车辆-有砟轨道-桥梁系统动力分析模型及验证

针对桥上有砟轨道,利用耦合动力学理论,建立了车辆-有砟轨道-桥梁系统动力分析模型,编制了仿真计算程序.通过与既有理论分析结果和软件计算结果的对比,对本文所建模型的正确性进行了验证.该模型可用于研究车辆、轨道和桥梁结构的动力相互作用,可用于对车辆运行的舒适性以及桥上有砟轨道结构的动力特性进行预测评价.     

Valtimet公司将向卡塔尔某海水淡化项目供应钛管

法国无缝钢管生产商瓦克瑞克（Vallourec）的子公司Valtimet公司2013年夏季将向卡塔尔地区某海水淡化项目供应42000余根长度在25．9m以上的无缝钛管材,其总长度累计达到1．09×10^6m。     

河北隆化县钛业基地建设取得初步成效

河北省隆化县超贫钒钛磁铁矿资源较为丰富，已探明储量12×10^8t左右，其中钛金属量0．6×10^8t，平均品位为0．2％，远景储量在20×10^8t以上，其中钛金属量1×10^8t左右。为最大限度地用好有限的矿产资源，该县从重点项目入手，在“一次采、综合选、深加工”上下功夫，2008年已生产钛精粉2．6×10^8t，实现销售收入1600万元，钛业基地建设取得初步成效。     

基于Matlab的4200轧机垂直振动仿真

 建立了具有6自由度的4200轧机有阻尼垂直振动系统的动力学模型，并用Matlab对其进行了参数计算和仿真分析，得到了该振动系统的固有频率、相应振型以及系统的响应曲线，获得了一种求解中厚板轧机动力学问题的简捷有效的方法。     

典型约束条件下锚杆受瞬态激振时的位移响应衰减规律研究

为了研究锚杆在典型约束条件下受瞬态激振作用的响应特征,假定锚杆受激振动的范围均在弹性限度内且截面保持为平面、材料均匀各向同性,基于一维波动理论,根据达朗贝尔原理引入抗剪刚度和摩擦阻尼系数建立锚杆受激振动的波动方程。在求解过程中,引入狄拉克δ函数,运用特征值法得到两端自由和一端自由一端固定2种边界条件下锚杆的位移、速度和加速度场的解析解。分析锚杆受激振时的位移、加速度响应曲线,结果表明：因阻尼影响,一端固定一端自由的锚杆受瞬态激振时位移响应的衰减比两端自由的锚杆要快;另外,受锚杆侧向阻尼和抗剪刚度影响,一端固定一端自由的锚杆加速度响应振动幅值比两端自由状态下低大约4个数量级。     

无机陶瓷超滤膜清洗方式选择

探讨了超滤清洗的工作条件和清洗剂的选择组合，结果表明，理想清洗方案为清洗温度48～50℃，膜的进出口压力分别是4．0×10^5、1．9×10^5Pa，依次使用浓度为2％～2．5％的阴离子表面活性剂、pH值为3的酸液及pH值为11的碱液清洗30min。     

某矿山地下开采对地表公路的影响分析

某矿山地下开采矿体在地表公路的保安矿柱范围内,为了确保公路的稳定性,采用Flac^3D软件的数值分析方式进行了开采影响分析,同时论证了采矿爆破振动对公路的影响。结果表明：-300 m中段矿体开采后,地表公路最大沉降为1.2 mm,地表x向倾斜值最大为0.185 mm/m,y向倾斜值最大为0.13 mm/m;地表x向曲率值最大为0.011×10^-3m^-1,y向曲率值最大为0.012×10^-3m^-1;地表x向水平变形最大值为0.15 mm/m,y向水平变形最大值为0.12 mm/m,均满足相关规范要求。采矿爆破时的地表质点振速小于规范规定的安全允许振速,采场爆破振动对地表影响很小。研究结果对该矿山深部开采提供了技术支撑。     

