Analytical modeling of reinforced concrete columns subjected to bidirectional shear

Under general seismic loading, reinforced concrete columns may be subjected to lateral loads in more than one direction. Available experimental data on columns subjected to bidirectional forces indicate that higher levels of damage and a higher loss of ductility and strength have been observed compared to similar tests under unidirectional shear forces. In this study, an experimental program was conducted in which six lightly reinforced concrete columns were subjected to unidirectional and bidirectional cyclic shear forces. This observation was used to identify the mechanisms and parameters governing the behavior of columns subjected to cyclic bidirectional lateral loads. Hence, a new conceptual model was developed to obtain the capacity of member. The shear forces were analyzed and an analytical formulation was derived to account for the effects in the concrete stress-strain relationship, the moment-curvature diagram and the plastic hinge length. These equations were used along with a structural model with concentrated plastic hinges to obtain the capacity curve of the column. The results of the formulations developed were verified using the results of the experiments performed on columns subjected to unidirectional and bidirectional cyclic lateral forces.Peer ReviewedPostprint (author's final draft

Relations between the terms of the stiffness matrix of a finite element three-dimensional hexaedric of eight nodes

El cálculo de los términos de la matriz de rigidez de un elemento finito viene dado por integrales múltiples de funciones racionales, lo cual amerita un alto costo de tiempo de CPU. En el presente trabajo analizaremos esta matriz para el elemento finito hexaédrico de 8 nodos con tres grados de libertad por nodo para problemas de elasticidad tridimensional y para este elemento en particular, el denominador del integrando es un polinomio en tres variables. La matriz de rigidez es de orden 24 × 24, simétrica y está particionada en 64 bloques de orden 3 × 3, correspondientes a la incidencia de los grados de libertad de cada par de nodos. Así, se presenta un conjunto de ecuaciones, donde dado un término de la matriz de rigidez que no pertenece a la diagonal principal del bloque que le corresponde, se puede calcular directamente el otro término del mismo bloque que esta en posición simétrica con la diagonal principal del bloque. Estas ecuaciones relacionan un total de 84 pares de términos de la matriz de rigidez, lo que representa un ahorro superior al 28% del total de 300 términos que definen la matriz. Además, se mantiene la precisión con que se calculan los términos a introducir en las ecuaciones.Peer Reviewe

Elaboración de guías de laboratorio de estructuras de la Universidad Católica de Colombia

Práctica EmpresarialEn el presente trabajo se encontrarán las pautas y orden lógico para la realización de prácticas de laboratorio de estructuras en ingeniería civil, donde se tendrán en cuenta aspectos como funcionamiento adecuado de los equipos existentes, manejo apropiado de los materiales a ensayar y los requerimientos exigidos por las normas técnicas (ICONTEC y ASTM), para el correcto procedimiento y desarrollo en las prácticas.INTRODUCCIÓN 1. GENERALIDADES 2. METALES 3. UNIDADES DE MAMPOSTERÍA (LADRILLO) 4. LA MADERA 5. EL CONCRETO 6. CEMENTO. 7. AGREGADOS PARA CONCRETO. CONCLUSIONES RECOMENDACIONES BIBLIOGRAFÍA ANEXOPregradoIngeniero Civi

On the Use of Ground Antenna Arrays for Satellite Tracking: Architecture, Beamforming, Calibration and Measurements

Nowadays, ground stations which integrate the control segment of a satellite mission have as a common feature, the use of large reflector antennas for space communication. Apart from many advantages, large dishes pose a number of impairments regarding their mechanical complexity, low flexibility, and high cost. In the user segment, the use of planar arrays to substitute domestic reflectors will provide a more compact and easy to install antenna system and is an interesting solution e.g. for Satellite-On-The-Move (SOTM) systems

Analytical evaluation of uncertainty on active antenna arrays

An analytical method for evaluating the uncertainty of the performance of active antenna arrays in the whole spatial spectrum is presented. Since array processing algorithms based on spatial reference are widely used to track moving targets, it is essential to be aware of the impact of the uncertainty sources on the antenna response. Furthermore, the estimation of the direction of arrival (DOA) depends on the array uncertainty. The aim of the uncertainties analysis is to provide an exhaustive characterization of the behavior of the active antenna array associated with its main uncertainty sources. The result of this analysis helps to select the proper calibration technique to be implemented. An illustrative example for a triangular antenna array used for satellite tracking is presented showing the suitability of the proposed method to carry out an efficient characterization of an active antenna array

Diseño preliminar de una estación terrena basada en software radio para aplicaciones docentes

Most of student satellite missions are based on the design, construction and launch of a picosatellite (cubesat) including the design of the ground station (GS). Traditional GS are based on commercial elements and are designed to support only one mission. These stations access the mission data very inefficiently, as only contact the satellite during short visibility periods. In this paper, we present a novel GS concept based on software defined radio technology that can be integrated in a global network for satellite tracking. The station will be implemented by a group of students as a part of a space project under the supervision of a faculty coordinator. The design must fulfil the requirements of low cost, remote operation, and flexibility to operate in different frequency bands. The set-up of this mid-term educational space project to build an operational GS will hopefully motivate Telecommunication Engineering students to participate and gain real hands-on experience in an international space environment

