Life-Cycle Cost Based Maintenance Plan for Steel Bridge Protection Systems

Life-cycle cost analysis was used to compare different alternative strategies for steel bridge paint systems. It was also used as a tool for steel bridge paint rehabilitation planning. The existing paint systems are lead-based and zinc-vinyl, while the new system is an inorganic/organic zinc, epoxy, and urethane paint system (three-coat). Economic analysis using present value (PV) and equivalent uniform annual cost (EUAC) was applied to compare several steel bridge paint system alternatives. The PV and EUAC were also used to compare different rehabilitation scenarios within the same alternative. Life-cycle cost analysis computations indicate that the three-coat paint system was better than others. Researchers concluded that the best scenario for three-cost system rehabilitation was doing spot repairs every 15 years of paint life. A maintenance plan based on life-cycle cost analysis also favored the “spot repairs every 15 years” scenario. A sensitivity analysis was also conducted to account for uncertainty in the cost, conditions, and subjective data.     

Comparative Analysis of Life-Cycle Costing for Rehabilitating Infrastructure Systems

Metro systems usually offer an attractive alternative for mass transit transportation system in most large cities. Such infrastructures require proper maintenance and rehabilitation (M&R) programs to maintain them within an acceptable level of operational and safety performance. The Markov decision process (MDP) has been widely used to find the optimal M&R decision policy for situations that deal with uncertainties. A drawback of the traditional MDP approach is that it uses discrete number of states in the analysis as well as a stationary transition probability matrix (TPM). Also the MDP is based on the Markovian or “memory-less” property, which is not necessarily the fact for all aging infrastructures. This research presents a case study on a deteriorating slab in a Montreal metro. The traditional MDP is employed with linear programming to determine the optimal rehabilitation profile. Three different methods are employed for calculating life-cycle cost: (1) the average expected discount cost per time period that is normally used with the traditional MDP; (2) continuous rating approach; and (3) dynamic or time-dependent TPM. Results revealed that the continuous rating approach provides lower values compared to the traditional approach. Dynamic TPM reflects better the infrastructure behavior but necessitate additional data gathering. This research mainly benefits metro management agencies and enhances the MDP practice by overcoming some downsides of the traditional methodology.     

Temporal Thermal Behavior and Damage Simulations of FRP Deck

The finite-element method (FEM) has been employed to study the structural behavior of the fiber-reinforced polymer (FRP) bridge deck. The numerical results were verified with the field-test results provided by New York State Department of Transportation. Fully coupled thermal-stress analyses were conducted using the FEM to predict the failure mechanisms and the “fire resistance limit” of the superstructure under extreme thermal loading conditions. Furthermore, damage simulations of the FRP deck as a result of snow and ice plowing process were performed to investigate any possibility of bridge failure after damage occurs. Thermal simulations showed that FRP bridge decks are highly sensitive to the effect of elevated temperatures. The FRP deck approached the fire resistance limit at early stages of the fire incident under all cases of fire scenarios. The damage simulations due to the snow plowing showed minimal possibility of bridge failure to take place under the worst-case damage scenario when the top 5 mm of the FRP deck surface was removed. The results of both phases of simulations provide an insight into the safety and the reliability of the FRP systems after the stipulated damage scenarios were considered. Moreover, this paper provides discussions concerning the recommended immediate actions necessary to repair the damaged region of FRP deck panels and possible use of the bridge after the damage incident.     

中国钢铁工业流程结构、能耗和排放长期情景预测

为了准确预报我国钢铁工业未来生产结构、能耗和排放情况,构建了钢铁生产、加工、消费、折旧的全生命周期模型和基于人均钢铁存储量的产量预测模型,结合工序能耗和排放特征,针对基准、折旧寿命延长、废钢回收率提升、能源效率提高及综合等五种情景进行了情景预测.中国钢铁产量、能耗和排放会历经一个峰值后下降,电炉短流程会逐渐替代高炉长流程成为主流.流程结构转变是未来中国钢铁行业节能减排的关键"红利",而节能技术的作用在后期越发凸显.中国钢铁行业要达到2050年减排一半的目标,需结合综合情景实施生产结构调整、废钢回收、节能减排技术推广等相应措施.      

