Performance of prestressed concrete box bridge girders under hydrocarbon fire exposure

This article presents an approach for investigating performance of prestressed concrete box bridge girders under hydrocarbon fire exposure. A three-dimensional nonlinear finite element model, developed in computer program ANSYS, is utilized to analyze the response of prestressed concrete box bridge girders under combined effects of fire exposure duration and simultaneous structural loading. The model validation is performed using a scaled prestressed concrete box girder exposed to ISO834 fire in furnace. Subsequently, the validated model is used to investigate fire performance of prestressed concrete box bridge girders through taking into consideration some variables, namely concrete cover thickness to prestressing strands, prestress degree, load level, fire exposure length, and position. Through a case study, results from numerical analysis show that concrete cover thickness to prestressing strands and load level has significant effect on fire resistance of prestressed concrete box bridge girders. Increasing prestress degree in prestressing strands can speed up the progression of deflection (sudden collapse) in prestressed concrete box bridge girder toward the final fire exposure stage. Reducing fire exposure length or preventing fire exposure on mid-span zone can highly enhance the fire resistance of simply supported prestressed concrete box bridge girders. Failure of prestressed concrete box bridge girder, under hydrocarbon fire exposure conditions, is governed by rate of deflection failure criterion in particular cases.

Research on Fabricating of Square Aperture Spherical Micro-Lens Array through the Laser Lithography

Due to the practical problems nowadays that the duty cycle is small and the utility rate of solar energy is low of photoelectric sensor light sensitive array, and having analyzed the advantages on solar energy utilization of square aperture spherical micro-lens than traditional circular aperture micro-lens array, we conduct a research on the fabricating of square aperture spherical micro-lens and testing technology. With the help of light spread theory, we analyses the relationship between light amplitude distributing rules, exposure length and exposure energy, establish a mathematical model of light distributing rules and use computer software to emulate the model. The results indicate solar energy distributes regularly in adhesive film. If the energy is fixed, exposure length will gradually become saturated following time. At the same time, we fabricate infrared quartz micro-lens array with array 256×256, single element lens 40×40μm, spherical radius 60μm, single element spacing 1μm.The experiment data are the same as emulation results.

Effects of Moxa Smoke on Monoamine Neurotransmitters in SAMP8 Mice

Objectives. To investigate the anti-aging effects of moxa smoke on SAMP8 mice.Methods. Using2×3factorial design, exposure length (15 or 30 minutes daily), and concentration (low, 5–15 mg/m3; middle, 25–35 mg/m3; high, 85–95 mg/m3), 70 SAMP8 mice were randomly assigned,n=10/group, to a model group or one of six moxa smoke groups: L1, L2, M1, M2, H1, or H2. Ten SAMR1 mice were used as normal control. Mice in moxa smoke groups were exposed to moxa smoke at respective concentrations and exposure lengths; the model and normal control mice were not exposed. Cerebral 5-HT, DA, and NE levels were determined using ELISA.Results. Compared to normal control, the model group showed a significant decrease in 5-HT, DA, and NE. Compared to model group, 5-HT and NE were significantly higher in groups L2, M1, and M2and DA was significantly so in L2and M1. 5-HT, DA, and NE levels were the highest in group M1among moxa smoke groups. A marked exposure length × concentration interaction was observed for 5-HT, DA, and NE.Conclusion. Moxa smoke increases monoamine neurotransmitter levels, which varies according to concentration and exposure length. Our finding suggests that the middle concentration of moxa smoke for 15 minutes seems the most beneficial.

The Effect of Exposure Length on Vortex Induced Vibration of Flexible Cylinders

This paper addresses a practical problem: “What portion of fairing or strake coverage may be lost or damaged, before the operator must take corrective measures?” This paper explores the effect of lost fairings (the exposure length) on Vortex-Induced Vibration (VIV) of flexible cylinders. The source of data is a recent model test, conducted by SHELL Exploration and Production. A 38m long pipe model with varying amounts of fairings was tested. Response as a function of percent exposure length is reported. Unexpected results are also reported: (i) the flexible ribbon fairings used in the experiment did not suppress VIV at speeds above 1 m/s; (ii) Above 1 m/s, a competition was observed between VIV excited in the faired and bare regions of the cylinder, (iii) Unusual traveling wave behavior was documented—waves generated in the bare region periodically changed direction, and exhibited variation in VIV response frequency. The results of these tests showed that (1) the excitation on the bare and faired regions could be identified by frequency, because the faired region exhibited a much lower Strouhal number; (2) as expected, the response to VIV on the bare region increased with exposure length; (3) the response to VIV on the faired region decreased with exposure length.