How To Design a Cross Girder or Floor Beams in Bridges or Railway Bridge.

Cross girder are provided in each panel, joining the corresponding lower panel points of two truss girder.

The design procedure is given by:-

Step 1:-
               Loads:-

Effective span of cross girder = 4 m (say)
The dead load as transformed as the point load at 1 m from the ends of cross girder.
Self weight of cross-girder = 3 kN/m (Assumed), it acts as uniformly distributed.
The cross girder is subjected to maximum live load when both the adjacent spans loaded.
EUDLL (Effective uniformly Distributed Live Load) for 8 m span = 1056 KN (Say)
Impact factor = 0.909 (say)
[Note: - Impact factor is calculated by using this formula = 0.15 + [8 / (6+L)]
So, Impact load is given by,
                                                      = 0.909 × 1056
                                                      = 960 KN
Live Load + Impact Load = 2016 KN
Half of live load and impact load is carried by girder as two point’s loads at 1 m from each end.
Point load due to superimposed dead load {(1/2) × dead load per track for two stringer as calculated in design of stringer}.
Point load due to live load & impact load = [(1/2) × {1/2) × 2016}]
Total point load = sum of two calculated load above in KN
Draw the loading diagram with UDL and point load at 1 m from the edges.
The reactions at the ends = Total point load + UDL span × span length KN

Step 2:-
                Bending Moment at centre:-

M = [(Reaction at each end span / 2) – Point Load × 1 – (UDL load × span) / 2]
Allowable stress in bending = 165 N/mm2.

Step 3:-
               Section Modulus:-
                                                 Z = M / Sigmacbc  ,            
                                                                 Where Sigmacbc = 165 N/mm2
From the Steel Table Select ISWB section having greater than the value of Z as we calculated.

Step 4:-
             Shear stress:-

Vn = Shear force at the end / height of section selected above/ thickness of web tw and it should be less than 100 N/mm2. Otherwise revise the section. Hence, safe.
Provide the details of the section provided.
The connection of stringer with cross girder is designed for end reaction






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