Deterioration Assessment and Rehabilitation Design of Existing Steel Bridge

Diagnostic truck-load tests and microstructural analysis were applied for structural deterioration assessment of a steel truss bridge and its rehabilitation design. The feasibility and potential benefits of using advanced field experimental techniques within a structural-identification framework have been demonstrated. Experimental information, coupled with visual inspection, engineering experience, and intuition, increased the level of confidence in the results of the condition-assessment process, permitting a more rational and cost-effective rehabilitation design. Based on the condition assessment, a two-step rehabilitation is recommended for the bridge: Restoration for a safe service life of 5–7 years, and a subsequent effort for preservation beyond.     

Predicting Truck Load Spectra under Weight Limit Changes and Its Application to Steel Bridge Fatigue Assessment

Truck weight-limit regulations have significant influence on truck operating weights. These regulations directly influence loads applied to highway facilities, such as bridges and pavements. “Truck weight” herein collectively refers to a vehicle’s gross weight, axle weights, and axle configuration. Truck load spectra as a result of truck weight limits are important to bridge engineering in many respects, such as that of determining requirements for evaluation and design of bridges for both strength and fatigue. This paper’s objective is to present a new method for predicting truck weight spectra resulting from a change in truck weight limits. This method is needed to estimate impacts of the change on highway bridges such as accelerated fatigue accumulation. Historical and recent truck weight data are used to test and illustrate the proposed method, and the results show its good prediction capability. This method is also applied here to an example of estimating the impact on steel bridge fatigue due to a possible increase in the gross-vehicle-weight limit from 356 kN (80 kips) on five axles to 431 kN (97 kips) on six axles. Also included is an investigation of the AASHTO fatigue truck model for steel bridge evaluation. Results show that the current fatigue truck model may become invalid under the studied scenario of truck weight-limit increase.     

The impact of extratherapeutic encounters: Individual reactions to both hypothetical and actual incidental contact with the therapist.

Participants (N = 763) responded to a hypothetical scenario in which they imagined encountering their therapist outside of the therapy setting. The intimacy of the setting (i.e., anonymous vs. intimate encounter) and the perceived success of the therapy (i.e., helpful vs. unhelpful) were manipulated between subjects. Based on a principal components analysis of participant reactions to these hypothetical scenarios, 4 subscales were derived: “Acknowledgement,” “Violation of Expectations,” “Awkwardness and Discomfort,” and “Professional Responsibility.” Results indicate that reactions to the hypothetical encounter on these subscales were related to both the setting and the success of therapy. In general, participants indicated that they preferred acknowledgment from their therapists, especially in less intimate settings. However, Asian Americans, in contrast to European Americans, indicated less desire for acknowledgment and greater perceived expectation violations. Implications for psychotherapy process and training of clinicians are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateral-Torsional Buckling of Stepped Beams with Continuous Bracing

Continuous span multibeam steel bridges are common along the state and interstate highways. The top flange of the beams is typically braced against lateral movement by the deck slab, and in many bridges the cross section is stepped at discrete points along the span. Design equations for lateral–torsional buckling (LTB) resistance in the American Association of State Highway and Transportation Officials “Load and resistance factor design bridge design specifications” are for prismatic beams and ignore the lateral restraint provided by the bridge deck. A new design equation is proposed that can be applied to I-shaped stepped beams with continuous top flange lateral bracing. By including the effects of the change in cross section size and the continuous top flange bracing, the calculated LTB resistance is significantly increased. Critical bending moment values from the proposed equation are compared to values from finite element method buckling analyses. The new equation is sufficiently accurate for use in design and in the evaluation of existing bridges.     

