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 as this: 

This applies for PRE-Stress 6.7.020 and later versions