Orthotropic steel deck reinforcement technique for super-long span bridges with thin dense-reinforced UHPC Layers

Most of the long-span bridges over the last few decades adopted the traditional OSD (orthotropic steel deck) system, which has suffered from serious fatigue cracking after operation. This cracking phenomenon even directly affects the service life of those bridges. Therefore, it is necessary to develop a reinforcement technology to increase the stiffness of the existing OSD system to prevent further cracking. This paper proposes a reinforcement technique using thin dense-reinforced UHPC layers. Compared to LWCD (light weight composite deck) and previous reinforcement methods, the challenges of the proposed method are that the existing OSDs of super-long span bridges have thicker top steel plates, and have to use relatively thinner UHPC layers since the super-long span bridges are extremely sensitive to the added self-weight. Therefore, the neutral axis of the UHPC-based reinforced composite decks is near the interface between the steel plate and the UHPC layer or even within the steel plate. As a result, this reinforced composite deck shows different mechanical properties and the previous related calculation formula is no longer applicable. Based on the second Jiujiang Bridge in China, the corresponding global and local finite element analysis first verifies the feasibility and effectiveness of the proposed method. Then, several sets of specimens are carried out to investigate the bending performance of this UHPC-based composite decks under sagging and hogging moments, considering four parameters, i.e., the steel plate thickness, t_s, stud spacing, d, UHPC layer thickness, h_u and the number of transverse rebars, n_r. The failure modes, cracking process, relative slip and mechanical properties analysis are discussed. In addition, the theoretical calculation methods are proposed to predict the cracking and ultimate loads. Moreover, with the proposed calculation methods, the parameter analysis and sensitivity of the bending behavior of the reinforced steel-UHPC composite decks are also investigated. Based on the tests and theoretical analysis, some design recommendations for UHPC-based reinforcement for OSDs of super-long span bridges have been conducted. The findings of this study can provide a reference for the reinforcement technology of dense-reinforced UHPC layers in super-long span bridges.