Browsing by Author "Riddell, Rafael"

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    A Simple Stepped-Column Buckling Model and Computer Algorithm
    (AMER INST STEEL CONSTRUCTION, 2011) Vasquez, Jorge; Riddell, Rafael
    The paper presents a solution to the problem of obtaining the effective length ratios needed for the design of stepped columns. The formulation of a discrete model is presented, and a numerical algorithm is implemented to solve it as a matrix eigenvalue problem. The method is an alternative to using tabulated results, which have been obtained from closed-form solutions for a number of ideal boundary conditions, which in most practical cases is cumbersome and almost always unpredictably inaccurate. A MATLAB coding of the algorithm is provided, and examples illustrating its use are included.
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    Inelastic response spectrum: Early history
    (WILEY-BLACKWELL, 2008) Riddell, Rafael
    Detailing the time period from, roughly, 1950 through 1980, this Historical Note documents the development of the initial concept of the inelastic response spectrum and how it evolved to become the basis for rational procedures for earthquake-resistant design, which are used even today. Copyright (c) 2008 John Wiley & Sons, Ltd.
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    On ground motion intensity indices
    (SAGE PUBLICATIONS INC, 2007) Riddell, Rafael
    The characterization of strength of earthquake demands for seismic analysis or design requires the specification of a level of intensity. Numerous ground motion intensity indices that have been proposed over the years are being used for normalizing or scaling earthquake records regardless of their efficiency. An essential point of this study is that a ground motion index is appropriate, or efficient, as long as it can predict the level of structural response. This study presents correlations between 23 ground motion intensity indices and four response variables: elastic and inelastic deformation demands, and input energy and hysteretic energy; nonlinear responses are computed using elastoplastic, bilinear, and bilinear with stiffness degradation models. As expected, no index is found to be satisfactory over the entire frequency range. Indeed, indices related to ground acceleration rank better in the acceleration-sensitive region of the spectrum; indices based on ground velocity are better in the velocity-sensitive region and, correspondingly, generally occur in the displacement-controlled region. Despite frequent criticism, the peak ground motion parameters passed the test successfully. A ranking of indices is presented, thus providing a choice of the most appropriate one for a particular application in the frequency range of interest.
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    Optimal Strut-and-Tie Models Using Full Homogenization Optimization Method
    (2012) Pablo Herranz, Juan; Santa Maria, Hernan; Gutierrez, Sergio; Riddell, Rafael
    An optimization method based on homogenization is proposed for finding optimal strut-and-tie (ST) models for reinforced concrete (RC) elements. The method uses a layout that minimizes displacement for a given loading state in a linearly elastic regime by mixing two materials. Although this optimal layout might contain fine mixtures, one can still obtain a strongly resembling ST model without mixtures that performs closely to the optimal configuration through a penalization procedure. Two examples from the ST literature are used to illustrate the application of the method: the dapped beam and the beam on beam. The reinforcement layouts obtained make the element more efficient in terms of ultimate load divided by the weight of the steel used and having smaller deflections and crack widths. It is remarkable that the used optimization method, which considers the structure in the linearly elastic regime, gives a very good performance for the nonlinear regime.