This paper presents a novel, non-iterative, general formulation for the transient analysis of interacting elastodynamic systems in contact that may exhibit relative motion with respect to each other. ...The overall system consists of a collection of individual structures (subsystems). Each of the structure is solved at first independently of the others assuming no interactive contact forces exist. The solution of the overall system is obtained by enforcing compatibility of displacements and dynamic force equilibrium at the interface boundaries using dynamic 'mortar elements'. The proposed method obtains the solution in a time marching fashion without the need for iterations. The proposed coupling algorithm is versatile and is designed to accommodate different numerical time integration schemes and different mathematical model solving techniques. The proposed method is computationally advantageous to the substructure methods reported in the literature, which usually use the iterative procedure. It is also computationally efficient to the methods using the monolithic approach, since smaller systems are solved at a time and there is no need to update structural matrices at every time step. The proposed method is verified through comparisons with results reported in the literature. The verification examples demonstrate the accuracy and the computational efficiency of the proposed algorithm.
Continuous welded rail has become the standard in modern railway track construction around the world because it alleviates well-documented disadvantages of rail joints in a track. Continuous welded ...rail practice results in long segments of continuous rail in track that will develop significant thermal longitudinal stresses due to the absence of expansion joints. Before a continuous welded rail is laid, the rail is free of thermal stresses; the temperature at that time is known as the rail neutral temperature. The design rail neutral temperature is calculated based on local climate projections. As a continuous welded rail is laid, it may be stretched or compressed if the current temperature is not within the calculated design rail neutral temperature range, prior to anchoring the rail down. Upon anchoring, as temperatures deviate from the rail neutral temperature, significant tensile or compressive longitudinal stresses develop, leading to a track buckling or rail pull-apart that compromise the integrity of the track and the safety of train operation. Existing methods to estimate the rail neutral temperature and determine the state of stress in the rail have significant shortcomings related to the ease of implementation, system complexity, practicality, reliability, simplicity, cost, and instrumentation demands. We propose a novel concept for measuring stress in rail segments and determining the rail neutral temperature. The proposed method is based on measurements of nonuniform deformations of the rail under thermal loading, as observed in computer simulations and laboratory investigations. The implementation uses thermal imaging and three-dimensional stereo-digital image correlation technology to acquire full-field deformations. The acquired data are processed to estimate rail neutral temperature and quantify the longitudinal stress in the rail. This article presents the analytical and experimental work that led to the conception of the method and introduces the systematic approach to develop the method along with verification and validation studies.
•Prestressed concrete railroad ties crack prematurely under center binding conditions due to high rigidity.•A high strength reduced modulus (HSRM) concrete is developed at USC and used in railroad ...ties.•Computer models of HSRM ties for FEA simulations are validated through experimental data.•The use of HSRM concrete in railroad ties reduces the stress amplitude and regularizes the stress gradient.•The use of HSRM concrete in railroad ties delays cracking initiation and yields higher ultimate loads.
Concrete ties, also referred to as sleepers or crossties, have become a promising alternative to timber ties for freight lines in demanding territories with high curvature, high grade, and high axle loads. Concrete ties have also become popular in rail transit systems. High strength (HS) concrete is the material of choice in the fabrication of prestressed concrete railroad ties. The higher strength of the concrete is directly related to higher values of the elastic modulus, thus increasing the rigidity of the material. The combination of increased strength, rigidity, and the material brittleness may lead to premature cracking and deterioration which has raised major concerns within the rail industry. With experience in frontier concrete material research, researchers at the University of South Carolina (USC) have developed a High Strength Reduced Modulus (HSRM) concrete by introducing weathered granite aggregates into concrete mix designs. A comprehensive study has been conducted at USC to quantify the benefits of using HSRM concrete in railroad ties. Both laboratory experiments and computer simulations at the material, component, and structural levels were performed. HSRM can improve the cracking resistance and fatigue performance and extend the service life of the concrete ties. This paper presents the details of the computer simulations used to quantify the benefits of using the HSRM material in ties subjected to center binding conditions. Three-dimensional nonlinear Finite Element (FE) models have been developed for the HSRM and the “Standard” concrete ties. Nonlinear material models based on concrete damaged plasticity are implemented. The concrete-steel bond interface is also modeled. The numerical models are first validated through comparisons with laboratory testing results of prestressed concrete prisms and commercial prestressed ties, which showed excellent agreement. Results from a parametric study simulating the center binding conditions in a tangent track have shown that the HSRM concrete tie outperforms the Standard concrete tie by: (i) showing smoother stress distribution, (ii) delaying the initiation of cracks, and (iii) failing at higher ultimate loads.
This paper utilizes and expands on existing coupled BEM–FEM (finite element method) methods for the investigation of the effects of soil structure interaction (SSI) on both an un-retrofitted and ...seismically isolated typical bridge structure. A simple numerical model of the bridge and surrounding soil is formulated and excited by an earthquake excitation. Utilizing Newmark's
β
FEM solution method along with the closed form B-spline BIRF method, the structural damped period, composite damping ratio, pier relative displacement, and base shear demand are monitored. From these results, the effects of SSI on this structure are identified. Additionally, the importance of the relative rigidity between the soil-foundation system and the bridge structure is also investigated. The results of the studies indicate that the response of the complete structure system considered is affected by the inclusion of SSI effects. Furthermore, the efficiency of the isolation measures designed using fixed base conditions is decreased by considering SSI over a certain relative rigidity range that is quantified using the structure to soil-foundation natural frequency ratio.
