A Comparitive Design of One Cell and Twin Cell RCC Box Type Minor Bridge

Bridges are required to be provided under earth embankment for crossing of water course like streams, Nallas across the embankment as road embankment cannot be allowed to obstruct the natural water way. Bridges are also required to balance the flood water on both sides of earth embankment to reduce flood level on one side of road thereby decreasing the water head consequently reducing the flood menace. These can be constructed with different material such as masonry (brick, stone etc) or reinforced cement concrete. Since bridge pass through the earthen embankment, these are subjected to same traffic loads as the road carries and therefore, required to be designed for such loads. Culverts are required to be provided under earth embankment for crossing of water course like streams,. This Paper deals with box culverts made of RCC, with and without cushion. The size, invert level, layout etc. are decided by hydraulic considerations and site conditions. The cushion depends on road profile at the culvert location. The scope of this Paper has been further restricted to the structural design of box. The structural design involves consideration of load cases (box empty, full, surcharge loads etc.) and factors like live load, effective width, braking force, dispersal of load through fill, impact factor, co-efficient of earth pressure etc. Relevant IRC Codes are required to be referred. The structural elements are required to be designed to withstand maximum bending moment and shear force. The Paper provides full discussions on the provisions in the Codes, considerations and justification of all the above aspects on design. Proper design covering these aspects has also been given in the Annexure. To our knowledge, these matters have neither been covered in any text book nor in any special publication at one place. This project deals with box minor bridges made of RCC. The size, invert level, layout etc. are decided by hydraulic considerations and site conditions. The cushion depends on road profile at the bridge location. The structural design involves consideration of load cases (box empty, full, surcharge loads etc.) and factors like live load, effective width, braking force, dispersal of load through fill, impact factor, co-efficient of earth pressure etc. Relevant IRC Codes are referred. The structural elements are designed to withstand maximum bending moment and shear force.