Fatigue life estimates for a slender orthotropic steel deck

Fatigue cracks in several types of welded joints and geometrical details have been reported to occur in a large number of slender orthotropic decks of existing steel bridges in many parts of the world. Some of these cracks are initiated very early, a few years after the bridge is brought into service. That is why it is said that fatigue life estimation for the welded joints of orthotropic decks is not an easy designing task. This is so because the random variation of local stresses is sensitive to many factors, in particular to those involved in the dynamic interaction between the vehicle’s tyres, the pavement and the steel structure.This paper presents and discusses the main causes for the observed cracks and the outcome of the ultimate fatigue life estimates for typical welded and geometrical details of a slender orthotropic deck with trapezoidal cross-section longitudinal ribs. This is the deck of an existing long-span steel bridge, which has been strengthened by adding a reinforced concrete layer fixed with shear studs to the steel deck top plate. This was done to avoid continued and extensive repair work and to enhance the fatigue life expectancy of the steel deck structure. The fatigue life estimation is done with the aid of refined numerical modelling and in situ experimental strain measurements and also by taking into account all the built-in structural alterations, changes in volume of traffic and in vehicles loading which have occurred during this bridge’s 32 years of service life.     

钢桥面铺装层结构设计指标近似计算新方法

在行车荷载作用下,钢桥面铺装层的受力与变形较一般公路沥青路面或机场道面复杂得多,也是钢桥面铺装层结构设计的一个重要因素。从使用条件、工程实践、试验研究和受力特点等角度出发,提出钢桥面铺装层结构设计指标:一是铺装层拉应力,二是铺装层表面局部挠跨比。采用有限元方法建立在车载作用下钢桥面铺装层的力学响应计算模型。在结构设计参数常用取值范围内,对不设纵隔板和设置纵隔板两种常用钢桥面铺装层的结构设计指标关键影响因素进行正交敏感性分析。同时,通过逐步线性回归方法拟合出钢桥面铺装层结构设计指标的近似计算公式。得到的近似计算公式的精度检验和工程实例分析结果表明,近似计算公式精度很好,满足工程设计和理论研究的需要。研究结果可为钢桥面铺装层结构设计提供近似计算的新方法。     

正交异性钢桥面铺装层疲劳寿命的断裂力学分析

计算和分析正交异性钢桥面铺装层表面裂缝应力强度因子,在此基础上应用Paris扩展公式预测铺装层疲劳寿命。将奇异单元布置在铺装层表面裂缝前沿,建立正交异性钢桥面系三维断裂力学有限元模型,计算铺装层表面裂缝的应力强度因子;分析裂缝应力强度因子随轴载作用位置的变化规律,确定了带裂缝铺装层轴载作用的最不利荷位;以最不利荷位作为轴载作用的标准荷位,计算应力强度因子随裂缝扩展深度的变化,并数值拟合得到了应力强度因子与裂缝深度的关系式;将应力强度因子的深度关系式代入Paris公式,积分得到铺装层的疲劳寿命。计算结果表明,基于钢桥面铺装层带裂缝工作的事实,应用断裂力学方法预测钢桥面铺装层疲劳寿命是可行的。     

Fatigue analysis of a pre-fabricated orthotropic steel deck for light-weight vehicles

An orthotropic steel deck designed for carrying light-weight vehicles was investigated to assess its fatigue life. Fracture mechanics analysis was performed with consideration of pre-existing flaws at the fatigue-sensitive region. Three-level models were used to accurately evaluate the stress-intensity factors at the rib-to-diaphragm connection. The crack growth was simulated by numerical integration of the Paris formula. In order to assess the severity of pre-existing flaws at the welded joint of the rib-to-diaphragm connection, the fatigue life of the deck was investigated with different sizes of initial crack. This approach provides a rational quality assessment method for the orthotropic steel deck.     

