Diseño automático de tableros óptimos de puentes de carretera de vigas artesa prefabricadas mediante algoritmos meméticos híbridos

This paper deals with the minimum cost automatic design of precast bridge decks made of U-beams and an upper slab. It uses a hybrid memetic algorithm that combines the population search of solutions by genetic algorithms and a search by variable neighborhood. This algorithm is applied to a bridge made of two isostatic U-beams of 20-40 m of span and a width of 12 m. This example has 40 discrete variables. The evaluation module takes into account the service and ultimate limit states usually considered for these structures, i.e. flexure, shear, torsion, cracking, deflections, etc. The use of the memetic algorithm requires its previous calibration. Each of the heuristics is run 12 times, obtaining information about the minimum and average values, as well as the scatter. The parametric study showed a good correlation for the cost, the number of strands and the steel and concrete quantities with the span length. Savings have been found between 8 and 50% compared to other structures really executed. The presented procedure allows the practical application to the real design and its adaptation to the precast process.     

Sol-Gel processing of silica nanoparticles and their applications

Recently, silica nanoparticles (SNPs) have drawn widespread attention due to their applications in many emerging areas because of their tailorable morphology. During the last decade, remarkable efforts have been made on the investigations for novel processing methodologies to prepare SNPs, resulting in better control of the size, shape, porosity and significant improvements in the physio-chemical properties. A number of techniques available for preparing SNPs namely, flame spray pyrolysis, chemical vapour deposition, micro-emulsion, ball milling, sol-gel etc. have resulted, a number of publications. Among these, preparation by sol-gel has been the focus of research as the synthesis is straightforward, scalable and controllable. Therefore, this review focuses on the recent progress in the field of synthesis of SNPs exhibiting ordered mesoporous structure, their distribution pattern, morphological attributes and applications. The mesoporous silica nanoparticles (MSNPs) with good dispersion, varying morphology, narrow size distribution and homogeneous porous structure have been successfully prepared using organic and inorganic templates. The soft template assisted synthesis using surfactants for obtaining desirable shapes, pores, morphology and mechanisms proposed has been reviewed. Apart from single template, double and mixed surfactants, electrolytes, polymers etc. as templates have also been intensively discussed. The influence of reaction conditions such as temperature, pH, concentration of reagents, drying techniques, solvents, precursor, aging time etc. have also been deliberated. These MSNPs are suitable for a variety of applications viz., in the drug delivery systems, high performance liquid chromatography (HPLC), biosensors, cosmetics as well as construction materials. The applications of these SNPs have also been briefly summarized.     

MULTI-SCALE NUMERICAL MODEL FOR SIMULATING CONCRETE MATERIAL BASED ON FRACTAL THEORY

A new multi-scale numerical model is presented using the fractal theory and adopting FEM to simulate the failure of concrete.The relation between the fractal box dimension in large scale and the damage to concrete in small scale is deduced.And the evolutionary process of elastic modulus and strength in small scale is given.Consequently,the multi-scale numerical model is proposed to describe the constitutive relation of concrete between small scale and large scale.A two-dimensional static analysis of a concrete block is performed by using this model and the calculation result is discussed.The propagation of cracks of the concrete block is also studied.     

Ionic effects on the behavior of thermoresponsive PEO–PNIPAAm block copolymers

The temperature‐dependent aggregation and recovery of the copolymer poly(ethylene oxide)₂₂‐b‐poly(N‐isopropylacrylamide)₂₉ with a C₁₂ end‐cap in aqueous solutions of salts and acids are investigated. Salt solutions affected the critical aggregation temperature of the copolymer in a manner predictable according to the Hofmeister series, with the kosmotropic adipic ion lowering the critical aggregation temperature and the chaotropic iodide raising it. Also, both salts and acids increased the size of copolymer aggregates formed with heating, due to the electrostatic shielding of aggregated structures provided by the electrolytes. Additionally, the presence of ionic additives caused a thermohysteretic increase in the size of copolymer aggregates with temperature cycling. The transitions of polymer structure with increasing temperature were surprisingly sharp with the C₁₂ end‐cap present, and particularly broad in samples in which the end cap had been cleaved. This observation suggested that the hydrophobic end group was responsible for imparting some degree of order to the polymer at low temperatures, which allowed for rapid reconfiguration with increasing temperature. Finally, in addition to the transitions expected from the least critical solution temperature behavior of the polymer blocks, we have observed an unexpected additional transition which we attribute to the contraction of the poly(ethylene oxide) chains of the copolymer aggregates at higher temperatures. This work illustrates the importance of considering the environment and composition of thermoresponsive block copolymers in certain applications, particularly in solutions with even modest electrolyte concentrations (1–10 mM), as it can have a profound effect on transition temperatures and morphology. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 507–516     

