Testing of composite steel top-and-seat-and-web angle joints at ambient and elevated temperatures: Part 2 — Elevated-temperature tests

An experimental programme of eight elevated-temperature tests on composite steel top-and-seat-and-web (TSW) angle joints was carried out to investigate the behaviour of this form of joints under fire conditions. It is found that the inherent strength and stiffness of composite joints can significantly improve the structural behaviour of steel framed structures under fire conditions. However, experimental works on composite steel TSW angle joints under fire conditions have not been published yet. To develop a versatile model to predict the joint moment-rotation characteristics, the authors have developed a component-based mechanical model for this form of joints. The objectives of this study are to ascertain the moment-rotation characteristic for this form of joint at elevated temperatures and to validate the authors’ mechanical model. The effects of some parameters on the overall joint behaviour, such as elevated temperatures, longitudinal shear strength of RC slabs, steel beam depth and bolt behaviour were observed and investigated. The mechanical model predictions are compared with the test results and showed good agreement.     

Impact of magnetic field on the enhancement of performance of thermal solar collectors using nanofluids

A numerical mathematical model has been developed to predict the thermal behaviour of thermal solar collectors using nanofluids under different magnetic fields. The model is based upon energy conservation equations for nanofluids flow, heat transfer for different nanofluids and magnetic field. The thermal behaviour of the solar collectors during charging phase has been studied, predicted numerically and analysed using different nanofluid materials and magnetic fields. Comparisons were made against literature data for validation purposes of the predictive model. The model fairly predicted heat absorbed and solar panel efficiency under different nanofluids conditions, magnetic fields and compared well with existing data on the subject.     

Behaviour of Granular Materials in Relation to Their Fabric Dependencies

The roles of dilatancy and fabric on the behaviour of granular materials are both numerically and experimentally explored for the study of material instability and failure. This investigation has two basic ingredients: namely a stress dilatancy model with microstructural information embedded through a fabric tensor, and an experimental rendition of force transmission and structure in an assembly of 2-D photoelastic disks. In order to highlight material instability, model simulations of sand behaviour are carried out in axi-symmetric stress conditions along proportional strain paths with varying degrees of controlled dilation (or compaction) including isochoric deformations as a special case. It is shown that sand, otherwise stable under isochoric (undrained) conditions, can actually succumb to an instability or a liquefaction behaviour under other loading paths. This suggests that flow type of failures in soils may not be necessarily restricted to the classic saturated loose sand case in undrained conditions, but could manifest itself under other conditions as well.     

A Water-Resources and Water-Quality Management Plan for the City of Tallinn, Estonia

The increasingly common occurrence of eutrophic conditions in shallow lakes and reservoirs, including the presence of potentially toxic blue-green algae, has given rise to water-quality concerns throughout the world. The need to undertake active catchment management to improve raw-water quality is a key component of the new EC Water Framework Directive.
This paper describes the investigations which were undertaken in Tallinn (the capital of Estonia, the northernmost of the Baltic States) to develop an integrated approach to catchment and lake management, in order to improve the quality of the surface-water resource which provides 90% of the total drinking-water needs of the city. Several tools, including 'geographical information systems'and spreadsheet-based financial and water-resources models, were developed to investigate the source of the water-quality problems. Practical solutions comprising an innovative and cost-effective catchment-management approach to overcome the seasonal raw-water quality issues, whilst also reducing treatment plant operating costs, are described. Some of the recommendations have been tested by Tallinn Water following the investigations, and some improvements in raw and treated water quality have been attained.     

Component modelling of flexible end-plate connections in fire

This paper describes a component-based model for simulating the behaviour of flexible end-plate connections between beams and columns in steel framed structures in fire conditions. In this method, a simple steel connection was split into a number of active components for which mechanical properties are represented by non-linear springs. The behaviour of a steel connection is then determined by assembling the individual behaviour for each active component into a spring model. The component model presented in this paper is capable of predicting the behaviour of steel connections under varied loading conditions. It is also capable of predicting the tying resistance and critical components of failure for steel connections in fire. Compared with experimental test data, a good correlation with the simplified model has been achieved and this method, combined with finite element modelling, may be used to examine the performance of simple steel connections in fire conditions.     

