主跨348m+348m三塔单索面PC梁斜拉桥

宜昌市夷陵长江大桥采用三塔斜拉桥，总体布置为(128．08 348 348 120．35)m。介绍了该桥的合理性及结构特点。     

A simple technique to minimize heat damage to specimens during thermal polymerization of LR White in plastic and gelatin capsules

London Resin (LR) White is a commonly used resin for embedding specimens to be used for immuno- and/or cytochemical studies. In some instances, due to either the properties of the specimen or the availability of various reagents and equipment, it becomes necessary and/or more convenient to polymerize LR White using heat rather than chemical accelerators or UV light. It is known, however, that heat can reduce or even eliminate the anti genicity of the tissue being embedded. It is therefore desirable to polymerize specimens at the lowest temperature possible and to remove the specimens from the oven as soon as polymerization is complete. We have developed a technique that provides a visual marker that allows the exothermic polymerization of LR White to be monitored, thus minimizing the amount of time a specimen must stay in the oven while excluding oxygen from capsules of polymerizing LR White.     

Prevention and Mitigation Strategies to Address Recent Brittle Fractures in Steel Bridges

Brittle fracture results in unplanned loss of service, very costly repairs, concern regarding the future safety of the structure, and potential loss of life. These types of failures are most critical when there is no evidence of fatigue cracking leading up to the fracture and the fracture origin is concealed from view. Hence, the failure occurs without warning and the details are, essentially, noninspectable. In these cases, it appears desirable to take a proactive approach and introduce preventative retrofits to reduce the potential for future crack development. These efforts will help ensure that the likelihood of unexpected fractures is minimized. This paper examines the behavior of two bridge structures in which brittle fractures have developed in recent times, discusses the causes of the failures, and offers suggested design strategies for prevention and retrofit mitigation techniques. In situations where considerable uncertainty exists in the prediction of accumulated damage or in the ability to reliably inspect critical details, preemptive retrofit strategies appear to be highly desirable.     

Enhancement of Flexural Design of Horizontally Curved Prestressed Bridges

In this paper, flexural behavior of horizontally curved prestressed (posttensioned) box bridges is studied by using three-dimensional and refined finite-element modeling and analysis. Bridge length, section geometry, and material properties are the same in all the models, while angle of curvature varies from 0 to 90°. The results of analysis show that in curved bridges, stress distribution is significantly different in comparison to straight bridges. Also, the level of stresses at some locations of section width is considerably high. It is proposed to vary the distribution of the prestressing tendons across section width in order to optimize the bridge capacity. Results show that by proper redistribution of prestressing in section width, significant reduction in resultant stress is possible.     

Communications on energy: Fighting London's cold war

This communication illustrates the work of the London Energy and Employment Network. LEEN has the twin aims of promoting a rational energy policy for London and, in the process, generating much needed employment. In cooperation with Hackney, one of Britain's poorest boroughs, LEEN organized Hackney's Cold War — a series of initiatives showing the practical measures, informational back-up and funding sources necessary for a local energy policy. LEEN intends to repeat this project in other London Boroughs, with the eventual aim of helping to persuade central government to adopt a more comprehensive approach to energy conservation nationally.     

Orthotropic Plate Model for Estimating Deflections in Filled Grid Decks

Concrete filled grid bridge decks exhibit orthogonal elastic properties and significant two-way bending action enabling orthotropic plate theory to determine structural response for these elements. Current American Association of State Highway and Transportation Officials load and resistance factor design (LRFD) specifications employ an orthotropic plate model to predict live load moment in concrete filled grid bridge decks but provide no guidance for computing displacement, a potentially important serviceability consideration. This paper presents equations to approximate the maximum deflection in concrete filled grid bridge decks based on orthotropic plate theory, multiple patch loads, LRFD design truck and tandem load cases, the influence of multiple spans, and the two most common deck orientations.     

Obtaining shorter regular expressions from finite-state automata

We consider the use of state elimination to construct shorter regular expressions from finite-state automata (FAs). Although state elimination is an intuitive method for computing regular expressions from FAs, the resulting regular expressions are often very long and complicated. We examine the minimization of FAs to obtain shorter expressions first. Then, we introduce vertical chopping based on bridge states and horizontal chopping based on the structural properties of given FAs. We prove that we should not eliminate bridge states until we eliminate all non-bridge states to obtain shorter regular expressions. In addition, we suggest heuristics for state elimination that leads to shorter regular expressions based on vertical chopping and horizontal chopping.     

Assessment of Shear Forces on Bridge Abutments: Simplified Method

The conventional application of reduction factors to response spectrum analysis results is inappropriate for the abutment shear forces, which are based on elastic action. On the other hand, adopting the unreduced values from the elastic dynamic analysis does not achieve equilibrium among the abutment shear forces, deck inertia forces, and reduced pier forces. A simplified method is here proposed for the assessment of the shear on the abutments, documented by comparison with response spectrum and time history nonlinear analyses for several bridge configurations. For the analyzed configuration of the bridge with an internal movement joint, the response spectrum analysis underestimates the shear on the abutment for low values of the abutment flexibility and overestimates it when the stiffness of the abutments becomes higher than that of the piers. In all the case studies analyzed, the proposed method approximates the time history results better than the response spectrum.     

Estimation of Aeroelastic Parameters of Bridge Decks Using Neural Networks

A new method of estimating flutter derivatives using artificial neural networks is proposed. Unlike other computational fluid dynamics based numerical analyses, the proposed method estimates flutter derivatives utilizing previously measured experimental data. One of the advantages of the neural networks approach is that they can approximate a function of many dimensions. An efficient method has been developed to quantify the geometry of deck sections for neural network input. The output of the neural network is flutter derivatives. The flutter derivatives estimation network, which has been trained by the proposed methodology, is tested both for training sets and novel testing sets. The network shows reasonable performance for the novel sets, as well as outstanding performance for the training sets. Two variations of the proposed network are also presented, along with their estimation capability. The paper shows the potential of applying neural networks to wind force approximations.     

Routine Highway Bridge Inspection Condition Documentation Accuracy and Reliability

Routine inspection is the most common form of highway bridge inspection to satisfy the requirements of the National Bridge Inspection Standards. The accuracy and reliability of documentation generated during these inspections are critical to the allocation of Department of Transportation construction, maintenance, and rehabilitation resources. Routine inspections are typically completed using only the visual inspection technique and rely heavily on subjective assessments made by bridge inspectors. In light of this, and given the fact that visual inspection may have other limitations that influence its reliability, the Federal Highway Administration initiated an investigation to examine the reliability of visual inspection as it is currently applied to bridges in the United States. This paper will summarize results from this study related to the accuracy and reliability of routine inspection documentation. A number of important conclusions were developed from the experimental study. Generally, it was found that all structural condition documentation is collected with significant variability. Specifically, 95% of primary element condition ratings for individual bridge components will vary within two rating points of the average and only 68% will vary within one point. Documentation generally collected to support condition ratings also has significant variability as exemplified by the number and types of field notes and photographs taken by inspectors. With respect to the use of element-level inspections, it was found that element usage was generally consistent with the Commonly Recognized Element Guide. However, there is significant variability in the condition state assignments of those elements and in some cases the condition states are not applied correctly to particular elements.