Field Performance of FRP Bridge Repairs

Many reinforced concrete bridges throughout the United States on county and state highway systems are deteriorated and∕or distressed to such a degree that structural strengthening of the bridge or reducing the allowable truck loading on the bridge by load posting is necessary to extend the service life of the bridge. The structural performance of many of these bridges can be improved through external bonding of fiber-reinforced plastic (FRP) laminates or plates. This paper describes the rehabilitation of an existing concrete bridge in Alabama through external bonding of FRP plates to the bridge girders. Field load tests were conducted before and after application of the FRP plates, and the response of the bridge to test vehicle loadings was recorded. Results of the field tests are reported, and the effects of the FRP plates on the bridge response are identified. The repaired bridge structure exhibited a decrease in steel reinforcing bar stresses and vertical midspan deflections. These decreases ranged from 4 to 12% for various static and dynamic loading cases.     

Life Cycle Assessment of Internal Recycling Options of Steel Slag in Chinese Iron and Steel Industry

 The internal recycling process of BOF slag which is one of the huge solid wastes from iron and steel industry was emphasized. Based on the four scenarios of different internal recycling strategies for BOF slag, life cycle assessment (LCA) as a valuable tool for industrial solid waste management was applied to analyze the contribution to reducing environmental impacts and resources burdens for each scenario. The global warming potential (GWP) results of the four scenarios show that the scenario which performs best in carbon reduction cuts off 14.2% of GWP impacts of the worst scenario. The results of this study show that the optimized internal recycling process of BOF slag can improve the environmental performance of crude steel. It is important to assess and choose an appropriate strategy to recycle BOF slag from LCA perspective to reduce the environmental impacts and resource burdens as much as possible.     

Short- and Long-Term Effects of Element Costs and Failure Costs in Pontis

Experts familiar with bridge maintenance in Idaho estimated unit costs for Pontis bridge elements. These costs were compared to those provided by the California and Oregon departments of transportation. Some of the differences are due to regional variations in repair and rehabilitation costs, some reflect decisions to avoid certain actions by assigning them prohibitively high costs, and others reflect modeling decisions regarding the cost of leaving an element in its current condition. For a 5-year scenario, the projected needs using the Oregon element costs were from 1.6 to 6 times higher than those based on Idaho or California element costs. Likewise the projected benefits using Oregon element costs ranged from 2.2 to 40 times higher than the benefits projected using Idaho and California element costs. A 25-year scenario indicates that Pontis’ cost-optimal priorities allowed the Network Health Index to decrease, even when a more-than-ample budget was provided.     

Analysis of Life-Cycle Maintenance Strategies for Concrete Bridge Decks

This paper presents the development of a project-level decision support tool for ranking maintenance scenarios for concrete bridge decks deteriorated as a result of chloride-induced corrosion. The approach is based on a mechanistic deterioration model and a probabilistic life-cycle cost analysis. The analysis includes agency and user costs of alternative maintenance scenarios and considers uncertainties in the agency cost and the corrosion rate in the deterioration model. The tool presented in this paper can be used to find the optimal condition index of a given bridge deck that minimizes life-cycle cost. Based on the results obtained on three existing bridge decks, it is shown that the total life-cycle cost (user cost plus agency cost) is a nonlinear function of the maximum tolerable condition of the deck, Sm, and that for a practical range of Sm, the relationship between total life-cycle cost and Sm is convex.     

Seismic Retrofit of State Street Bridge on Interstate 80

The State Street Bridge, in Salt Lake City, was designed and built in 1965 according to the 1961 AASHO specifications; the design did not include earthquake-induced forces or displacements since only wind loads were considered. The bridge consists of four reinforced concrete (RC) bents supporting composite welded steel girders; the bents are supported on cast-in-place concrete piles and pile caps. A vulnerability analysis of the bridge was conducted that determined deficiencies in (1) confinement of column lap splice regions, (2) anchorage of longitudinal column bars in the bent cap, (3) confinement of column plastic hinge zones, and (4) shear capacity of columns and bent cap–column joints. Seismic retrofit designs using carbon-fiber-reinforced-polymer (CFRP) composites and steel jackets were performed and compared for three design spectra, including the 10% probability of exceedance in 250 years earthquake. The CFRP composite design was selected for implementation and application of the composite was carried out in the summer of 2000 and 2001, while the bridge was in service. The paper describes the CFRP composite design, which, in addition to column jackets, implemented an “ankle wrap” for improving joint shear strength and a “U-strap” for improving anchorage of column bars in the bent cap; other retrofit measures were implemented, such as bumper brackets and a deck slab retrofit. A capacity versus demand evaluation of the as-built and retrofitted bents is presented.     