This paper presents three case studies that were part of a 1-year study that explores the feasibility of using commercially available satellite and other aerial imagery to monitor the right of way of ...railroads for effects and conditions that could potentially trigger landslides and other geohazards. Two satellite image processing techniques in the Interferometric Synthetic Aperture Radar (InSAR) family have been studied and employed, that is, the Differential Interferometric Synthetic Aperture Radar (DInSAR) and the Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR). All satellite images used in this work are in the public domain and the software is open source. Showcase studies have demonstrated that the current satellite technology makes it feasible to monitor the railway right of way for large- and small-scale deformations and changes in the ground moisture content in adequate resolution. The frequency of acquisition of satellite images is adequate for the long-term monitoring of the infrastructure. The satellite analysis results can be superimposed to visual imagery for ease of visual inspection and evaluation. Future work for the development of a monitoring system of the railway right of way needs to focus on verifying the accuracy of the techniques with in situ measurements through conventional means and quantifying the changes of the moisture content.
Differentiated Services (DiffServ) and other scheduling strategies are now widespread in the traditional, “best effort” Internet. These Internet Architectures offer Quality of Service (QoS) ...guarantees for important customers at the same time as supporting less critical applications of lower priority. Strict priority queuing (PQ), weighted round robin (WRR), and class-based weighted fair queuing (CBWFQ) are three common scheduling disciplines for differentiation of services in telecommunication networks. In this paper, a comparative performance study of the above PQ, WRR and CBWFQ queuing scheduling policies applied on a double-buffered, 6-stage Multistage Interconnection Network (MIN) that natively supports a 2-class priority mechanism is presented and analyzed using simulation experiments. We also consider a 10-stage MIN, to validate that the conclusions drawn from the 6-stage MIN apply to MINs of different sizes. The findings of this paper can be used by MIN designers to optimally configure their networks.
Next-generation network architectures strive to achieve high bandwidth and ultralow latency for the packets traversing the offered end-to-end paths. Multistage Interconnection Networks (MINs) are ...often employed for implementing NGNs, but while MINs are fairly flexible in handling varieties of traffic loads, they tend to quickly saturate under broadcast and multicast traffic, especially at increasing size networks. As a response to this issue, multilayer MINs have been proposed, however their performance prediction and evaluation has not been studied sufficiently insofar. In this paper, we evaluate and discuss the performance of multilayer MINs under multicast traffic, considering also two levels of packet priorities, since support for multiple QoS levels is an indispensible requirement for NGNs. Different offered loads and buffer size configurations are examined in this context, and performance results are given for the two most important network performance factors, namely packet throughput and delay. We also introduce and calculate a universal performance factor, which includes the importance aspect of each of the above main performance factors. The findings of this study can be used by NGN system designers in order to predict the performance of each configuration and adjust the design of their communication infrastructure to the traffic requirements at hand. Index Terms-performance analysis, multistage interconnection networks, banyan networks, multicast traffic, multilayer networks
This work presents an efficient methodology for the analysis of vibrations in a railroad track system, induced by the passage of conventional and high-speed trains. To this end the Boundary Element ...Method is used to model the soil-tie system within the framework of impulse response techniques. Conventional Finite Element Methods along with Newmark's integration is used for the modeling of the rail system. The two methods are coupled at the tie-rail interface and the solution is obtained following a staggered, time marching scheme in an efficient manner. The methodology accounts for Soil-Structure Interaction and traveling wave effects. In addition, this work identifies the parameters that affect the efficient modeling of railroad track systems as they pertain to the proposed solution methodology.
This research studies the structural behavior of a GFRP bridge deck system. The study develops FEM models of the GFRP bridge deck system using ANSYS 7.0 software package. Data collected from field ...measurements and laboratory testing is used to validate and calibrate the proposed FEM models. Parametric studies through computer simulations are conducted to investigate the characteristics of the system. Four parameters are considered for service load conditions: (a) presence of diaphragms, (b) girder stiffness, (c) girder spacing, and (d) composite action. In addition, geometric and material nonlinearities are considered in the investigation of the capacity of the new bridge system. The analysis results are discussed and conclusions on the GFRP deck system are presented.
There is a net emissions change when adopting new materials for use in civil infrastructure design. To evaluate the total net emissions change, one must consider changes in manufacture and associated ...life-cycle emissions, as well as changes in the quantity of material required. In addition, in principle one should also consider any differences in costs of the two designs because cost savings can be applied to other economic activities with associated environmental impacts. In this paper, a method is presented that combines these considerations to permit an evaluation of the net change in emissions when considering the adoption of emerging technologies/materials for civil infrastructure. The method factors in data on differences between a standard and new material for civil infrastructure, material requirements as specified in designs using both materials, and price information. The life-cycle assessment approach known as economic input-output life-cycle assessment (EIO-LCA) is utilized. A brief background on EIO-LCA is provided because its use is central to the method. The methodology is demonstrated with analysis of a switch from carbon steel to high-performance steel in military bridge design. The results are compared with a simplistic analysis that accounts for the weight reduction afforded by use of the high-performance steel but assuming no differences in manufacture.
PDF