Finite element modelling of steel fin plate connections in fire

Recent structural collapses caused by fire have focused attention on research concerning fire safety in building design. Steel connections are an important component of any structural steel building, as they provide links between the principal structural members. The evaluation of the performance of steel connections at elevated temperatures has been a topic of several research programmes in the last few years. Determining the behaviour, available strength and stiffness of moment connections in fire conditions has been a dominant theme in these research works; however very little information on the behaviour of simple shear connections in fire conditions has been disseminated. Fin plate shear connections are easy to fabricate and install; as a result, they have gained popularity with fabricators because of their economy. In this research, the robustness of simple fin plate beam-to-column connections is being investigated under catenary tension from highly deflected beams in fire. A highly detailed three-dimensional (3-D) finite element (FE) model has been created using the ABAQUS software. This is a complex model accounting for material and geometric non-linearity, large deformation and contact behaviour. Contact is critical to model the shear behaviour of the joint, and contact elements have been used both at the bolt–hole interface and also at the surface between the web of the beam and the fin plate, taking into consideration friction between the surfaces. The connection model has been analysed through the elastic and plastic ranges up to failure. Bolt shear and bending, and plate and web bearing have been observed as failure modes. A comparison between available experimental data at ambient and elevated temperatures and other analytical results shows that the model has a high level of accuracy. When the connection model was extended to include an attached beam, it was found that it eventually experiences large tensile force when exposed to fire.     

Whole-building behaviour of bonded post-tensioned concrete floor plates exposed to fire

This paper discusses the whole-building behaviour of post-tensioned concrete floor plates under fire conditions. Based on the results of eight fire tests on one-way spanning bonded post-tensioned concrete slab strips, recently conducted by the authors, a nonlinear finite element model was developed to model an entire typical concrete floor plate. The considered floor plate was post-tensioned using bonded tendons and was supported on traditional reinforced concrete columns. The overall objective of the study was to provide an understanding of the structural response and modes of failure of these floor plates under fire conditions. The mechanical and thermal material nonlinearities of the floor’s components, consisting of the concrete, grout, prestressing tendon, and the anchorages, as well as the reinforced concrete columns, have been considered in the model. The interface between the tendon and grout was also considered, allowing the bond behaviour to be modelled and the tendon to retain its profile shape during the deformation of the floor. The model has been validated against published finite element results on a floor plate under normal temperature conditions. The temperature distribution throughout the floor slab and supporting columns, together with the developed displacement and stress due to heating, and the overall fire resistance of the floor were predicted by the model. Furthermore, the variables that influence the structural behaviour comprising different natural fires, applied static load during fire, use of non-tensioned reinforcement, as well the difference between unbraced and braced frames were investigated in a parametric study. The study has shown that the failure mode of the floor under fire conditions is mainly due to tensile splitting along the tendons that extended to the top surface, while at ambient conditions the mode of failure is punching shear. The restraint provided by shear walls in the considered braced frame and the use of non-tensioned flexural reinforcement affected the vertical displacement behaviour under fire conditions, but did not affect the fire resistance due to the predicted tensile splitting failure mode. From the studies presented it is concluded that the design fire resistance of the floor specified in Eurocode BSEN1992-1-2 is acceptable, while that in the UK code BS8110 is unconservative and should be modified.     

Variations between Continuous and Spot-Sampling Techniques in Monitoring a Change in River-Water Quality

Following significant expenditure by Thames Water Utilities Limited at Crawley and Horley sewage-treatment works, the quality of the final effluents being discharged to the River Mole improved considerably.
The automatic quality-monitoring station operated by the former National Rivers Authority downstream from both discharges showed a distinct improvement in water quality which was not recorded to the same degree by the NRA's formal sampling programme. The quality of data provided by the formal sampling programme can be misleading, and such data should be used cautiously in water-quality assessment and modelling.
The reasons why spot-sample data were unreliable were investigated, and the possibility and benefits of developing a systematically biased continuous monitoring strategy to produce water-quality data under comparative environmental conditions are explored.     