Seismic Design of Concrete-Filled Circular Steel Bridge Piers

The adequacy of the existing design provisions for concrete-filled steel pipes subjected to axial forces and flexure is reviewed by comparing the strengths predicted by the CAN/CSA-S16.1-M94, AISC LRFD 1994, and the Eurocode 4 1994 codes and standards against experimental data from a number of investigators. New proposed design equations are then developed, in a format compatible with North American practice. The new equations, based on a simple plasticity model calibrated using experimental data, are shown to provide improved correlation between predicted strength and experimental data. This paper provides information and data in support of the proposed design equations, which have already been implemented in the 2001 edition of the CSA-S16-01 “limit state design of steel structures” (CSA 2001) and in the “Recommended LRFD Guidelines for the Seismic Design of Highway Bridges” (MCEER/ATC 2003).     

Proposed Method for Determining the Interval for Hands-on Inspection of Steel Bridges with Fracture Critical Members

The proposed assessment procedure presented in this paper may be used to establish inspection intervals for steel bridges with fracture critical members (FCMs) (if adopted by the Federal Highway Administration). The procedure proposed herein only applies to FCM inspections which are defined as follows: a hands-on inspection of a FCM or member components that may include visual and other nondestructive evaluations. The method is rather simple and provides an alternative procedure to the pure calendar based inspection methodology currently specified in the Code of Federal Regulations for all FCMs. There are only two requirements which must first be satisfied in order to use the assessment. The first is that the routine 24-month inspection must continue to be performed on the bridge under evaluation. The second is that a FCM inspection must be performed on the bridge or the FCM under evaluation prior to the implementation of the resulting inspection intervals given from this assessment. The “initial inspection” should be performed as a typical FCM inspection. The assessment procedure is intended to be applied to individual FCMs and not the entire bridge itself. However, on bridges with multiple FCMs, the “worst case” FCM may be evaluated using the assessment and the resulting inspection interval may be applied to all FCMs on the bridge (for simplicity and bookkeeping purposes). The decision of whether to apply the assessment to all FCMs or the bridge’s worst case FCM is left up to the owner or engineer. The approach is not based on more rigorous damage tolerant design concepts or other fracture mechanics based methods. Nevertheless, the method is a first step in providing a more rational alternative to calendar based inspection and allows owners to prioritize structures and resource allocation. Using engineering experience and judgment, the interval for the hands-on inspection of steel bridges with FCMs can then be selected based on upper limits established through a consensus. Although the focus is on fracture critical bridges and members, the writers believe that the concept could be extended to a variety of structure types and configurations.     