Statistical analysis of online strain response and its application in fatigue assessment of a long-span steel bridge

This paper covers reliability assessment of the fatigue life of a bridge-deck section based on the statistical analysis of the strain–time histories measured by the structural health monitoring system permanently installed on the long-span steel bridge under study. Through statistical analysis of online strain responses in the frequency domain using multiple linear regression, a representative block of daily cycles of strain history is obtained. It is further assumed that all cycles of online strain response during bridge service are repetitions of the representative block. The rain-flow counting method is then used to determine the stress spectrum of the representative block of daily cycles. The primary assessment of fatigue life at a given value of failure probability is undertaken for the sample component in a bridge-deck section by using the classification of details for welded bridge components and the associated statistical fatigue model provided by the British Standard BS5400. In order to evaluate bridge fatigue at any value of failure probability, a modified probability model is proposed based on BS5400. The fatigue life of the considered component in the bridge-deck section is then evaluated for some other values of probability of failure which are not included in BS5400 by use of the modified probability model. The analytical results show that the modified model is practical for reliable evaluation of the service life of existing bridges under random traffic loading.     

Risk-based maintenance strategy for deteriorating bridges using a hybrid computational intelligence technique: a case study

The current bridge inspection and maintenance protocol that is used in most countries focuses primarily on the visible aspects of bridge fitness and underestimates the invisible aspects, such as resistance to scouring and earthquake hazards. To help transportation authorities to better consider both aspects, the present study developed a new computational intelligence system, the so-called risk-based evaluation model for bridge life-cycle maintenance strategy (REMBMS). This model considers the three main risk factors of component deterioration, scouring and earthquakes in order to minimise the expected life-cycle cost of bridge maintenance. Monte Carlo simulation is used to estimate the probability of bridge maintenance. The evolutionary support vector machine inference model (ESIM) was applied to estimate the risk-related maintenance cost using historical data from the Taiwan Bridge Management System (TBMS) database. The time-influenced expected costs were obtained by multiplying each maintenance probability with its associated cost. Finally, the symbiotic organisms search (SOS) algorithm is used to identify the bridge maintenance schedule that optimises the life-cycle maintenance cost. The present study provides to bridge management authorities an effective approach for determining the optimal timing and budget for maintaining transportation bridges.     

Efficient 1D model for blind assessment of existing bridges: simulation of a full-scale loading test and comparison with higher order continuum models

Assessing the structural performance of existing concrete bridges is nowadays a major task. Nonlinear finite element (FE) analysis can quantify their capacity, evaluate strengthening interventions and prevent premature dismantle. However, this technique, mainly performed with 2D/3D FE, is seldom used at true scale due to the great complexity and computational costs involved. In this paper, the loading test of a strengthened concrete bridge in Sweden (Örnsköldsvik) is simulated using a 1D model. The bridge failed in combination of shear–bending–torsion triggered by fibre-reinforced polymer bond failure. Consecutive levels of refinement of the 1D model are presented and available results from higher order models are compared. The study of the structural response involved comparing displacements, strains, cracking patterns and failure mechanisms. The demonstrated robustness and efficiency of the proposed model makes it adequate for blind assessments of existing bridges.     

Social effects of urban restructuring: a case study in Amsterdam and Utrecht,the Netherlands

In the Netherlands, urban restructuring has been a major policy since 1997. Its principal aim is to improve neighbourhoods by demolishing or upgrading low-rent social dwellings and building more expensive rental or owner occupied units. A fundamental idea underlying this policy is to break up the physical and social monotony of urban areas and to achieve a mixed population in terms of income. The consequence of this new mix should be that people interact better and fully enjoy all kinds of facilities in the restructured area. This paper addresses the question of whether this new policy has indeed had these effects. The focus point is the role of the neighbourhood, featuring changes for traditional inhabitants while accommodating the newcomers. Do they use the area? Are their social contacts made there? Or can the restructured area be seen as a dormitory, where the residents have no contact with other people in the immediate environment? The paper is based on a fieldwork study undertaken in the cities of Amsterdam and Utrecht. Lessons for future policies of urban restructuring are formulated.     

Optimization model for the selection of materials using a LEED-based green building rating system in Colombia

Buildings have a significant and continuously increasing impact on the environment because they are responsible for a large portion of carbon emissions and use a considerable number of resources and energy. The green building movement emerged to mitigate these effects and to improve the building construction process. This paradigm shift should bring significant environmental, economic, financial, and social benefits. However, to realize such benefits, efforts are required not only in the selection of appropriate technologies but also in the choice of proper materials. Selecting inappropriate materials can be expensive, but more importantly, it may preclude the achievement of the desired environmental goals. In order to help decision-makers with the selection of the right materials, this study proposes a mixed integer optimization model that incorporates design and budget constraints while maximizing the number of credits reached under the Leadership in Energy and Environmental Design (LEED) rating system. To illustrate this model, this paper presents a case study of a building in Colombia in which a modified version of LEED is proposed.     

