Challenge

Week 3 Challenge

AAkash Singh1 Dec 2022

Aim:

Prepare the model according to the given problem and apply the suitable Live load as recommended by IRS and perform analysis accordingly.

Introduction:

The project is about to understand the behavior of structure i.e., I-Girder Bridge under the action of Live Loads as recommended by IRS due to different classes of trains.

Live loads are the temporary or movable load that used to acts either partial or long span of time on the structure (such as Building, bridge etc.), which can load from weight of occupant, architecture members, household accessories etc.

As per IRS (Indian Railway Standard), Classification of loading as per gauge are as follows:

Metro Rail Loading
Broad Gauge loading
Electric Train
Gauge A and Gauge B loading

Given Data (for calculation):

Width of bridge deck = 26 m
Span of bridge = 25 m
Size of pier = 2.3 m in diameter
Height of Pier = 10 m

Procedure:

After detailed study of the query, the same is modelled in Staad.Pro. by the general conditions as mentioned below:

Loading is considered of Metro Rail of 21.1m long in length & width of 1.8 m having,

Axle Loading = 17 tons (170KN)
Maximum Number of cars = 6 nos.
Number of wheels each side = 4 nos.

Assumption:

Model will be only analyzed for Live load as per IRS, factor as self-weight of the structure and other dead loads such as weight of parapet wall, pavement etc., are assumed not to act on it.

Live Load on the footway is assumed to be 500 kg/sqm. of 2.5m wide.

Centre to centre distance of Pier = Width of Deck slab

Thickness of Deck slab is assumed to 250 mm thick.

Dimensions of I girders are as figure below,

Dimension of Cross Beams are to be assumed as 1 m x 2 m.

Solution:

Span of bridge = 25 m

Length of Class A vehicle = 16.9 m

Increment per combination = 1 m

No. of Load combination = (span of bridge + length of vehicle) / increment per combination

= (25+16.9)/1

= 41.9 ≈ 42

Computer Proficiency:

Create a model by putting the necessary inputs as file location, units etc.

Create two nodes (x,y,z) represents as (0,0,0) & (0,10,0). Because the height of piers is assumed to be 10m.

Click on Add beam option from Geometry tab, and connect the two nodes.

Select the drawn beam and click on transition repeat and in z axis, place spacing as 26m as the center-to-center distance between the piers is 26m according to given data. And from add beam option, connect the two piers from top, this makes the end cross beam.

Select the cross beam and divide it into seven parts by adding 6 nodes in between with equal distance apart.

Go to Properties tab, define different section of structure as per the assumptions and given data discussed above and assign them accordingly, then Transitional repeat the whole assembly and paste it at 25m distance in x direction by link steps. And delete the unnecessary bottom beams. Assign the Girder beams accordingly.

Transitional repeat the cross beams into the x direction at spacing of equal distance.

From geometry tab, select generate mesh plate option and connect the 4 end nodes of cross beams in order to make plate mesh and from select quadrilateral meshing.

Then select the number of divisions wants to provide onto respective length. For an instance, if I want to create mesh of 0.5m then on 8m length provide 16 division and 7.7m length provide 15 divisions. Then click apply. And replicate the plate mesh over the whole area.

Now from select tab, choose plate cursor and select all the plate by dragging the cursor over it. And assign defined plate size.

Go to the supports tab, select the create button and select fixed supports and assign them to the bottom of pier’s nodes.

In 3D render view, the modelled structure reflects as figure mentioned below.

In order to separate the different parts of bridge, we assigned them into different groups. Go to utilities tab and select groups, and then create group.

In order to create group and mentioned the name of group and type of assignment want to associate in that group. For an instance, name the group GIRDER and select beam in “select type” option and associate the select girder beam to it. In a same manner, associate all the different member into their respected groups.

Define the Live load of Footway and assign to the selected plate.
Define the metro rail loading into the vehicle/moving loads as discussed above.
Go to Load Cases and generate load combination, number of combinations will calculate as discussed above in case. And provide detail of starting of moving and their ranges in one direction and create the same in opposite direction as well as illustrated in images below.
Go to Analysis tab, sselect analysis commands and then add.