Peak Displacements and Interstory Drifts on Nonlinear Multi Degree of Freedom Systems Using Principal Component Analysis.

Principal Components Analysis (PCA) is a method to extract the principal components (or modes) of response from recorded or computed response data, of systems exhibiting linear and/or nonlinear response. For linear systems, the PCA mode shapes coincide with the elastic mode shapes, if the nodal mass is uniformly distributed. For nonuniform mass distributions, the PCA modes are related to the elastic modes. The PCA technique is particularly valuable when applied to systems responding nonlinearly, because it identifies the 'predominant mode' of response and the degree to which the response is in this mode. This paper illustrates the use of the PCA technique for estimating floor and interstory drifts for a 12-story moment-resistant frame responding to earthquake ground motions. Linear and nonlinear responses are considered, and the observed mode shapes and the accuracy of drift estimates are discussed. The interaction of modal amplitudes in time is considered in detail. The peak roof drift and interstory drifts are expressed as linear combinations of the PCA modes, and are represented graphically, together with the observed interaction response. A technique is described to determine peak values of these quantities by maximizing the drift functions relative to the observed modal interactions

Dimensionamiento en rotura a flexión de secciones de hormigón armado. Un planteamiento compacto

This paper is an overview of the traditional method of strength design of reinforced concrete sections. The procedure, presented in the current textbooks, dates from the 50's of XX century and it can be simplified. In this work the approach is reformulated and presented in a more compact way, which implies a change both from the educational point of view and from the professional point of view of reinforced concrete. Theorem of Optimal Reinforcement of RC Sections confirms that the ingenious solutions proposed by Whitney and Wuczkowsky correspond to the minimum of a general problem that can be developed more rationally. Presenting the problem in compact form, using diagrams RSD allowed to choose alternative solutions of reinforcement with reduced environmental impact.Este artículo es una revisión general del procedimiento tradicional de dimensionamiento en rotura de secciones de hormigón armado. El procedimiento que recogen la mayor parte de los libros de texto actuales data de los años 50 del siglo XX y es susceptible de ser simplificado. En este artículo el planteamiento se reformula y se presenta de una manera más compacta, lo que supone un cambio tanto desde el punto de vista docente como desde el punto de vista profesional del hormigón armado. El Teorema de Armado a Flexión confirma que las ingeniosas soluciones propuestas por Whitney o Wuczkowsky, corresponden a los mínimos de un problema general que puede ser planteado de una forma más racional. El hecho de presentar el problema de forma compacta, empleando los diagramas RSD permite poder elegir soluciones alternativas de armado de menor impacto medioambiental

Ernst Jünger and the problem of Nihilism in the age of total war

As a singular witness and actor of the tumultuous twentieth century, Ernst Jünger remains a controversial and enigmatic figure known above all for his vivid autobiographical accounts of experience in the trenches of the First World War. This article will argue that throughout his entire oeuvre, from personal diaries to novels and essays, he never ceased to grapple with what he viewed as the central question of the age, namely that of the problem of nihilism and the means to overcome it. Inherited from Nietzsche’s diagnosis of Western civilization in the late nineteenth century to which he added an acute observation of the particular role of technology within it, Jünger would employ this lens to make sense of the seemingly absurd industrial slaughter of modern war and herald the advent of a new voluntarist and bellicist order that was to imminently sweep away timorous and decadent bourgeois societies obsessed with security and self-preservation. Jünger would ultimately see his expectations dashed, including by the forms of rule that National Socialism would take, and eventually retreated into a reclusive quietism. Yet he never abandoned his central problematique of nihilism, developing it further in exchanges with Martin Heidegger after the Second World War. And for all the ways in which he may have erred, his life-long struggle with meaning in the age of technique and its implications for war and security continue to make Jünger a valuable interlocutor of the present

Direct damage controlled seismic design of plane steel degrading frames

A new method for seismic design of plane steel moment resisting framed structures is developed. This method is able to control damage at all levels of performance in a direct manner. More specifically, the method: (a) can determine damage in any member or the whole of a designed structure under any given seismic load, (b) can dimension a structure for a given seismic load and desired level of damage and (c) can determine the maximum seismic load a designed structure can sustain in order to exhibit a desired level of damage. In order to accomplish these things, an appropriate seismic damage index is used that takes into account the interaction between axial force and bending moment at a section, strength and stiffness degradation as well as low cycle fatigue. Then, damage scales are constructed on the basis of extensive parametric studies involving a large number of frames exhibiting cyclic strength and stiffness degradation and a large number of seismic motions and using the above damage index for damage determination. Some numerical examples are presented to illustrate the proposed method and demonstrate its advantages against other methods of seismic design. © 2014, Springer Science+Business Media Dordrecht

USEE 2001: Utility Software for Earthquake Engineering Report and User's Manual

National Science Foundation EEC-970178

flexibility

Empirical observations and analysis of the recorded response of two California bridges indicate that the flexibility of the bridge embankments has a significant effect on the displacement demands sustained by the columns of short bridges under seismic excitation. Because the deck and abutments provide a capable load path, the columns only need to maintain gravity load support while accommodating the lateral displacement demands associated with the response of the embankments. This is in contrast to conventional R (or Z) factor approaches, which require the columns to provide substantial lateral resistance and, hence, lead to relatively large diameter columns that have limited displacement capacity. A displacement-based approach to the design of the columns is proposed. Displacement demand is assessed for one or multiple performance objectives using a simple extension of the "N2" model to address the nonlinear response of the embankments. Relative to conventional designs, the smaller diameter columns obtained with this approach have better seismic performance. The columns have a larger displacement capacity and sustain less damage because they have larger yield displacements. The columns also are much less vulnerable to shear failures because of their more slender aspect ratios. Normalized embankment capacity curves are provided, and their use is illustrated with an example.C1 Pamukkale Univ, Dept Civil Engn, Denizli, Turkey.Santa Clara Univ, Santa Clara, CA 95053 USA