Finite element analysis of the plastic deformation in tandem process of simple shear extrusion and twist extrusion

Recently, simple shear extrusion (SSE) and twist extrusion (TE) are introduced to fabricate ultrafine grained bulk rod metallic materials. The SSE and TE processes generate significant deformation inhomogeneity, with higher and lower strains in the center, respectively, which easily causes mechanical instability of the materials. In this study, to overcome this deformation inhomogeneity problem in SSE and TE, a tandem process of SSE and TE (TST) is suggested. The finite element method is applied for plastic deformation behavior during the TST process. The results demonstrate that the TST process can produce relatively homogeneously deformed materials. In particular, the effects of back pressure and processing order on the plastic deformation behaviors in the TST process are systematically analyzed.     

Role of cement content on the properties of self-flowing Al2O3 refractory castables

In this work, Al₂O₃ self-flowing castables (SFCs) were produced based on various cement contents. The SFCs were sintered at 1273 K, 1573 K and 1773 K and the exhibited properties were experimentally determined. Among the properties determined in this work are bulk density (BD), apparent porosity (AP), water absorption (WA), cold crushing strength (CCS), modulus of rupture (MOR) and fracture toughness (K_IC). It is found that additions of 5% cement lead to SFCs with maximum MOR and K_IC values after firing at 1773 K. Firing at 1573 K leads to a reduction in both, MOR and K_IC. In SFC containing 3% cement, maximum K_IC values of 3.53 MPa m^1/2 were achieved after firing at 1573 K. In the low cement SFCs (1 wt%) after firing at 1773 K the exhibited K_IC values were below those obtained in either the SFC-3 or SFC-5, but they were significantly high (3.43 MPa m^1/2).     

数码建筑——新的空间概念

介绍了数码建筑的定义,论述了数码建筑的发展历史——计算机从三维绘图手段发展到可以辅助于方案构思、推敲的智能化设计,产生了新的设计媒介如VR技术、网络运用等。20世纪末,在数字化技术的冲击下,计算机技术作为一种新方法、新手段、和新工具,使传统的建筑设计方法及建筑观念受到了前所未有的挑战,产生了新的空间概念,解放了建筑的形体与空间、建构了新的数字化类型,并能进行参数化智能设计。最后,分析了今后一个时期数码建筑的发展前景。     

Shear capacity of masonry walls externally strengthened by a cement-based composite material: An experimental campaign

Composite materials are getting more and more common for strengthening existing members and structures; fiber-reinforced polymers (FRP) are widely used, while carbon-fiber-reinforced cement matrix (CFRCM) materials have been more recently proposed especially for strengthening masonry members. In the present paper, the results of an experimental campaign carried out on tuff-masonry walls strengthened in shear by a cement-based composite are reported and commented. The reinforced masonry walls failed after loss of adhesion between the strengthening layer and the masonry substrate. Comparisons between the experimental results and some analytical formulations available in the scientific literature for determining shear resistance of strengthened masonry walls are finally proposed. Huge variability can be observed by applying those alternative formulations which are not able to reproduce the premature nature of the observed failure mode. Consequently, the present study is a thorough experimental report which can be useful for developing and validating more refined theoretical models for describing the ultimate behaviour of masonry walls externally strengthened by FRP.     

Geo-Referencing of Video Flow From Small Low-Cost Civilian UAV

This paper presents a method of geo-referencing the video data acquired by a small low-cost UAV, which is specifically designed as an economical, moderately functional, small airborne platform intended to meet the requirement for fast-response to time-critical events in many small private sectors or government agencies for the small areas of interest. The developed mathematical model for geo-locating video data can simultaneously solve the video camera's interior orientation parameter (IOP) (including lens distortion), and the exterior orientation parameters (EOPs) of each video frame. With the experimental data collected by the UAV at the established control field located in Picayune, Mississippi, the results reveal that the boresight matrix, describing the relationship between attitude sensor and video camera, in a low-cost UAV system will not be able to remain a constant. This result is inconsistent with the calibrated results from the previous airborne mapping system because the boresight matrix was usually assumed to be a constant over an entire mission in a traditional airborne mapping system. Thus, this paper suggests that the exterior orientation parameters of each video frame in a small low-cost UAV should be estimated individually. With the developed method, each video is geo-orthorectified and then mosaicked together to produce a 2-D planimetric mapping. The accuracy of the 2-D planimetric map can achieve 1-2 pixels, i.e., 1-2 m, when comparing with the 43 check points measured by differential GPS (DGPS) survey.     

