Experimental Investigation on Interface Performance of UHPC-Strengthened NC Structure through Push-Out Tests.

Strengthening concrete structures with ultra-high performance concrete (UHPC) can both improve the bearing capacity of the original normal concrete (NC) structure and prolong the service life of the structure due to the high strength and durability of UHPC. The key to the synergistic work of the UHPC-strengthened layer and the original NC structures lies in the reliable bonding of their interfaces. In this research study, the shear performance of the UHPC-NC interface was investigated by the direct shear (push-out test) test method. The effects of different interface preparation methods (smoothing, chiseling, and planting straight and hooked rebars) and different aspect ratios of planted rebars on the failure mode and shear performance of the pushed-out specimens were studied. Seven groups of push-out specimens were tested. The results show that the interface preparation method can significantly affect the failure mode of the UHPC-NC interface, which is specifically divided into interface failure, planted rebar pull-out, and NC shear failure. The critical aspect ratio for the pull-out or anchorage of planted rebars in UHPC is around 2. The interface shear strength of straight-planted rebar interface preparation is significantly improved compared with that of the chiseled and smoothened interfaces, and as the embedding length of the planted rebar becomes longer, it first increases greatly and then tends to be stable when the rebar planted in UHPC is fully anchored. The shear stiffness of UHPC-NC increases with the increase of the aspect ratio of planted rebars. A design recommendation based on the experimental results is proposed. This research study supplements the theoretical basis of the interface design of UHPC-strengthened NC structures.

Effects of High Temperature on the Burst Process of Carbon Fiber/PVA Fiber High-Strength Concretes.

This paper carried out burst tests on the carbon and polyvinyl alcohol (PVA) fiber high-strength concrete specimens to investigate the effects of fiber type, fiber content, water content, heating rate and test specimen size on the burst, and the whole burst process of fiber-high concrete was photographed and recorded. The results indicated that fiber addition will improve the high temperature burst behavior of the high-strength concrete, and the performance of PVA is greatly different from that of carbon fiber. The water content and heating rate have little influence on the burst of the PVA test specimen, but they will greatly affect the carbon fiber test specimen. The size of the test specimen has a great influence on the burst. For the PVA concrete test specimen, the large size test specimen bursts on the surface; as for the carbon fiber test specimen, the large size test specimen delays the initial burst time, but the burst becomes fiercer.

Epidemiology of migraine in the She ethnic minority group in Fujian province, China.

OBJECTIVES: We examined the prevalence and risk factors of migraine among the She population. The prevalence of migraine among She Chinese in Fujian province is high. METHODS: This study is a cross-sectional survey. Subjects completed a questionnaire that collected demographic and clinical data related to migraine. Physical examination and clinical laboratory tests were performed. Data were analyzed by regression analysis. RESULTS: Of the 5519 subjects enrolled, 2377 were male (43·1%) and 3142 female (56·9%). Of these, 581 (10·53%) experienced migraine annually, including 6·18% of males and 13·82% of females. Highest prevalence rate was among those aged 40-49 years (11·28%). The 141 (24·3%) subjects who had migraine with aura had higher incidence of family history of headache than those without aura (38·5% vs 19·9%, P < 0·0001). CONCLUSION: Female gender and insomnia are possible risk factors for migraine in the She population.