Frequent
Normal reinforcement
Prestressed reinf.
Normal reinforcement
Prestressed reinf.
NorwayX0
0,40No value given
No value given0,20
Norway
XC1

0,40No value given
No value given
0,20
Norway
XC2

0,30DecompressionNo value given
0,20
Norway
XC3

0,30Decompression
No value given
0,20
Norway
XC4

0,30Decompression
No value given
0,20
Norway
XD1

0,30No value givenNo value given
Decompression
Norway
XD2

0,30No value given
No value given
Decompression
Norway
XD3

0,30No value given
No value given
Decompression
Norway
XS1

0,30No value given
No value given
Decompression
Norway
XS2

0,30No value given
No value given
Decompression
Norway
XS3

0,30No value given
No value given
Decompression
Norway
XA1

No value given
No value given
No value given
No value given
Norway
XA2

No value given
No value given
No value given
No value given
Norway
XA3

No value given
No value given
No value given
No value given
National annex
Exposure class
Life classQuasi-permanent
Frequent
Normal reinforcement
Prestressed reinf.
Normal reinforcement
Prestressed reinf.
SwedenX0L100----
L50-
---
L20----
Sweden
XC1L100
0,450,40--
L50
-0,45--
L20----
Sweden
XC2L100
0,400,30--
L50
0,450,40--
L20
-0,45--
Sweden
XC3L100
0,300,20--
L50
0,400,30--
L20
-0,40--
Sweden
XC4L100
0,300,20--
L50
0,400,30--
L20
-0,40--
Sweden
XD1L100
0,200,15--
L50
0,300,20--
L20
0,400,30--
Sweden
XD2L100
0,200,15--
L500,300,20--
L20
0,400,30--
Sweden
XD3L100
0,150,10--
L50
0,200,15--
L20
0,300,20--
Sweden
XS1L100
0,200,15-
-
L50
0,300,20-
-
L20
0,400,30-
-
Sweden
XS2L100
0,200,15-
-
L50
0,300,20-
-
L20
0,400,30-
-
Sweden
XS3L100
0,150,10-
-
L50
0,200,15--
L20
0,300,20--
Sweden
XA1L100
No value given
No value given
--
L50
No value given
No value given
--
L20
No value given
No value given
--
Sweden
XA2L100
No value given
No value given
--
L50No value given
No value given
--
L20
No value given
No value given
--
Sweden
XA3L100
No value given
No value given
--
L50
No value given
No value given
--
L20
No value given
No value given
--

This applies for PRE-Stress 6.7.020 and later versions

F
Fredrik is the author of this solution article.

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