Truck Loading and Fatigue Damage Analysis for Girder Bridges Based on Weigh-in-Motion Data

Based on data collected by weigh-in-motion (WIM) measurements, truck traffic is synthesized by type and loading condition. Three-dimensional nonlinear models for the trucks with significant counts are developed from the measured data. Six simply supported multigirder steel bridges with spans ranging from 10.67 m (35 ft) to 42.67 m (140 ft) are analyzed using the proposed method. Road surface roughness is generated as transversely correlated random processes using the autoregressive and moving average model. The dynamic impact factor is taken as the average of 20 simulations of good road roughness. Live-load spectra are obtained by combining static responses with the calculated impact factors. A case study of the normal traffic from a specific site on the interstate highway I-75 is illustrated. Static loading of the heaviest in each truck type is compared with that of the American Association of State Highway and Transportation Officials standard design truck HS20-44. Several important trucks causing fatigue damage are found.     

Parametric effects on embedded delamination buckling in composite structures using the EAS three-dimensional element

This study deals with parametric effects on bucking behaviors of laminated composite structures containing an embedded rectangular delamination using the enhanced assumed strain (EAS) three-dimensional element. The three-dimensional finite element (FE) formulation based on the EAS method for composite structures shows excellence from the standpoints of computational efficiency, especially for distorted element shapes. Using the EAS FE formulation developed for this study, the effects of embedded delamination sizes and ply orientations on the elastic buckling behaviors for various aspect ratios and width-to-thickness ratios are studied. The numerical results obtained are in good agreement with those reported by other investigators. Furthermore, the new results reported in this paper show the progression of local buckling and its influence on global buckling and vice versa. Key observation points are discussed and a brief design guideline is given.     

The influence of curing on restrained shrinkage cracking of bonded concrete overlays

The influence of seven practical curing regimes on restrained shrinkage cracking of bonded concrete overlays was investigated. The influence of the curing regimes on the individual material properties governing restrained shrinkage cracking and on the age at cracking and crack area of ring tests and composite overlay–substrate specimens was investigated for three laboratory-made mixes of differing strengths and one commercial repair mortar. The results of the experimental testing showed that curing influences all of the material properties governing restrained shrinkage cracking. Prolonged or more effective curing was shown to either delay or reduce the rate of shrinkage respectively (dependent on the curing method), increase the tensile strength and elastic modulus, and decrease the tensile relaxation. In general, prolonged or more effective curing was shown to have a positive influence on restrained shrinkage cracking by increasing the age and net age at cracking.     

隧道施工过程大比尺模型试验系统的研制及应用

 为研究隧道不同开挖方法的施工力学过程,研制大比尺三维模型试验系统,该系统最大外部尺寸为5.2 m×4.5 m×2.7 m(宽×高×厚),结构合理,可任意拆卸,组合拼装,自动液压控制系统具有压力高、保压时间长、可进行稳步梯级加载等特点,能够满足各类地下工程的三维和平面地质力学模型试验的要求。在既有地质力学相似材料的基础上,通过大量的不同材料配比及其力学参数测试,获得满足V级软弱围岩的相似材料配比。基于此开展铁路隧道施工过程的大比尺三维地质力学模型试验,真实模拟隧道在开挖和支护过程中不断变化的力学过程。试验结果表明,该系统稳定可靠,可广泛应用于其他地下工程的地质力学模型试验研究,其研究方法技术及所得结果对类似工程研究具有一定的借鉴和指导意义。     

Post-Northridge connections with slit dampers to enhance strength and ductility

In 1994 and 1995, Northridge and Kobe earthquakes caused unexpected damages to beam-to-column connections which were followed by extensive investigations on the connections' behavior to resolve problems in their performance and to improve their strength and ductility. During these years methods were proposed by researchers which were mainly based on reducing the beam section or strengthening the connection. Adding slit dampers at the top and bottom of the beam flanges plates is another way to improve the connection behavior. These dampers are able to absorb and dissipate a significant amount of energy. Slit dampers caused a remarkable reduction in the plastic strain at the column face area and consequently kept plastic hinge formation away from the column face. In this study a total of 8 small slit dampers were used at the column face area. To find out best configuration for slit dampers which can only be used for newly designed connections, a parametric study was carried on their geometry. Generally the slit damper yields in shear or in flexure. Hence, for two different yield mechanisms (shear yielding and flexural yielding) details for designing of slit dampers were proposed and connection's strength and ductility were compared.     

