Apis Structural Calcs


Tutorial 1 - design of rectangular section under uni-axial bending


We need to design reinforcement for the rectangular column which is compressed and bent about the x-axis.

The structure is located in the UK.

From the preliminary design:

  • Section dimensions: 300 x 400 mm
  • Concrete grade: C30/37
  • Steel grade: B500B

Minimum cover due to environmental conditions (Cmin,dur) must be determined manually in accordance with EC2 Cl. (5).

  • Minimum cover due to environmental conditions: 40 mm

Design values of the applied forces must be calculated manually taking into account geometric imperfections and second order effects, in accordance with EC2 Cl. 5.2 and Cl. 5.8

  • axial force = 2000 kN
  • bending moment = 140 kNm
  • design situation: persistent or transient
Step by step

1. Open the home page of RC Section Calculator (http://www.apiscalcs.com/rc/).

2. Click Data Input.

3. The fields may be already filled in with the data from your previous calculations. If this is the case, then click Reset button. This will clear the data and let us start form scratch.

4. Because the structure being designed is located in the UK, we want to use the British version of the Eurocode 2. Therefore, set Building code to BS-EN 1992-1-1:2004.

5. Now, we'll set material properties to the given values.

6. Set Strength grade for concrete to C30/37.

7. Set Design situation to Persistent & Transient

8. Set Grade for steel to B500B.

9. The detailed steel properties are updated to correspond to the selected steel grade.

10. Now, we'll set parameters for calculations of concrete cover and bar spacing.

11. Set Validator type to Automatic to code rules. The layout will be checked in accordance with the rules in the building code. Choosing other options turns off automatic validation and lets the user to control the layout manually.

12. In accordance with Eurocode 2, the stirrup diameter must be at least 6mm and at least 0.25 of the longitudinal reinforcement diameter. Therefore, let's try the value of 6mm. The units used in the application are shown in the bar at the bottom of the page. We can see there that length is in mm, therefore enter in the field Stirrup diameter 6.

13. In the field Cmin,dur enter 40.

14. We don't know what level of quality assurance is going to be provided, so we'll assume the worst case scenario. Set Quality assurance to No quality assurance system.

15. In the field Cover deviation enter 5. This is intentionally incorrect value, so that we could get later familiar with data validation and error reporting mechanism.

16. Aggregate size may influence required bar spacing. In order not to impose unnecessary restrictions on the aggregate, we'll use the value of 40mm, because the aggregate size will very rarely be larger than that. If later it turns out that we need dense reinforcement, then we'll limit this value. In the field Aggregate size enter 40. It's also possible to leave this field empty, then the relevant spacing check will not be performed.

17. Now, we'll define the section shape.

18. Set Shape type to Rectangle.

19. In the field Width enter 300 and in the field Height enter 400.

20. Note that the section preview on the right was updated.

21. Now, we'll define the reinforcement.

22. Let's try 4 No. 20mm diameter reinforcing bars. In the field Default diam. enter 20. In the field Automatic reinforcement - Top - No. enter 2 and in the field Automatic reinforcement - Bottom - No. enter 2.

23. Click show/update layout button to display the reinforcement in the section preview.

24. Oops! The error message was displayed above the Cover deviation field. The validation mechanism detected that the value which we specified is incorrect. Following the explanation in the error message, we'll change it to 10mm. In the field Cover deviation enter 10.

25. Click show/update layout button again. The reinforcing bars were distributed automatically in compliance with the building code provisions and are displayed in the section preview. The reinforcement ratio is displayed below the section and it is 1.0%. This looks like a good starting point.

26. For now, we're finished with defining the section properties. Click Submit button, this will submit the data and bring you to the main menu.

27. It's going to be convenient to open the results in a new tab in your browser. Right-click Uniaxial bending and open a new tab. Go to this newly-opened tab.

28. On the right there is an interaction diagram. The vertical axis is axial force and the horizontal axis is bending moment. When you put the mouse cursor over the interaction diagram, the values of forces in the picked point are displayed below in the Data information panel.

29. Positive bending moments, positive axial force.Sign convention is show in the picture on the right. Positive x-moment means the top of the section is in compression. Positive y-moment means the right of the section is in compression. Positive axial force means compression.

30. We need to design the section, so let's focus on the Applied forces panel. In the field Force enter 2000 and in the field Moment enter 140. Click Check button.

31. The page is reloaded and the message with the check result is displayed - the applied forces exceed the section capacity. The point representing applied forces is displayed in the interaction diagram.

32. We need to increase the reinforcement area. Go to the first tab (where the main menu is opened) and click Data Input.

33. We'll add 4 No. additional bars. In the field Automatic reinforcement - Top - No. enter 4 and in the field Automatic reinforcement - Bottom - No. also enter 4.

34. Click show/update layout button. The bars were distributed in two rows. Let's see if we can squeeze the bars in a single row by limiting the maximum aggregate size. In the field Aggregate size enter 30 and click show/update layout button again.

35. Now the bars are in a single row. Click Submit button.

36. Open the second tab (where the results are opened) and reload the page (click Reload icon in your browser or press F5 key, confirm reload if needed). The check for the updated section was performed and now, the capacity is sufficient. In the interaction diagram we can see that the utilisation ratio is high. The exact positions of bars may be found in Neutral axis page. Our design task is finished.