Patrícia Lopes

Vibrations inside buildings due to subway railway traffic. Experimental validation of a comprehensive prediction model

The present paper focuses on the experimental validation of a numerical approach previously proposed by the authors for the prediction of vibrations inside buildings due to railway traffic in tunnels. The numerical model is based on the concept of dynamic substructuring and is composed by three autonomous models to simulate the following main parts of the problem: i) generation of vibrations (train-track interaction); ii) propagation of vibrations (track-tunnel-ground system); iii) reception of vibrations (building coupled to the ground). The experimental validation consists in the comparison between the results predicted by the proposed numerical model and the measurements performed inside a building due to the railway traffic in a shallow tunnel located in Madrid. Apart from the brief description of the numerical model and of the case study, the main options and simplifications adopted on the numerical modeling strategy are discussed. The balance adopted between accuracy and simplicity of the numerical approach proved to be a path to follow in order to transfer knowledge to engineering practice. Finally, the comparison between numerical and experimental results allowed finding a good agreement between both, fact that ensures the ability of the proposed modeling strategy to deal with real engineering practical problems.

ACCOUNTING FOR FINANCIAL INSTRUMENTS: A COMPARISON OF EUROPEAN COMPANIES' PRACTICES WITH IAS 32 AND IAS 39*

This paper analyses accounting for financial instruments of STOXX 50 companies and compare them to the requirements of IAS 32 and IAS 39, before IFRS are mandatory in the European Union. We use a list of 120 categories of inquiry and 370 possible responses and analyse companies’ annual reports. The results show that the majority of companies disclose the fair value amounts and methods of calculation but the information is neither clear nor objective, preventing the fair value information from being relevant and useful. We conclude that companies have a long way to go in terms of accounting and disclosure of financial instruments, namely derivatives. The mandatory adoption of more stringent standards such as the IAS 32 and IAS 39 may improve the information disclosed by companies. Doubts about the compliance degree and the usefulness of the information still remain. This paper brings new perspectives to the challenges of IAS/IFRS adoption, namely to what relates to fair value measurement.

Accounting for electricity derivatives under IAS 39

This paper analyses the impact of accounting rules on the accounting for hedges with energy derivatives in the context of the launch of MIBEL Derivatives Market. Specifically, the key questions of accounting for nonfinancial derivatives raised by IAS 39, following the mandatory adoption of IFRS in Europe, are described. Under certain conditions, IAS 39 allows contracts on commodities to be exempted from its rules. Those conditions are, however, quite strict and require a case-by-case analysis. IAS 39 requires all derivatives to be reported at fair value. Nevertheless, it allows for hedge accounting, provided that certain conditions are met, eliminating undesirable income volatility. Futures contracts pay-off profile is generally the inverse of the underlying item, and so futures tend to be easily qualified for hedge accounting rules of IAS 39, due to the way in which hedge effectiveness is measured. The paper shows that as far as energy producers and users are concerned, when hedges are accomplished with exchange-traded futures, compliance with IAS 39 hedge accounting rules is simple and straightforward.

GROUND-BORNE VIBRATIONS DUE TO RAILWAY TRAFFIC IN URBANIZED AREAS: A NUMERICAL STUDY ABOUT TRAFFIC IN TRENCH CROSS-SECTIONS

Modern cities require efficient mass transportation systems like subway and railway networks. Due to the lack of available space and also due to environmental concerns, it is usually preferable to use the underground space to construct such kind of infrastructures. In this context, several railway lines run in trench cross-sections in urbanized regions. This option permits to save space, allowing reducing the distance between railway lines and existing buildings. Due to that reduced distance, nearby buildings are exposed to relevant levels of vibrations that can annoys their inhabitants. In the present paper a numerical investigation about the dynamic aspects related with wave propagation due to railway traffic in trench cross-sections is presented. For that purpose, a 2.5D FEM-PML formulation is adopted for the simulation of the main system (track-retaining structure-ground), while the rolling stock is simulated by a multi-body approach. A reference scenario is previously presented, being followed by a parametric study where the influence of the geotechnical properties of the ground was analyzed. 1982 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 1982-1993

THE INFLUENCE OF DEGRADATION OF SHEAR MODULUS OF SOIL ON PREDICTED RAILWAY VIBRATIONS IN TUNNELS EXCAVATED WITH TBM: A NUMERICAL ANALYSIS

In this paper the influence of the stress state within the soil on predicted railway vibrations in tunnels is studied, regarding Gs modulus degradation that occurs when the tunnel is excavated with Tunnel Boring Machine (TBM). The adopted procedure is uncoupled, using a 2D FEM model to simulate the process of tunnelling which incorporates the constitutive model known as Hardening Soil with small strain stiffness (HS-small). The Gs modulus values are then used in a dynamic numerical model based on a 2.5D FEM-PML approach in order to simulate the vibrations induced by railway traffic. Simulations are then performed assuming two different scenarios for the elastic properties of the ground: i) assuming Gs modulus for low strain deformation for whole domain, i.e., neglecting the perturbation of the soil due to the tunnel construction; ii) assuming values of Gs modulus computed taking into account the strains induced by the tunnel construction. The numerical results show a clear influence of tunnelling process, being more relevant at closest distances to the tunnel.

VIBRATIONS IN BUILDINGS DUE TO RAILWAY TRAFFIC IN TUNNELS: MODELLING STRATEGIES AND INFLUENCE OF SOIL STIFFNESS

Abstract. In this paper a numerical study about the influence of soil stiffness on the assessment of vibrations induced by railway traffic in tunnels is performed. A comprehensive numerical model is used to achieve the lumped objective, where the source of vibration (traintrack interaction), the propagation of vibrations (tunnel-ground system) and their reception (building close to the railway infrastructure) are simulated by a sub-structuring approach. It was found that the soil stiffness plays a relevant role on the mechanisms of propagation of vibrations through the ground as well as on the soil-structure interaction. Regarding the last topic, different approaches were attended for the inclusion of the SSI effects, namely a detailed boundary elements formulation and a simplified lumped-parameter model. The study performed revealed that the usage of lumped parameter models can be faced as a good option taking into account the compromise between accuracy of the solution and reduction of the computation effort.