基于神经网络的连续刚构桥施工线形控制参数预测研究

结合白果渡嘉陵江大桥施工线形控制的具体实践,采用BP神经网络进行连续刚构桥施工线形控制中的参数识别及预测工作。基于影响桥梁线形主要参数的截面尺寸、距离及标高建立神经网络系统,并对其进行计算训练样本、训练神经网络和网络仿真分析。运用神经网络仿真分析进行连续刚构桥施工线形的具体方法是,先计算当前施工状态的标高,再预测下一节段的标高。经过往复循环,逐一进行节段预测调整,从而指导连续刚构桥顺利施工。网络学习及仿真预测结果表明:该法对数据的处理及预测,在操作简单的基础上,分析结果具有较高的精度。该结论可推广到采用悬臂法施工的连续梁桥、拱桥、斜拉桥等桥型的施工线形控制工作及研究。     

Dynamic Impact Factor Induced by Idling Vehicle-Bridge Coupling Vibration

怠速车-桥耦合振动下城市桥梁动力冲击系数

刘浪^1,2,王杰²,杨洪²

(1. 省部共建山区桥梁及隧道工程国家重点实验室,重庆交通大学,重庆 400074;

2. 重庆交通大学,土木工程学院,重庆 400074)

摘要：

为计算拥堵状态下怠速车-桥耦合振动对城市桥梁的冲击作用,持续定点采集了大量拥堵车列图像,利用图像数字化处理技术,建立了3种车辆模型及6种典型城市桥梁拥堵车列模型。根据实桥参数建立了怠速状态下车-桥耦合振动有限元模型,计算了各种典型拥堵车列荷载工况下车-桥耦合振动产生的动力系数,并与规范冲击系数进行了对比。结果表明,6种拥堵工况产生的最大动力系数分别为规范值的1.15~2.67倍,说明拥堵状态怠速车-桥耦合振动产生的冲击系数较正常交通状况大。针对拥堵严重的桥梁的设计及评估,本文建议采用1.7的规范修正系数。文中提出的分析模型及方法可为本领域的进一步研究提供有益的参考。

关键词：动力冲击系数;车-桥耦合振动;交通拥堵模;规范设计值

     

An analytical method for calculating torsional constants for arbitrary complicated thin-walled cross-sections

In this paper, an analytical method is proposed for calculating torsional constants for complicated thin-walled cross-sections with arbitrary closed or open rib stiffeners. This method uses the free torsional theory and the principle of virtual work to build governing equilibrium equations involving unknown shear flows and twisting rate. After changing the form of the equations and combining these two unknowns into one, torsional function, which is a function of shear flow, shear modulus, and twisting rate, is included in the governing equations as only one of the unknowns. All the torsional functions can be easily obtained from these homogeneous linear equations, and torsional constants can be easily obtained from the torsional functions. The advantage of this method is that we can easily and directly obtain torsional constants from the torsional functions, rather than the more sophisticated shear flow and twisting rate calculations. Finally, a complicated thin-walled cross-section is given as a valid numerical example to verify the analytical method, which is much more accurate and simpler than the traditional finite element method. __________ Translated from Journal of Tongji University (Natural Science), 2006, 34(9): 1 170–1 174 [译自: 同济大学学报 (自然科学版)]     

“梁式桥静力体系划分”教学案例分析

从简支梁桥恒栽弯矩图出发,逐步演变到悬臂梁和连续梁桥,再根据连续梁桥的恒载弯矩图,通过不同弯矩零点的组合,演变出工程上常用的悬臂梁桥、T构刚构桥和连续刚构桥,具有力学概念清晰、教学内容紧凑等优点,可以有效地节省教学用时。     

风火山隧道温度特性非线性分析

风火山隧道是青藏铁路的控制性工程之一,全隧道位于多年冻土之中,这种特殊隧道的温度分布将直接影响隧道结构的稳定性。根据带相变瞬态温度场问题的热量平衡控制微分方程,应用Galerkin法推导出了三维有限元计算公式。根据风火山隧道内的实测大气温度,利用三维有限元计算公式,计算分析了该隧道在未来50 a的温度特性,并与现场实测围岩温度进行了对比分析,分析表明计算理论、模型、参数和条件是可靠的,风火山隧道在未来50 a内不会出现季节性融化。从而为寒区工程设计提供理论依据和计算方法。     

Soil freezing point as obtained on melting

The method of numerical analysis of the differential scanning calorimetry (DSC) thermogram obtained during warming makes it possible to obtain a complete curve of the unfrozen water content in frozen soil, including the highest temperature at which last ice crystals melt and the unfrozen water content becomes equal to the total water content. This is referred to as the freezing point of the soil–water system obtained on melting. Statistical analysis of 137 results obtained for 6 monomineral and homoionic model soils implies that, similarly to the freezing point obtained from the cooling curves, the soil freezing point obtained on melting strongly depends on the water content. An empirical equation, found basing on the reported results, has proved to be useful as a predicting tool with reference to 33 foreign data points obtained in the typical way (i.e., from the cooling curve).     

