Failure of Chauras bridge

• Case study of collapse of Chauras bridge, Uttarakhand, India is presented.
• The bridge collapsed while deck slab casting was in progress.
• Buckling of a top chord compression member of the steel truss caused the failure.
• It is recommended to check design at limit state of strength also.
• 2.25 Load factor for compression and 1.5 for tension members and joints is suggested.

Sudden collapse of 190 m long Chauras bridge in Uttarakhand, India, which was a three span (40 m + 110 m + 40 m) continuous deck type truss bridge, took place during casting of the deck slab after successful launching of the truss. The incidence occurred when 52.5 m length of the deck slab was cast starting from middle of the 110 m span towards the right pier. Whereas, collapse of I-35W bridge took place due to failure of one of its gusset plates, analysis results show that Chauras bridge collapsed due to buckling of its U13U14 top chord compression members when 173.8 N/mm2 stress in the member occurred against calculated permissible compressive stress of 149.8 N/mm2. Sudden collapse of the bridge claiming six lives with it, due to slight increase in stress beyond the permissible compressive stress indicates that steel girder bridges must also be checked for reserve strength at the limit state of strength. As per Indian and European Standards, in addition to 1.1 material safety factor and 1.5 load factor used for compression and tension members in limit state of serviceability for fatigue design, additional load factor of 1.5, both for dead and live loads, for laterally unsupported compression members should be used for checking the design at the limit state of strength. No such additional load factor for tension members and joints is required.