Live Load Bending Moment IRC Class 70R Tracked Vehicle for Slab Bridge Design Manually || Part 2

 

Maximum Bending Moment and Maximum Shear Force Calculation for Live Load (IRC Class 70R-Tracked Vehicle) ||  Bridge Deck Slab Design Example as per IRC || Part 2: 

Before going to calculate bending moment due to live load, you have to know about live load for Bridge Design. We will calculate bending moment due to live load as per IRC 6 2017.

At first you have to know Indian standard loading classes.

1.      IRC Class AA Loading Vehicle (Applicable for special loading cases),

2.      IRC Class A Loading Vehicle (Applicable for all bridges),

3.      IRC Class 70R Loading Vehicle (Applicable for all bridges but minimum clear carriage way shall be more than 1.2m+2x2.9m=5.30m). 

4.      IRC Class B Loading Vehicle (applicable for wooden bridges).

  

Maximum Live Load Bending Moment Calculation for  IRC Class 70R  Tracked Vehicle:

Now I am going to calculate the maximum bending moment for IRC Class70R Tracked Vehicle.

Picture-1: LIve Load Calculation for IRC Class 70R Tracked Vehicle

Here some term has been applied i.e. “c”

c: distance between the inner face of kerb rise or crash barrier to the outer edge of the wheel or track. It will be minimum 1.20m for IRC Class 70R Loading Vehicle as per IRC 6 2017, clause 204.1.1, Page-10

Impact factor: 10% (10 percent upto a span of 40.00m as per IRC 6 2017, clause 208.3.b, page-30)

Our main target is to find out the maximum bending moment. We will get maximum bending moment while centre of gravity (IRC Class 70R Tracked vehicle) will pass through the mid-span of the bridge.

Picture-2: IRC CLASS 70R TRACKED VEHICLE-TOP VIEW.

Effective breadth of Dispersion along span: 

Effective breadth of dispersion along span= 4.57+2(0.1+0.75) =6.27m

Effective Width of Dispersion:

Picture-4: Total Effective width of dispersion for IRC Class 70R (double Tracked)

Effective width for single track=

b_eff= α.a (1-a/l_eff) + b1

Where, α: Constant value depending on B/l_eff ratio.

a: the distance of the centre of gravity of the concentrated

load from the nearer support,

l_eff: Effective length of the bridge.

b1: the breadth of concentration area of the load, i.e., the dimension of the tyre or track contact area over the road surface of the slab in a direction at right angles to the span plus twice the thickness of the wearing coat or surface finish above the structural slab.

 

B/l_eff=8.4/9.6=0.875

α=2.45 (interpretation values from IRC: 21 2000, clause 305.16.2, page-53)

l_eff =9.60m

a=9.6/2=4.8m

b1=0.84+2(0.1)=1.04m

beff= 2.45*4.8*(1-4.8/9.6)+1.04)

      =6.92m

Total effective width for both tracks  (beff net) =0.45+1.2+2.9-0.84/2+6.92/2 = 7.59m

 

Loading intensity:

=70T/(effective breadth along span)  X (total effective width for both tracks)

=1.1x700/(6.27x7.59) (multiplied by Impact Factor to get dynamic load)

=16.18 kN/m2

Now find out maximum bending moment at mid-span due to loading intensity 16.18 kN/m2.

 

This udl load is distributed over 6.27m along the span.

Maximum Live Load bending moment

= (9.6x16.18x6.27/4-16.18x6.27^2/8)

= 163.967 kN-m/m width

Maximum shear force calculation for IRC Class 70R Tracked Vehicle:

To be continued in the next part....

Maximum Shear Force Calculation for IRC Class 70R Tracked Vehicle || Slab Bridge Design Manually || Part 3

You may visit my youtube channel: 

1.  Slab-Bridge-Design-In-Midas-Civil-as Per Indian Code IRC 112

More Posts: 

1. RCC Slab Bridge Analysis And Design Step-By-Step Manually || Part-1

2. Live Load Bending Moment IRC Class 70R Tracked Vehicle for Slab Bridge Design Manually || Part 2

3. Maximum Shear Force Calculation for IRC Class 70R Tracked Vehicle || Slab Bridge Design Manually || Part 3

4. 4. Bridge Deck Slab Design Example as per IRC || Slab Bridge Design example || LSM Method-Part 4