Guidelines for Fabrication and Erection of Steel Bridges
2015 Edition

Steel used in bridge fabrication must conform to IS:2062 or as specified in design documents, supported by Mill Test Certificates indicating compliance. Cast or heat mark numbers and plate identifications are recorded prior to fabrication to ensure traceability. Samples from each steel batch are submitted to an independent approved laboratory for testing, and fabrication proceeds only after satisfactory correlation of test results. Ultrasonic testing is mandatory for plates 25 mm thick or more to detect internal flaws. Surface inspections for defects and edge laminations are conducted during fabrication and cleaning processes. Repair of discontinuities follows specific criteria based on depth and length, aligned with the standard's guidelines. Rolling and cutting tolerances adhere to IS:1852 for dimensional accuracy.

HSFG bolt installation begins with surface preparation involving aluminium metalizing of steel interfaces to a thickness of approximately 150 microns without additional coatings. For existing structures, cleaning by wire brushing or flame cleaning is required; if not possible, the slip factor is reduced accordingly. Installation involves placing washers—two for Class 10.9 bolts or one DTI and one plain washer depending on bolt class—and aligning holes carefully. Bolts are first tightened to a snug stage, followed by a preliminary torque reaching about 75% of the final value. Final tightening induces plastic deformation by exceeding the bolt's yield strength using calibrated torque wrenches or DTI washers until specified tension levels from IS:4000 are met. Verification includes checking permanent markings on bolts and nuts, ensuring proper sequence from the stiffest section outward, and prohibiting reuse of fully tensioned bolts once removed.

Inspection during welding includes continuous visual monitoring of welding parameters such as arc stability, travel speed, electrode condition, and slag removal to ensure quality. Pre-welding inspections verify the absence of cracks, proper edge preparation, parent metal condition, dimensional accuracy, and welder qualifications. Non-destructive testing methods recommended include Visual Testing (VT), Magnetic Particle Testing (MPT) for ferromagnetic materials, Dye Penetrant Testing (DPT) for non-ferromagnetic materials, Ultrasonic Testing (UT) for internal flaws, and Radiographic Testing (RT) for critical welds requiring high reliability. All inspection procedures must comply with relevant IS standards, and defective welds must be removed and properly re-welded.

Protective coatings and metallizing involve abrasive surface preparation by compressed air or centrifugal blasting to clean and roughen steel surfaces. Metalizing is performed by spraying high-purity aluminium wire (3 or 5 mm diameter) immediately after surface preparation, applying a nominal thickness of at least 150 microns, with local minimums of 110 microns, over at least two passes. For corrosive environments like coastal or industrial areas, a painting schedule includes two coats of epoxy zinc phosphate primer, followed by zinc chrome primer and epoxy micaceous iron oxide intermediate coats, capped by two coats of aluminium or polyurethane finishing paint. Where metallizing is not feasible, an alternative painting system comprising zinc chrome and red oxide primers with aluminium finishing coats is used. All coatings are applied per relevant IS specifications, with drying times ensured between layers.

Steel bridge components must be securely packed and fastened to prevent movement, sliding, or damage during transportation. Prior to transit, route surveys should be conducted to identify restrictions and confirm availability of appropriate transport methods. Components are tightly lashed, with protruding and threaded parts protected and coated with oil or grease to prevent corrosion. Loose or sub-assembled items are clearly marked and dispatched in containers with detailed inventories. Underloading consignments is avoided to maintain stability. Upon arrival, materials are stored above ground on platforms or skids with sloped floors for drainage, and handled using lifting beams and proper slings to minimize distortion or damage. These practices ensure safety for personnel and preservation of component integrity throughout transport and handling.