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

Evaluation of the marginal fit of three margin designs of resin composite crowns using CAD/CAM

OBJECTIVES: To examine the marginal fit of resin composite crowns manufactured with the CEREC 3 system employing three different margin designs; bevel, chamfer and shoulder, by means of a replica technique and a luting agent. METHODS: Three master casts were fabricated from an impression of a typodont molar tooth and a full-coverage crown prepared with a marginal finish of a bevel, a chamfer and a shoulder. Each cast was replicated 10 times (n = 10). Scanning of the replicas and crown designing was performed using the CEREC ScanTM system. The crowns were milled from Paradigm MZ100TM composite resin blocks. The marginal fit of the crowns was evaluated with a replica technique (AquasilTM LV, Dentsply), and with a resin composite cement (RelyXTM Unicem, AplicapTM) and measured with a travelling microscope. Statistical analysis was performed using two-way ANOVA. RESULTS: For the replica technique the average marginal gaps recorded were: Bevel Group 105±34 mm, Chamfer Group 94±27 mm and Shoulder Group 91±22 mm. For the resin composite cement the average marginal gaps were: Bevel Group 102±28 mm, Chamfer Group 91±11 mm and Shoulder Group 77±8 mm. Two-way ANOVA analysis showed that there was no statistically significant difference between the three groups of finishing lines regardless of the cementation technique used. CONCLUSIONS: The marginal gap of resin composite crowns manufactured with the CEREC 3 system is within the range of clinical acceptance, regardless of the finishing line prepared or the cementation technique used

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

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

The Bhuj Earthquake of 2001

The decision to send a team of earthquake engineering researchers and seismologists half way around the world to investigate a tragic earthquake was indeed a difficult one to make considering the circumstances. Logistical problems, from obtaining visas to transporting large equipment packages to mobilization in the field, were enough by themselves to find every reason for not having a reconnaissance effort. Moreover, risks posed by health and safety of investigators in the disaster region, along with the myriad of political issues and high costs associated with an international study of this degree, required much contemplation before a decision was made to deploy a team of investigators. However, an affirmative decision was made because of the benefits that the investigation would have with regard to the Center???s emphasis on earthquake loss reduction in the Central United States. Whereas no two earthquakes and their resulting consequences are identical, similarities between the New Madrid and Bhuj earthquakes, as noted is this report, were sufficient to justify sending a team.National Science Foundation EEC-970178