Design of Gantry Girders Dr N Subramanian 1

Design of Gantry Girders Dr. N. Subramanian 1

Components of an Overhead Crane Dr. N. Subramanian 2

Crane Notations Dr. N. Subramanian 3

Data For Overhead Cranes Load and other details of crane should be obtained from the manufacturers of cranes. Dr. N. Subramanian 4

Typical Data for 40 t Crane Dr. N. Subramanian 5

Loads on Gantry Girder Dr. N. Subramanian 6

Impact Loads Dr. N. Subramanian 7

Maximum Load Effects Dr. N. Subramanian 8

Max. S. F. , B. M. , and Deflection Dr. N. Subramanian 9

Two Cranes at the Same Span Dr. N. Subramanian 10

Max. BM for Two Cranes At the Same Span Dr. N. Subramanian 11

Limiting Deflection Dr. N. Subramanian 12

Profiles Used for Gantry Girders Dr. N. Subramanian 13

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 14

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 15

Fatigue Strength Curve-IS 800 Dr. N. Subramanian 16

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. 1. Find the maximum wheel load: This load is maximum when the trolley is closest to the gantry girder. Increase it for the impact 2. Calculate the maximum bending moment in the gantry girder due to vertical loads. 3. To simplify the calculations, add the maximum bending moment due to dead load to the maximum wheel load moment Dr. N. Subramanian 17

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 = M u / f y Zp (trial) = k Zp (k = 1. 40 -1. 50) Economic depth ≈ 1/12 th of the span. Width of flange ≈ 1/40 to 1/30 th of the span 5. The plastic section modulus of the assumed combined section Mp = 2 f y A / 2 = A f y where A is called the plastic modulus Zp Dr. N. Subramanian 18

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 / γm 0 <Mu 7. Check top flange for bending in both the axes using the interaction equation (My / Mndy)+ (M 2/Mndz) ≤ 1. 0 8. 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 19

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 20

Allowable Ecc. Of Load and Clamping Rails to Girder Dr. N. Subramanian 21

Column Profiles Dr. N. Subramanian 22

Column Bracket Details -Light Cranes Dr. N. Subramanian 23

Connection at the Top Flange Dr. N. Subramanian 24

Torsion on Column due to Longitudinal Forces Dr. N. Subramanian 25

Gantry Supported on Stepped Column Dr. N. Subramanian 26

Two Adjacent Gantry Supported on Column Dr. N. Subramanian 27

Do not Connect Girder Webs to Columns Dr. N. Subramanian 28

Bracings for Columns Dr. N. Subramanian 29

Crane Stops Dr. N. Subramanian 30

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 Dr. N. Subramanian 31

Example for Fatigue Design Dr. N. Subramanian 32

Example for Fatigue Design (cont. ) Dr. N. Subramanian 33

Example for Fatigue Design (cont. ) Dr. N. Subramanian 34

THANK YOU! Dr. N. Subramanian 35