Structural Response of Thin-Web Beams to Various Web Opening Retrofit Techniques

Accidental web openings caused by impact, corrosion, or conflict-related damage can substantially reduce the strength, stiffness, and stability of steel bridge girders. Although numerous studies have examined beams containing intentionally designed web openings, limited experimental research has systematically compared practical rehabilitation methods for accidental openings in slender-web plate girders. This study experimentally and numerically evaluates several rehabilitation configurations incorporating welded patch plates and transverse stiffeners. Ten slender-web steel girder specimens, each 1800 mm long, 800 mm deep, and 300 mm wide, were tested under monotonic concentrated loading at mid-span. Nonlinear finite element models were also developed to qualitatively examine the principal deformation and instability trends. Relative to the control specimen, the untreated web opening reduced the ultimate load by approximately 43% and exhibited approximately 10% greater deflection at its respective ultimate load. One-sided and two-sided welded patch plates increased the ultimate load of the damaged specimen by approximately 22% and 26%, respectively. Transverse stiffeners increased the ultimate load by approximately 73% while exhibiting substantially lower ultimate-load deflections. The combined use of patch plates and transverse stiffeners provided the greatest improvement, increasing the ultimate load by approximately 101–123% relative to the untreated damaged specimen and substantially reducing lateral instability. The findings demonstrate that effective rehabilitation of slender-web girders requires not only restoration of the interrupted load path but also restraint of web instability.