Guidelines for Repair and Rehabilitation of Steel Bridges
2007 Edition

IRC SP 74 recommends starting with a thorough visual examination, using the naked eye or binoculars to spot rust and cracks. For detailed analysis, non-destructive testing (NDT) techniques such as dye penetration for surface cracks, ultrasonic testing for subsurface flaws, radiographic imaging for internal defects, and magnetic particle testing for surface and near-surface cracks are advised. Critical areas like fatigue-prone welds, high-stress members, and concealed joints require special attention.

The code advises assessing the severity and extent of corrosion before repair. For web plates with significant corrosion, it recommends bolting corrosion plates on both sides using high-strength turned and fitted bolts. Secondary members with minor corrosion can be strengthened similarly, but those with widespread damage should be replaced. This approach focuses on restoring structural integrity by supplementing lost sections rather than welding, preserving existing material.

Key design factors include assessing and possibly relieving dead load stresses through jacking or external prestressing, ensuring structural redundancy to prevent fracture-critical failure, and accounting for fatigue by avoiding stress concentrators and using butt welds where applicable. Strengthening may involve modifying the structural system (e.g., continuous spans, added supports), external post-tensioning to counterbalance loads, and stepwise reinforcement starting with the weakest components. Compatibility of new fasteners and minimizing eccentricity between old and new sections are also vital.

Protective coating selection should begin with evaluating existing paint conditions. If adequate, reapplication of the same system is acceptable; otherwise, a new coating must be chosen based on compatibility with existing surfaces, environmental factors like pollution and salinity, availability of materials and applicators, accessibility of the site, ease of application, and life cycle costs. Surface preparation is crucial, including thorough cleaning and addressing section loss. The coating thickness should be controlled to avoid cracking, with special care to protect hard-to-reach areas where corrosion risk is higher.

Post-rehabilitation, IRC SP 74 suggests two detailed inspections within the first year: the first at six months after reopening to traffic and the second at twelve months. Following these, routine inspections should occur every three years. The competent authority may adjust this schedule for special cases. Maintenance should emphasize preventative measures such as repainting and corrosion protection, supported by a bridge management system that records condition and enables timely interventions.