An ensemble wavelet bootstrap machine learning approach to water demand forecasting: a case study in the city of Calgary,Canada

This paper explores a hybrid wavelet, bootstrap and neural network (WBNN) modeling approach for daily (1, 3 and 5 day) urban water demand forecasting in situations with limited data availability. This method was tested using 3 years of daily water demand and meteorological data for the city of Calgary, Alberta, Canada. The performance of the WBNN method was compared to that of three other methods: traditional neural networks (NN), wavelet NNs (WNN), and bootstrap-based NN (BNN) models. While the hybrid WBNN and WNN models equally provided 1-day lead-time forecasts of greater accuracy than those obtained with other methods, for longer lead-time (3- or 5-day) forecasts the WBNN model alone outperformed the other models. The confidence bands generated using the WBNN model displayed the uncertainty associated with the forecasts.     

A GIS-based multi-criteria decision making approach to forest conservation planning at a landscape scale: a case study in the Kinabalu Area, Sabah, Malaysia

This paper presents a geographic information system (GIS)-based multi-criteria decision making approach for forest conservation planning at a landscape scale. This approach enables decision makers to evaluate the relative priorities of conserving forest areas based on a set of preferences, criteria and indicators for the area. Compromise programming techniques are used to integrate the forest conservation priority maps of decision groups where a separation distance is calculated. A clustering analysis was applied to identify potential conservation areas as the basis of delineating potential new protected areas. The study was conducted in the Kinabalu area, Sabah, Malaysia where two polygons neighboring the Kinabalu Park were delineated. A group of 11 polygons totaling 2050 ha has also been detected in the western part of Kinabalu Park. The study recommends the inclusion of a forest polygon (359 ha) neighboring Kinabalu Park and another (4361 ha) to the west of the park as new protected areas. A green corridor linking the potential new protected areas and Kinabalu Park should also be constructed to facilitate animal movement and interaction. This study reveals that riparian vegetation is an important aspect to forest conservation and the legislation to protect riparian zones should be strengthened.     

A conceptual model for project management of exploration and production in the oil and gas industry: The case of a Brazilian company

The objective of this study was to obtain a better understanding of factors that influence Exploration and Production (E&P) project management success and corporate financial performance. The study follows structural equation modeling (SEM) methodology to achieve greater understanding of the intricate network of relationships between variables involved in E&P project management. A comprehensive theoretical framework was needed to formulate the conceptual basis of research. Observation of the real world and practical experiences were also important. To that end, we conducted a case study in a large Brazilian oil company. Field research was essential because of the lack of similar studies in the oil and gas sector. The model developed is a theoretical construct known as a structural and measurement model (set of latent variables, observed variables and hypotheses, depicted in a path diagram). This model contributes significantly to the company because it is a global representation of the main factors for improving E&P project management. However, the findings should be interpreted with caution because adjustment and validation of the theoretical model were not performed.     

Structural and spatial characteristics of personal actor networks: The case of industries for the elderly in Korea*

This paper studies the relationship between geography and dynamics of network in the evolutionary process of a newly emerging industry. Core actors are well connected with one another through policy‐related project networks, as well as temporary clusters, such as trade fairs, conventions, and seminars. Although geographical proximity is not significantly related to the occurrence of co‐operation between individuals, position of an actor in the network is significantly related to his/her geographical reach. Despite the importance of other industrial network in the Capital Region, actors in non‐Capital Regions played important positions in the networks and assumed key roles in institutional‐building processes. Resumen. Este artículo estudia la relación entre la geografía y las dinámicas de red en el proceso evolutivo de una nueva industria emergente. Los actores esenciales están bien conectados entre sí mediante redes de proyectos relacionados con políticas, así como por conglomerados temporales como ferias de exposiciones, convenciones y seminarios. Aunque no hay una relación significativa entre la proximidad geográfica y la aparición de una cooperación entre individuos, la posición de un actor en la red está relacionada significativamente con su alcance geográfico. A pesar de la importancia de otras redes industriales en la región capital, los actores del resto de regiones ocuparon posiciones importantes en las redes y asumieron papeles clave en procesos de desarrollo institucional.      

