沥青混合料集料接触特性切片图像评价方法

为了评价沥青混合料集料的接触特性,提出了一种较能准确有效评价沥青混合料集料接触特性的新方法。研究中建立了表征集料接触特性的量化指标——接触对,以AC20型沥青混合料为例,对车辙板试件的72幅切片图像进行了分析,通过对所有切片的集料接触数据进行统计分析,得到了集料接触对数目的分布规律。在此基础上,还进行了集料接触特性的影响因素分析,并提出了影响集料接触特性的3个主要因子：4．75mm以上集料含量C〉4.75、细度指数FI和离析指数SI。结果表明这3个因子与集料接触对之间有较好的关联度,集料接触特性变化受3个因子共同作用的影响,单因素或双因素都不能正确反映样本的接触对数目。     

混沌神经网络综合法在边坡位移预测中的应用

根据混沌理论具有分析非线性动态系统的混沌特性和人工神经网络具有考虑多因素影响的特点,本文提出了混沌神经网络综合预测模型.该方法首先利用非线性科学和理论分析滑坡位移时间序列的动态特性,然后将重构相空间计算的最小嵌入维数作为输入神经元的数目引入到人工神经网络预测模型中.分析算例预测结果表明,混沌神经网络综合预测模型计算精度较高.     

管片衬砌配合碎石可压缩层与锚杆的支护型式研究

针对深埋地层中修建盾构隧道,特别是围岩表现蠕变特性,研究一种管片衬砌配合压缩层与锚杆的联合支护技术.采用有限差分与离散元的耦合计算方法,进行了管片衬砌壁后注浆、管片衬砌壁后填充碎石可压缩层、管片衬砌配合碎石可压缩层和高强预应力锚杆的支护效果对比研究.从围岩塑性区发展、沉降随时间变化、管片衬砌弯矩和轴力分析了联合支护效果.从碎石可压缩层的压缩变形路径、锚固围岩的位移矢量等角度揭示了联合支护的细观作用机理.研究结果表明:仅采取管片衬砌配合碎石可压缩层的让压支护手段无法维持管片衬砌的长期稳定;联合支护结构型式既可以提高围岩自身承载能力,也能够有效吸收围岩的蠕变变形.联合支护的作用机理由两部分构成:碎石可压缩层的让压作用与高强预应力锚杆加固围岩作用.其中,碎石可压缩层的让压机理主要通过颗粒间相互嵌挤和错动移位作用调减管片衬砌壁后接触力;高强预应力锚杆的加固机理是由锚杆形成的锚固区控制了蠕变变形的过大发展.研究结果对未来盾构工法修建深部高地应力、强蠕变隧道的支护型式设计具有一定参考价值.     

浅析拱桥的一般加固技术

文章利用拱桥加固理论,分析说明了拱桥加固的依据,并由此举例说明一些常见拱桥的一般加固技术,提出加固拱桥时可根据现状而采取合适的加固方法。     

Depercolation threshold of porosity in model cement: approach by morphological evolution during hydration

The depercolation threshold of porosity is an important parameter to assess the permeability of cement-based materials. The depercolation threshold is usually defined as the porosity whereby the volume fraction of connected pores in the cement paste decreases to zero. In this paper, the depercolation threshold is defined and determined with respect to the morphological development of pore space during hydration. The morphology of solid phase and pore structure is studied on model cement simulated by the SPACE system, using stereological theory. The influences of particle size distribution and water to cement ratio (w/c) on the depercolation threshold of porosity are discussed. It is found that particle size distribution of cement has significant influence on the depercolation threshold of porosity. The depercolation threshold is higher for finer cement system. However, the influence of w/c on the depercolation threshold of porosity is negligible. For a model cement of moderate fineness, depercolation is not possible at a relatively high w/c (say, 0.6), because the porosity of cement paste remains above the depercolation threshold even at complete hydration.     

Investigation on the cracking behavior of concrete cover induced by corner located rebar corrosion

Non-uniform corrosion of reinforcement causes concrete cracking in chloride contaminated RC structures. Due to the special boundary conditions, the concrete cover with corner located rebar is often subjected to the attack of chloride ions in a marine environment from two directions, and thus the corresponding non-uniform corrosion distribution should be different from the one for side-located rebar. The aim of the work is to explore the effect of corner located rebar corrosion on the cracking of cover concrete. For corner located rebar, an improved non-uniform corrosion distribution model was established based on the analysis results of two-dimensional chloride diffusion in concrete. Considering the heterogeneities of concrete, a meso-scale mechanical model and method for the study on the failure behavior of concrete cover was built. In the analysis model and method, the non-uniform radial displacement distribution was adopted to simulate the corrosion expansion behavior of the rebar. The cracking of concrete cover with corner located rebar was simulated and studied. The present approach was verified by the available experimental observations. The influences of concrete heterogeneity, corrosion distribution types, rebar diameter and concrete cover thickness on the failure patterns of concrete cover and the expansive pressure were investigated. The simulation results indicate that the developed approach can well describe the cracking behavior of cover concrete and the corrosion-expansion behavior of steel rebar.     

