Abstract: In order to investigate the bending behavior of the prestressed composite steel-concrete box beams which have been damaged by torsion,five composite box beams are tested by symmetrical load at mid-span.Considering the history of the torsion loading on the beams,and comparing with the test about the intact beam,by tests and analysis are given some important parameters,such as the ultimate bending capacity of the composite beams,curve of moment-deflection at mid-span and curve of the increases of strain in st...