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INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 1, No 3, 2010

Copyright 2010 All rights reserved Integrated Publishing services

Research article

  • 2.

    Formulation

    • 2.1

      Loads on the top of slab

ISSN 0976

4399

Total load for bending moment and shear force is considered from IRS code rules specifying the loads for designing the super­structure and sub­structure of bridges and for assessing the strength of existing bridges. For span of 8m total load for bending moment

981kN and total load for shear force is 1154kN is considered. Dead load of earth fill over the box = Area x depth x density

­­ 1.1

Total vertical pressure on top slab = Imposed load + Dead load + Live load

­­ 1.2

2.2 Loads on sidewalls

The coefficient of active earth pressure of the soil is given by the equation

Ka

cos

2

cos

2

1 c o s

sin

  • sin i

c o s

c o s

i

2

­­ 1.3

where,

γ = Density of soil, ф = Angle of internal friction,= angle of friction between wall and earth fill Where value of is not determined by actual tests, the following values may be assumed.

(i) (ii)

  • = 1/3

  • = 2/3

for concrete structures. for masonry structures.

i = Angle which the earth surface makes with the horizontal behind the earth retaining structure ( i =00 for embedded structure). Since this concrete structure is embedded in soil, the value of is considered as 1/3 (for concrete structures) considered for calculation of coefficient of active earth pressure

of the soil.

    • 2.3

      Earth pressure acting on the sidewalls:

    • 2.3.

      a) Earth pressure due to backfill

Earth pressure center of top slab = Earth pressure center of bottom slab = Ka H Ka H

­­ 1.4 ­­ 1.5

2.3. b) Earth pressure due to dead load surcharge

Earth pressure acting on sidewalls: At Top = Imposed load of track + Earth pressure on the top of slab + Live load

­­ 1.6

AT Bottom = Horizontal effect of surcharge + Earth pressure center of bottom slab ­­1.7

560

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