冲刷条件下桥梁结构动力性能仿真分析

水流冲刷造成的桥梁损毁会给人类带来重大的经济损失和人员伤亡。冲刷对桥梁安全性的影响,可以通过分析冲刷条件下桥梁动力性能的变化来进行评价。本文将从冲刷深度和冲刷所造成的桥梁基础截面损失两个方面,分析水流冲刷对桥梁动力性能的影响。在总结已有的模型分析方法的基础之上,提出本文的有限元建模思路。并以密西西比河上被冲毁的33号公路桥为例,通过SAP2000软件建立有限元模型并进行模态分析,得到冲刷条件与桥梁动力性能之间的关系。     

Treatment of waste printed wire boards in electronic waste for safe disposal

The printed wire boards (PWBs) in electronic waste (E-waste) have been found to contain large amounts of toxic substances. Studies have concluded that the waste PWBs are hazardous wastes because they fails the toxicity characteristic leaching procedure (TCLP) test with high level of lead (Pb) leaching out. In this study, two treatment methods - high-pressure compaction and cement solidification - were explored for rendering the PWBs into non-hazardous forms so that they may be safely disposed or used. The high-pressure compaction method could turn the PWBs into high-density compacts with significant volume reduction, but the impact resistance of the compacts was too low to keep them intact in the environment for a long run. In contrast, the cement solidification could turn the PWBs into strong monoliths with high impact resistance and relatively high compressive strength. The leaching of the toxic heavy metal Pb from the solidified samples was evaluated by both a dynamic leaching test and the TCLP test. The dynamic leaching results revealed that Pb could be effectively confined in the solidified products under very harsh environmental conditions. The TCLP test results showed that the leaching level of Pb was far below the regulatory level of 5mg/L, suggesting that the solidified PWBs are no longer hazardous. It was concluded that the cement solidification is an effective way to render the waste PWBs into environmentally benign forms so that they can be disposed of as ordinary solid wastes or beneficially used in the place of concrete in some applications.     

TCLP Heavy Metal Leaching of Personal Computer Components

Electronic waste (E-waste), including all obsolete electronic products, has become the fastest growing component in the solid waste stream. Personal computers (PCs)—the most significant component in E-waste stream—were studied for their potential leaching toxicity of contaminants. All the components in a PC that are composed of, or contain printed wire boards (PWBs) including the motherboard, various expansion cards, disk drives, and power supply unit were tested by the toxicity characteristic leaching procedure (TCLP). The total contents of eight heavy metals including arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver in the PWBs and their TCLP leaching from the PWBs were examined. Among these eight heavy metals lead was found to be the predominant element that causes the toxicity characteristic of the PC components. The lead concentrations in the TCLP extracts of the vast majority of the PWBs ranged from 150 to 500?mg/L, which are 30–100 times the regulatory level of 5?mg/L for classifying a waste as hazardous. The motherboard in a PC contributed 50–80% of the total lead that could leach out from all the PWBs in the PC under the TCLP test conditions. The contents of barium and silver were found to be high in some components, but they were not leachable under the TCLP test conditions. The contents of other five elements in all the PC components were hardly detectable. They would not have the potential to cause toxicity characteristic leaching concern.     

Settlement based load capacity curve for single helix helical pile in c - ϕ soil

Helical piles are getting increasingly popular for lightweight engineering applications. Currently, the helical pile is mostly designed with torque capacity; however, it cannot explain the foundation's anticipated settlement. The current study developed a settlement-based design technique to determine the capacity of a single helix in small diameter helical piles. A three-dimensional nonlinear finite element analysis (FEA) was conducted using PLAXIS 3D. At first, the numerical models were calibrated and verified using load testing data from representative soil properties and realistic modeling assumptions. Then a parametric study was extended to determine the load settlement curve in different c- ? soil types, along with varying helix and shaft configurations. The load-deformation curves were grouped to develop multiple load capacity curves. Finally, the load capacity curve was validated by load test data. The range of calculated vs measured (from load tests) capacities (Q_c/Q_m) is 0.68 to 2.67, where the mean Q_c/Q_m is 1.10.