Static and dynamic displacement measurements of structural elements using low cost RGB-D cameras

Abstract

Optical displacement measurements can provide data of the behavior of structural elements without altering key parameters such as damping, stiffness, or mass. Optical techniques can also reduce costs and substantially simplify the equipment required to acquire data effectively and map displacements at specific locations of elements with complex geometries, such as steel connections. In addition, these techniques can provide simultaneous data at multiple points using a single device, hence lowering instrumentation costs. For example, motion capture systems are used in applications that range from medicine to cinematography, and involve different types of imaging techniques. However, their application to civil and mechanical structures is complex and costly. On the other hand, range/depth cameras can provide a 3-D imaging solution to capture motion at an affordable cost. These cameras are widely available and used in the videogame industry. This paper presents the characterization and implementation of a methodology for the measurement of large-displacements using artificial vision techniques, for structural applications such as experimental modal analysis, cyclic loading tests, creep tests, and static displacements tests. Two low cost depth-cameras, one a time-of-flight camera and the other a structured light camera, were calibrated, evaluated and implemented in static and dynamic tests, during a full-scale reinforced concrete wall cyclic load test and shaking table tests. The results show that both devices provide high accuracy measurements in comparison with commonly used sensors for displacement measurements, with the added advantages of being contactless and providing three-dimensional information.