Browsing by Author "Lopez Garcia, Diego"

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    A bidirectional and homogeneous tuned mass damper: A new device for passive control of vibrations
    (Elsevier Sci. Ltd., 2007) Almazan, Jose L.; Llera Martin, Juan Carlos de la; Inaudi, Jose A.; Lopez Garcia, Diego; Izquierdo, Luis E.
    Passive tuned-mass dampers (TMDs) are a very efficient solution for the control of vibrations in structures subjected to long-duration, narrow-band excitations. In this study, a Bidirectional and Homogeneous Tuned Mass Damper (BH-TMD) is proposed. The pendular mass is supported by cables and linked to a unidirectional friction damper with its axis perpendicular to the direction of motion. Some advantages of the proposed BH-TMD are: (1) its bidirectional nature that allows control of vibrations in both principal directions; (2) the capacity to tune the device in each principal direction independently; (3) its energy dissipation capacity that is proportional to the square of the displacement amplitude, (4) its low maintenance cost. Numerical results show that, under either unidirectional or bidirectional seismic excitations, the level of response reduction achieved by the proposed BH-TMD is similar to that obtained from an "ideal" linear viscous device. Moreover, experimental shaking table tests performed using a scaled BH-TMD model confirm that the proposed device is homogeneous, and, hence, its equivalent oscillation period and damping ratio are independent of the motion amplitude. (C) 2006 Elsevier Ltd. All rights reserved.
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    Experimental Investigation of Multihazard Resistant Bridge Piers Having Concrete-Filled Steel Tube under Blast Loading
    (ASCE-AMER SOC CIVIL ENGINEERS, 2008) Fujikura, Shuichi; Bruneau, Michel; Lopez Garcia, Diego
    This paper presents the development and experimental validation of a multizard bridge pier concept, i.e., a bridge pier system capable of providing an adequate level of protection against collapse under seismic and blast loading (but not acting simultaneously). A multicolumn pier-bent with concrete-filled steel tube (CFST) columns is the proposed concept, and the adequacy of this system is experimentally investigated under blast loading. This paper describes simplified blast analysis, multihazard design of bridge piers, and blast experimental program and results. Additionally, the results from the blast experiments are compared with the results from the simplified method of analysis considering an equivalent single degree of freedom system having an elastic-perfectly plastic behavior. It is found that prototype bridge CFST columns can be designed to provide both satisfactory seismic performance and adequate blast resistance. It is also shown that the CFST columns exhibited a ductile behavior under blast load in a series of tests at 1/4 scale. Maximum deformation of the columns could be calculated using simplified analysis considering a factor to account for the reduction of pressures on the circular column and determined from this experimental program.
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    Linear isolation of stainless steel legged thin-walled tanks
    (ELSEVIER SCI LTD, 2007) Almazan, Jose L.; Cerda, Fernndo A.; De la Llera, Juan C.; Lopez Garcia, Diego
    Because of the booming wine industry in some seismic countries such as the US, Chile and Argentina, seismic protection of wine storage systems is of practical importance. In this study, the dynamic response of thin-walled legged wine tanks with seismic isolation is investigated. Linear fluid-structure interaction has been considered in the analyses performed with SAT-LAB and ADINA and two choices for the seismic isolation system have been evaluated: (i) a traditional lateral isolation system (LAI), and (ii) a vertical-rocking isolation system (VRI). As far as the authors know, the latter has not been considered in previous studies, and results show that it is a viable alternative for legged tanks. Moreover, all isolation devices have been designed considering the space limitations that are inherent to the implementation of these systems in practice. Results obtained for a suite of records and different structures have shown that both types of isolation lead to response reductions of the tank stresses. The reduction ranges from 20% to 79% for the LAI models and 31%-91% for the VRI, relative to the case without isolation. These promising results have implications in the selection of the thickness of the wall and the overall dimensions of the tank. (C) 2006 Elsevier Ltd. All rights reserved.
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    Seismic Response of Adjacent Steel Structures Connected by Passive Device
    (MULTI-SCIENCE PUBL CO LTD, 2011) Roh, Hwasung; Cimellaro, Gian P.; Lopez Garcia, Diego
    In this study, the seismic response of adjacent steel structures linked to one another at different floor levels by passive devices is evaluated. Two types of connectors are considered: linear viscous dampers and linear springs. Various combinations of type and location of the connectors are analyzed for wide ranges of their characteristics. Influence of the structural properties (ratio of number of stories and ratio of fundamental periods) and the properties of the excitation (frequency) on the story response are also investigated. The results show that reduction of the story drift and the floor acceleration is not possible if the structures are connected to one another solely by the springs. However, it is feasible if the structures are linked to one another by either: (a) viscous dampers or (b) combinations of viscous dampers and springs. Herein, response reductions corresponding to case (b) are generally smaller than those corresponding to case (a). Also, the coupling control approach is more effective in controlling the response than the uncoupled approach.