Experimental Research On Static And Fatigue Flexural Performance Of UHPC Layer In Light-weighted Composite Bridge Deck

To meet the requirement in development of modern bridges and composite structures, an innovative composite bridge deck system that consists of an orthotropic steel deck and a thin reinforced Ultra-high performance concrete(UHPC) layer was proposed by Prof. SHAO Xudong to relieve damage in asphalt surfacing and fatigue cracking in orthotropic steel decks. The resultant OSD-UHPC composite deck is referred to as a steel-UHPC lightweight composite deck(LWCD) system.In order to investigate the transversal flexural behavior of the steel-UHPC composite deck under wheel loads, eight steel-UHPC composite slabs were subjected to negative bending, and two were exposed to positive bending. The tests indicated that the reinforcement ratio and the cover thickness of steel rebars were two primary factors that significantly affect the crack strength of the UHPC layer. In the tests, the load raised approximately linearly with the cracking width when the crack width was less than 0.2 mm. Further, the crack spacing in the UHPC layer at the pure bending portion of the slabs was almost the same as the spacing of the transverse steel rebars. The maximum crack in the UHPC layer was only about 0.2 mm because of the contribution of the steel plate. In addition, theoretical analyses were performed to compare the theoretical results to those obtained in tests, and good agreement was achieved. According to the analyses, the cracking strength of UHPC in the composite slabs was 18.1 ~ 32.7 MPa, which exceeded the demanded stress in UHPC in design. Studies in this paper can be used to guide the design of the steel-UHPC composite deck in resisting transversal bending load.To investigate the static and fatigue flexural performance of the LWCD with open ribs, fatigue tests were carried out on a compostie beam that consists of a steel I-beam and a thin reinforced UHPC layer. The specimen was fabricated based on two pilot projects, i.e., the Mafang Bridge and the Dongting Lake 2nd Bridge. The UHPC layer had different reinforcement ratios at two ends of the specimen. In the static tests, the UHPC layer at the low and high reinforcement ratio ends had static flexural tension cracking strengthcrf of 33.2MPa and 54.6MPa, respectively. Consequently, in the fatigue tests, the constant-amplitude tensile stress range in the UHPC layer was set as 0.49 crf ~0.15 crf. According to fatigue damage equivalent principles, the equivalent maximum tensile stress of the UHPC layer with low and high reinforcement ratio was 14.8MPa and 24.3MPa respectively. Initial fatigue cracks were observed in the UHPC layer after experiencing 2.734 million and 3.74 million cycles of loading at the low and high reinforcement ratio ends, respectively. The visible crack was single and tiny. However, the load-deflection curves showed limited changes during the fatigue loading, indicating that the overall stiffness of the composie beam only decreased slightly. These reflected that the fatigue performance of the steel-UHPC compostie beam in negative bending was excellent. Moreover, when the reinforcement ratio raise, the fatigue cracking life of the UHPC layer increased significantly, and smimilar increase was observed in the residual cracking strength as well as the ratio of the residual craking strength relative to the static cracking strengthcrf.The maximal crack width of steel-UHPC composites slabs was calculated according to several specifications:the Mode Code 2010, UHPFRC-2013 French Recommandations, and the modified formula based on Chinese RC code(GB50010-2010). The predicted results were compared to the test results. The comparisons revealed that, in negative bending, the modified formula in the Chinese RC code(GB50010-2010) showed higher accuracy in fatigue crack width prediction than those in other specifications, and the calculated results were conservatively. However, with regard to the steel-UHPC composites slabs with large covers, the formulas in UHPFRC-2013 French Recommandations, involving use of a reduction factor, outperformed the others when the crack width was less than 0.1 mm.