Abstract This study focused on the experimental assessment of the effect of the spacing between longitudinal stiffeners welded to I-shaped beams under the action of lateral-torsional buckling. In this procedure, 192 aluminum beams on a 1:9 scale were tested under simple-support conditions with a laterally unbraced length ranging from 0.55 m through 1.95 m. Moreover, the stiffeners’ spacing was also ranged from 3 to 9 times the depth of section. The structural behavior of the beams is discussed in terms of their flexural capacity, spacing between longitudinal stiffeners, lateral displacement of compression flange and failure angle twist. Results show that the spacing of longitudinal stiffeners influences the flexural capacity of I-shaped beams, so that, when the spacing of longitudinal stiffeners decreases, flexural capacity tends to increase, especially in the elastic buckling zone.

Abstract The use of concrete reinforced with steel fibers is relatively limited in Latin America due to its high cost. However, its mechanical performance is very useful in the construction of reinforced concrete structures. This article describes and discusses the results of an experimental research, which reflects the chloride ion effects at a short term, on the durability properties of concrete reinforced with RC-65-35-BN steel fibers using dosages of 30 and 60 kg/m3. In order to predict the effect of chloride ion on the steel fiber reinforced concrete, trends of corrosion were estimated during 56 days by half-cell potential and linear polarization resistance tests. Additionally, the surfaces of the steel fibers were analyzed by X-ray diffraction with the purpose to determinate the corrosion products that were generated. The obtained results demonstrates an adequate performance of the fibers embedded in the concrete for this phase of corrosion initiation, due to its low probability of corrosion.

Resumen El uso del concreto reforzado con fibras de acero es relativamente limitado en Latinoamérica debido a su alto costo. Sin embargo, su desempeño mecánico es muy útil en la construcción de estructuras de concreto reforzado. Este artículo describe y discute los resultados de un estudio experimental que refleja el efecto del ion cloruro a corto plazo, sobre las propiedades de durabilidad del concreto reforzado con fibras de acero RC-65/35-BN usando dosificaciones de fibra de 30 kg/m3 y 60 kg/m3. Con el fin de predecir el efecto del ion cloruro sobre el concreto reforzado con fibras de acero, las tendencias de la corrosión se estimaron durante 56 días mediante ensayos de potencial de media celda y resistencia a la polarización lineal. Adicionalmente, las superficies de las fibras de acero se analizaron por difracción de rayos X con el propósito de determinar los productos de corrosión generados. Para esta fase de iniciación de la corrosión, los resultados obtenidos demuestran un adecuado desempeño de las fibras embebidas en el concreto debido a su baja probabilidad de corrosión.

The paper compares and discusses displacement ductility ratios of reinforced concrete walls typically used in one- and two-story houses. Ductility is investigated by assessing response measured on 39 walls tested under shaking table excitations and quasi-static lateral loads. Variables studied were the height-to-length ratio and walls with openings, type of concrete and, steel ratio and type of web reinforcement. An equation to estimate the available ductility of a wall is proposed. Based on statistical analysis of data, values of displacement ductility capacity are recommended. Displacement ductility ratios can be used to compute both strength modification and displacement amplification factors for code-based seismic design.

Based on both ambient vibration measurements and numerical models using the wide-column analogy and the finite element method, vibrations periods of low-rise concrete dwellings are estimated in this study. A brief review of parametric and nonparametric techniques is presented and discussed, and in-situ measurements techniques are critically compared. The results of ambient vibration tests are used to calibrate numerical models. Advantages, drawbacks and accuracy of parametric techniques, as well as particular recommendations to build numerical models for assessing the elastic behavior of low-rise concrete wall dwellings, are proposed.

Based on steel strains recorded during shake table tests of six wall specimens, the effect and contribution of steel reinforcement to peak shear strength and displacement capacity of low-rise concrete walls is assessed and discussed. The experimental program included four variables such as wall geometry, concrete type, web steel ratio and type of web reinforcement. Wall response was assessed through effective steel strains in vertical reinforcement, efficiency factors of wall reinforcement, contribution of web horizontal reinforcement to wall shear strength, and the effect of type of web reinforcement to wall displacement.

Las mesas vibratorias son herramientas experimentales para evaluar el comportamiento de estructuras y elementos no estructurales sometidos a excitaciones sísmicas representativas. Debido a limitaciones de tamaño y peso de las mesas, ha sido necesario ensayar modelos a escala reducida o ensayar sólo los elementos estructurales principales. En estos casos, para cumplir con los requerimientos de similitud, deben adicionarse cantidades importantes de masa extra al espécimen. El artículo revisa y discute los sistemas de soporte de masa para ensayos en mesa vibratoria. Se comparan y discuten críticamente las ventajas y debilidades de cada sistema. Para evitar el riesgo de inestabilidad lateral de los modelos y mantener el peso de los especímenes de ensayo dentro del límite de carga de la mesa, los dispositivos externos de transmisión de fuerzas inerciales a los modelos se han convertido en una opción preferida, cuando los ensayos se realizan utilizando mesas vibratorias de tamaño pequeño o mediano.

