Subjects Covered

• General stress strain materials

Outline

For the Steel/Concrete composite beam, defined in section 2, it is required to calculate the bending resistance (sagging and hogging) about the horizontal axis and to examine the stress distribution due to an axial tensile load of -4000kN and a sagging bending moment of 4000kNm.

This is done using the “General Stress Strain” analysis type, but before this can be carried out the material properties need to be defined as “general stress strain” type material with specific strain limits.

The concrete has the same configuration and strain limits as Eurocode concrete with the characteristic strength of grade C32/40 concrete.

The structural steel is defined as elastic/plastic with a stress limit set to 355/1.0 = 355N/mm² (S355 grade steel as defined in EN10025-2).

The reinforcement is modelled as 'reinforcing steel – inclined' and specified as a general stress-strain material of type 'elastic-plastic with offset'. The stress and strain limits should be set with the start yield strain set as ±0.002 (stress = ±435N/mm²) and full yield strain set as ±0.045 (stress = ±466N/mm²).

Procedure

1. Start the program, close the Home using the ESC key and open the supplied data file “EU Example 2_6.sam” via the menu item Help | Tutorials | Open Tutorial Model.
2. Use the File | Titles menu item to change the Section Title to “General Stress Strain Analysis”, the Sub-title to “Example 3.6” and the Job Number to “3.6”. Click ✓ OK to close the Titles form.
3. Display the Materials navigation window and add an additional “Defined StressStrain” type material using the button in the toolbar. This should open the Defined Property Details form.
4. Change the Factored Strength to “21.25” (i.e. fcd = fck / γc = 31.875/1.5) and choose “Parabolic-Rectangular” from the dropdown in the Defined StressStrain Type field. This opens a secondary form in which the Set Curve Default to: field should be set to “Eurocode 2”. Close this secondary form and set the Modulus of Elasticity to 33.3145GPa and the Property Name to be “Defined grade C32/40 Concrete” before closing the Define Property Details form with the ✓ OK button.

Define Property Details

5. Add another material as a “Defined Stress-Strain” type. Set the Factored strength to “355MPa” (ie. 355/1.0) and the Defined Stress-Strain Type to “Elastic Plastic”. Note that the default strain at yield is +/-0.001775 (giving an elastic modulus of 200kN/mm².) Change both tension and compression values to +/-0.00169048 to give an elastic modulus of 210kN/mm². Close the secondary form and ensure that the Strain Limit is set to 0.01. Set the Property Name to “Defined Structural Steel” before closing the Define Property Details form with the ✓ OK button.

Define Stress-Strain Relation	Define Property Details

6. Add a third new material as a “Defined Stress-Strain” type. Set the Factored strength to “466MPa” and the Defined Stress-Strain Type to “Elastic-Plastic with offset.” For reinforcement to Eurocodes the compressive full yield stress is reduced to 466MPa at a strain of 0.045. The compressive start yield stress 435Mpa at a strain of 0.002. Enter this information in the Define Stress-Strain Relation data form and then close this form using the ✓ OK button. Set the Strain Limit to 0.04501 and the Property Name to “Defined Reinforcement” before closing the Define Property Details form. Click ✓ OK on the Define Property Details form.

Define Stress-Strain Relation	Define Property Details

7. This has now completed the new material property definition so close the Define Material Properties form with the ✓ OK button.

8. This file is now going to be saved as a template that can be used as a starting point for other general stress strain section analyses.

9. Use the menu item File| Save as Template | My Template to open the save template form and save it as “My EU Example 3_6.sbt” in the folder that holds all the “My Template” files (which can be found using the Options | Preferences menu item).

10. Change to the Design Section navigation window

11. Select the “slab” element in the navigation tree, which will open the Define Section Element form.

12. Change the property to be the “Defined grade C32/40 Concrete” property and close the form with the ✓ OK button.

    

13. Repeat this for the steel section changing the property to be the “Defined Structural Steel” property. Close this form with the ✓ OK button.

    

14. Select “Reinforcement” in the navigation tree, which will open the Define Reinforcement form and click on the “Edit bars...” button. Click in the graphics screen to place a window around all the bars (they will turn red) and a secondary Edit Reinforcement data form will be displayed. Change the Edit Option to “Change Property” and set the Bar property to “DefinedReinforcement”.

15. Close both forms with the ✓ OK button.

16. Open the Define Loadcase data form using the button in the navigation window toolbar, and select Loadcase. Then enter “4000” and “-4000” in the My and Ax fields in the Ultimate sections of the top table. Close the Define Loads data form using the ✓ OK button.

    

17. To analyse the section click on the drop down part button in the navigation toolbar and select General Stress Strain.

18. Set the Loadcase to “SL1: Loadcase” and Resistance to “Not used”. Ensure that the Analysis type field is set to “General Stress/Strain”. The maximum and minimum stresses can be obtained from the results viewer by clicking on the Results button.

    

19. Produce a print preview of the combined text output and graphics by using the Print Preview menu item which may be found under the “More Buttons” tab located immediately to the right of the “Save as...” button on the Results Viewer form. Both the print Preview and results viewer windows can be closed.

    

20. To obtain the sagging bending moment resistance set the Loadcase field to “None” (clicking ✓ OK on the error message) and the Resistance to “Y Moment – Positive”. The resistance will be shown as the Limiting Additional Load on the Bending, Axial and Shear form.

    

21. Click ✓ OK To close the form.

22. Close all the data forms and save this data file as “My EU Example 3_6.sam” using the File | Save As menu item.

23. Close the program.

Summary

This example shows how any material with a known stress strain relationship can be defined. These materials can then be assigned to components of a section and a general strain compatibility analysis carried out to obtain limiting capacities or stresses for a given set of loads.