应用脉冲熔融法和感应热抽取法探讨钢中超低氢分析“零峰值”问题

应用脉冲熔融法测定钢中超低氢,仪器显示值为“0.0 μg/g”。实验对该“零峰值”现象进行了系统的研究和探讨,结果发现如果将现用石墨套坩埚换成单坩埚于同样条件下检测,可见到明显的氢峰,然而,用内控标样10点分析,确认此峰为单坩埚产生的干扰峰;尝试换用添加浴料的技术手段解决问题未能成功。转机源于另一台不同原理的同类仪器,应用感应热抽取法仪器测定数百个“零峰值”样品,可见稳定的氢峰,峰值落在0.1~0.4 μg/g范围内。以力可502-457钢中氧氮氢联标样(氢认定值为(0.9±0.4) μg/g)和阿尔法AR546钢中氢标样(认定值为(0.63±0.2) μg/g)标定,线性良好数值可信。采用感应热抽取法分析内控钢中氢标样,测定值与认定值(0.5±0.2) μg/g基本一致,平行测定10次的标准偏差(SD)为0.07 μg/g。分别采用脉冲熔融法和感应热抽取法对添加稀土和未添加稀土钢样品中超低氢进行分析对比试验,结果表明:对于添加稀土钢样品中氢的分析,基于脉冲熔融法的两台仪器分析均显示“0.0x μg/g”;基于感应热抽取法仪器分析可知氢测定值在0.4 μg/g附近;对于未添加稀土钢样品,两种方法所用的仪器分析所得氢测定值基本一致。由此分析认为:添加稀土可以造成对钢中氢分析的负干扰,对于感应热抽取法此干扰值甚微,可忽略;而对于脉冲熔融法,可见的氢分析负干扰值在0.2~0.4 μg/g范围内。综上所述,对氢质量分数小于0.4 μg/g的钢中超低氢分析,不宜使用脉冲熔融法;对0.4~0.9 μg/g钢中超低氢分析,慎重应用脉冲熔融法;感应热抽取法样品始终保持固态,避免了因挥发所产生的负干扰,实验中未出现“零峰值”现象,适合于钢中超低氢分析。     

Robust Optimal Design of Activated Sludge Bioreactors

This paper proposes an algorithm for a robust optimal design of the biological reactor and secondary settling facilities in suspended growth nitrogen and phosphorus removal systems. Robust optimization includes uncertainty in the decision-making procedure and seeks a solution that remains “close” to optimal for all potential operation scenarios. It thus differs fundamentally from the deterministic and stochastic approaches, where uncertainty is ignored or a solution based on either the most likely scenario or the average performance over all potential scenarios is produced. The robust optimization of a suspended growth system is a multiobjective optimization problem concerned with minimization of the global costs and variability of the system’s performance around the optimal. The proposed robust optimization approach uses the ASM3 model, making use of its performance prediction capabilities to produce a powerful tool for designing activated sludge systems. The algorithm was applied to the design of the biological reactor and secondary settling facilities for the Vila Real municipal wastewater treatment plant (Portugal).     

Thermodynamic study on calcium treatment of “liquid phase window” and inclusions modification

It is important to study the “liquid phase window” and control non metallic inclusions modification for prevention of submerged entry nozzle blocking during continuous casting. Based on the production practice of medium and high carbon steel in a steel plant, the “liquid phase window” during calcium treatment was studied by combining thermodynamic theoretical calculation and industrial test, which was based on considering the influence of silicon element and temperature on the “liquid phase window”. The results show that the “liquid phase window” varies with T［O］, T［Al］, ［S］ content and temperature, and the low temperature “liquid phase window” must be within the range of high temperature “liquid phase window”, and the silicon content in molten steel has a great influence on the “liquid phase window”. The concepts of “partial liquid phase window” and “complete liquid phase window” are proposed, and the optimum calcium content range of S50C production in a steel plant is determined to be (18-27)×10-6。     

Ca处理“液相窗口”及夹杂物变性热力学研究

摘要：研究“液相窗口”控制钢液中非金属夹杂物变性对于防止连铸过程浸入式水口堵塞具有重要意义。基于某钢厂中高碳钢生产实践,在重点考虑Si元素和温度对“液相窗口”影响的基础上,通过热力学理论计算与工业试验相结合,对Ca处理过程“液相窗口”进行了研究。结果表明：“液相窗口”随钢液中T［O］、T［Al］、［S］含量及温度变化而变化;低温“液相窗口”一定位于高温“液相窗口”范围内;钢液中［Si］含量在某些条件下对“液相窗口”影响较大;并提出了“部分液相窗口”和“完全液相窗口”的概念;确定了某钢厂S50C生产最佳Ca质量分数范围为（18~27）×10-6。