Dynamic analysis of the train-bridge interaction: an accurate and efficient numerical method

The dynamic behavior of railway bridges carrying high-speed trains can be analyzed with or without the consideration of the vehicle's own structure. However, due to the amount of kinetic energy carried at high speeds, the train may interact significantly with the bridge, especially when resonance occurs. Equally important is the riding comfort and the stability of the track and train cars, which are usually the most critical limit states in the design of this type of structures. With the aim of studying this problem a computer code was developed, being the interaction between the bridge and the train implemented by means of contact conditions between each train wheel (nodal point) and the structure (point inside a finite element). The treatment of the interaction between a train wheel and a point on the surface of a finite element is directly and efficiently implemented by means of an extended stiffness matrix, which includes stiffness, flexibility and additional terms that stem from the compatibility equations between the displacements of the vehicle and the bridge. This methodology was applied to the study of the dynamic behavior of a bowstring arch bridge and proved to be very accurate and efficien

Development of an efficient finite element model for the dynamic analysis of the train-bridge interaction

The design of high-speed railway bridges comprises a set of demands, from safety and serviceability aspects, to new types of equipment and construction solutions. In order to perform an accurate and realistic evaluation of the corresponding dynamic behavior, adequate analysis tools that take into account the complexity of the train-bridge system are required. These computational tools must be based on efficient algorithms to allow for the completion of detailed dynamic analyses in a reasonable amount of time. The classical methods of analysis may be unsatisfactory in the evaluation of the dynamic effects of the train-bridge system and fully assessment of the structural safety, track safety and passenger comfort. A direct and versatile technique for the simulation of the train-bridge interaction was implemented in the FEMIX code, which is a general purpose finite element computer program. The presented case study is an application of the proposed formulation, which proved to be very accurate and efficient

A nonlinear vehicle-structure interaction methodology with wheel-rail detachment and reattachment

. A vehicle-structure interaction methodology with a nonlinear contact formulation based on contact and target elements has been developed. To solve the dynamic equations of motion, an incremental formulation has been used due to the nonlinear nature of the contact mechanics, while a procedure based on the Lagrange multiplier method imposes the contact constraint equations when contact occurs. The system of nonlinear equations is solved by an efficient block factorization solver that reorders the system matrix and isolates the nonlinear terms that belong to the contact elements or to other nonlinear elements that may be incorporated in the model. Such procedure avoids multiple unnecessary factorizations of the linear terms during each Newton iteration, making the formulation efficient and computationally attractive. A numerical example has been carried out to validate the accuracy and efficiency of the present methodology. The obtained results have shown a good agreement with the results obtained with the commercial finite element software ANSY

Kinematics of a Spacetime with an Infinite Cosmological Constant

A solution of the sourceless Einstein's equation with an infinite value for the cosmological constant \Lambda is discussed by using Inonu-Wigner contractions of the de Sitter groups and spaces. When \Lambda --> infinity, spacetime becomes a four-dimensional cone, dual to Minkowski space by a spacetime inversion. This inversion relates the four-cone vertex to the infinity of Minkowski space, and the four-cone infinity to the Minkowski light-cone. The non-relativistic limit c --> infinity is further considered, the kinematical group in this case being a modified Galilei group in which the space and time translations are replaced by the non-relativistic limits of the corresponding proper conformal transformations. This group presents the same abstract Lie algebra as the Galilei group and can be named the conformal Galilei group. The results may be of interest to the early Universe Cosmology.Comment: RevTex, 7 pages, no figures. Presentation changes, including a new Title. Version to appear in Found. Phys. Let

Wheel–rail contact formulation for analyzing the lateral train–structure dynamic interaction

A wheel-rail contact formulation for analyzing the train-structure nonlinear interaction that takes into account the wheel and rail geometry is proposed. Most of the existing methods treat the contact forces as external forces, whereas the present formulation uses a finite element to model the behavior in the contact interface, based on Hertz's theory and Kalker's laws. The equations of motion are complemented with constraint equations that relate the displacements of the vehicle and structure, being the complete system solved directly using an optimized algorithm. The formulation is validated with experimental data from a test performed on a rolling stock plant

Cytotoxicity of triterpenoids-enriched extracts from bark of Eucalyptus nitens against colorectal HCT116 cancer cells

