Rojas-Mercedes, Norberto J.

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2005 - 200912010 - 20111
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    Seismic response of RC frame buildings with non reinforced exterior beam column joints
    (2011) Rojas-Mercedes, Norberto J.; López-Rodríguez, Ricardo R.; College of Engineering; Portela Gautier, Genock; Martínez Cruzado, José A.; Suárez Colche, Luis E.; Department of Civil Engineering; Gutiérrez, Gustavo
    Recent earthquakes have demonstrated the risk that reinforced concrete structures constructed before 1970 represent for society since these structures were designed with design codes in which the seismic provisions were not as strict as they are nowadays. This makes such structures vulnerable to strong earthquakes. Generally these codes did not have special provisions for the design of beam-column connections and therefore it was common that these elements were not confined with transverse reinforcement. Past earthquakes also have demonstrated that exterior connections without reinforcement are more prone to fail that the interior ones in some cases initiating the collapse of structures. This investigation is focused in the development of a model of exterior connections without reinforcement that can be used in the study of the seismic vulnerability of reinforced concrete frames designed before 1970. This model consisted of an envelope curve that identifies three important points of the behavior of such connections: the point of cracking, the point of maximum resistance and the residual strength point. The model was corroborated with 19 experimental tests of the literature. The results of the predictions compare favorably with the experimental results. The model was implemented in the Opensees program for the static and dynamic analysis of structures designed with the Puerto Rico building code of 1968, whose main system of lateral resistant was the moment resisting frames. For each structure two models were created. In one the connections were modeled as rigid and in the other they were modeled as flexible with the proposed model. From the static analysis one concluded that the frames modeled with flexible joints experienced a decrease in the lateral load capacity ranging from 16 to 32% with respect to the frames modeled with rigid joints. From the dynamic analysis it was observed that the maximum drifts increased between 10 and 78% with respect to the drifts obtained from the analysis with rigid connections. This increase was related directly with the damage of the exterior joints in the analysis.
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    Consideración de las columnas cortas en la vulnerabilidad sísmica de las estructuras
    (2005) Rojas-Mercedes, Norberto J.; Martínez-Cruzado, José A.; College of Engineering; López Rodríguez, Ricardo R.; Suárez Colche, Luis E.; Department of Civil Engineering; Huérfano Moreno, Víctor
    It has been observed that in recent earthquakes the short column effect has caused damage. The main objective of this investigation was to develop a simple methodology to identify the short column effect. The methodology was based on the aspect ratio of columns of typical sections laterally confined up to certain height. The results of this study are summarized in several graphs that allow to discern between brittle failures (shear) and ductile (flexure) of short columns. Having observed the damages caused by several earthquakes from the past, a plot has been proposed to estimate damages from such short column effect.