变截面门式刚架的平面内弹性稳定计算

对楔形变截面轴压杆在各种边界条件(包括弹性约束)下的稳定性进行了详细研究,提出了简单而精度较高的计算式;对门架有侧移失稳时变截面梁对柱子提供的转动约束进行了分析,提出了高精度的近似计算式,可直接用于计算变截面门式刚架的计算长度或临界荷载.     

Development of a consistent buckling design procedure for tapered columns

EC3–EN 1993-1-1 provides several methodologies for the stability verification of members and frames. When dealing with the verification of non-uniform members in general, with tapered cross-section, irregular distribution of restraints, non-linear axis, castellated, etc., the code mentions the possibility of carrying out a verification based on 2nd order theory; however, several difficulties are noted when doing so, in particular when the benefit of plasticity should be taken into consideration.Other than this, there are yet no guidelines on how to apply standardized, easily reproducible rules as those contained in Section 6.3.1 to 6.3.3 of the code to non-uniform members. As a result, practical safety verifications for these members are often carried out using conservative assumptions, not accounting for the advantages non-uniform members provide. In this paper, firstly, available approaches for the stability verification of non-uniform members are discussed. An Ayrton–Perry formulation is then derived for the case of non-uniform columns. Finally, and followed by a numerical parametric study covering a range of slenderness, cross-sections and fabrication process, a design proposal is made for the relevant case of in-plane flexural buckling of linearly tapered columns subject to constant axial force. The proposal is consistent with current rules for uniform columns provided in EC3-1-1, i.e., clause 6.3.1.     

CFD study to determine the optimal configuration of aerators in a full-scale waste stabilization pond

Aerated lagoons (ALs) are important variants of the pond wastewater treatment technology that have not received much attention in the literature. The hydraulic behaviour of ALs and especially the Facultative aerated lagoons (FALs) is very complex since the aeration in these systems is designed for oxygen transfer but not necessarily to create complete mixing. In this work, the energy expenditure of the aerators was studied by means of a scenario analysis. 3D CFD models (one phase and multiphase) of a 3 ha FAL in a waste stabilization pond system in Cuenca (Ecuador) were built for different configurations of aerators. The thrust produced by the aerators was modelled by an external momentum source applied as velocity vectors into the pond fluid. The predictions of a single phase model were in satisfactory agreement with experimental results. Subsequently, a scenario analysis assessing several aeration schemes with different numbers of aerators in operation were tested with respect to velocity profiles and residence time distribution (RTD) curves. This analysis showed that the aeration scheme with all 10 aerators switched on produces a similar hydraulic behaviour compared to using only 6 or 8 aerators. The current operational schemes comprise of switching off some aerators during the peak hours of the day and operating all 10 aerators during night. This current practice could be economically replaced by continuously operating 4 or 6 aerators without significantly affecting the overall mixing. Furthermore, a continuous mixing regime minimises the sediment oxygen demand enhancing the oxygen levels in the pond.     

Control of activated sludge filamentous bulking—I. Effect of the hydraulic regime or degree of mixing in an aeration tank

Laboratory experiments were conducted on four activated sludge systems with various flow patterns. The systems were characterized by dispersion numbers which are a numerical expression of the degree of mixing. Perfect mixing has a dispersion number of infinity. The dispersion numbers in the four systems were ∞, 1·06, 0·17 and 0·033. All systems were operated at the same detention period of 8 h and approximately at the same sludge loadings. A mixture of starch and peptone was used as the substrate. The mixed cultures developed in the systems mentioned possessed average SVI values of 517, 300, 91 and 51 ml g⁻¹ respectively. The high SVI values were caused by a high content of the filamentous microorganisms, which consisted mainly of Leucothrix and Sphaerotilus, in the developed mixed cultures. It is concluded that the complete mixing systems tend to lead to excessive growth of the filamentous microorganisms. Aeration systems with a low degree of the axial mixing, i.e. with low dispersion numbers and higher concentration gradients of the substrate along the systems, lead to the growth of non-filamentous and suppress the growth of filamentous microorganisms. It is possible to control the growth of filamentous microorganisms in the mixed cultures by maintaining the concentration gradient of the substrate along the aeration system. The concentration gradient of the substrate depends on the degree of mixing in the aeration system.     