Eucalyptus nitens crops are used in Portugal mainly by the pulp and paper industries, producing substantial bark residues with no added value use [1]. They can, however, be an interesting source of bioactive triterpenic compounds. Here, a lipophilic crude extract (CE) from bark of E. nitens prepared with dichloromethane [1] with about 70% (w/w) of triterpenoids, and a fraction of this (F2) more enriched in triterpenoids (93% w/w), as well as their main compounds betulinic acid (BiA) and betulonic acid (BoA), were used to determine their potential cytotoxicity against the colorectal HCT116 cancer cells. After 48h of incubation, the extracts/compounds inhibited significantly cell growth in a concentration-dependent manner (assessed by the MTT assay), with a GI50 s of 1.3 µg/mL and 2.2 µg/mL for F2 and CE extracts, respectively, and of 0.8µM and 3.9µM for BoA and BiA, respectively. The inhibition of cell growth was shown to be dependent on both the arrest of cell cycle at the G2/M phase, and the induction of cell death (assessed by PI staining). At the higher concentrations tested (up to 25µM), apoptosis was the major contributor to the observed cell death, and that was associated with JNK activation. Using the JNK inhibitor SP600125 and the pan-caspase inhibitor z-VAD, apoptosis induced by the extracts/compounds was shown to be dependent on JNK and caspases activation. At intermediate concentrations of extracts/compounds, a delayed and non-apoptotic type of cell death was present, which was associated with a significant activation of AMPK and a decrease of p53 levels. Altogether, these results demonstrate that the wasted bark of E. nitens can be used as a potential source of interesting cytotoxic natural triterpenoids against cancer cells

Very special relativity as relativity of dark matter: the Elko connection

In the very special relativity (VSR) proposal by Cohen and Glashow, it was pointed out that invariance under HOM(2) is both necessary and sufficient to explain the null result of the Michelson-Morely experiment. It is the quantum field theoretic demand of locality, or the requirement of P, T, CP, or CT invariance, that makes invariance under the Lorentz group a necessity. Originally it was conjectured that VSR operates at the Planck scale; we propose that the natural arena for VSR is at energies similar to the standard model, but in the dark sector. To this end we provide an ab initio spinor representation invariant under the SIM(2) avatar of VSR and construct a mass dimension one fermionic quantum field of spin one half. This field turns out to be a very close sibling of Elko and it exhibits the same striking property of intrinsic darkness with respect to the standard model fields. In the new construct, the tension between Elko and Lorentz symmetries is fully resolved. We thus entertain the possibility that the symmetries underlying the standard model matter and gauge fields are those of Lorentz, while the event space underlying the dark matter and the dark gauge fields supports the algebraic structure underlying VSR.Comment: 19 pages. Section 5 is new. Published version (modulo a footnote, and a corrected typo

Statistical analysis of fatigue crack propagation data of materials from ancient portuguese metallic bridges

In Portugal there is a number of old metallic riveted railway and highway bridges that were erected by the end of the 19th century and beginning of the 20th century, and are still in operation, requiring inspections and remediation measures to overcome fatigue damage. Residual fatigue life predictions should be based on actual fatigue data from bridge materials which is scarce due to the material specificities. Fatigue crack propagation data of materials from representative Portuguese riveted bridges, namely the Pinhão and Luiz I road bridges, the Viana road/railway bridge, the Fão road bridge and the Trezói railway bridge were considered in this study. The fatigue crack growth rates were correlated using the Paris’s law. Also, a statistical analysis of the pure mode I fatigue crack growth (FCG) data available for the materials from the ancient riveted metallic bridges is presented. Based on this analysis, design FCG curves are proposed and compared with BS7910 standard proposal, for the Paris region, which is one important fatigue regime concerning the application of the Fracture Mechanics approaches, to predict the remnant fatigue life of structural details

A direct method for analyzing the nonlinear vehicle-structure interaction in high-speed railway lines

This article presents an accurate, efficient and stable algorithm to analyse the nonlinear vertical vehicle-structure interaction. The governing equilibrium equations of the vehicle and structure are complemented with additional constraint equations that relate the displacements of the vehicle with the corresponding displacements of the structure. These equations form a single system, with displacements and contact forces as unknowns, that is solved using an optimized block factorization algorithm. Due to the nonlinear nature of contact, an incremental formulation based on the Newton method is adopted. The track and structure are modelled using finite elements to take into account all the significant deformations. In the numerical example presented, the passage of the KHST over a railway viaduct is analysed, being the accuracy and computational efficiency of the proposed method clearly demonstrated

A nonlinear vehicle-structure interaction methodology for the assessment of the train running safety

A nonlinear vehicle-structure interaction methodology for the assessment of the train running safety is proposed in this article. The contact formulation between wheel and rail consists in three main steps: the geometrical problem, where the contact point position is detected; the normal contact problem, in which the forces are determined based on the Hertz theory, and the tangential contact problem, where the creep forces are calculated using the rolling friction laws proposed by Kalker. The behavior in the contact interface is reproduced by a contact element developed for this problem. Constraint equations that relate the displacements of the vehicle and structure are imposed using a direct method. The formulation is validated using results of an experimental test performed in a rolling stock test plant of the Railway Technical Research Institute in Japa