Desarrollo de un banco de experimentos para la determinación del pandeo en columnas.
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Date
2025
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Publisher
Universidad de Concepción
Abstract
El presente proyecto tiene por objetivo diseñar, construir y validar un banco de pruebas para el estudio del pandeo en columnas bajo tres condiciones de contorno: apoyos articulado-articulado, articulado empotrado y empotrado-empotrado, donde cada condición tiene un comportamiento diferente según el valor de la longitud efectiva.
Se determina que solo se pueden utilizar columnas con sección rectangular con dimensiones pequeñas, que garantizan valores de carga crítica bajos. Además, se restringe el uso de columnas esbeltas para aplicar la Fórmula de pandeo de Euler. Se define la carga de diseño del banco de 400 [𝑁] en tres puntos diferentes. Así, se decide fabricar la estructura exterior del banco con un perfil costanera de 40 ×80×15×3 [𝑚𝑚], que garantiza una alta resistencia a flexión y pandeo.
Los apoyos articulados se diseñan con una ranura triangular truncada, de base 4 [mm] y apertura máxima de 18 [mm] por su inclinación de 22°, que permite la rotación libre de la pletina. Los apoyos empotrados incorporan un perno que presiona la columna contra un bloque de acero, restringiendo su movimiento lateral y rotación. El sistema de carga asegura que las fuerzas se apliquen de forma concéntrica, facilitando la comparación con la Fórmula de Euler.
Para validar el banco, se realizan diez pruebas por cada condición de contorno, donde se alcanzó en promedio entre todas las condiciones un 86,2% de la carga teórica. Se tiene que la condición de apoyos articulados es la más cercana al valor teórico, mientras que los apoyos empotrados son los más lejanos. Asimismo, el error de experiencia múltiple para cada condición no supera el 3,5%.
Además, se realizan mediciones de la deflexión lateral sufrida por la columna una vez superada la carga crítica, donde se aprecian zonas de estabilidad previo a que ocurran deflexiones abruptas. A su vez, se pudo notar que al utilizar pletinas adquiridas en otro local comercial y que presentan defectos geométricos mayores a las pletinas ensayadas anteriormente, el valor de la carga crítica experimental disminuyó considerablemente. Por lo tanto, se deduce que la variación entre la carga teórica y la experimental se debe principalmente a las imperfecciones iniciales del material, así como a posibles desalineamientos o fricciones en el banco de ensayos.
Se realizan tres ensayos finales, donde se mide previamente el ancho, el espesor y la desviación de cada columna antes de realizar la experiencia. Luego, se determina la carga crítica y los valores de deflexión para cada condición de borde, con lo que se analiza el efecto de las imperfecciones iniciales sobre una columna articulada en ambos extremos. Se obtienen valores cercanos entre la teoría y la experiencia, que demuestra la importancia de estas imperfecciones en el análisis de pandeo.
Para aumentar la precisión de la medición de carga crítica, deflexión y las imperfecciones iniciales, se propone incluir un sistema de medición, ya sea con medidores de distancia láser, sensores ultrasónicos o sensores ópticos, siendo el último la opción más precisa.
The objective of this project is to design, construct, and validate a testing bench for studying buckling in columns under three boundary conditions: pinned-pinned, pinned-fixed, and fixed-fixed. Each condition exhibits different behavior based on the effective length factor. It was determined that only rectangular columns with small dimensions can be used to ensure low critical load values. Furthermore, the use of slender columns is restricted to apply Euler's buckling formula. A design load of 400 [𝑁] is defined for the bench, applied at three different points. Consequently, the external structure of the bench is made using a channel section of 40 ×80×15×3 [𝑚𝑚], ensuring high resistance to bending and buckling. The pinned supports are designed with a truncated triangular groove, having a 4 [𝑚𝑚] base and a maximum opening of 18 [𝑚𝑚] at a 22° inclination, allowing free rotation of the flat plate. The fixed supports incorporate a bolt that presses the column against a steel block, restricting lateral movement and rotation. The load system ensures that forces are applied concentrically, facilitating comparisons with Euler's formula. To validate the bench, ten tests were conducted for each boundary condition. On average, across all conditions, 86.2% of the theoretical load was achieved. The pinned support condition was the closest to the theoretical value, while the fixed support condition was the furthest. Additionally, the multiple test error for each condition did not exceed 3.5%. Lateral deflection measurements were also taken after the critical load was surpassed, revealing stability zones prior to abrupt deflections. Furthermore, when flat plates purchased from another supplier with larger geometric defects were tested, the experimental critical load value decreased significantly. It was concluded that the variation between theoretical and experimental loads is primarily due to initial material imperfections, as well as possible misalignments or friction within the testing bench. Three final tests were conducted, measuring the width, thickness, and deviation of each column prior to testing. The critical load and deflection values were then determined for each boundary condition, analyzing the effect of initial imperfections on a column pinned at both ends. Results showed values close to theory, highlighting the importance of these imperfections in buckling analysis. To enhance the accuracy of measuring critical load, deflection, and initial imperfections, the inclusion of a measurement system is proposed, such as laser distance meters, ultrasonic sensors, or optical sensors, with the latter being the most precise option.
The objective of this project is to design, construct, and validate a testing bench for studying buckling in columns under three boundary conditions: pinned-pinned, pinned-fixed, and fixed-fixed. Each condition exhibits different behavior based on the effective length factor. It was determined that only rectangular columns with small dimensions can be used to ensure low critical load values. Furthermore, the use of slender columns is restricted to apply Euler's buckling formula. A design load of 400 [𝑁] is defined for the bench, applied at three different points. Consequently, the external structure of the bench is made using a channel section of 40 ×80×15×3 [𝑚𝑚], ensuring high resistance to bending and buckling. The pinned supports are designed with a truncated triangular groove, having a 4 [𝑚𝑚] base and a maximum opening of 18 [𝑚𝑚] at a 22° inclination, allowing free rotation of the flat plate. The fixed supports incorporate a bolt that presses the column against a steel block, restricting lateral movement and rotation. The load system ensures that forces are applied concentrically, facilitating comparisons with Euler's formula. To validate the bench, ten tests were conducted for each boundary condition. On average, across all conditions, 86.2% of the theoretical load was achieved. The pinned support condition was the closest to the theoretical value, while the fixed support condition was the furthest. Additionally, the multiple test error for each condition did not exceed 3.5%. Lateral deflection measurements were also taken after the critical load was surpassed, revealing stability zones prior to abrupt deflections. Furthermore, when flat plates purchased from another supplier with larger geometric defects were tested, the experimental critical load value decreased significantly. It was concluded that the variation between theoretical and experimental loads is primarily due to initial material imperfections, as well as possible misalignments or friction within the testing bench. Three final tests were conducted, measuring the width, thickness, and deviation of each column prior to testing. The critical load and deflection values were then determined for each boundary condition, analyzing the effect of initial imperfections on a column pinned at both ends. Results showed values close to theory, highlighting the importance of these imperfections in buckling analysis. To enhance the accuracy of measuring critical load, deflection, and initial imperfections, the inclusion of a measurement system is proposed, such as laser distance meters, ultrasonic sensors, or optical sensors, with the latter being the most precise option.
Description
Tesis presentada para optar al título profesional de Ingeniero Civil Mecánico
Keywords
Estabilidad de estructuras, Resistencia de materiales, Pandeo (Mecánica)