AbstractComposite box girders with corrugated steel webs (CBGCSWs) are used worldwide owing to their light self-weight, high efficiency of prestressing application, and reasonable distribution of shear force and bending moment. An improved composite box girder with corrugated steel webs (ICBGCSWs) has been recently introduced to further reduce the dead weight and improve its durability. Because the innovative ICBGCSW has emerged as a new structure, very few studies have been conducted on its dynamic characteristics. In the present study, a theoretical analysis was first conducted. By comprehensively considering the shear lag effect and the shear deformation of CSWs, the element stiffness matrix of ICBGCSW was derived based on the principle of stationary potential energy. The natural frequencies and mode shapes in vertical bending vibration were calculated via a self-developed software program. The proposed method was verified by comparing the results with finite-element analysis and experimental results. Then, sensitivity studies were performed to investigate the influences of the shear lag and shear deformation on the natural frequencies of vertical bending vibration. Finally, vibration frequencies of the continuous ICBGCSW were calculated, and a general formula for calculating the fundamental frequency of simply supported girders, continuous girders with equal spans, and continuous girders with unequal spans was proposed. The proposed method, being able to consider both the effects of shear lag and shear deformation of the box girder, delivered very good performance in studying the dynamic characteristics of the ICBGCSW, whereas the proposed general formula of fundamental frequency could serve as a good reference for the bridge design in practice.