Mathematical models of biological waste treatment processes for the design of aeration tanks

The paper discusses the application of formal mathematical models of biological treatment in designing aeration tanks. It deals with a complete mixing aeration tank, an ideal plug-flow tank, and a many-step aeration tank.Selection is substantiated of the simplest non-linear Monod's model for biochemical oxidation. A new model is advanced taking into consideration, among others the effect of pollutant sorption by activated sludge. The model permits calculating the optimal volumes of the aeration tank and stabilization tank in the contact stabilization system.     

Elastic flexural buckling of non-uniform members: Closed-form expression and equivalent load approach

Experienced structural engineers have an intuitive understanding of the buckling behavior of uniform members subjected to compressive loads. The Euler critical load and the concept of buckling length are extensively used in this context. Unfortunately, the extension of this intuitive approach to cases with non-uniform load or non-uniform members is not straightforward. Based on an extensive numerical parametric study, the paper first presents a closed-form expression for the buckling load of constant cross-section members with non-uniform axial loading. Consequently, an equivalent load approach for non-uniform members subjected to non-uniform axial load distribution is proposed and validated. The combination of both procedures has the power of transforming the general complex case of a non-uniform member under non-uniform load into an equivalent simple case of a uniform member subjected to uniform load. The new methodology is simple and direct, and produces more than acceptable approximate results.     

On the design of Web-tapered,unequal-flanged structural steel columns

A study directed towards the development of an efficient and economical design for stability of structural steel members is described. A finite element method is presented for determining the lateral-torsional buckling load for linearly tapered I-section members with unequal flange areas. Solutions are obtained for different flange-area ratios and tapering ratios. Such solutions are used to develop an interaction relationship for tapered unequal-flanged steel structural colums subjected to both axial and bending stresses.The formulation is intended to provide a more rational approach to the design of tapered steel columns—a step towards an optimum stability design for structural steel members.     

变截面门式钢刚架结构体系平面内稳定研究

本文论述了变截面梁单元平面内稳定分析方法,比较了不同类型梁单元（等截面梁单元、普通位移模式变截面梁单元、积分位移模式变截面梁单元）对变截面刚架平面内稳定分析的差异。利用上述有限元法,给出了对称刚架变截面柱计算长度系数的实用计算公式,并分析了横梁轴力对刚架柱稳定的影响。     

Axial response and material efficiency of tapered helical piles

Different techniques have been proposed to increase the bearing capacity of open-ended piles.Welding helices to the shaft and tapering the pile shaft could be used simultaneously to enhance the static and dynamic behaviors of these piles.This paper subjects the bearing capacity,stiffness,frictional behavior,and material efficiency of the tapered helical piles to scrutiny.Tapered helical piles are introduced herein as an alternative option to improve the material efficiency of hollow piles.Based on the Taguchi method,a series of experiments was designed and conducted.The axial responses of tapered helical piles are also investigated using finite element analyses.The results derived from loadedisplacement curves and strain gages are used to characterize the axial compression responses of tapered helical piles.The effects of tapered angle,helices diameter and helices distance are examined using dimensionless parameters,and the degree of contribution of these factors is calculated on each of the enumerated variables individually.Experimental results show that the shaft friction resistance of tapered helical piles increases continuously with the pile head settlement.Furthermore,the effect of tapered wall on the shaft friction resistance is more tangible at low stress levels.The results showed that the relative material efficiency factor of the optimum pile could be 2.5 times that of unoptimized pile with a similar quantity of material.     

