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 annexExposure class
EuroCode (wmax)
Quasi-permanentFrequent
Normal reinforcementPrestressed reinf.Normal reinforcementPrestressed reinf.
StandardX0
0,40No value givenNo value given0,20
StandardXC1
0,40No value given
No value given0,20
StandardXC2
0,30DecompressionNo value given0,20
StandardXC3
0,30DecompressionNo value given0,20
StandardXC4
0,30DecompressionNo value given0,20
StandardXD1
0,30No value givenNo value given0,20
StandardXD2
0,30No value givenNo value given0,20
StandardXD3
No value givenNo value givenNo value givenNo value given
StandardXS1
0,30No value givenNo value givenDecompression
StandardXS2
0,30No value givenNo value givenDecompression
StandardXS3
0,30No value givenNo value givenDecompression
StandardXA1
No value givenNo value givenNo value givenNo value given
StandardXA2
No value givenNo value givenNo value givenNo value given
StandardXA3
No value givenNo value givenNo value givenNo value given
National annexExposure class
Quasi-permanentFrequent
Normal reinforcementPrestressed reinf.Normal reinforcementPrestressed reinf.
FinlandX0
0,40-No value given0,20
FinlandXC1
0,40-No value given0,20
FinlandXC2
0,30DecompressionNo value given0,20
FinlandXC3
0,30DecompressionNo value given0,20
FinlandXC4
0,30DecompressionNo value given0,20
FinlandXD1
0,30DecompressionNo value given0,20
FinlandXD2
0,20-No value givenDecompression
FinlandXD3
0,20-No value givenDecompression
FinlandXS1
0,30DecompressionNo value given0,20
FinlandXS2
0,20-No value givenDecompression
FinlandXS3
0,20-No value givenDecompression
FinlandXA1
No value givenNo value givenNo value givenNo value given
FinlandXA2
No value givenNo value givenNo value givenNo value given
FinlandXA3
No value givenNo value givenNo value givenNo value given


National annex


Exposure class

Quasi-permanentFrequent
Normal reinforcementPrestressed reinf.Normal reinforcementPrestressed reinf.
UKX0
0,30No value givenNo value given0,20
UKXC1
0,30No value givenNo value given0,20
UKXC2
0,30DecompressionNo value given0,20
UKXC3
0,30DecompressionNo value given0,20
UKXC4
0,30DecompressionNo value given0,20
UKXD1
0,30No value givenNo value givenDecompression
UKXD2
0,30No value givenNo value givenDecompression
UKXD3
0,30No value givenNo value givenDecompression
UKXS1
0,30No value givenNo value givenDecompression
UKXS2
0,30No value givenNo value givenDecompression
UKXS3
0,30No value givenNo value givenDecompression
UKXA1
No value givenNo value givenNo value givenNo value given
UKXA2
No value givenNo value givenNo value givenNo value given
UKXA3
No value givenNo value givenNo value givenNo value given
National annexExposure classEnvironmental classQuasi-permanentFrequent
Normal reinforcementPrestressed reinf.Normal reinforcementPrestressed reinf.
DenmarkX0PassiveNo value givenNo value givenNo value givenNo value given
DenmarkXC1PassiveNo value givenNo value givenNo value givenNo value given
DenmarkXC2Moderate0,400,300,400,30
DenmarkXC3Moderate0,400,300,400,30
DenmarkXC4Moderate0,400,300,400,30
DenmarkXD1Aggressive0,300,200,300,20
DenmarkXD2Extra aggressive0,200,100,200,10
DenmarkXD3Extra aggressive0,200,100,200,10
DenmarkXS1Aggressive0,300,200,300,20
DenmarkXS2Aggressive0,300,200,300,20
DenmarkXS3Extra aggressive0,200,100,200,10
DenmarkXA1Moderate0,400,300,400,30
DenmarkXA2Aggressive0,300,200,300,20
DenmarkXA3Extra aggressive0,200,100,200,10
National annexExposure class
Quasi-permanentFrequent
Normal reinforcementPrestressed reinf.Normal reinforcementPrestressed reinf.
NorwayX0
0,40No value givenNo value given0,20
NorwayXC1
0,40No value givenNo value given0,20
NorwayXC2
0,30DecompressionNo value given0,20
NorwayXC3
0,30DecompressionNo value given0,20
NorwayXC4
0,30DecompressionNo value given0,20
NorwayXD1
0,30No value givenNo value givenDecompression
NorwayXD2
0,30No value givenNo value givenDecompression
NorwayXD3
0,30No value givenNo value givenDecompression
NorwayXS1
0,30No value givenNo value givenDecompression
NorwayXS2
0,30No value givenNo value givenDecompression
NorwayXS3
0,30No value givenNo value givenDecompression
NorwayXA1
No value givenNo value givenNo value givenNo value given
NorwayXA2
No value givenNo value givenNo value givenNo value given
NorwayXA3
No value givenNo value givenNo value givenNo value given
National annexExposure classLife classQuasi-permanentFrequent
Normal reinforcementPrestressed reinf.Normal reinforcementPrestressed reinf.
SwedenX0L100----
L50----
L20----
SwedenXC1L1000,450,40--
L50-0,45--
L20----
SwedenXC2L1000,400,30--
L500,450,40--
L20-0,45--
SwedenXC3L1000,300,20--
L500,400,30--
L20-0,40--
SwedenXC4L1000,300,20--
L500,400,30--
L20-0,40--
SwedenXD1L1000,200,15--
L500,300,20--
L200,400,30--
SwedenXD2L1000,200,15--
L500,300,20--
L200,400,30--
SwedenXD3L1000,150,10--
L500,200,15--
L200,300,20--
SwedenXS1L1000,200,15--
L500,300,20--
L200,400,30--
SwedenXS2L1000,200,15--
L500,300,20--
L200,400,30--
SwedenXS3L1000,150,10--
L500,200,15--
L200,300,20--
SwedenXA1L100No value givenNo value given--
L50No value givenNo value given--
L20No value givenNo value given--
SwedenXA2L100No value givenNo value given--
L50No value givenNo value given--
L20No value givenNo value given--
SwedenXA3L100No value givenNo value given--
L50No value givenNo value given--
L20No value givenNo 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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