非线性差异沉降分析

本文提出一种单向压-剪模型来解释北京某幢房屋在兴建过程中所观测到的非线性差异沉降现象,这种模型是建立在波速与动、静三轴试验中所得到的剪切模量与应变之间的双对数折线关系上的。为了能够在类似情况下进行设计,已经通过载荷试验与建筑物的实测沉降倒算出半经验参数。     

Density currents in the Chicago River: characterization, effects on water quality, and potential sources

Bidirectional flows in a river system can occur under stratified flow conditions and in addition to creating significant errors in discharge estimates, the upstream propagating currents are capable of transporting contaminants and affecting water quality. Detailed field observations of bidirectional flows were made in the Chicago River in Chicago, Illinois in the winter of 2005-06. Using multiple acoustic Doppler current profilers simultaneously with a water-quality profiler, the formation of upstream propagating density currents within the Chicago River both as an underflow and an overflow was observed on three occasions. Density differences driving the flow primarily arise from salinity differences between intersecting branches of the Chicago River, whereas water temperature is secondary in the creation of these currents. Deicing salts appear to be the primary source of salinity in the North Branch of the Chicago River, entering the waterway through direct runoff and effluent from a wastewater-treatment plant in a large metropolitan area primarily served by combined sewers. Water-quality assessments of the Chicago River may underestimate (or overestimate) the impairment of the river because standard water-quality monitoring practices do not account for density-driven underflows (or overflows). Chloride concentrations near the riverbed can significantly exceed concentrations at the river surface during underflows indicating that full-depth parameter profiles are necessary for accurate water-quality assessments in urban environments where application of deicing salt is common.     

A new steel structural system of a suspension pedestrian bridge

The paper deals with a new structural system of pedestrian steel bridge consisting of carrying suspension members made of stiff (in bending) rolled or welded sections and a flexible cylindrical deck. Structural behaviour of such a suspension member subjected to unsymmetrical live loading has been discussed on a basis of kinematic conditions. Ways of stabilization of kinematic displacements have been under consideration. Effects of bending stiffness and geometrical non-linearity of the suspension structure are taken into account. Analytical expressions for the analysis of the flexible cylindrical deck have been proposed. In an alternative concrete deck, a layered model has been applied for the stress and strain analysis.     

Design and simulation of type II fuzzy logic controller for capturing maximum wind energy

The main purpose of this paper is to capture the maximum output power of the wind turbine under various environmental conditions. To achieve this goal, the wind turbine model has been studied and analysed under both low-wind and high-wind circumstances and due to the noisy behaviour of the wind, type II fuzzy logic controller is used for this purpose. Simulations with MATLAB show that type II fuzzy logic controller has better performance than type I.     

Numerical simulation of concrete filled steel tube columns against BLAST loads

Concrete filled steel tubes (CFST) have been widely used in constructing high-rise buildings, arch bridges and factories for the past few decades. In this research, numerical studies were carried out to investigate the flexural behaviour of CFST columns under both static and dynamic loads. The numerical models were calibrated and validated against a number of experimental data where the proposed models showed very good agreement with the test results. The results indicated that CFST columns showed good resistance against flexural loads under both static and dynamic loading conditions and therefore it has the potential to be widely used in these areas where potential blast attacks or frequent earthquakes are expected. The verified numerical model can also be extended to predict performances of concrete-infilled steel tubes under different loading conditions.     

复杂裂隙岩体水–力耦合模型及溶质运移模拟

 在刚块弹簧法中引入非线性的裂隙本构关系,同时考虑裂隙法向的非线性应力变形关系、切向的剪切滑动以及剪胀效应,使得该方法可以较为真实地模拟裂隙开度在复杂应力作用下的变化。结合离散裂隙网络方法,建立采用隐式求解的复杂裂隙岩体的水–力耦合模型。该模型显式考虑裂隙存在,能很好地模拟裂隙网络在应力和渗流作用下的演化特征。在水力耦合达到平衡状态后,进行溶质运移分析,采用粒子追踪法模拟溶质在裂隙网络中随渗流的运移过程。根据所提出的模型编制相应程序,对DECOVALEX项目中的典型算例进行分析,研究不同应力条件对渗流以及溶质运移结果的影响以及不同应力条件下水力耦合的控制性机制。研究发现,低应力比条件和高应力比条件下对水力耦合作用起控制作用的分别是法向应力变形关系和剪胀效应。通过对比分析,验证模型的合理性。在此基础上,讨论高水头条件下考虑水力耦合效应的必要性。     

