1. Design of Gantry Girders
Dr. N. Subramanian

2. Components of an Overhead Crane
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3. Crane Notations
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4. Data For Overhead Cranes
Load and other details of crane should be obtained from the manufacturers of cranes.
Dr. N. Subramanian

5. Typical Data for 40t Crane
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6. Loads on Gantry Girder
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7. Impact Loads
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8. Maximum Load Effects
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9. Max. S.F., B.M., and Deflection
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10. Two Cranes at the Same Span
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11. Max. BM for Two Cranes At the Same Span
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12. Limiting Deflection
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13. Profiles Used for Gantry Girders
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14. Fatigue Effects
Gantry girders are subjected to fatigue effects due to the moving loads.
Normally, light and medium duty cranes are not checked for fatigue effects if the number of cycles of load is less than 5 x 106.
For heavy duty cranes, the gantry girders are to be checked for fatigue loads. (See also IS: 1024 and IS: 807).
Dr. N. Subramanian

15. Fatigue Effects (Cont.)
The fatigue strength is governed by the following factors
Number of repetitions of load: In most cases 2 x 106 cycles of repetitions are considered to be the limit of endurance.
The ratio of the maximum stress to the minimum stress at a section due to repetitions
R = f min / f max
Where, f max = maximum stress
f min = minimum stress
Dr. N. Subramanian

16. Fatigue Strength Curve-IS 800
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17. Steps for Design
Assume that the lateral load is resisted entirely by the top flange of the beam plus any reinforcing plates, channels etc. and the vertical load is resisted by the combined beam.
Find the maximum wheel load: This load is maximum when the trolley is closest to the gantry girder. Increase it for the impact
Calculate the maximum bending moment in the gantry girder due to vertical loads.
To simplify the calculations, add the maximum bending moment due to dead load to the maximum wheel load moment
Dr. N. Subramanian

18. Steps for Design (cont.)
4. The maximum shear force is calculated. When the gantry is not laterally supported, the following may be used to select a trail section.
Zp = Mu / fy Zp (trial) = k Zp (k = )
Economic depth ≈ 1/12th of the span.
Width of flange ≈ 1/40 to 1/30th of the span
5. The plastic section modulus of the assumed combined section
Mp = 2 fy A / 2 = A fy
where A is called the plastic modulus Zp
Dr. N. Subramanian

19. Steps for Design (cont.)
6. Check for moment capacity of the whole section (as lateral support is provided at the compression flange) Mcz = βb Zp fy ≤ 1.2 Ze fy / γm0 <Mu 7. Check top flange for bending in both the axes using the interaction equation (My / Mndy)+ (M2/Mndz) ≤ If the top (compression) flange is not supported, Check for buckling resistance in the same way as in step 6 but replacing fy with the design bending compressive stress fbd.
Dr. N. Subramanian

20. Steps for Design (cont.)
9. Check web of the girder at points of concentrated load for local buckling or local crushing, and provide load carrying/ bearing stiffeners, if necessary.
10. Check for deflection under working loads
Dr. N. Subramanian

21. Allowable Ecc. Of Load and Clamping Rails to Girder
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22. Column Profiles
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23. Column Bracket Details -Light Cranes
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24. Connection at the Top Flange
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25. Torsion on Column due to Longitudinal Forces
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26. Gantry Supported on Stepped Column
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27. Two Adjacent Gantry Supported on Column
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28. Do not Connect Girder Webs to Columns
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29. Bracings for Columns
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30. Crane Stops
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31. Case Study: Hoan Bridge (Milwaukee Harbor Bridge)
Fatigue Fractures in Center Girder E and outside Girder F. These girders collapsed on Dec. 23, 2000 after 26 years of Service
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32. Example for Fatigue Design
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33. Example for Fatigue Design (cont.)
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34. Example for Fatigue Design (cont.)
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35. THANK YOU!
Dr. N. Subramanian