Experimental behavior and strength of steel beams strengthened while under load

W-shaped beams were tested under a four-point loading to investigate the behavior and capacity of flexural members strengthened while under load. Experimental results revealed that for specimens tested at a long span and failing predominantly by lateral–torsional buckling, an increase in the preload level up to 53% of the capacity of the unstrengthened beam resulted in a maximum decrease of 14.2% in the lateral buckling load of the strengthened beam but the variation in the ultimate loads was insignificant for all preload levels. Those tested at a shorter span with the same strengthening pattern showed a decrease of 13% in the ultimate capacity as the preload level increased to 50% of the capacity of the unstrengthened beam. The load versus deflection behavior, however, showed less variation between specimens strengthened under load and under no load. For specimens failing predominately by flexural yielding, the preload level showed negligible effect on the ultimate capacity of strengthened specimens.