植筋参数对UHPC-石材界面抗剪性能的影响研究

在桥梁结构的加固工程中，植筋是最常用的界面连接增强措施。为明晰UHPC加固石砌结构植筋界面的力学性能，通过30个UHPC-石材组合试件推出试验，研究不同界面植筋率、植筋深度和植筋间距对UHPC-石材界面抗剪性能的影响，分析不同植筋参数下组合试件的裂缝开展及分布情况和荷载 滑移曲线特征。结果表明：①未植筋UHPC-石材组合试件的破坏模式均为脆性破坏，而植筋试件则主要表现为以界面滑移和石材局部劈裂为主要特征的延性破坏模式，石材表面裂缝形态均呈现“八”字形的斜向裂缝；②当植筋率小于0.29%时，组合试件的界面抗剪强度和延性随植筋率的增大而逐级提升，植筋率为0.09%、0.19%和0.29%的抗剪强度分别是未植筋组合试件的1.54倍、1.98倍和2.66倍；当植筋率继续增大时，UHPC-石材界面强度却出现降低的趋势；③植筋深度和植筋间距对组合试件界面抗剪强度影响较小，而对UHPC-石材界面延性影响较大；④基于试验结果和有限元分析，建议UHPC加固石砌体结构中带肋钢筋的最大锚固长度为10d(d为钢筋公称直径)，植筋间距取50～100mm较为合理；考虑安全和经济等因素，建议UHPC与石材的界面最优植筋率为0.29%，而UHPC加固层厚度以50mm为宜。     

高层建筑连梁设计及处理方法

分析了高层建筑连梁的工作和破坏机理,提出了连梁的概念设计,并对实际工程提出了处理连梁超筋的方法以及连梁的配筋计算方法及配筋要求.     

基于ABAQUS的抗滑桩三维有限元分析

在现行计算方法中,通常采用不平衡推力法设计抗滑桩,尽管国内外岩土工程技术人员做了不少的工作使该方法得到了很大的发展,但仍有许多不完善的地方。基于ABAQUS有限元软件,结合有限元强度折减法对抗滑桩加固的边坡进行三维数值分析。通过桩-土相互作用的机理分析和稳定分析,揭示了埋入式抗滑桩相对于全长桩而言更具经济性和合理性,同时就桩间距对加固效果的影响进行了分析。研究表明,采用有限元强度折减法可以考虑桩-土之间共同作用,得到不同桩长和桩间距条件下治理工程的稳定性,计算结果更合理。     

Analysis of the influence of operational strategies in plant performance using SimulCET,simulation software for parabolic trough power plants

This paper analyzes the influence of operational strategies on the performance of parabolic trough (PT) solar power plants with the aid of SimulCET a computer program for the simulation of the energy behavior of PT plants developed by the National Renewable Energy Centre of Spain (CENER).SimulCET uses state of the art techniques to simulate solar energy absorption and others energy conversion processes that take place in a PT plant. The simulation of these energy conversion processes is based on both empirical and physically derived expressions and produces highly accurate electricity generation estimates. The holistic approach adopted in SimulCET to carry out the analysis of PT solar power plants makes this program a very effective tool in optimizing the operation of such plants. Furthermore, SimulCET’s capabilities for simulating the operation of gas boilers make it possible to compare different operational strategies scenarios, and enable the testing of new hybrid plants concepts.To assess the validity of the results generated by SimulCET, these results were compared with current experimental data. The comparison showed good agreement among daily averaged estimates and the corresponding measured energy values. The comparison of SimulCET daily estimations against twelve reference days of measured data showed a mean deviation of ?3.14% in terms of daily total gross electricity production.This paper focuses on the simulation and analysis of different PT plant operational strategies to explore the consequences and side effects of the way the fossil fuel is used, which have been seldom analyzed up to now, although they may significantly affect the long term performance of the plant.Four different operational strategies were compared. In all of them, the yearly amount of gas used was the maximum allowed for a solar PT power plant to be considered eligible to receive the benefits of the Spanish feed-in tariff legislation. Differences in gross electric energy output larger than 10% and differences in yearly gas consumption of up to 15% were obtained during the simulation of the PT power plant running for a year under each one of the four operational strategies considered. The results of these simulations make clear the need for further techno-economic optimization of the operational strategies defined, since revenues, costs and other operational factors depend not only on the amount of gas used, but also on when this gas is burned.