Computer simulation and energy absorption of tapered thin-walled rectangular tubes

Tapered thin-walled tubes have been considered desirable energy absorbers under axial loading due to their relatively stable crush load and deformation response compared with straight tubes. This paper compares the energy absorption response of straight and tapered thin-walled rectangular tubes under quasi-static axial loading, for variations in their wall thickness, taper angle and number of tapered sides. Overall the study highlights the advantages of using tapered tubes as energy absorbers. In particular, the peak load required to crush the tubes decreases with the introduction of a taper, and as the taper angle increases. This is desirable for minimising the impact loads transmitted to the protected structure. The practical outcome of the study is design information for the use of tapered thin-walled rectangular tubes as energy absorbers in impact loading applications. Analysis has been undertaken using a finite element model, validated using existing theoretical and numerical models.     

Comfort and airflow evaluation in spaces equipped with mixing ventilation and cold radiant floor

In this work the comfort and airflow were evaluated for spaces equipped with mixing ventilation and cold radiant floor. In this study the coupling of an integral multi-nodal human thermal comfort model with a computational fluid dynamics model is developed. The coupling incorporates the predicted mean vote (PMV) index, for the heat exchange between the body and the environment, with the ventilation effectiveness to obtain the air distribution index (ADI) for the occupied spaces with non-uniform environments. The integral multi-nodal human thermal comfort model predicts the external skin and clothing surfaces temperatures and the thermal comfort level, while the computational fluid dynamics model evaluates the airflow around the occupants. The air distribution index, that was developed in the last years for uniform environments, has been extended and implemented for non-uniform thermal environments. The airflow inside a virtual chamber equipped with two occupants seated in a classroom desk, is promoted by a mixing ventilation system with supply air of 28 °C and by a cold radiant floor with a surface temperature of 19 °C. The mechanical mixing ventilation system uses a supply and an exhaust diffusers located above the head level on adjacent walls.     

在悬浮填料床工艺中对硝化实施自动控制的研究

在分析悬浮填料床硝化反应机理的基础上,为悬浮填料床中试装置设计、配备了自动控制系统,通过在线检测溶解氧和氨氮浓度来实现对硝化反应过程的实时控制。中试结果表明,控制系统运行稳定、反应灵活,处理出水中的氨氮浓度保持稳定,并达到了控制要求。此外,该自动控制系统还优化了曝气过程,使曝气量减少了约20％,降低了运行成本。     

Comparison of the conventional cage rotor and jet-aero-mix systems in oxidation ditch operations

The Jet-Aero-Mix system, designed on the basis of Fanning's for Darcy's Equation, was tested at the USDA Fur Animal Research Farm at Cornell. Oxygenation studies with tap water showed fairly good comparison with that of a conventional cage-rotor system, and the performance with mink waste resulted in high degrees of treatment.From a general maintenance standpoint, the Jet-Aero-Mix (JAM) system does not have the problems of bearings and belt slippage associated with a cage rotor. One potential problem still exists and would be resolved only by testing. The problem is the possibility of plugging the nozzles by strawlike materials such as large feathers and straw bedding from cattle.From an economic standpoint the operating cost of the JAM system (in terms of energy consumption) is comparable to that of the cage rotor. The capital expenditure offers substantial savings. Because of the simplicity of this device, the JAM system also offers the flexibility of being able to be installed in phases to meet the desired quality of treatment, especially in large systems where fairly large initial capital outlay may be required.Based on the oxygenation studies, economic analysis and field testing with mink waste, the JAM system appears a reasonable alternative to a cage rotor for aeration and mixing in an oxidation ditch process. The system appears to be especially useful for small systems and should receive consideration in situations where aerobic treatment is contemplated.     

