Assessment of Strength of Steel Bridge as per IS: 800 - 1984 and Draft Code

Abstract

Generally bridges are designed for a particular life span and designer should predefine the life span of the bridge. However strength of the bridge reduces with time and age due to factors like corrosion, fatigue, heavy loading and earthquake. Out of all these factors, the corrosion of bridge members is very critical. Some times, the corrosion is so severe that member strength is reduced to zero and member needs strengthening or replacement. Before taking any such action, visual inspection should be carried out of existing bridge structure.

The visual inspection report is prepared considering the following points. 1. Inspection of all existing bridge members, gusset plates, rivets and joints showing severe corrosion condition. 2. Photographs and measurement of corroded area of members. 3. Sketches of all members, sections, joint details and rivet details. 4. Calculation of member strength from sectional property and strength of joint.

As per visual inspection, the assessment of strength of existing bridge members from its connection details and from its sectional properties is evaluated. Where strength of member is reduced due to corroded area, an attempt has been made for replacement design of such corroded or damaged member.

The entire bridge is redesigned using same configuration and same span and as per I.S.800 (Draft Code). For the entire new design, member force in all the members is evaluated using influence line diagrams, drawn for the dead load, live load IRC class-A loading plus impact load for the same carriage width of bridge.

For the entire new design of a truss, an attempt has been made here to design the truss as per I.S. 800 Draft Code. This method, of the design is based on characteristic values for material strengths and applied loads, with separate partial factors for different loads.

Separate work sheets are prepared for the design of all the members using limit state method with help of Microsoft Excel for this complete new design. Work sheets for the design of all the replaced members as per existing I.S.800 are also prepared for the study.

The existing Ellise Bridge is considered for this study, After visual inspection and strength assessment of all the members of this bridge, the following designs are carried out using Excel sheets.

1. Replacement design of corroded or damaged members of bridge using I.S. 800 -1984 2. Entire new design of members of bridge keeping the same configuration of bridge and with IRC Class-A loading as per I.S. 800 Draft Code.