河谷场地地震波传播解析模型及放大效应

从形态上看,自然界存在平坦、凸起和凹陷3种常见的地形及场地条件,而河谷场地是一种常见的凹陷地形,且在河谷场地修建了大量工程(如土石坝、桥梁等)。实际震害调查表明地形及场地条件对地震灾害影响很大。针对河谷场地地震波传播解析模型及放大效应,全面总结了笔者及其课题组长期以来的研究成果。主要包括以下4个方面:(1)提出了近源地形与场地效应的概念,用线源柱面SH波模拟入射地震波,平面波是其远场入射的特例,构造了线源柱面SH波自由场,定义了近源激励下的放大因子,实现了入射波波前弯曲及其地形放大效应,为其它地形和场地引起的近源放大效应研究开启了新的可能。(2)构建了非对称V形河谷地震波传播解析模型,包括亥姆霍兹运动方程、河谷表面自由边界条件及虚拟辅助边界应力与位移连续条件,提出了区域分解与区域匹配分两步走的策略,首先将整个区域分解成3个符合极坐标系的子区域,在子区域中对运动方程进行求解获得相应的波场(含有未知系数),然后将各个子区域的波场在边界进行匹配,利用边界条件求解未知系数,从而获得整个区域的波场解答以及柱面SH波的二维散射规律,揭示了非对称V形河谷的差异放大效应,这将对建在非对称V形河谷上的长大跨度工程有着不可忽视的影响。(3)U形河谷在地球表面是普遍存在的,由于缺少实际地震记录和理论研究,U形河谷的地形放大效应仍然未知。构建了U形河谷解析模型,本质上也就是亥姆霍兹方程的边值问题,并得到了这个问题的波函数级数解,发现了U形河谷谷底对地震波的异常放大现象,改变了学术界以往认为凹陷地形底部地震动一定会衰减的不全面认识,并被用来解释中世纪暖期美国亚利桑那州的大量山体落石与滑坡现象。(4)河谷常有沉积物(覆盖层),覆盖层将进一步加剧地震放大效应。构建了线源柱面SH波半圆形沉积谷解析模型,并给出了其解析级数解,发现覆盖层对地震波有明显的放大效应,且覆盖层阻尼比较小时剧烈放大,这将加剧工程结构的破坏。最后,考虑河谷场地地震放大效应进行河谷两侧边坡地震稳定性分析,及土石坝地震反应分析与坝坡地震稳定性分析,认为河谷场地地震放大效应对边坡工程与土石坝工程抗震分析有着重要的影响。     

Influential fluid–structure interaction modelling parameters on the response of bridges vulnerable to coastal storms

Analysis of coastal bridges under hurricane-induced wave and surge loads is essential for safety and performance assessment of water crossing bridge inventories. A reliable numerical model that can be employed to study the behaviour of bridges in hurricane events is beneficial because it reduces the cost and effort required for experimental models. Furthermore, it is important to identify modelling parameters that have a significant effect on the simulated response in order to guide uncertainty treatment for future bridge reliability studies. To address these needs, a high fidelity numerical model for simulation of coastal bridges is utilised that takes into account the fluid–structure interaction and includes contact surfaces that permit deck shifting and unseating during surge and wave passage. After validation of the model with experimental test data, it is implemented to examine the response of a typical water crossing bridge in the Houston area, revealing the values of wave and surge loads and also the potential of deck unseating under extreme wave and surge conditions. A sensitivity study is conducted to determine the uncertain structural modelling parameters that significantly affect the bridge response when subjected to surge and wave. Concrete strength and density, coefficient of friction between super- and substructure and soil shear strength are found to influence the bridge response and should be considered in probabilistic analyses and reliability assessments of coastal bridges.     

