Épsilon

11

Authors: Carlos Mario Piscal Arévalo, Lucio Guillermo López Yépez, Nelson Afanador García

The structural system of reinforced concrete moment-resistant portal frames has been commonly used in buildings constructed in Colombia, due to both functional and technical aspects. Of the latter, extensive knowledge regarding analysis, design and construction is highlighted. Despite its widespread use in the country, this system is characterized by excessive flexibility to horizontal loads, so, in many cases, it is necessary to have large structural elements in order to meet the stiffness requirements stipulated by regulations on earthquake resistant design and construction. This often makes it unfeasible to use this structural system from economic, structural, and architectural points of view. This research, by designing 200 computer models of typical portal frame buildings with occupation listed as standard (group of use I), seismic parameters corresponding to intermediate seismic hazard zones, and variation in height and soil type, demonstrated the quantities of concrete needed per square meter to meet the stiffness requirements stipulated in the Colombian regulations on earthquake resistant constructions (NSR-10). These results allow the design engineer to count on a tool to assess the economic and operational feasibility of using portal frame systems in possible projects to develop, as long as they are within the number of storeys evaluated in this research. Moreover, if the use of the system is considered feasible, a pre-sizing of the structure can be rapidly obtained, considering horizontal effects generally predominant in this type of constructions, to select sections to be used.

19

Authors: Jorge Eliécer Rangel Díaz, Sandra Cristina Prada Rodríguez, Jenniffer Marcela Rodríguez Prada

This article focuses on the design and implementation of a monitoring system of variables used in the extraction and pumping of oil wells during the exploration of land made by Drilling and Production Services SAS. Currently, operators of the company use sensors to perform the monitoring of pressure and flow variables at three different points of the perforations, since it is important to know the exact amount of oil that travels along the tube and to detect any leakage problem. Furthermore, as a result of the location of these sensors the data storage process becomes inaccurate and expensive for operators, due to displacement from one place to another and to the difficulty to gather all the information after an exploration. For this reason, the article proposes a system for the centralization of information which allows to monitor and generate reports of each individual processes carried out

21

Authors: Francisco E. Moreno García, José A. Becerra Vargas & Juan J. Quiroz Omaña

This document presents an angular velocity PID tuning for a control system with electronic differential for two brushless electric motors with permanent magnets in the wheel axles in Lizard vehicle. The main objective is to allow the vehicle to make a smooth curve, since it has no mechanical differential due to independent motors at each wheel. Three tunings were performed, two of them based on the open-loop response curve in s, by Ziegler-Nichols and Cohen-Coon, and a third trial and error tuning. The three tunings are compared for a step input, a sinusoidal input and a ramp-type input. A very similar response is observed between the Ziegler-Nichols tuning method and the Cohen-Coon one, being slightly faster the Cohen-Coon response for step and sinusoidal inputs, but slightly slower for a ramp-type input. However, both types of tunings had high overdamping for a step response. The trial and error tuning was slower than the others but presented a balanced answer, due to lesser overdamping. Manual tuning achieved better results; having the mathematical model of the system and the simulation software allow us to optimize the results of tunings like the Ziegler-Nichols and the Cohen-Coon ones.

21

Authors: Guillermo Armando Briceño Vanegas, Alejandra Camacho Osman, Laura Rincón Valero

The ecological integrity of gallery forests on the San José de Matadepantano Farm was observed between July 2010 and October 2011 to determine the current state of the ecosystems. Gallery forests border the Tiestal, Güio, and Las Flores streams, surrounded by savannah covering 1200 acres of territory. Ecological integrity was measured by variables such as coverage, density, extent of forest corridors, richness, diversity, and fragmentation levels or discontinuities of forests along the waterways. The structure was described by scale representations in plan views and side views. Forest cover was determined as the percentage of area occupied by each of the following categories: 1) non-intervened forest, 2) regenerating forest, 3) intervened forest, 4) agricultural crops, and 5) paths and works. Gallery forests showed high ecological integrity, especially in places that are the farthest from the Utopia campus, which is the biggest center of human activity. Close to campus there is a wide range of activities represented in agriculture, constructions and paths, and, therefore, the gallery forests located in the vicinity exhibited a smaller ecological integrity, lowest forest cover, and higher structural degradation than those in other parts of the farm. Forests surrounding the Güio stream are in a good state of conservation, covering 70% of forested formations in the farm.