Urban water capacity: Irrigation for heat mitigation

Our world has been continuously urbanized and is currently accommodating more than half of the human population. Despite that cities cover only <3% of the Earth's land surface area, they emerged as focal points of human activities, and confront numerous environmental challenges as a result of changes in landscapes, hydroclimate, ecosystems, and biodiversity. In particular, the built environment usually experiences exacerbated heat stress induced by global climate and landscape changes, commonly known as the urban heat island effect. Urban irrigation, as a climate adaptation and mitigation strategy, is effective in cooling the built environment, but exhibits large uncertainties in the trade-off between water use and heat mitigation capacity. Here we show the efficiency of cooling effect induced by irrigation of urban vegetation, represented by a novel metric, viz. urban water capacity, analogous to the heat capacity, across the contiguous United States (CONUS) during summertime via numerical simulations. The urban water capacity is calculated as the average irrigation depth per degree of urban temperature reduction; the values are 4.52 ± 0.77 mm day⁻¹ °C⁻¹ and 7.27 ± 1.27 mm day⁻¹ °C⁻¹ (mean ± standard deviation) for surface and near-surface air cooling, respectively, over the CONUS. The robustness of urban water capacity is further exemplified in an extreme heat wave event, during which the warming anomaly is partially offset by the additional cooling from urban irrigation. Estimates of water capacity provide a quantitative metric for evaluating the efficacy of irrigation in urban planning under current heat stress and future warming.     

Solving fuzzy capacitated location routing problem using hybrid variable neighborhood search and evolutionary local search

A fuzzy capacitated location routing problem (FCLRP) is solved by using a heuristic method that combines variable neighborhood search (VNS) and evolutionary local search (ELS). Demands of the customer and travel times between customers and depots are considered as fuzzy and deterministic variables, respectively in FCLRP. Heterogeneous and homogeneous fleet sizes are performed together to reach the least multi-objective cost in a case study. The multi-objective cost consists of transportation cost, additional cost, vehicle waiting cost and delay cost. A fuzzy chance constrained programming model is added by using credibility theory. The proposed method reaches the solution by performing four stages. In the first stage, initial solutions are obtained by using a greedy heuristic method, and then VNS heuristic, which consists of seven different neighborhood structures, is performed to improve the solution quality in the second stage. In the third stage, a perturbation procedure is applied to the improved solution using ELS algorithm, and then VNS heuristic is applied again in the last stage. The combination of VNS and ELS is called VNSxELS algorithm and applied to a case study, which has fifty-seven customers and five distributing points, effectively in a reasonable time.     

Combined use of waste glass powder and cullet in architectural mortar

The use of 100% waste glass cullet (WGC) as fine aggregates in architectural cement-based mortar had been proven to be feasible in previous works. This paper reports a further study on investigating the influence of using waste glass powder (WGP) as a supplementary cementitious material on the properties of glass-based architectural cement mortars. The experimental results showed a good linear relationship between the particle size of WGP and the flow values of the fresh mortar, revealing that the particle size of WGP played an important role in controlling the workability. For the hydration of white cement, the inclusion of WGP not only affected the second exothermic peak of hydration but also changed the third peak. In particular, the result indicated that the use of finer WGP had an advantage in increasing the flexural strength of the cement mortar when compared with the corresponding compressive strength, which was attributed to the morphological and pozzolanic effect of WGP. In addition, the very fine WGP could act as micro-fibers and micro-aggregates in filling the microstructure of the mortar. At 90 days of curing, the mortar prepared with finer WGP showed a distinct improvement in strength due to the improved interfacial transition zone and the pore-size refinement.     

Fatigue-induced in-situ strength deterioration of micro-polyvinyl alcohol (PVA) fiber in cement matrix

For soft fiber and brittle matrix system such as polymeric fiber-reinforced cementitious composites, the fiber strength deterioration dominates the performance of composites subject to fatigue loading. The fatigue-induced in-situ fiber strength deterioration in brittle matrix, however, has rarely been studied. In this paper, fatigue-induced in-situ strength deterioration of micro-polyvinyl alcohol (PVA) fiber in cement matrix was experimentally investigated. The effects of fiber embedment, fiber inclination, and fiber surface treatment on the in-situ strength of micro-PVA fibers are reported. The results show that fiber embedment into cement matrix not only reduces the in-situ strength of fiber but also changes the fatigue stress-cycle (S-N) curve and failure mode of fiber. Fiber inclination further decreases the in-situ strength of embedded fiber due to local stress concentration of bent fibers. Oil-treatment on fiber surface can effectively delay fatigue-induced in-situ strength deterioration of micro-PVA fiber.