Análisis de la capacidad de soporte sísmica de fundaciones superficiales

Indexación: Web of Science; Scielo.In the context of engineering practice, the problem of the seismic bearing capacity of shallow foundations has been solved indirectly, either due an increase of the static allowable soil pressures related to the probability of occurrence of the design earthquake or by adopting an equivalent pseudo-static approach. However, during last decades, a series of analytical methods that directly address the problem from the seismic point of view has been developed. This paper presents a parametric comparative analysis of different methods for estimating seismic bearing capacity of shallow strip foundations. Analytical methods, developed in the framework of both limit equilibrium and limit analysis theories, and also simplified design procedures typically used in practice were considered. The results obtained show an important decrease of the bearing foundation capacity with increasing of the maximum earthquake acceleration, which highlights the need to obtain a measure of the reliability associated with both calculation methods and safety factors commonly used for seismic design.En el contexto de la práctica ingenieril, el problema de la capacidad de soporte sísmica de fundaciones superficiales generalmente ha sido resuelto, de modo indirecto, ya sea considerando un incremento en las tensiones admisibles estáticas del suelo, asociado a la probabilidad de ocurrencia de un cierto evento sísmico de diseño, o bien adoptando un enfoque de tipo pseudoestático equivalente. Sin embargo, durante las últimas décadas se han desarrollado una serie de métodos analíticos que abordan directamente el problema desde el punto de vista sísmico. Este artículo presenta un análisis comparativo de tipo paramétrico entre diferentes métodos para estimar la capacidad de soporte sísmica de fundaciones superficiales corridas. Se consideraron métodos analíticos, desarrollados en el contexto de las teorías de equilibrio límite y análisis límite, y también procedimientos de diseño simplificados típicamente utilizados en la práctica. Los resultados obtenidos muestran un importante deterioro de la capacidad de soporte de la fundación en la medida que la aceleración máxima del sismo aumenta, lo cual pone de manifiesto la necesidad de establecer una medida de la confiabilidad asociada a los métodos de cálculo y factores de seguridad comúnmente usados para diseño sísmico.http://ref.scielo.org/kp4j8

On weak and strong magnetohydrodynamic turbulence

Recent numerical and observational studies contain conflicting reports on the spectrum of magnetohydrodynamic turbulence. In an attempt to clarify the issue we investigate anisotropic incompressible magnetohydrodynamic turbulence with a strong guide field $B_0$. We perform numerical simulations of the reduced MHD equations in a special setting that allows us to elucidate the transition between weak and strong turbulent regimes. Denote $k_{\|}$, $k_\perp$ characteristic field-parallel and field-perpendicular wavenumbers of the fluctuations, and $b_{\lambda}$ the fluctuating field at the scale $\lambda\sim 1/k_{\perp}$. We find that when the critical balance condition, $k_{\|}B_0\sim k_{\perp} b_{\lambda}$, is satisfied, the turbulence is strong, and the energy spectrum is $E(k_{\perp})\propto k^{-3/2}_{\perp}$. As the $k_{\|}$ width of the spectrum increases, the turbulence rapidly becomes weaker, and in the limit $k_{\|}B_0\gg k_{\perp} b_{\lambda}$, the spectrum approaches $E(k_{\perp})\propto k_{\perp}^{-2}$. The observed sensitivity of the spectrum to the balance of linear and nonlinear interactions may explain the conflicting numerical and observational findings where this balance condition is not well controlled.Comment: 4 pages, 2 figure

Low frequency vibration isolation technology for microgravity space experiments

The dynamic acceleration environment observed on Space Shuttle flights to date and predicted for the Space Station has complicated the analysis of prior microgravity experiments and prompted concern for the viability of proposed space experiments requiring long-term, low-g environments. Isolation systems capable of providing significant improvements in this environment exist, but have not been demonstrated in flight configurations. This paper presents a summary of the theoretical evaluation for two one degree-of-freedom (DOF) active magnetic isolators and their predicted response to both direct and base excitations, that can be used to isolate acceleration sensitive microgravity space experiments

Shadows and strong gravitational lensing: a brief review

For ultra compact objects (UCOs), Light Rings (LRs) and Fundamental Photon Orbits (FPOs) play a pivotal role in the theoretical analysis of strong gravitational lensing effects, and of BH shadows in particular. In this short review, specific models are considered to illustrate how FPOs can be useful in order to understand some non-trivial gravitational lensing effects. This paper aims at briefly overviewing the theoretical foundations of these effects, touching also some of the related phenomenology, both in General Relativity (GR) and alternative theories of gravity, hopefully providing some intuition and new insights for the underlying physics, which might be critical when testing the Kerr black hole hypothesis.Comment: 32 pages, 9 figures; Review paper in the General Relativity and Gravitation (GRG) Topical Collection "Testing the Kerr spacetime with gravitational-wave and electromagnetic observations" (Guest Editor: Emanuele Berti); v2: Typo corrected and two references adde