松花江水环境质量评价模糊可变集合工程方法

为对松花江哈尔滨江段的水质进行科学准确的评价,首先证明该江段水环境质量评价物元分析法关联函数基本公式的错误,然后在工程可变模糊集理论的基础上,提出以相对差异函数表示的模糊可变集合工程方法,对该江段水环境质量进行评价.通过实例,将结果与物元分析法进行比较,验证模型与方法的合理性.同时分析物元分析法对松花江哈尔滨江段的水质评价成果的逻辑错误,指出物元分析法不能用于水环境质量评价等领域.     

Blind bolted moment connection to sides of hollow section columns

This paper presents the results of an experimental programme for a new blind bolted connection to unfilled hollow section (HS) columns under static loading. In this connection, channels with side plates connect beam flanges to the side face of HS columns. This is a simple alternative connection to typical face connections, i.e. the extended endplate connection or the T-stub connection (with T-stubs connecting the top and bottom flanges of the beam to the face of the column). The channel side plate connection was found to be much stiffer than a typical face connection and has the potential to achieve a rigid connection status for braced frames according to the EC3 classifications. Comparison of the test results and three dimensional finite element (FE) modelling indicates that the FE analyses can be used to predict the connection behaviour with sufficient accuracy. The preliminary investigation for the channel side plate connection shows promising results and forms the basis for the development of other blind bolted side connections for applications in the low rise construction industry.     

Reliability-based evaluation of design and performance of steel self-centering moment frames

Recently developed steel self-centering moment-resisting frames (SC-MRFs) have been analytically and experimentally validated as having the potential to eliminate structural damage under a design basis earthquake and restore their original vertical position following a major earthquake. Using Monte Carlo simulation, we subjected three nonlinear models of prototype SC-MRFs to thousands of synthetic ground motions, and recorded peak demand responses such as story drift and beam-column relative rotation. We used this data to examine the sensitivity of SC-MRF behavior to structural properties and geometry, seeking to generate recommendations to improve the existing design procedure. A reliability-based methodology was used to assess the likelihood of reaching the limit state of post-tensioned strand yielding. This study proposes modifications to the existing design procedure and illustrates a reliability-based methodology for developing improved seismic design recommendations.     

大跨网壳结构非一致激励竖向地震响应分析

考虑大跨结构的地震响应随地震动空间变化的特性,研究非一致激励下大跨结构的运动方程,运用虚拟激励法的原理对非一致激励下的大跨网壳结构的地震响应进行分析,在ANSYS软件中将非一致激励考虑为静力计算和谐响应计算。通过对平面直径为80 m的单层球面网壳结构的算例分析,得到了竖向地震作用下网壳结构的地震响应变化规律,并与一致激励下地震影响进行对比分析。结果表明,考虑了行波效应的非一致激励,网壳节点位移和杆件内力分布较一致激励复杂,充分说明大跨结构的非一致激励竖向地震响应分析是十分必要的。     

Morphological and separation performance study of polysulfone/titanium dioxide (PSF/TiO2) ultrafiltration membranes for humic acid removal

In this study, polysulfone (PSF) hollow fiber membranes with enhanced performance for humic acid removal were prepared from a dope solution containing PSF/DMAc/PVP/TiO₂. The main reason for adding titanium oxide during dope solution preparation was to enhance the antifouling properties of membranes prepared. In the spinning process, air gap distance was varied in order to produce different properties of the hollow fiber membranes. Characterizations were conducted to determine membrane properties such as pure water flux, molecular weight cut off (MWCO), humic acid (HA) rejection and resistance to fouling tendency. The results indicated that the pure water flux and MWCO of membranes increased with an increase in air gap distance while HA retention decreased significantly with increasing air gap. Due to this, it is found that the PSF/TiO₂ membrane spun at zero air gap was the best amongst the membranes produced and demonstrated > 90% HA rejection. Analytical results from FESEM and AFM also provided supporting evidence to the experimental results obtained. Based on the anti-fouling performance investigation, it was found that membranes with the addition of TiO₂ were excellent in mitigating fouling particularly in reducing the fouling resistances due to concentration polarization, cake layer formation and absorption.