Concrete beams with CSWs were idealized as sandwich beams with an orthotropic core, according to the characteristics of the corrugated steel web (CSW). The assumptions of a zig-zag displacement and a layer-wise parabolic distribution of the transverse shear stress were introduced to derive the governing equations for the free vibration of concrete beams with CSWs based on the variational principle of mixed energy. The transverse shear stress in the developed theory satisfied the traction-free condition at both top and bottom surfaces of the beam, as well as the continuity condition at the interfaces between adjacent layers. The shear correction factor is therefore not necessary. The frequency equation of the beam with CSWs was derived and solved analytically for the frequencies and corresponding mode shapes under various boundary conditions. Comparisons with other methods indicate that the present theory can accurately predict the dynamic behavior of such beams.