三异丁基硫膦萃取银的动力学研究

L.Boyadzhiev等用溶解在正-辛烷中的三异丁基硫膦研究了从硝酸盐溶液中萃取银的动力学。试验在旋转扩散槽中进行。正、逆化学反应速率常数为:K正=1.064×10-3m9/mol3.s,K逆=2.085×10-1/s。获得的活化能值表明,三异丁基硫膦萃取银的过程受扩散控制。三异丁基硫膦萃取银的动力学     

轨道车辆车体用6008合金吸能型材工艺研究

轨道车辆用吸能盒型材要求变形呈均匀折叠的环状、无撕裂现象。现有型材经高速碰撞易撕裂、飞溅,增加了对乘客造成二次伤害的几率;且吸能效果差,难以应用于轨道车辆吸能部件上。本文研究6008合金添加适量的Mn、Cr、V元素,采用铝棒温度510～520℃,模具温度450～480℃,挤压速度1～1.5 m/min,在线风冷的挤压工艺,经280℃×1 h热处理后,可满足型材压缩试验均匀,无撕裂现象的要求。     

板坯结晶器板簧振动系统非线性特性分析

应用大型有限元商业计算软件ANSYS,计算得到了板弹簧导向结晶器振动系统刚度系数在不同的变形条件下并非常数这一结论,从而引出板弹簧导向结晶器振动系统的非线性特征.通过对系统模态的分析以及瞬态分析计算,得到了系统在低阶激励频率下具有高阶频率共振响应的结果,并通过将计算得到的水平位移-垂直位移图谱与文献中测试得到的结果比较,进一步验证了模型的合理性.此外,对可能引起超谐波响应的系统阻尼非线性机制及原因进行了讨论.     

变频调速控制系统在桥式起重机上的优势分析

通过对传统桥式起重机电动机转子串电阻调速控制系统存在安全隐患多、效率低、耗能高等缺点,以及对变频调速控制系统应用在桥式起重机上的优势进行分析比较,充分体现变频调速控制系统应用在桥式起重机上是非常理想的选择。     

System for In-Service Strain Monitoring of Ordinary Bridges

An in-service bridge monitoring system (ISBMS) has been developed to provide near real-time web-based monitoring of live load strains in a bridge. The monitoring system is small, battery operated, can be rapidly deployed, and is programmed and interrogated via a user-friendly web interface. The ISBMS has been designed to be portable and used on an “as-needed” basis as a diagnostic tool or for health monitoring of ordinary bridges. The system is based on a small single-board computer with analog inputs; it also includes a cellular digital packet data modem for communication via the existing cellular network. Strains are measured using either a full bridge strain transducer or a quarter bridge foil strain gauge. The system has three modes of operation; The peaks program records peak live load strains that exceed a specified threshold, the time history program captures dynamic waveforms that exceed a specified threshold, and the rainflow program counts varying amplitude strain cycles. The selection and setup of the program, and retrieval of data is handled through a custom designed web interface. The system has been tested in the laboratory and in the field on a heavily traveled steel girder bridge. The data obtained from the ISBMS can be used for load rating using site specific data, fatigue investigations, monitoring bridge performance under permit loads, and as part of the biannual inspection of ordinary bridge.     

Bridge Health Index for the City and County of Denver, Colorado. II: Denver Bridge Health Index

Current bridge health index (BHI) in Pontis bridge management system applied to assess the bridge health conditions for 615 bridges in the city and county of Denver (CCD) does not provide CCD engineers a valuable analysis of the health condition of its relatively small bridge network. Both the calculation results and the computing methodology of the current BHI reveal that it is subjective to a municipality’s often imprecise cost data. This paper focuses on developing an alternate BHI. In order to understand the principle and procedure of the BHI calculation, the element weighting point was developed as a new concept in the analysis. The study concluded that the weighting point should reflect the effect of element damage on bridge health and function instead of a percentage of element value. Based on this conclusion, the current BHI was modified. The Denver BHI, a new diagnostic tool, was developed. It has already been adopted in the Pontis bridge management system of the CCD public works department.     

