Resumo O risco devido à corrosão do aço em particular foi avaliado, utilizando sensores galvânicos internos de aço carbono/aço inoxidável e o eletrodo externo de Cu/CuSO4. Os sensores foram utilizados para monitorar os potenciais e correntes de macrocélulas de corpos de prova prismáticos de concreto armado, com relações água-cimento de 0,4 e 0,6, imersos em solução de NaCl a 5% por 18 meses. Os resultados dos potenciais mostraram uma boa correlação entre os dois eletrodos de referência, podendo avaliar a corrosão do sistema. Além disso, a técnica de ruído eletroquímico suporta o efeito dos íons cloreto. Portanto, sensores galvânicos podem ser considerados para implementação no monitoramento e avaliação do status de risco de corrosão em estruturas de concreto armado.

Abstract The corrosion risk of steel in concrete was assessed using internal galvanic carbon/stainless steel sensors and the external Cu/CuSO4 electrode. The sensors were used to monitor the macrocell potentials and currents of reinforced concrete prismatic specimens, with water to cement ratios of 0.4 and 0.6, immersed in 5% NaCl solution, for 18 months. The results of the potentials showed a good correlation between the two reference electrodes, being able to evaluate the corrosion of the system. In addition, the electrochemical noise technique supports observations of the effect of chloride ions. Therefore, galvanic sensors can be considered for implementation in the monitoring and evaluation of corrosion risk of reinforced concrete structures.

Resumen Se evaluó el riesgo por corrosión del acero en concreto, utilizando sensores galvánicos internos de acero al carbono/acero inoxidable y un electrodo externo de Cu/CuSO4. Los sensores se utilizaron para monitorear los potenciales y corrientes de macrocelda de probetas prismáticas de concreto reforzado con relaciones agua-cemento de 0.4 y 0.6, inmersas en solución de NaCl al 5% durante 18 meses. Los resultados de los potenciales mostraron buena correlación entre los dos electrodos de referencia, pudiendo evaluar la corrosión del sistema. Además, la técnica de ruido electroquímico respalda el efecto por iones cloruro. Por lo tanto, los sensores galvánicos pueden considerarse para su implementación en el monitoreo y evaluación del estado de riesgo por corrosión en estructuras de concreto reforzado.

Abstract In this paper the authors summarize the results of a study devoted to assess, using nonlinear static analyses, the impact of increasing the structural redundancy in ductile moment-resisting reinforced concrete concentric braced frames structures (RC-MRCBFs). Among the studied variables were the number of stories and the number of bays. Results obtained were compared with the currently proposed values in the Manual of Civil Structures (MOC-08), a model code of Mexico. The studied frames have 4, 8, 12 and 16-story with a story height h=3.5 m. and a fixed length L=12 m., where 1, 2, 3 or 4 bays have to be located. RC-MRCBFs were assumed to be located in soft soil conditions in Mexico City and were designed using a capacity design methodology adapted to general requirements of the seismic, reinforced concrete and steel guidelines of Mexican Codes. From the results obtained in this study it is possible to conclude that a different effect is observed in overstrength redundancy factors respect to ductility redundancy factors due to an increase of the bay number considered. Also, the structural redundancy factors obtained for this particular structural system varies respect to the currently proposed in MOC-08.

<p>In this paper the author summarize the results of a study devoted to evaluate, using nonlinear static analyses, the influence of two different bracing configurations on the behavior of low to medium rise ductile moment-resisting reinforced concrete concentric braced frames structures (RC-MRCBFs), as well as its impact in some specific design parameters. RC-MRCBFs height ranges from 4 to 20 stories, using both chevron and X-steel bracing. From the results obtained in this study it is possible to conclude that overstrength reductions factors (<italic>R</italic>) are dependent on the bracing configuration, therefore equations for the estimation of <italic>R</italic> factors for each studied bracing configuration are proposed. A story drift limit for service purposes, independent of bracing configuration, is proposed. It was also found that the peak story drift limit proposed in NTCS-04 is suitable for both bracing configurations. For the two bracing configurations, an equation to estimate the minimum shear strength provided by the columns of the RCMRCBFs as a function of the slenderness ratio of the building is proposed. Finally, it was observed that if proposed capacity design methodology is used, it is possible to design low and medium rise ductile RC-MRCBFs when the columns of the moment frames resist at least 50% of the total seismic shear force, obtaining a collapse mechanism that correlate reasonably well with the expected failure mechanism of strong column-weak beam-weaker brace.</p>

<p>Se presenta un estudio en que se evalúa, mediante análisis estáticos no lineales, la influencia de dos esquemas de contraventeo en el comportamiento estructural de marcos dúctiles de concreto reforzado, así como su impacto en algunos parámetros de diseño. Los marcos diseñados se encuentran en el intervalo de los cuatro a 20 niveles, contando con contraventeo metálico tipo chevrón y en cruz. De los resultados obtenidos, es posible concluir, que existe dependencia de los factores de reducción por sobrerresistencia (<italic>R</italic>) con el esquema de contraventeo considerado, por tal razón, se proponen expresiones para el cálculo de los factores <italic>R</italic> para cada caso. Asimismo, se propone un valor de distorsión para la revisión del estado límite de servicio independiente del esquema de contraventeo. Se muestra que la distorsión propuesta en las NTCS-04 para la revisión del estado límite de prevención de colapso es adecuada para ambos esquemas de contraventeo. También, se propone una expresión para la determinación del aporte mínimo de las columnas al cortante resistente del sistema ante carga lateral como función de la relación de esbeltez de la estructura, aplicable a las dos configuraciones de contraventeo estudiadas. Finalmente, del conjunto de resultados, se concluye que para los modelos de cuatro a 16 niveles, para ambas configuraciones de contraventeo, es posible obtener diseños con capacidades de deformación adecuadas que cumplan con un mecanismo de colapso cercano al esperado de columna fuerte-viga débil-contraviento más débil si se emplea la metodología de diseño por capacidad propuesta y las columnas aportan al menos el 50% del cortante resistente de entrepiso.</p>

In this paper the authors summarize the results of a study devoted to evaluate, using nonlinear dynamic analyses, the seismic behavior of ductile moment-resisting reinforced concrete concentric braced frames structures (RC-MRCBFs) using chevron steel bracing (eight, 15 and 24 stories in height). RC-MRCBFs were assumed to be located in three different soil conditions in Mexico (coastline zone of the state of Guerrero and lakebed zones IIIa and IIIb of Mexico City). From the results obtained, it is possible to conclude that if capacity design principles and specific design parameters for the new design of RC-MRCBFs are used, suitable global ductility capacities and overstrength demands are obtained, and a satisfactory structural performance is achieved.

Se presenta un estudio en que se evalúa, mediante análisis dinámicos no lineales paso a paso, el comportamiento sísmico de edificios de diferentes alturas (ocho, 15 y 24 niveles) estructurados con base en marcos dúctiles de concreto reforzado con contraventeo metálico tipo chevrón. Los edificios se diseñaron para tres diferentes zonas (zona costa del estado de Guerrero y zonas IIIa y IIIb del lago del Distrito Federal), de acuerdo a la altura de cada modelo. De los resultados expuestos, es posible concluir que si se emplean conceptos de diseño por capacidad, así como parámetros de diseño específicos al sistema estructural considerado, es posible obtener capacidades de deformación y sobrerresistencia adecuados, así como un desempeño estructural satisfactorio.