Static and fatigue test on lightweight UHPC-OSD composite bridge deck system subjected to hogging moment

A cost-effective Lightweight Composite Bridge Deck (LCBD) system, including Orthotropic Steel Deck (OSD) and lightweight Ultra-High Performance Concrete (UHPC) layer is proposed to increase the stiffness and fatigue performance of conventional OSD. Static and fatigue tests on two full-scale strip models subjected to four-point bending were carried out. The static nominal cracking stress of the UHPC layer with reinforcement spacing of 80 mm is 24.59 MPa, while it increases to 35.68 MPa when the reinforcement spacing is reduced to half (40 mm); both values are far greater than the nominal stress of 12.7 MPa obtained in the prototype bridge. Increasing the reinforcement ratio can increase the bending stiffness of LCBD and decrease the tensile strain of the UHPC layer, while the change in range is relative slight. Furthermore, the flexural strength of UHPC and the reinforcement ratio are important factors affecting the fatigue life of the UHPC layer. When the reinforcement spacing increases from 40 mm to 80 mm, the fatigue life of the UHPC layer still satisfies related code requirements. Thus, for reduction in the engineering cost and construction complexity, the reinforcement spacing can be set as 80 mm. However, the application of the UHPC as the steel deck pavement, the rib-to-diaphragm welded joint is still prone to fatigue cracks. In addition, the existing S-N curves are hard to directly use for fatigue life prediction of the UHPC layer because of the great differences in the definition of stress level and evaluation index of failure in the fatigue test, which need to be modified in further studies.