Bridges & Structures

Concrete Deck Design Example

1. Obtain Design Criteria Design Step 2.1

   Commentary for 1: Includes: Girder spacing, Number of girders, Top and bottom cover, Concrete strength, Reinforcing steel strength, Concrete density, Future wearing surface, Concrete parapet properties, Applicable load combinations, Resistance factors

2. Determine Minimum Slab Thickness S2.5.2.6.3 & S9.7.1.1 Design Step 2.2

   Commentary for 2: To compute the effective span length, S, assume a girder top flange width that is conservatively smaller than anticipated.

3. Determine Minimum Overhang Thickness S13.7.3.1.2 Design Step 2.3

   Commentary for 3: The deck overhang region is required to be designated to have a resistance larger than the actual resistance of the parapet.

4. Select Slab and Overhang Thickness Design Step 2.4

   Commentary for 4: Based on Design Steps 2.3 and 2.4 and based on client standards.

5. Equivalent Strip Method? (S4.6.2)

6. Other deck design methods are presented in S9.7.

7. Compute Dead Load Effects S3.5.1 & S3.4.1 Design Step 2.5

   Commentary for 7: Includes moments for component dead load (DC) and wearing surface dead load (DW).

8. Compute Live Load Effects S3.6.1.3 & S3.4.1 Design Step 2.6

   Commentary for 8: Considerations include: Dynamic load allowance (S3.6.2.1), Multiple presence factor (S3.6.1.1.2), AASHTO moment table for equivalent strip method (S Table A4.1-1)

9. Compute Factored Positive and Negative Design Moments S4.6.2.1 Design Step 2.7

10. Design for Positive Flexure in Deck S5.7.3 Design Step 2.8

    Commentary for 10: Resistance factor for flexure is found in S5.5.4.2.1. See also S5.7.2.2 and S5.7.3.3.1.

11. Check for Positive Flexure Cracking under Service Limit State S5.7.3.4 & S5.7.1 Design Step 2.9

    Commentary for 11: Generally the bottom transverse reinforcement in the deck is checked for crack control.

12. Design for Negative Flexure in Deck S4.6.2.1 & S5.7.3 Design Step 2.10

    Commentary for 12: The live load negative moment is calculated at the design section to the right and to the left of each interior girder, and the extreme value is applicable to all design sections (S4.6.2.1.1).

13. Check for Negative Flexure Cracking under Service Limit State S5.7.3.4 & S5.7.1 Design Step 2.11

    Commentary for 13: Generally the top transverse reinforcement in the deck is checked for crack control.

14. Design for Flexure in Deck Overhang S5.7.3.4, S5.7.1 & SA13.4 Design Step 2.12

15. Design Overhang for Horizontal Vehicular Collision Force SA13.4.1 Design Case 1

16. Check at Inside Face of Parapet Case 1A

17. Check at Design Section in Overhang Case 1B

18. Check at Design Section in First Span Case 1C

19. Design Overhang for Vertical Collision Force SA13.4.1 Design Case 2

    Commentary for 19: For concrete parapets, the case of vertical collision never controls.

20. Design Overhang for Dead Load and Live Load SA13.4.1 Design Case 3

21. Check at Design Section in Overhang Case 3A

22. Check at Design Section in First Span Case 3B

23. As(Overhang) > As(Deck)?
    Commentary for 23: As(Overhang) = maximum of the above five reinforcing steel areas. The overhang reinforcing steel must satisfy both the overhang requirements and the deck requirements.

24. Use As(Overhang) in overhang

25. Use As(Deck) in overhang

26. Check for Cracking in Overhang under Service Limit State S5.7.3.4 & S5.7.1 Design Step 2.13

    Commentary for 26: Does not control the design in most cases.

27. Compute Overhang Cut-off Length Requirement S5.11.1.2 Design Step 2.14

28. Compute Overhang Development Length S5.11.2 Design Step 2.15

    Commentary for 28: Appropriate correction factors must be included.

29. Design Bottom Longitudinal Distribution Reinforcement S9.7.3.2 Design Step 2.16

    Commentary for 29: Compute Effective Span Length, S, in accordance with S9.7.2.3.

30. Design Top Longitudinal Distribution Reinforcement S5.10.8.2 Design Step 2.17

    Commentary for 30: Based on temperature and shrinkage reinforcement requirements.

31. Design Longitudinal Reinforcement over Piers Design Step 2.18

32. Continuous steel girders?

33. For continuous steel girders, design top longitudinal reinforcement over piers according to S6.10.3.7.

34. For simple span precast girders made continuous for live load, design top longitudinal reinforcement over piers according to S5.14.1.2.7.

35. Draw Schematic of Final Concrete Deck Design Design Step 2.19

36. Return to Main Flowchart

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