Graphical 3D Visualization of Highway Bridge Ratings

Aging highway infrastructure requires effective rating methodologies to prioritize bridges for rehabilitation and repair. To aid engineers in decision making regarding bridge maintenance, a three-dimensional (3D) visualization system is developed for rating reinforced concrete deck-girder bridge. Color codings show the most probable mode of failure for girder cross sections under combined moment-shear forces and allow an engineer to determine a rehabilitation strategy. The visualization system relies on 3D finite-element analyses using the open source framework OpenSees, making the system readily extensible to a wide range of bridge types and loading scenarios, as well as emergent reliability-based rating methodologies. Important features of the visualization system are emphasized, including the use of lighting and feature edge detection to improve the visual quality of a bridge model. Recent developments in scientific visualization are discussed for potential application to civil engineering problems.     

Seismic Reliability Assessment of Bridges with User-Defined System Failure Events

Bridge-level failure event definitions per limit state have evolved from failure of one key bridge component as representative of the whole bridge system to failure of at least one of multiple components. However, an entire set of bridge failure event possibilities exists between these two extremes in the same limit state, such as failure of any two, any three, or any desired subset of bridge components. This paper proposes a closed-form combinatorial method to evaluate all possible ways in which bridge components can fail within and across limit states. It also highlights bridge component importance measures as key by-products of the closed-form solution. Calculations are illustrated with a particular yet illustrative system failure event, called the augmented event, which incorporates failures of at least one component in a given limit state and joint failures of multiple important components in a previous limit state. Bridges in as-built and retrofitted conditions are used to illustrate the augmentation calculation under seismic loads and the application of the proposed system reliability method. The results reveal an increase in median system fragility at the moderate limit states in the range of 4–20% relative to traditional approaches that neglect augmentation. This methodology to connect bridge components to bridge system reliability can readily support infrastructure stakeholder decision making and risk management through an efficient approach that can adapt to evolving system failure event definitions.     

Rating and Reliability of Existing Bridges in a Network

Currently, the load rating is the method used by State DOTs for evaluating the safety and serviceability of existing bridges in the United States. In general, load rating of a bridge is evaluated when a maintenance, improvement work, change in strength of members, or addition of dead load alters the condition or capacity of the structure. The AASHTO LRFD specifications provide code provisions for prescribing an acceptable and uniform safety level for the design of bridge components. Once a bridge is designed and placed in service, the AASHTO Manual for Condition Evaluation of Bridges provides provisions for determination of the safety and serviceability of existing bridge components. Rating for the bridge system is taken as the minimum of the component ratings. If viewed from a broad perspective, methods used in the state-of-the-practice condition evaluation of bridges at discrete time intervals and in the state-of-the-art probability-based life prediction share common goals and principles. This paper briefly describes a study conducted on the rating and system reliability-based lifetime evaluation of a number of existing bridges within a bridge network, including prestressed concrete, reinforced concrete, steel rolled beam, and steel plate girder bridges. The approach is explained using a representative prestressed concrete girder bridge. Emphasis is placed on the interaction between rating and reliability results in order to relate the developed approach to current practice in bridge rating and evaluation. The results presented provide a sound basis for further improvement of bridge management systems based on system performance requirements.     