Análise da confiabilidade de estruturas de concreto armado com uma metodologia para inclusão de efeitos estocásticos de propriedades dos materiais

In this paper, special emphasis is given to the inclusion of uncertainties in the evaluation of structural behaviour aiming at a better representation of the system characteristics and the quantification of the importance of these uncertainties in the project. It deals with the structural reliability analysis problem accounting the effect of spatial variability of material properties. To this end it is proposed a finite element model to represent the behaviour of reinforced concrete for short and long-term loads, which includes the main features observed in this material. It was developed a model for the generation of multidimensional non-Gaussian stochastic fields for the material properties that is independent of the finite element mesh. First, an example of a two-dimensional non-Gaussian stochastic field generation in a square steel plate is presented. Latter, the reliability analysis is performed to a limit state function based on prescribed values of mid-span displacements on a simply-supported reinforced beam. Finally, the influence of long-term effects on the reliability of a reinforced concrete beam is studied considering the effect of steel reinforcement corrosion.     

A (3,6)-connected metal-organic framework consisting of chair-like {Fe6} clusters and BTC linkers

A 2-D framework composed of a chair-like {Fe₆} cluster and BTC linkers, [Fe₆(BTC)₂(HCOO)₆(DMF)₆] (1, BTC?=?1,3,5-benzenetricarboxylate), has been synthesized under solvothermal conditions and characterized by elemental analysis, infrared spectroscopy, thermal gravimetric analysis, and single-crystal X-ray diffraction analysis. The {Fe₆} cluster contains six iron ions and six formate ligands, with each formate coordinating with three iron ions to construct the hexa-nuclear iron wheel. The {Fe₆} wheels are further connected via BTC ligands resulting in the first example of a 2-D framework based on {Fe₆} clusters and BTC linkers. A magnetic study indicates that intramolecular antiferromagnetic interactions exist in the hexa-nuclear iron cluster.     

支化侧链偶氮无规共聚物中空和类囊泡聚集体研究

研究了支化侧链型偶氮无规共聚物(PMAPB6P-AA)在THF/H2O混合溶液中的自组装行为.研究发现,通过缓慢增加体系的水含量,可以制备出具有中空结构的非球形聚集体.调节聚合物的初始浓度,可以得到不同粒径的聚集体.聚集体中偶氮生色团的光致异构化速率与异构化程度随聚合物初始浓度的增大而减小.在此基础上,采用更加缓慢的增加水含量的方法,使聚合物分子进行充分的疏水聚集与H-聚集,制备出类囊泡状聚集体.在紫外光照射条件下,观察到类囊泡聚集体发生了光致解聚集.     

混凝土搅拌车搅拌筒磨损数值分析

混凝土运输过程中搅拌筒的磨损一直是一种常见潜在危害,磨损严重时会导致叶片失效,对搅拌的质量和出料匀质性产生影响。通过实验获取搅拌筒内部的磨损费时费力,因此有必要采取一种数值分析方法对搅拌筒的磨损进行预测并提出改进。本文采用摩擦磨损实验的方法来标定颗粒与搅拌筒之间的Archard磨损常数,采用JKR接触模型表征混凝土的流动性能,采用离散元方法(DEM)对搅拌筒筒体及叶片磨损进行预测分析。通过法向接触能量与切向接触能量的对比,证明搅拌筒中的磨损主要为伴有冲击作用的磨粒磨损,搅拌车搅拌筒中搅拌叶片顶部的磨损较为严重。针对磨损比较严重的叶片顶部进行改进,采用T型耐磨结构等改进叶片结构,叶片顶部结构改进后搅拌筒使用寿命能得到明显提升。     

NORMAL EXPANSION THEORY FOR PENETRATION OF PROJECTILE AGAINST CONCRETE TARGET

Based on the equations which describe the dynamic behavior of material under high-velocity and high-pressure shock, corresponding equations at shock front whose surface is general space curve surface were established. For concrete material, a normal expansion theory was proposed by which some deceleration about time history of the projectile can be analytically given. This normal expansion theory is not only suitable for spherical and cylindrical-nose projectile, but also suitable for other general nose projectile, for example conical nose or ogive-nose. And it is not only suitable for perpendicular shock but also for oblique shock.     

优化设计理论在抗滑桩工程中的应用

采用数学规划方法中的直接最优化方法———复合形法,对已知荷载或内力的抗滑桩,以结构成本为目标函数进行满足工程使用要求的有约束最优化设计,编制了相应的程序,并用VisualBasic6 .0开发了应用程序界面,将优化以后所得结果与使用传统设计方法结果比较,有较大降低结构成本的效果。