Live Load IRC Class AA Wheeled Vehicle || RCC Slab Bridge Design Part-5

Picture: IRC Class AA Tracked and Wheeled Vehicles

Impact factor:

 23% up to 23-meter long span. (As per IRC 6: 2017; Clause 208.3-b)

>>Determination of Maximum Live Load Bending Moment for IRC Class AA Wheeled Vehicle: 

To get maximum bending moment due to IRC Class AA Tracked Vehicle, the vehicle shall be placed at the mid span as shown in the figure.

1. Effective Breadth of Dispersion along span: 

Wheel dimension:  

Width of wheel along transverse direction (W)=300mm

Breadth of the wheel along longitudinal direction (B)=150mm

Centre to center of wheel distance along longitudinal diection=1.20m

Assumed, load is dispersed from top to bottom in 45-degree angle with horizontal direction.

So, effective breadth of dispersion along the span will be
=(0.1+0.75)+(0.15/2)+1.20+(0.15/2)+(0.1+0.75)

=3.05m

2. Effective Width of Dispersion along Transverse Direction:

Effective width for single wheel=

b_eff= α.a (1-a/l_eff) + b1

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

a: the distance of the center 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)-(1.2/2)=4.20m

b1=0.3+2(0.1)=0.5m

beff= 2.45x4.2x(1-4.2/9.6)+0.5)

      =6.288m for single wheel

Total effective width for all wheels   (beff net) =0.45+1.2+(0.30/2)+2.05+6.288/2 = 6.994m<Width of deck slab (8.40m) 2. Loading Intensity:

=40T  x  impact factor/(effective breadth along span)  X (total effective width for all wheels)

=400x1.23/(3.05x6.994)

=23.06 kN/m/m-width

Now find out the maximum bending moment at mid-span due to loading intensity of 23.06 kN/m/m-width.

 This UDL load is distributed over 3.05m along the span.

3. Maximum Live Load bending moment

= (23.06x3.05x9.6/4)-(23.05x3.05x3.05/8)

= 142.01 kN-m

>>Determination of Maximum Shear Force for IRC Class AA Wheeled Vehicle: 

To get maximum shear force due to IRC Class AA-Wheel vehicle, the vehicle shall be placed nearest to the support as shown in figure-

1. Effective Breadth of Dispersion along span: 

Wheel dimension:  

Width of wheel along transverse direction (W)=300mm

Breadth of the wheel along longitudinal direction (B)=150mm

Centre to center of wheel distance along longitudinal diection=1.20m

Assumed, load is dispersed from top to bottom in 45-degree angle with horizontal direction.

So, effective breadth of dispersion along the span will be
=(0.1+0.75)+(0.15/2)+1.20+(0.15/2)+(0.1+0.75)

=3.05m

2. Effective Width of Dispersion along Transverse Direction:

Effective width for single wheel=

b_eff= α.a (1-a/l_eff) + b1

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

a: the distance of the center 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=(0.150/2)+0.1+0.75=0.925m

b1=0.3+2(0.1)=0.5m

beff= 2.45x0.925x(1-0.925/9.6)+0.5)

      =2.548m for single wheel

Total effective width for all wheels   (beff net) =0.45+1.2+(0.30/2)+2.05+2.548/2 = 5.124m<Width of deck slab (8.40m) 2. Loading Intensity: =40T  x  impact factor/(effective breadth along span)  X (total effective width for all wheels) =400x1.23/(3.05x5.124) =31.48 kN/m/m-width Now find out the maximum shear force due to loading intensity of 31.48kN/m2  This UDL load is distributed over 3.05 m along span. Taking bending moment at point B, Ra X 9.6=31.48x3.05(9.6-3.05/2) Ra=80.76 kN Rb=(31.48x3.05-80.76) kN    =15.25 kN So, the maximum shear force due to IRC Class AA-Tracked Vehicle is 80.76 kN.

To read more:

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

5. Live Load IRC Class AA Wheeled Vehicle || RCC Slab Bridge Design Part-5

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