English：

To investigate the strengthening effect of the section⁃enlarging strengthening method onprestressed concrete hollow slabs with pretensioning method, four prestressed concrete hollow slabs withpretensioning method under identical technical condition, which had been in service on an expressway for20 years, were selected. Three of them were strengthened using three different section⁃enlargingstrengthening schemes respectively, and then three⁃point monotonic static loading tests were carried outseparately. The cracking load, ultimate bearing capacity, failure mode and stiffness degradation law ofthe unstrengthened beams and the strengthened beams were compared and analyzed. The results showthat the unstrengthened beams suffer from shear failure at the oblique section in the local prestress⁃deficient region. For the specimens strengthened by increasing section method, the cracking load andultimate bearing capacity are effectively improved, and the insufficient shear capacity at the obliquesection is remedied. All strengthened beams finally exhibited flexural failure at the normal section, withthe ultimate bearing capacity increased by 40%, 58% and 60% respectively compared with theunstrengthened beams.