AdSec 8.0 Patch
SLS Bug Fix
This affects Australian and American code sections where the 'interpolated' stress strain assumption is used for tension in the SLS limit state. The interpolated assumption is the default setting for concrete materials, so all sections which use the standard material list will be affected.
Sections with 'no tension' or user stress-strain relationships selected will not be affected by the bug.
The bug affects a sub section of the results.
Correct results are given in the following output tables:
- SLS Loads Analysis - Summary
- Moment summary for SLS axial loads
- Strain Planes at SLS Loads
Stresses and strains calculated using the strain planes above will be correct. Stiffness and neutral axis values are correct and relate to the partial tension stiffness model ('interpolated strain plane')
The program looks up the incorrect set of stresses and strains for output in the following tables:
- Section Material Stresses/Strains at SLS Loads
- Reinforcement Stresses/Strains at SLS Loads
This is an indexing type problem in that the strains selected which
- belong to the 'cracked' case are output for the un-cracked situation. - Results are conservative.
- belong to the 'interpolated' case are output for the cracked case. - Results are not conservative. Results don't represent the maximum possible stress or strain in the section. In reality stresses in the section will vary from a maximum of the tension strength of the concrete midway between cracks and zero concrete stress at crack locations.
Some codes would allow some form of interpolated stresses in this case, or a tension stiffness model to approximate this behaviour. This is not explicit in the Australian or American codes and the interpolated results should only be used for stiffness analysis and strain checks. The AdSec tables should have shown the fully cracked or 'No tension' results.
With the patch, AdSec will output detailed stress strain output for both the fully cracked and un-cracked models for all cases. It will continue to give the interpolation factor which can be used to derive partially cracked strains, and the strain plane definitions. This will allow users to select the assumption which fits to their situation.
Clearly, once the cracking strain has been exceeded, the fully cracked results should only be used for studies of partial tension stiffness and cannot represent true stresses in the section.
If users are un-interested in partially cracked behaviour they are advised to select a 'no tension model' in the materials wizard as before. The output will then be much simplified. This is done by creating a new concrete material using the 'right click' menu in the material input. Copying the desired properties from a standard concrete to save time, and then selecting 'no tension' in the drop down menu for SLS tension curve.
Change to treatment of partially cracked stiffness for long term loads in Australian codes
The patch also changes the way the interpolation factor is calculated for long term loads. The interpolation factor is used to determine how close the section is to the fully cracked state. This approach replicates the effects of the following formula from the Australian code:
Let the uncracked curvature be κI and the fully cracked curvature be κII. The interpolation factor ζ, is the proportion of the fully cracked strain plane to add to (1-ζ) of the uncracked plane. The interpolated strain plane is then found from:
This approach is used to calculate the results in the SLS Loads Analysis - Summary table such as EI. AdSec will now use the results of a short term analysis to establish this factor, even for long term analysis cases. This is to the letter of the Australian code. However users should note that this will be found to be a generous assumption compared to more recent codes such as Eurocode which are included in AdSec. These more recent approaches have taken into account the rapid drop in tension stiffness once cracking has occurred to roughly half of the short term value.
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