Simulation studies of methods to delay corrosion and increase service life for cracked concrete exposed to chlorides

The ingress of chlorides in reinforced concrete leads to the onset of steel reinforcement corrosion and eventually compromises a structure’s integrity. To extend its service life and improve safety, it is crucial to develop sound repair strategies for our nation’s infrastructure. In this paper, results are presented for numerical simulations to study the effectiveness of fillers for repair of cracks in concrete, so as to delay the onset of corrosion in reinforcing steel. Concretes without cracks and with either a 50 μm or 500 μm wide crack located directly above the steel reinforcement are simulated, with the addition of silica fume, a corrosion inhibitor, or epoxy-coated reinforcement being considered as additional scenarios. The effectiveness of the crack filler depends not only on its inherent diffusivity with respect to chloride ions, but also on its ability to penetrate and fill the damaged zone or interface between the open crack region and the bulk concrete. Additional simulations indicate that using continuum models instead of models that include details of the rebar placement can lead to underestimating the chloride concentration and overestimating the service life. Experiments are needed to study the ingress of chlorides in damaged (interfacial) regions adjacent to the crack or at the reinforcement surface, as the local transport properties of these regions can significantly influence service life predictions.     

Improving construction industry process interoperability with Industry Foundation Processes (IFP)

With massive amounts of information generated during the life cycle of large-scale construction projects, interoperability among project stakeholders’ information systems is a requirement for effective and timely communication, collaboration, and information exchange, and ultimately for project success. While data interoperability has been substantially improved by initiatives such as IFC (Industry Foundation Classes) standardizing construction industry data, emphasis on process interoperability which facilitates timely and effective exchange of information via interaction of workflow processes is in its early stage. By conforming to a reference model such as IFP (Industry Foundation Processes), project stakeholders can communicate and collaborate using workflow processes while abstracting the information exchange to essential items to preserve their privacy. This paper explores interoperability in the AEC/FM domain, reviews the main components of the IFP system, presents two IFP interoperability models, and discusses their relationships with the IFP system. The models are demonstrated with specific examples and implemented with a process customization framework based on workflow inheritance rules. Interoperability models that conform to the IFP system not only allow seamless information exchange but can also yield active interaction and communication among stakeholders.     

SDOF—TMD控制系统能量响应特性与能量谱研究

目的研究弹性单自由度（SDOF）结构调谐质量阻尼（TMD）控制系统的能量响应特性和控制系统的能量谱变化规律．方法采用地震激励下结构位移均方值最小为优化目标的TMD最优参数表达式,基于相对能量计算公式,并考虑了TMD子结构的不同频率比、质量比和阻尼比等参数摄动来分析控制系统能量谱变化规律．结果在El centro地震作用下,TMD能较好地控制主结构的各项能量响应．TMD控制系统在短周期0—0．5s和长周期3．2—4s范围内,系统能量对TMD参数变化不敏感;在1．0～3．2s范围内,质量比越大,其动能、势能和输入能的控制效果越好,且存在最优调谐频率比;控制系统的能量反应对TMD子结构的阻尼比变化不敏感．结论TMD需要积累较大的能量才能对结构有较好的控制效果,TMD子结构参数是影响TMD控制系统能量谱变化规律的重要指标．     

Simulation of temperature-compensated voltage limit curves for aerospace NiCd batteries using a first principles' model

Temperature-compensated voltage limits (V/T limits) are routinely used in Low Earth Orbit (LEO) satellites to permit fast charging of the NiCd battery with minimum overcharge and without the problems of thermal runaway during overcharge. The voltage limits are experimentally determined from extensive testing of cells for a proper design of the charge control system to achieve the desired charge/discharge ratio in orbit. Here, we demonstrate the use of first-principles', mathematical models to construct the V/T curves theoretically. The predicted charge/discharge ratios under various orbit conditions such as different states of charge, in-rush currents and temperatures are compared with the experimental data.     

Behaviour of precast reinforced concrete pile caps

The objective of this investigation is to study the behaviour of precast reinforced concrete pile caps and the ultimate load-carrying capacity. Three pile cap units were cast and tested to failure. One unit was a control pile cap cast in situ and the other two were precast reinforced units with in situ concrete infill. The experimental results showed that the precast pile cap behaved in a similar manner as compared with the conventional cast in situ pile cap. Furthermore, all the three units failed at loads exceeding the failure loads predicted using conventional design methods and exhibited predicted failure modes. In addition, there was a substantial increase in productivity as the precast pile caps could be constructed quickly and thus reducing the risk of exposing the excavated pit to rain and possible failure of the unsupported sides.