In-service prestressed concrete box girder bridges have received increasing attention in recent years due to a large number of bridges reaching decades in service. Therefore, the ageing of infrastructure demands the development of robust condition assessment methodologies based on affordable technology such as vehicle-induced vibration tests (VITs) in contrast with more expensive existing technologies such as tests using hammers or shakers. Ambient vibration tests (AVTs) have been widely used worldwide, taking advantage of freely available ambient excitation sources. However, the literature has commonly reported insufficient input energy to excite the structure to obtain satisfactory modal identification results, especially in long-span concrete bridges. On the other hand, the use of forced vibration tests (FVTs) requires more economic resources. This paper presents the results of field measurements at optimally selected locations in VITs consisting of a 32-ton truck and a springboard with a height of 50 mm. AVTs using optimal sensor placement (OSP) provide similar results to VITs without considering OSP locations. Additionally, the VIT/AVT cost ratio is reduced to 2 since a shorter data collection time is achieved within a one-day (8 h) test framework, which minimizes temperature effects, thus leading to improvements in AVT identification results, especially in vertical modes.
La percepción de calidad de carne es un concepto complejo y requiere de análisis multivariados para entender su estructura y conceptualización. El objetivo del estudio fue valorar la percepción de calidad de carne por parte del consumidor y la disponibilidad a pago por información de calidad. Se aplicaron 400 encuestas bajo un cuestionario estructurado. La encuesta indagó sobre el perfil socioeconómico del consumidor y la percepción sobre características intrínsecas y extrínsecas de la carne, perfil de consumo por información nutricional, estilo de vida, preferencias de cortes y frecuencia de compra, y disposición a pago por información nutricional, empleando una escala Likert. Los datos se analizaron mediante modelos de ecuaciones estructurales (SEM) y pruebas chi2. El SEM registró un ajuste satisfactorio (CFI=0,978, RMSEA=0,17). Los resultados indicaron que el consumidor conceptualiza (P < 0,05) la carne con base en aspectos intrínsecos (color, suavidad y pérdida de agua), extrínsecos (precio, bienestar animal y confianza) y la actitud de consumo saludable. El encuestado no consideró el concepto de calidad para la disposición a pago por información. Las mujeres, los consumidores entre 37-55 años y los empleados, registraron la puntuación más alta (P < 0,05) en el concepto de calidad de la carne.
This paper presents a comparative study of an Optimal Sensor Placement (OSP) implementation conducted in a box girder bridge using experimental and numerical mode shapes obtained at different construction stages. It is widely recognized that monitoring the dynamic response of bridges during different construction stages provides valuable information to adjust design considerations. Therefore, there is a need for the development of OSP implementations in order to find the optimal number of sensors needed for real applications. In the present study, an OPS method based on the maximization of the Fisher Information Matrix (FIM) is used. The use of experimentally derived and numerical based mode shapes is considered in the determination of the optimal sensor locations. Field testing results previously conducted before connecting the central segment of the main span are also included in this study. The asphalt pavement weight effect in OSP determination is also analyzed by considering field testing.
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