Fig. 7 shows the vertical deflection at the crown of Span 1 with the self-weight and increasing live load. The live load corresponding to a relative displacement of 1.2 mm on the crown (permissible value as per IRS 2006) caused by the live load alone is 441 kN (45 t). This corresponds to a margin of safety at 245 kN (25 t; proposed increase of axle load) equal to 1.8. This margin of safety is more than the margin provided by the code. Similarly, the horizontal deflection at the springing of abutment and piers of Spans 1 and 2 are computed with increasing axle load. The results indicate that for a relative displacement (for live load alone) of 0.2 mm (permissible horizontal deflection as per IRS 2006) at the springing of Span 1, the corresponding live load is 637 kN (65 t). This offers a margin of safety at a 245-kN (25-t) axle load of 2.6, which is more than the margin provided by the code.
Read More: http://ascelibrary.org/doi/full/10.1061/%28ASCE%29BE.1943-5592.0000338