This work is the result of experimental research conducted to determine the contribution of a composite material to improving the mechanical behavior of old, full-size reinforced T-beams in operation conditions under the action of short-term loads. The tension side of their ribs were strengthened by carbon strips of different lengths. Then, they were tested in loading by concentrated and uniformly distributed short-term loads. It was concluded that, for strengthening simply supported beams, there was no need for using CFRP strips longer than half of their length, and a lateral anchorage was not required. This refers to bending tests where no load increment exceeding 60% of the flexural strength is expected. The results obtained from this experiment may be of use in modern engineering practices, especially because tests conducted on old, full-size samples are very rare.