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This manual describes the implementation of the check of decompression according to chapter 7.3.1(5) EN 1992-1-1 in SCIA Engineer. Together with check of decompression the limited values of crack width for prestressed were implemented. Check of decompression is done only for prestressed concrete 1D member. The check of decompression means the prestressing strand or tendon lie in the predefined zone of the concrete which is in compression. The decompression distance (zdec) where the concrete is verified is set in the EN 1992-1-1 and default value is 25 mm. This value is measured from the edge of the strand (pre-tensioning) or edge of the duct (post-tensioning).
The theory of the check of decompression has been already described in the previous chapter. The idea is to verify the distance around the strand to be in compression in proper distance. This check is required according to chapter 7.3.1(5) from EN 1992-1-1. The check is performed as the following
Calculation zc is the distance from the edge of the strand or edge of the duct to the neutral axis.
Value zdec is set in setup
Calculation check value the zdec/zc
The check is performed for one or two plane bending. In case of two planes bending the distances from the strands are measured perpendicularly to the neutral axis.
New value was implemented in NA in branch Concrete > SLS > General. This value is active only if the prestressing is set ON in project data. The standard value EN 1992-1-1 value is 25 mm. The difference is only in German DIN NA.
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NA |
zdec |
NA setup |
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Standard EN |
25 mm |
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German DIN |
max( 50 mm; 1/10*H) |
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The check of decompression has been implemented in the prestressed crack control check as new additional value. Generally the check is implemented in Member check and in Single check as well.
As was written above the check of decompression is performed in service for prestressed concrete Crack control. New value decompression was implemented.
The check value of the decompression check is drawn in 3D window
The output table is printed as the following.
The values printed in table above are explained in the next table
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Value |
Explanation |
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dstrand/duct [mm] |
diameter of the strand or duct |
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ystrand [mm] |
y coordinate of strand from the centre of gravity of CSS |
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zstrand [mm] |
z coordinate of strand from the centre of gravity of CSS |
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zt [mm] |
depth of the tensile zone |
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zc [mm] |
Perpendicular distance from the edge of the strand (or duct) in the compressive concrete area to the neutral axis |
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zdec [mm] |
Minimal allowable distance from the strand (or duct) where the concrete has to be in compression |
The same check is performed in detail in Single check. There is brief information in the bottom part of the single check window and also output to the table.
The special new settings were added into Change of setup.
The table looks as the following
There is possibility to select load case, combinations or class in the service crack control. The following rules are applied for the selection:
When the loadcase is selected then:
Prestress crack width – is performed and limit values are set according to exposure class only and as for the PM (Freq.) or POST (freq.) for DIN and ÖNORM.
Decompression check - it is performed only for LC prestress; for other LC the E866 is printed because no prestressing reinforcement was found in the selected load case.
Three SLS combinations are possible to select in SCIA Engineer. They can be linear envelopes or generated from construction stages.
Characteristic – the check for this combination is supported only for DIN and ÖNORM NA.
Frequent – the check is dependent on the selected exposure class
Quasi-permanent – the check is dependent on the selected exposure class
The classes can be checked only if all combinations included in class are the same type. Otherwise the E299 appears.
If the check of decompression is performed depends on several items:
Type of structure – only prestressed members
Type of combination – frequent or quasi-permanent
Type of exposure class – from XC2 to XS3
It means the program verifies the type of the structure, the selected combination in the service and defined exposure class on whole structure or on the selected member. The decision when the check of decompression is done is based on the special table in the national annexes. Table is placed in Concrete > SLS > general as value w_max – for prestressed concrete.
Using three dots button you get access to the table of limit crack width (see chapter 3) and also table with information about check of decompression (the second table).
You can see from the table above the decompression check is performed only for prestressed member and exposure class XC2-XC4 together with quasi-permanent combination and for the exposure class XD1-XS3 together with frequent combination.
In case of phased CSS the decompression is checked for each phase. But each phase of CSS should have defined prestressing strand.
During decompression check the following W/E messages can appear
The maximum crack width is possible to set for prestressed concrete in National annexes now. New values appear only in case when Prestressing is ON in project data. Otherwise old three values related to non-prestressed concrete are there.
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Settings |
National annex |
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Prestressing OFF |
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Prestressing ON |
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The table is different for many national annexes
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National annex |
Table |
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Standard EN |
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Austrian ÖNORM NA |
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German DIN NA |
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French NF NA |
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British BS NA |
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Finnish SFS NA |
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Irish I.S. NA |
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