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






Comments

Post a Comment

Popular posts from this blog

Lane’s Weighted Creep Theory

Image
Bligh, in his theory, had calculated the length of the creep, by simply adding the horizontal creep length and the vertical creep length, thereby making no distinction between the two creeps. However, Lane, on the basis of his analysis carried out on about 200 dams all over the world, stipulated that the horizontal creep is less effective in reducing uplift (or in causing loss of head) than the vertical creep. He, therefore, suggested a weightage factor of 1/3 for the horizontal creep, as against 1.0 for the vertical creep. Thus in Fig–1,  the total Lane’s creep length (L l ) is given by L l = (d 1 + d 1 ) + (1/3) L 1 + (d 2 + d 2 ) + (1/3) L 2 + (d 3 + d 3 ) = (1/3) (L 1 + L 2 ) + 2(d 1 + d 2 + d 3 ) = (1/3) b + 2(d 1 + d 2 + d 3 ) To ensure safety against piping, according to this theory, the creep length Ll must no be less than C1H L , where H L is the head causing flow, and C 1 is Lane’s creep coefficient given in table –2 Table – 2: V
Read more

What is Soil in Geotechnical Engineering.

Image
Definition of Soil The word ‘soil’ is derived from the Latin word solium which, according to Webster’s dictionary, means the upper layer of the earth that may be dug or plowed; specifically, the loose surface material of earth in which the plants grow. The above definition of soil is used in the field of agronomy (The application of soil and plant sciences to land management and crop production) where the main concern is in the use of soil for raising crops. In geology, earth’s crust is assumed to consist of unconsolidated sediments, called mantle or regolith, overlying rocks. The top soil contains a large quantity of organic matter and is not suitable as a construction material or as a foundation for structure. The top soil is removed from the earth’s surface before the construction of structure. The term ‘ soil ’ in the soil engineering is defined as an unconsolidated material , composed of solid particles , produced by the disintegration of rocks . The void space
Read more

Khosla’s Method of independent variables for determination of pressures and exit gradient for seepage below a weir or a barrage

Image
In order to know as to how the seepage below the foundation of a hydraulic structure is taking place, it is necessary to plot the flow net. In other words, we must solve the Laplacian equations. This can be accomplished either by mathematical solution of the Laplacian equations, or by Electrical analogy method, or by graphical sketching by adjusting the streamlines and equipotential lines with respect to the boundary conditions. These are complicated methods and are time consuming. Therefore, for designing hydraulic structures such as weirs or barrage or pervious foundations, Khosla has evolved a simple, quick and an accurate approach, called Method of Independent Variables. In this method, a complex profile like that of a weir is broken into a number of simple profiles; each of which can be solved mathematically. Mathematical solutions of flow nets for these simple standard profiles have been presented in the form of equations given in Figure  and curves given in Plate, wh
Read more