网架结构极限承载能力的追踪分析

本文比较系统地研究了网架结构极限承载能力的追踪分析方法,并编制了相应的电算分析程序。运用这种方法可以确定各种形式网架的极限承载能力,并且还可以描绘出网架在杆件逐一破坏以后的工作形态。本文运用所述方法对正放四角锥网架进行了算例分析,同时还通过网架摸型试验进行了定性比较。     

Effluent Control: The Hong Kong Approach

Water pollution has existed for many years in Hong Kong, but the Government's strategy for pollution control is now beginning to take effect. The strategy includes planning, legislation, and the provision of sewage-disposal systems. In the past, the main thrust has been against traditional pollutants measured by BOD, suspended solids and various nutrients, but as these are brought under control, attention will be given to the need to control toxic pollutants. The existing policy and legislation does not deal with toxic pollutants well, and past work on toxic substances in Hong Kong has concentrated on individual chemicals. The Environmental Protection Department is now seeking to (a) develop ecotoxicological expertise to identify toxicant pathways in the environment, (b) introduce water-quality objectives for toxic substances which it can monitor effectively, and (c) improve standards for effluent control.     

Parameter optimization of the QUAL2K model for a multiple-reach river using an influence coefficient algorithm

An influence coefficient algorithm and a genetic algorithm (GA) were introduced to develop an automatic calibration model for QUAL2K, the latest version of the QUAL2E river and stream water-quality model. The influence coefficient algorithm was used for the parameter optimization in unsteady state, open channel flow. The GA, used in solving the optimization problem, is very simple and comprehensible yet still applicable to any complicated mathematical problem, where it can find the global-optimum solution quickly and effectively. The previously established model QUAL2Kw was used for the automatic calibration of the QUAL2K. The parameter-optimization method using the influence coefficient and genetic algorithm (POMIG) developed in this study and QUAL2Kw were each applied to the Gangneung Namdaecheon River, which has multiple reaches, and the results of the two models were compared. In the modeling, the river reach was divided into two parts based on considerations of the water quality and hydraulic characteristics. The calibration results by POMIG showed a good correspondence between the calculated and observed values for most of water-quality variables. In the application of POMIG and QUAL2Kw, relatively large errors were generated between the observed and predicted values in the case of the dissolved oxygen (DO) and chlorophyll-a (Chl-a) in the lowest part of the river; therefore, two weighting factors (1 and 5) were applied for DO and Chl-a in the lower river. The sums of the errors for DO and Chl-a with a weighting factor of 5 were slightly lower compared with the application of a factor of 1. However, with a weighting factor of 5 the sums of errors for other water-quality variables were slightly increased in comparison to the case with a factor of 1. Generally, the results of the POMIG were slightly better than those of the QUAL2Kw.     

Effects of organic solutes properties on the volatilization processes from water solutions

Effects of organic solutes properties, including Henry's law constant (H), molecular weight (M), molar volume at normal boiling point (Vb), and solubility (S), on the usefulness of rate estimation by reference to a reference substance (i.e., reference substance concept) and on the evaporation rate were investigated by measuring the volatilization rate constant of organic solutes under different environmental conditions, including mixing and surfactants. It was found that if benzene was used as a reference substance, the ratio of the solute rate to that of benzene (F) becomes insensitive to water mixing, whether the solute possessed high or low Henry's law constant. In the presence of surfactants, however, the F value changes sharply as the solute solubility decreases. For benzene, toluene, ethylbenzene, and xylenes (BTEX), the F values are essentially constant irrespective of the presence of other chemicals (including organic compounds, surfactants, and salinity) and of the variation in temperature. On the other hand, the volatilization rates are closely related to molecular weight (solubility) in the existence of mixing (surfactants). Three different approaches, i.e., mass-transport theory, modified Knudsen equation, and reaction rate concept, were used to evaluate the dependence of solute volatilization rates on solute properties. It was concluded that the interaction between solute properties and environmental parameters might play a key role in the volatilization process of organic solutes under different environmental conditions.