Experimental Study on Prefabricated Concrete Bridge Girder-to-Girder Intermittent Bolted Connections System

This paper reports on a new bridge deck slab flange-to-flange connection system for precast deck bulb tee (DBT) girders. In prefabricated bridge system made of DBT girders, the concrete deck slab is cast with the prestressed girder in a controlled environment at the fabrication facility and then shipped to the bridge site. This system requires that the individual prefabricated girders be connected through their flanges to make it continuous for live load distribution. The objectives of this study are to develop an intermittent bolted connection for DBT bridge girders and to provide experimental data on the ultimate strength of the connection system. This includes identifying the crack formation and propagation, failure mode, and ultimate load carrying capacity. In this study, three different types of intermittent bolted connection were developed. Four actual-size bridge panels were fabricated and then tested to collapse. The effects of the size and the level of the fixity of the connecting steel plates, as well as the location of the wheel load were examined. The developed joint was considered successful if the experimental wheel load satisfied the requirements specified in North American bridge codes. It was concluded that location of the wheel load at the deck slab joint affected the ultimate load carrying capacity of the connections developed. Failure of the joint was observed to be due to either excessive deformation and yielding of the connecting steel plates or debonding of the embedded studs in concrete.     

Dynamic Response of Suspension Bridge to High Wind and Running Train

A framework is presented for predicting the dynamic response of long suspension bridges to high winds and running trains. A three-dimensional finite-element model is used to represent a suspension bridge. Wind forces acting on the bridge, including both buffeting and self-excited forces, are generated in the time domain using a fast spectral representation method and measured aerodynamic coefficients and flutter derivatives. Each 4-axle vehicle in a train is modeled by a 27-degrees-of-freedom dynamic system. The dynamic interaction between the bridge and train is realized through the contact forces between the wheels and track. By applying a mode superposition technique to the bridge only and taking the measured track irregularities as known quantities, the number of degrees of freedom of the bridge-train system is significantly reduced and the coupled equations of motion are efficiently solved. The proposed formulation is then applied to a real wind-excited long suspension bridge carrying a railway inside the bridge deck of a closed cross section. The results show that the formulation presented in this paper can predict the dynamic response of the coupled bridge-train systems under fluctuating winds. The extent of interaction between the bridge and train depends on wind speed and train speed.     

Experimental Assessment of Dynamic Responses Induced in Concrete Bridges by Permit Vehicles

Results from experimental testing of three permit vehicles are presented in the paper. The selected heavy vehicles, which require permits from state DOTs, included two tractor-trailer systems and a midsize crane. The vehicles were experimentally tested on popular existing speed bumps and on a representative highway bridge. The selected bridge was a reinforced-concrete structure constructed in 1999, located on the U.S. 90 in Northwest Florida. The bridge approach depression, combined with a distinct joint gap between the asphalt pavement and the concrete deck, triggered significant dynamic responses of the vehicle-bridge system. Similar dynamic vibrations were observed and recorded when the permit vehicles were driven over the speed bumps. Time histories of relative displacements, accelerations, and strains for selected locations on the vehicle-bridge system were recorded. The analysis of experimental data allowed for assessment of actual dynamic interactions between the vehicles and the speed bumps as well as dynamic load allowance factors for the selected bridge.     

Effect of Common Cause Failures on Indirect Costs

Next generation bridge management systems will take into consideration multiple hazard scenarios and not only traffic loading and structural deterioration as they do now. The indirect costs used in these bridge management systems to determine optimal management strategies vary according to the hazard scenarios considered. The difference depends on whether or not the bridge failures are due to a common cause, such as a single flood or earthquake, or due to load events that may be considered statistically unrelated, such as truck loads. To illustrate the effect of common cause bridge failures on indirect costs, two examples are presented that treat the failures first as if they are due to statistically independent loading events and then as if they are due to a common cause. To examine the effect of bridge failures on indirect costs of the system, estimation is performed at the network level. The first example, on a simple network, shows the indirect cost estimate for all of the network condition states. The second example, on a complex network, shows the difference in the possible reduction of total indirect costs with a single bridge intervention as well as the change in intervention sequence. The main conclusions are that total indirect costs and optimal intervention sequences differ depending on whether or not bridge failures are due to a common cause, and that the largest changes in indirect cost estimation occur when simultaneously failed bridges affect the method of indirect cost incurrence.