An examination of a partial least squares-based dynamic water quota model for urban industries: a case study of the Wuhan City hospital industry

The establishment of water quotas has an important practical significance in promoting urban standards for water utilization. Currently, industrial water quotas are highly arbitrary, inadequately restrictive, and impractical. This paper considers the example of the Wuhan City hospital industry. Common factors of industrial water use and major differences in water utilization structures were considered, and the principles of partial least squares (PLS) analysis were applied to establish an evaluation model for water utilization levels in this industry. Residuals were used to introduce the corresponding adjustment coefficients, and a dynamic model of water quotas in the hospital industry was constructed. Experimental results revealed that for this dynamic model, 80% of the samples examined exhibited errors of |20%| or less; thus, the dynamic approach was superior to traditional approaches for quota determination, where only 40% of samples had errors of |20%| or less.     

Eutrophication of Tamar Lakes (1975–2003): a case study of land-use impacts, potential solutions and fundamental issues for the Water Framework Directive

Tamar Lakes is comprised of two reservoirs, which are located in South West England and in the headwaters of River Tamar at approximately 135 m above ordnance datum. Upper Tamar Lake (UTL) is a direct feed source reservoir of potable water in North Cornwall. Immediately following completion in 1975, UTL was subject to intense blue‐green algal blooms that continue to the present. These blooms create operational problems for water treatment, especially in hot‐dry years. Lower Tamar Lake (LTL) was constructed as a water supply reservoir in 1819 and became obsolete following UTL coming on‐line. Detailed water quality investigations over a period of some 28 years have confirmed the source of nutrient enrichment that fuels the algal blooms to be agriculturally derived, corresponding with a substantial increase in livestock farming. Associated poor land management practices, such as extensive field drainage and inappropriate slurry disposal to land, are linked with substantial elevations in organic contaminants such as ammonia, biochemical oxygen demand (BOD) and suspended solids (SS) during rainfall events. Evidence demonstrates that both reservoirs act as primary treatment lagoons, substantially reducing the worst of these pollutants and providing significant environmental gain. The implications of the Common Agricultural Policy (CAP), the Water Framework Directive (WFD) and regulatory monitoring are discussed in relation to resource management.     

Partial replacement of fossil fuel in a cement plant: Risk assessment for the population living in the neighborhood

In cement plants, the substitution of traditional fossil fuels not only allows a reduction of CO₂, but it also means to check-out residual materials, such as sewage sludge or municipal solid wastes (MSW), which should otherwise be disposed somehow/somewhere. In recent months, a cement plant placed in Alcanar (Catalonia, Spain) has been conducting tests to replace fossil fuel by refuse-derived fuel (RDF) from MSW. In July 2009, an operational test was progressively initiated by reaching a maximum of partial substitution of 20% of the required energy. In order to study the influence of the new process, environmental monitoring surveys were performed before and after the RDF implementation. Metals and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were analyzed in soil, herbage, and air samples collected around the facility. In soils, significant decreases of PCDD/F levels, as well as in some metal concentrations were found, while no significant increases in the concentrations of these pollutants were observed. In turn, PM₁₀ levels remained constant, with a value of 16 μg m^− 3. In both surveys, the carcinogenic and non-carcinogenic risks derived from exposure to metals and PCDD/Fs for the population living in the vicinity of the facility were within the ranges considered as acceptable according to national and international standards. This means that RDF may be a successful choice in front of classical fossil fuels, being in accordance with the new EU environmental policies, which entail the reduction of CO₂ emissions and the energetic valorization of MSW. However, further long-term environmental studies are necessary to corroborate the harmlessness of RDF, in terms of human health risks.     

Quantification of stormwater runoff using a combined GIS and curve number approach: a case study for an urban watershed in the Ozark Highlands,USA

Managing stormwater runoff is crucial to preserving water quality in rapidly developing urban watersheds. The objective of this study was to develop a methodology to test existing stormwater drainage infrastructure, identify potential areas of improvement, and estimate potentially contaminated runoff by combining two widely used stormwater runoff prediction models. A watershed containing much of the University of Arkansas-Fayetteville campus was targeted for this study because stormwater from this watershed drains into a local river designated as an impaired water body due to siltation. The curve number method was used to estimate runoff for various flood-return periods and antecedent moisture conditions, while a flow-direction model integrated topography, land use, and stormwater drainage infrastructure in a GIS. The methodology developed and results generated will help stormwater planners visualise localised runoff and potentially adapt existing drainage networks to accommodate runoff, prevent flooding and erosion, and improve the stormwater quality entering nearby surfacewater bodies.     

