The designer should have first seen and studied many bridges in the course of a long learning process. He should know what type of beam may be suitable in the available conditions, either a beam bridge, an arch bridge or a suspended one. He should also know the influence of foundation conditions on the choice of spans and structural systems etc.
1) A plan of the site showing all obstacles to the bridged such as rivers, streets, roads or railroads, the contour lines of valleys and the desired alignment of the new traffic route.
2) Longitudinal Section of the ground along the axis of the planned bridge.
3) Required width of the bridge, width of lanes, median, walkways, safety rails etc.
4) Soil Conditions for foundations, results of boring with a report on the geological situation and soil mechanics data.
5) Local conditions like accessibility for the transport of equipment, materials and structural elements.
6) Weather and Environmental conditions, floods, high and low tide levels, periods of drought, range of temperature and length of frost periods.
The designer should visit the bridge site and its Environment.
When the Engineer is sure that a design idea has emerged in his mind, he should pick up a pencil and a scale and by the help of sketching, learned at school, he should start from sketching the probable road direction, beam depth, the piers, the abutments and the bottom edge of the beam is drawn.
After the approval of the design, the final design work can begin with rigorous calculations of forces, stresses etc. For all kinds of loads or attacks and then the structural detailing has to be done.
The phase of conceptual and aesthetic design needs a comparatively small amount of time, but is decisive for the expressive quality of the work.