楔形变截面压杆的弹塑性稳定

研究了楔形变截面压杆平面内弹塑性弯曲失稳。提出了以大头截面为计算截面的压杆稳定性计算公式 ,给出了配套的变截面压杆计算长度系数公式和表格。对变截面压杆与等效的等截面压杆的弹塑性工作性能进行了比较 ,发现后者总是在悬臂柱的固定端截面开始出现塑性 ,而变截面压杆的塑性区在离固定端一定高度的地方先出现 ,这一差别导致弹塑性失稳的变截面压杆比等效的等截面压杆的承载力要高     

Design of Sewage-Treatment Plants in Brisbane, Australia

Brisbane City Council provides sewage-treatment facilities for a population of 800 000, together with industrial effluents having an organic loading equivalent to a further 600 000 people. Three projects are described to illustrate some of the different designs and operating parameters used in Brisbane, where the sewage temperatures range from 18°C to 29°C and stormwater is collected separately. The first project is a 400 000 population equivalent augmentation to a conventional activated-sludge plant located at Luggage Point. The two other plants have to comply, inter alia , with an effluent standard of 10 mg/l for total nitrogen. This requirement, together with site constraints and an economic evaluation of alternatives, resulted in the selection of the extended-aeration process incorporating anoxic zones and separate mixing and aeration. These contemporary designs are specific to Brisbane conditions, and are intended to facilitate reliable operation as well as being cost effective.     

采用楔形构件框架的塑性分析

对一些平面内楔形截面构件进行二阶简单塑性铰法分析,并利用有限元法及重叠原理推导I形钢楔形截面构件的刚度矩阵。为预测构件内部可能形成塑性铰的位置,以一个同时受弯矩及轴力作用的梁柱单元,仿真各种不同边界条件的楔形截面构件。若预测构件内会形成塑性铰的位置则要增设一个节点,将一个构件分割为两个单元,以获得最合理的荷载-挠度曲线。楔形截面构件的刚度矩阵应特别注意方向性的问题。若没有考虑到任一构件中可能形成塑性铰的位置,就不能准确地预测梁柱真实的极限承载能力。若仅用一个单元代表一个楔形截面构件就会高估极限承载能力。该方法可合理地应用于具有楔形截面构件框架的塑性分析。     

AmOn一体化污水生物处理装置的开发

AmOn一体化反应器将传统生物处理工艺的反应、沉淀和污泥回流集中于一个反应器中完成,并以自主开发的新型射流扩散式曝气代替了传统的鼓风曝气、表面曝气等形式,反应器的容积负荷大,水力停留时间短,节省了基建投资与运行费用,降低了操作管理强度,增加了系统运行的可靠性。通过自控系统的调节,可根据不同进水水质和出水要求,沿反应进程自动调节曝气量和搅拌程度,根据要求实现脱氮和除磷,具有广阔的应用前景。     

不同控制模式下SBR的短程硝化反硝化

以实际豆制品生产废水为处理对象，研究了传统固定时间控制和实时控制两种模式下SBR反应器的短程硝化反硝化效果。结果显示，实时控制下的硝化速率和反硝化速率分别为按固定时间控制时的1．40倍和1．86倍，硝化和反硝化时间则比传统运行方式分别缩短了60min和25min。因此，可采用DRP和pH值实时控制SBR法的短程硝化反硝化过程，它不仅可以合理分配曝气和搅拌时间，而且还能提高硝化速率并缩短反应时间，达到了降低运行成本的目的。     

楔形变截面压弯构件的平面内弹塑性稳定

通过数值积分法研究了楔形变截面压弯构件平面内弹塑性弯曲失稳问题 ,然后以大头截面为计算截面 ,建立了变截面压弯构件的轴向荷载和端弯矩之间的相关关系。     

楔形变截面钢管格构柱极限承载力研究

楔形变截面钢管格构柱在技术和经济上具有明显的优势,在实际工程中应用广泛.理论分析表明,考虑楔率、约束和剪切变形影响后,可将楔形变截面钢管格构柱极限承载力的计算转化为等效的等截面钢管格构柱极限承载力的计算.采用有限元计算分析楔形变截面钢管格构柱楔率影响系数、稳定系数和轴力-弯矩相关曲线,提出楔形变截面钢管格构柱极限承载力...