Effect of soil properties on the dynamic response of simply-supported bridges under railway traffic through coupled boundary element-finite element analyses

Abstract

Railway induced vibrations on short-to-medium span simply-supported (SS) bridges is addressed in this contribution. Such structures may experience high levels of vertical acceleration at the platform, leading to adverse consequences such as a premature degradation of the ballast layer and passenger discomfort. In the present study, the evolution of the bridge dynamic response when soil-structure interaction (SSI) is taken into account is investigated. To this end a coupled three-dimensional (3D) Boundary Element-Finite Element model (BEM-FEM) formulated in the time domain is implemented to reproduce the soil and structural behaviour, respectively. First, a set of soil-bridge systems of interest is defined, covering a wide range of lengths and natural frequencies for the structures, and an interval of expectable elastic properties and damping levels for the soil. Then, different types of analyses are performed on the soil-bridge systems extracting conclusions regarding the effect of including SSI in numerical models for predicting the bridge behaviour under railway traffic. In particular natural frequencies and modal damping levels are identified, and the structure amplification after the passage of a moving load in free vibration is investigated. Conclusions regarding how resonance and cancellation conditions may be affected by soil properties are extracted. Finally, the dynamic response of a real bridge, belonging to the Spanish railway network, is evaluated under the circulation of trains that induce second and third resonances of the bridge fundamental mode. The effect of the soil flexibility, soil material damping and the bridge resonance order are evaluated. Conclusions regarding the appropriateness of the results provided by common models which do not include SSI effects are extracted.

On the influence of shallow soil strata on the dynamic soil–structure interaction of simply supported high-speed railway bridges

“…There is a common perception in structural engineering that the effects of SSI are always beneficial and that the response of the structure is for all cases reduced; however, due to the decrease of the natural frequency, SSI may in some cases lead to a detrimental effect [7]. Including SSI in the analyses of railway bridges leads to a reduction of the natural frequency of the first bending mode of the bridge and an increase of the modal damping ratio [8][9][10][11]. The consequence is a reduction of the resonant amplitude during train loading, but also a decrease of the resonant train velocity.…”

“…The SSI of SS railway bridges have been studied assuming soil strata of infinite depth (half-spaces) and with homogeneous soil properties [8,9]. The bridges coupled to halfspaces exhibit increasing modal damping ratio and decreasing natural frequency, following the general trend of the relative stiffness parameter, which is the ratio between the flexural rigidity of the beam and the static stiffness of the soil-foundation system [12].…”

Interacción suelo-estructura en pérgolas de ferrocarril de alta velocidad

“…Figura 3.7: Resultados de aceleración. Doménech et al [4] En la figura 3.8 se aprecian los resultados de aceleración obtenidos por Martínez-Rodrigo et al [15]. Se establece un amortiguamiento estructural constante igual al 5 % y se realiza el análisis para cuatro tipos diferentes de terreno, desde suelo infinitamente rígido a blando.…”

“…Figura 3.8: Resultados de aceleración. Martínez-Rodrigo et al [15] De los trabajos que han estudiado la influencia de la interacción suelo-estructura sobre los fenómenos de resonancia se extrae una conclusión muy clara, y es que cuanto menos rígido es el terreno sobre el que se sustenta la construcción menor es el valor de dichos efectos.…”

“…Figura 3.6: Modelo de elementos finitos y de contorno. Doménech et al[4] y Martínez-Rodrigo et al[15] …”