STRUCTURAL APPLICATIONS OF COMPOSITES IN INFRASTRUCTURE
also being used in combination with concrete slabs to develop and test new model bridges by M. Saiidi and F. Gordaninejad at University of Nevada, Reno. Since the 1930's, glass fiber reinforced plastic (GFRP) has been considered a good substitute for steel as a reinforcement ofconcrete or to create an initial state ofcompressive stress in concrete by prestressing GFRP tendons~ Reinfofcement and prestressing of concrete are common ways to miti.gate the lo\v tensile strength of concrete in order to take advantage of its high compressive strength~ In fact, reinforced concrete is a fiber reinforced composite material in '''hieh the advantageous properties of the constituents are high tensile strength of the rebars (steel or FRP) and the high compressive strength of the concrete matrix.. Surface protection of certain types of continuous glass fibers, particularly E..glass fibers, from attacks by the environment or alkaline reaction with concrete has been accomplished by coatings, including resins. For example, a typical continuous E..glass fiber reinforced plastic rebar has a 55% glass vol.ume fraction enlbedded in a matrix ofv'inylester or isophthalic resin~ These thermoset resin systems have ex~ ceHent resistance to corrosion a.nd impact, are good electrical and thermal insulators, are easy to manufacture, and are cost effective~ Thermoplastic rebars, which are more expensive than thermosets, have a potential for reshaping and \velding in the field which motivates current investigation oftheir potential applications in constnlction# Aramid fibers (e.g#, DuPont's Kevlar® 29, 49, 149) with higher tensile strength (3~62 GPa) and stiffness (124 G·:Pa for Kevlar@ 49) than glass fibers are being used to devel.op high strength rebars and cables by DoS. and Japanese manufac~ turerso AraIuid fibers have good chemical resistance to sol .. vents, dilute ac...i.ds~ and bases, as well a..1O) excellent fatigue strength and low relaxationo Carbon fiber reinforced plastic rebars and seven wire strands (cables) \vith higher stiffness than glass or aramid fiber rehars are also manufactured as reinforcing or prestressing eleluents for structural appHca~ tions, Ho\vever, carbon fiber rebars and cables are even more expensive than aramid or glass rebars, Chopped fiber rein-· forced plastic rods are being manufactured by extrusion~ 'fhesr.
STRUCIURAL DESIGN EQUATION FOR FRP COLUMNS Ever
A design equation for fiber reinforced plastic columns is presented in this paper based on the interaction between local (flange) and global (Euler) buckling observed during testing of the FRP columns included in this investigation. An existing interaction equation is adapted to account for the modes of failure observed in columns made of fiber reinforced composite materials. Experimental data generated during this investigation is presented and used to validate the interaction equation and to obtain the interaction constant. A slenderness ratio is proposed and used to present a plot of buckling for all sections and column lengths (short, long, and intermediate). An'expression for the optimum column length to be used in the experimental determination of the interaction constant is proposed.
Human exposure to methylmercury from crayfish (Procambarus clarkii) in China
Methylmercury (MeHg) accumulation in aquatic food raises global concerns about human exposure to MeHg. Crayfish is the world’s third largest farmed crustacean species and a favorite aquatic food in many countries. However, human health hazard due to MeHg exposure via crayfish consumption is unclear, partly because appropriate survey data are lacking. We report on mercury concentrations and speciation in edible tail muscle of crayfish collected from restaurants in 23 Chinese cities. On average, MeHg constituted 99.1 % of mercury in tail muscle, and MeHg concentrations were comparable with those reported for fish in China. Variation in MeHg concentrations was not attributable to broad geographic region (i.e., provinces) or tail length. For different populations, potential health risk (characterized by hazard quotient or HQ) of MeHg exposure through crayfish consumption depended largely on crayfish consumption rates. In particular, a health hazard (HQ > 1) was found for high-rate consumers (i.e., 95 %ile or higher) in some cities in the middle and lower reaches of the Yangtze River (MLYR), during the peak consumption season. Our results suggest that more attention should be paid to dietary MeHg intake via crayfish consumption in China, particularly for communities with high consumption in MLYR.