On the Impact of Ultra Wide Band (UWB) On Downlink Range of GSM-900 and DCS-1800 Systems

The effect of the UWB interference on the GSM-900 and DCS-1800 downlink is studied for different UWB power densities. For relatively high UWB power density (-60 dBm/MHz), the effect of the UWB signals is very high when the distance between the UWB transmitter and the GSM-900 or DCS-1800 receiver is less than 1 m. For low UWB power density (-91 dBm/MHz), the effect of the UWB signals is very small if the distance between the UWB transmitter and the GSM-900 or DCS-1800 receiver is 1 m or higher. It is found that the spectrum mask proposed by the FCC for indoor application (-53 dBm/MHz in the DCS-1800 band and -41 dBm/MHz in the GSM-900 band) is too high to be tolerated by the two mobile system

desarrollo de un entorno programado para el análisis de confiabilidad con base en distribución Weibull biparamétrica

La ejecución en las labores de mantenimiento en una empresa, son a menudo permeadas por la visión empírica que posee el estamento encargado de las labores de mantenimiento, dando paso a prácticas deficientes que conllevan a la disminución del ciclo útil de las máquinas. Se hace necesario considerar las características principales y la forma en la cual los equipos están desarrollando sus funciones, debido a que el conocimiento o desconocimiento de estos elementos puede llevar a la correcta y clara anticipación ante posibles fallas, que en forma gradual fomenten un desgaste y un daño irreparable en las maquinas. Lo cual hace necesario implementar planes de conservación para los datos que contienen la información de fallas en los equipos, específicamente los tiempos en los cuales se presentaron y así a partir de estos registros entrar a analizar de manera precisa la confiabilidad que poseen los equipos, especialmente el tiempo en el cual entraría a fallar, sin la obligación de orientarse respecto a la visión experimental del organismo encargado de las funciones de mantenimiento en la empresa. A partir de bases de datos generadas aleatoriamente, así como registros históricos en los cuales se consideran los tiempos de falla de ciertos equipos, se desarrolla e implementa un entorno programado para el análisis de confiabilidad con base en la distribución Weibull biparamétrica, otorgando de este modo suficientes herramientas que permitan considerar planes de mantenimiento predictivo al grupo encargado de esta labor

Determining efficacy of monitoring devices on ceramic bond to resin composite

Objectives: This paper aims to assess the effectiveness of 3D nanoroughness and 2D microroughness evaluations, by their correlation with contact angle measurements and shear bond strength test, in order to evaluate the effect of two different acids conditioning on the bonding efficacy of a leucite-based glass-ceramic to a composite resin. Study Design: Ceramic (IPS Empress) blocks were treated as follows: 1) no treatment, 2) 37% phosphoric acid (H 3 PO 4 ), 15 s, 3) 9% hydrofluoric acid (HF), 5 min. Micro- and nano-roughness were assessed with a profilometer and by means of an atomic force microscopy (AFM). Water contact angle (CA) measurements were determined to assess wettability of the ceramic surfaces with the asixymetric drop shape analysis contact diameter technique. Shear bond strength (SBS) was tested to a resin composite (Z100) with three different adhesive systems (Scotch bond Multipurpose Plus, Clearfil New Bond, ProBOND). Scanning electron microscopy (SEM) images were performed. Results: Nanoroughness values assessed in 50x50 ?m areas were higher for the HF group, these differences were not detected by profilometric analysis. HF treatment created the nano- roughest surfaces and the smallest CA (p<0.05), producing the highest SBS to the composite resin with all tested adhesive systems (p<0.05). No diffe- rences existed between the SBS produced by the adhesive systems evaluated with any of the surface treatments tested. Conclusions: Nano-roughness obtained in a 50x50 ?m scan size areas was the most reliable data to evaluate the topographical changes produced by the different acid treatments on ceramic surfaces

Educational Ground Station Based on Software Defined Radio

Most of student satellite missions are based on the design, construction and launch of a picosatellite (cubesat) including the design of the ground station (GS). Traditional GS are based on commercial elements and are designed to support only one mission. These stations access the mission data very inefficiently, as only contact the satellite during short visibility periods. In this paper, we present a novel GS concept based on software defined radio technology that can be integrated in a global network for satellite tracking. The station will be implemented by a group of students as a part of a space project under the supervision of a faculty coordinator. The design must fulfil the requirements of low cost, remote operation, and flexibility to operate in different frequency bands. The set-up of this mid-term educational space project to build an operational GS will hopefully motivate Telecommunication Engineering students to participate and gain real hands-on experience in an international space environment