Load combination AASHTO group X = DL + ( LL + I ) + E with no increase in allowable unit stress will followed for the purpose of analysis, it is usual practice to consider one foot width of the box.
The culvert is subjected to the following load case for which moments, thrusts and shears have been calculated.
1.Live load, dead load and earth pressure acting from outside and no hydrostatic pressure acting from inside.
2.Live load, dead load and earth pressure acting from outside and hydrostatic pressure acting from inside.
3.Dead load and earth pressure acting from outside and hydrostatic pressure acting from inside.
The loading cases are shown systematically for loading combination as mentioned above.
Let, the thickness of the vertical and horizontal slab is 9 inches.
Dead load, live load and earth pressure acting from outside and no hydrostatic pressure from inside.
3.1.4 TOP SLAB LOAD :
The weight of top slab, filling earth, two outer and two inner walls with live loads are assumed to be uniformly distributed over foundation.
1. Weight of top slab = ( 9/12 )X( 150/1000 )
= 0.1125 k/ft 2
2. Weight of fill (8 ft) = 8*0.12*0.7 [ as per PCA manual page no.38, earth load may be taken as 70% of its actual load.]
= 0.672 k/ft2
≈ 0.7 k/ft2
3. Wearing coarse = ( 2/12 )*( 120/1000 )
= 0.02 k/ft 4
Total = ( 0.1125+0.7 +0.02 ) k/ft2
3.1.5 LIVE LOAD :
E = 4+0.06S
Where, S = Effective span in ft.
E = Effective width which should not be greater than 7 ft.
As per AASHTO 92 section 8.8.2,
In analysis of continuous and rigid frame members, distances to the geometric centers of members shall be used in the determination of moments.
Therefore the dimensions of center line,
Vertically = 4.75 ft = 57 inches
Horizontally, S = 4.75 ft = 57 inches
In case of exposed slab:
Effective width, E = 4+0.06S= 4+0.06 * 4.75
= 4.29 ft <7 ft