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Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
Engineering Structures | Year: 2013

As it is widely recognized, seismic design parameters used in most current codes are mainly intended for designing concrete walls in medium- or high-rise buildings. In low-rise concrete housing, thin walls with low concrete strength, web steel ratio smaller than the minimum ratio prescribed by codes, and in many cases, shear web reinforcement made of welded wire meshes are commonly used. In this paper, a simplified equation for estimating the period of vibration of low-rise concrete housing is proposed. The equation is based on response measured during shaking table tests of solid walls and walls with openings, on the results derived from conventional spectral analysis of ambient vibration tests, as well as on results obtained from mathematical models using the wide-column analogy and the finite element method. Statistical analysis of the ratios of predicted-to-measured periods demonstrated that predicted periods were very similar to those observed, and the scatter is also lower than in existing equations. The proposed equation is useful for seismic design, as well as for assessing the adequacy of available equations in current codes. © 2013 Elsevier Ltd. Source


Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
Earthquake Engineering and Structural Dynamics | Year: 2013

Experimental evidence supporting the fact that results from quasi-static (QS) test of low-rise reinforced concrete walls may be safely assumed as a lower limit of strength and displacement, and energy dissipation capacities are still scarce. The aim of this paper is to compare the seismic performance of 12 reinforced concrete walls for low-rise housing: six prototype walls tested under QS-cyclic loading and six models tested under shaking table excitations. Variables studied were wall geometry, type of concrete, web steel ratio, type of web reinforcement and testing method. Comparison of results from dynamic and QS-cyclic tests indicated that stiffness and strength properties were dependent on the loading rate, the strength mechanisms associated with the failure mode, the low-cycle fatigue, and the cumulative parameters, such as displacement demand and energy dissipated. Copyright © 2012 John Wiley & Sons, Ltd. Source


Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
Earthquake Engineering and Structural Dynamics | Year: 2012

Acceptance limits of the structural response of walls for low-rise concrete housing were developed. Proposed values are applicable within a performance-based seismic design framework. Acceptance limits are based on performance indicators of structural response-allowable story drift ratios, width of residual cracks and residual damage index, and expected damage of walls. Cracking limits were defined from parameters obtained at the unloading stage of walls (i.e., residual cracking stage). The residual cracking stage may be used for structural damage evaluation and cost estimation of structural rehabilitation after an earthquake has occurred. The performance indicators proposed herein were derived from test observations and measured response of 39 RC walls' specimens during shaking table and quasistatic testing, as well as from limiting values and results of previous studies. © 2012 John Wiley & Sons, Ltd. Source


Carrillo J.,University Militar Nueva Granada | Alcocer S.M.,National Autonomous University of Mexico
Earthquake Spectra | Year: 2012

The walls of modern low-rise economic housing in several Latin American countries are typically thin and have a low concrete strength, web steel ratios that are smaller than the minimum prescribed by current codes, and web shear reinforcement made of welded-wire mesh. In light of these particular wall characteristics, research was aimed at developing a performance-based backbone model capable of predicting the seismic behavior of reinforced concrete (RC) walls for one- and two-story housing. The selected tri-linear model is associated with three limit states: diagonal cracking, peak shear strength, and ultimate deformation capacity. The model was developed on the basis of the observed response of 39 quasi-static and shake table experiments. Iterative nonlinear regression analyses were performed for deriving the semi-empirical equations in this study. The paper also discusses the adequacy of some existing models to predict the seismic behavior of RC walls and the limitations of the proposed equations. © 2012, Earthquake Engineering Research Institute. Source


Patent
University Militar Nueva Granada | Date: 2014-03-14

The present invention relates to an automatic stimulator based on vibrations for cell cultures, fulfilling the function of activating the proliferation of osteoprogenitor cells and of activating the expression of the genes involved in the process of cell differentiation toward the osteogenic line. This effect is produced in the cells by the application of mechanical vibrational load. In this respect, the operation of the stimulator of the present invention comprises a system incorporating an actuator of mechanical type, controlled and regulated according to the specific requirements defined by the user. The actuator is the source of the vibrations which will be applied upon the flasks containing the cell cultures. The automatic stimulator for cell cultures is characterized by being controllable and programmable from a computer through the storage of routines of stimulation and repose, with programming of intensity of the load graduated in G (gravitational) units, being repeated in an automatic manner a number of times determined by the user, it being appropriate for performing routines in the laboratory.

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