Week 3 Challenge

Aim

For the I Girder bridge to be designed for the following data, the centre to centre distance of piers along the width of the bridge deck is 26m , Span of the bridge is 25m, Pier height is 10m, Apply the IRS railway loads and model in Staad pro and perform the structural analysis.

Introduction:

In Week 3, we are introduced to IRS, that is, Indian Railway Standards. The lessons taught in this Week were:

1. Introduction to Indian Railway Standards (IRS) Code.
2. IRS Gauge Calculation.
3. Broad Gauge Loading.
4. Metre Gauge Loading.
5. Metro Rail Loading.

Discussion:

1. Introduction to Indian Railway Standards (IRS) Code

• Indian Railway Standards or briefly the IRS Code were developed by Indian Railways for the purpose of designing and construction of Railway related structures.
• The various IRS loads for design of bridges includes

1. Metro Rail Loading
2. Broad gauge Loading
3. Electric Train
4. Gauge A and Gauge B Loading
   
   Metro Rail Loading

• Axle Loading = 17 tons
• Maximum No. of cars = 6 nos.
• Wheel Configuration

• Lengh a = 2150mm
• Length b = 2200mm
• Length c = 12400mm
• Length of the car = 21100mm
• 

Broad Gauge Loading

• Here there is no symmetry in loading and distance between wheels also differs.
• The Maximum Axle loading is in the middle wheel portion which is around 19.25 tonnes and Minimum Axle Loading is in the front wheel which is 11.84 Tonnes.
• There is one small wheel followed by four big wheels and then 5 small wheels of differing sizes, distances and axle loading.
• Unlike Metro Loading, Broad Gauge Loading is more complicated.

Electric Train Loading

• Electric Train Loading is nothing but Metre Gauge Loading.
• It has been used for several decades.
• In most cities this has been upgraded to Broad Gauge Loading.
• This is to accomodate more population.
• Each carriage has has six wheels in two sets. One set in front and the other set in the back.
• Distance between two sets is 2743mm while distcance between individual wheels is 914mm
• All three wheels in each set have same Axle Loading of 74.5kN.
• Overall Train Load is 27.8kN if we consider it as UDL.

Gauge A and Gauge B Loading

• Similar to Class A and Class B Loading in IRC, we have Gauge A and gauge B Loading in IRS.
• The maximum axle loading in Gauge A loading is 79.4. kN and minimum axle loading is 58.8 kN.
• Gauge A and Gauge B is also called 762mm Gauge.
• Unlike IRC, IRS has tables for calculation of Shear Force and Bending Moment for different spans between piers.
• Gauge B axle loading is same for all six wheels which is 59.8 kN.

Manual Live Load Calculation of Forces for IRS Metro Rail Loading:

• Live Load Type - Metro Live Loading
• Span L = 25m
• Width of Deck Slab = 26m

The diagram below shows the application of Live Loads on the superstructure:

The superstructure is analyzed for the above loading using equilibrium equations

• ∑V = 0
  170 + 170 + 170 + 170 = Ra+Rb
  680kN = Ra+Rb
• ∑Ma = 0
  (170 x 2.1) +(170 x 4.3) + (170 x 16.7) + (170 x 18.9) = 25Rb
  7140 = 25Rb
  Rb = 285.6 kN
  Ra = 394.4 kN
• Bending moment is calculated as follows:
  Ma = 0
  Mb = 0
  The Bending Moment as Midspan is
  Mc = (170 x 4.2) + (170 x 6.4) - (394.4 x 12.5) = - 3128 kNm
• The Maximum Bending Moment Due to Live Loading is - 3128 kNm

Analysis in StaadPro:

For the purpose of analysis, we will retain span of structure as 25m and width as 26m

The simple frame of the structure is as follows:

We will place the 8 Girders at 3.714m spacing as follows:

The following specifications were assigned

• Cross Girders = 0.5m x0.5 m
• I Girders (shown in the image below)

• Deck slab 0.35 m
• Pier diameter = 2m

Loading:

We will assign the Metro Loading in Definition> Vehicle Definitions>Add

Here we will specificy the axle loading in each wheel and distance between wheels as weel as width of vehicle as shown below:

Now we will go to Load Cases Details>Add>Load Generation

Here we will be asked "No. of Loads to be Generated"

This will be found by Adding (Length of Vehicle + Span) / Incrementor no. of iterations

Here as default we are taking 15

After this we will click on the generated load >Add

We will now specify the starting point of the load and then the increment direction. In this case starting node is (0,0,11.142) and increment is 1 in x direction.

We now Run Analysis.

The analysis has Zero Errors and Zero Warnings

Results:

We will now study the analysis in Post - Processing Mode

• Deflection in Fx

• Deflection in Fy

• Deflection in Fz

In conclusion, other forms of railway loading can be generated on a given model in the same way after defining the vehicle loads as per IRS.