Shaking tables are experimental tools to assess the behavior of structures and nonstructural components under characteristic seismic vibrations. Because of the size and weight limitations of the tables, testing reduced-scale models or testing only the main structural components are normally necessary. In these cases, to comply with modeling requirements, large amount of extra-mass should be added to the specimen. This paper reviews and discusses the mass-rig systems for shaking table testing. The advantages and drawbacks of each system are critically compared. To avoid the risk of lateral instability of models and to maintain the weight of test specimens within table payload, external devices for transmitting the inertial forces to the models have become a preferred choice when tests are performed using small- or medium-size shaking tables.

El análisis de deformación de elementos estructurales es una herramienta indispensable para investigar la relación fuerza lateral versus deformaciones de cortante, deslizamiento y flexión; evaluar el mecanismo de resistencia del modo de falla, asignar valores adecuados de rigidez lateral, estimar la contribución del acero de refuerzo a las capacidades de resistencia y desplazamiento, calibrar modelos analíticos y, para proponer parámetros apropiados para diseño sísmico basado en desempeño. Para evaluar los componentes de deformación de muros de concreto de baja altura, se llevó a cabo un estudio experimental y analítico. El programa experimental incluyó el ensayo en mesa vibratoria de seis muros de concreto de baja altura. Se recomienda el método y los esquemas de instrumentación que permiten la evaluación adecuada de los tres componentes de deformación de muros cuadrados y con aberturas. Se encontró que el método propuesto produce resultados que son consistentes con los ensayos evaluados.

Deformation analysis of structural elements is a valuable tool for researching the relationship of lateral force versus shear, sliding and flexural deformations, to assess the strength mechanism of failure mode, to assign suitable values of lateral stiffness, to estimate the contribution of steel reinforcement to strength and displacement capacities, to calibrate analytical models, and to propose appropriate parameters for performance-based seismic design. An experimental and analytical study was conducted to assess the components of deformation of low-rise reinforced concrete walls. The experimental program included shaking table tests of 6 low-rise concrete walls. The method and the instrumentation schemes to allow accurate assessment of the three components of deformations for squat walls and walls with openings are proposed. It was found that the proposed method produce consistent results for the tests evaluated.

En este artículo se compara el comportamiento de cuatro muros aislados de concreto reforzado (CR) con aberturas: dos muros prototipo ensayados bajo carga cuasi-estática cíclica (CEC) y dos muros ensayados bajo excitación de mesa vibratoria. Las variables estudiadas fueron la cuantía de acero en el alma, el tipo de acero de refuerzo en el alma y el método de ensaye. A partir de la respuesta medida se verificó que la historia de carga de los ensayos CEC ignora los efectos dinámicos fundamentales observados en estructuras sometidas a cargas sísmicas. Cuando las respuestas dinámicas y CEC cíclicas se compararon, se observó que las propiedades de degradación de rigidez y resistencia dependen de la velocidad de aplicación de carga, los mecanismos de resistencia asociados a los modos de falla, el número de ciclos y los parámetros acumulados de la demanda de ductilidad y energía disipada. Por lo tanto, los datos obtenidos a partir de ensayos CEC no siempre se pueden suponer de forma segura como un límite inferior de la capacidad esperada. En el artículo también se proponen modelos de degradación de rigidez y resistencia para muros de CR con aberturas sometidos a carga del tipo sísmica.

This paper compares the performance of four isolated reinforced concrete (RC) walls with openings: two prototype walls tested under quasi-static cyclic (QSC) loading, and two models tested under shaking table excitation. The variables studied were the web steel ratio, the type of web reinforcement, and the testing method. By means of the measured response, it was verified that loading history of the QSC testing ignores the foremost dynamic effects observed in structures subjected to earthquake loads. When dynamic and QSC responses were compared, it was apparent that stiffness and strength degradation properties depend on the loading rate, the strength mechanisms associated to the failure modes, number of cycles, and cumulative parameters such as ductility demand and energy dissipated. We deducted that data obtained from QSC tests cannot always be safely assumed to be a lower limit of the expected capacity. Stiffness and strength degradation models for RC walls with openings subjected to earthquake-type loading are also proposed.