Using the adaptive model of thermal comfort for obtaining indoor neutral temperature: Findings from a field study in Hyderabad,India

There is a dearth of thermal comfort studies in India. It is aimed to investigate into the aspects of thermal comfort in Hyderabad and to identify the neutral temperature in residential environments. This was achieved through a thermal comfort field study in naturally ventilated apartment buildings conducted during summer and monsoon involving over 100 subjects. A total of 3962 datasets were collected covering their thermal responses and the measurement of the thermal environment. The comfort band (voting within –1 and +1), based on the field study, was found to be 26–32.45°C, with the neutral temperature at 29.23°C. This is way above the indoor temperature standards specified in Indian Codes. It was found that the regression neutral temperature and the globe temperature recorded when voting neutral converged when mean thermal sensation of the subjects was close to 0. This happened during the period of moderate temperature when the adaptive measures were adequate. The indoor temperatures recorded in roof-exposed (top floor) flats were higher than the lower floors. The thermal sensation and preference votes of subjects living in top floors were always higher. Consequently, their acceptance vote was also lower. It was found that the subjects living in top floor flats had a higher neutral temperature when the available adaptive opportunities were sufficient. This was due to their continuous exposure to a higher thermal regime due to much higher solar exposure. This study calls for special adaptive measures for roof-exposed flats to achieve neutrality at higher temperature.     

Regional industrial production's spatial distribution and water pollution control: A plant-level aggregation method for the case of a small region in China

With fast economic growth, industrial water pollution has been a serious problem ubiquitously in China. More threatening is that lots of economic developing regions still strategically depend on fast industrialization, neglecting the relationship between production's spatial distribution and regional water environmental carrying capacity. As a small region, Deyang City is the objective case. We propose a plant-level aggregation method to estimate the spatial distribution of industrial water pollution pressure in the future five years. Based on discrete event simulation, newly added industrial projects' sizes and location choices (refer to industrial location theory) are regionally aggregated. COD (Chemical Oxygen Demand) emission into every river reach in the region is calculated respectively. In order to recover the water environmental function, the strategy aims at controlling emission within the carrying capacity of each river reach. And the strategy is assessed on its regional effects and spatial equity, from the perspective of government and industry. The results quantitatively show the diversified uncertain bounds of river reaches' COD adoptions which will aggravate the water pollution. And the pollution control strategy's effect indicates a large different level of spatial equity for industry and government respectively.     

Using Landscape Characteristics for Targeting Habitat Conservation and Restoration: a case study of ancient semi-natural woodland in the Chiltern Hills Area of Outstanding Natural Beauty, UK

Ancient semi-natural deciduous woodland is a rare and threatened habitat cited by the European Union's Habitats Directive (92/43/EEC). Current protection of this endangered habitat in the UK takes the form of site-specific reserve designations but, if the habitat is to be conserved and enhanced, a landscape-scale selective targeting system is required. In the absence of suitable species data, physical attributes of habitat patches are used as surrogate indicators of biodiversity. Using a land-use database held on a geographical information system, values of four abiotic criteria (patch area, patch shape, nearest-neighbour distance and surrounding land use) of 48 ancient semi-natural woodland patches in part of the Chiltern Hills Area of Outstanding Natural Beauty were calculated. In order to validate the findings, three lists of floral and faunal species, indicative of ancient semi-natural woodland, were compiled, and the patches ranked according to their alpha diversity using each list. Spearman's rank correlation coefficients were calculated for patch alpha diversity and patch area (0.322 to 0.482), patch shape (0.275 to 0.465) and nearest-neighbour distance ( - 0.092 to - 0.223). Multiple regression indicated that between 15 and 22% of the variation in alpha patch diversity was explained by the abiotic factors. It is suggested that spatial targeting at the landscape scale is a valuable approach to habitat conservation.