Abstract
Computer vision-based approaches are very useful for dynamic displacement measurement, damage detection, and structural health monitoring. However, for the application using a large number of existing cameras in buildings, the computational cost of videos from dozens of cameras using a centralized computer becomes a huge burden. Moreover, when a manual process is required for processing the videos, prompt safety assessment of tens of thousands of buildings after a catastrophic earthquake striking a megacity becomes very challenging. Therefore, a decentralized and fully automatic computer vision-based approach for prompt building safety assessment and decision-making is desired for practical applications. In this study, a prototype of a novel stand-alone smart camera system for measuring interstory drifts was developed. The proposed system is composed of a single camera, a single-board computer, and two accelerometers with a microcontroller unit. The system is capable of compensating for rotational effects of the camera during earthquake excitations. Furthermore, by fusing the camera-based interstory drifts with the accelerometer-based ones, the interstory drifts can be measured accurately even when residual interstory drifts exist. Algorithms used to compensate for the camera’s rotational effects, algorithms used to track the movement of three targets within three regions of interest, artificial neural networks used to convert the interstory drifts to engineering units, and some necessary signal processing algorithms, including interpolation, cross-correlation, and filtering algorithms, were embedded in the smart camera system. As a result, online processing of the video data and acceleration data using decentralized computational resources is achieved in each individual smart camera system to obtain interstory drifts. Using the maximum interstory drifts measured during an earthquake, the safety of a building can be assessed right after the earthquake excitation. We validated the feasibility of the prototype of the proposed smart camera system through the use of large-scale shaking table tests of a steel building. The results show that the proposed smart camera system had very promising results in terms of assessing the safety of steel building specimens after earthquake excitations.
Highlights
After a large earthquake, it is very important to perform damage assessments of affected buildings in order to ensure public safety during aftershocks
The calculated interstory drifts between the camera and the target points before the correction of rotational effects were observed
The direction of interstory drifts were even opposite to those measured by the linear variable differential transformers (LVDTs) in the Y-direction because the interstory drifts in the Y-direction due to the rotational effects were opposite to the actual interstory drifts, and the amplitudes of the interstory drifts due to the rotational effects were even larger than those of the actual ones
Summary
It is very important to perform damage assessments of affected buildings in order to ensure public safety during aftershocks. The acceleration responses of buildings are often used to calculate the maximum interstory drift during earthquake excitations for post-earthquake damage assessments. Naeim et al [1] proposed estimating the damage to buildings based on the maximum interstory drifts measured by the accelerometers provided by Sensors 2020, 20, 3374; doi:10.3390/s20123374 www.mdpi.com/journal/sensors. Trapani et al [5] proposed solving this problem by adding the residual displacement at the end of an excitation to the maximum value of displacement measured by the accelerometers. While this results in great improvements in the accuracy of maximum displacement measurements, a maximum error rate of approximately 30%
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