Optical Interstory Drift Meter Using Laser Position Sensitive Detector
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Solution Overview
Problem
Existing earthquake monitoring systems, particularly those using strong motion accelerometers, face challenges in accurately measuring interstory drift due to dynamic frequency limitations and the need for extensive post-processing, which can lead to errors in assessing building damage after an earthquake, especially in densely populated urban areas where timely assessment is critical for safety and re-occupancy.
Innovation Solution
An optically-based interstory drift meter system utilizing a broad frequency response Position Sensitive Detector Array (PDSA) with a staggered array of discrete photodiode sensors, capable of directly measuring interstory drift by tracking a diffracted laser beam, providing immediate and accurate data on building displacement without the need for complex data integration, and effectively measuring transient and inelastic drifts across a wide frequency range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strong motion accelerometers are used to measure building response, then the system can provide some insight on the degree to which the building was shaken, but it cannot accurately reproduce permanent displacements and requires extensive post-processing through double numerical integration which introduces errors
Solution Approach 1:
The patent replaces accelerometer-based mechanical measurement systems with an optical measurement system. A laser beam is projected onto a position-sensitive detector (PSD) mounted on the building facade. The laser spot position directly indicates floor displacement, eliminating the need for double numerical integration of accelerometer data and providing accurate permanent displacement measurements without complex post-processing.
Solution Approach 2:
The patent introduces a position-sensitive detector (PSD) as an intermediary device between the laser beam and the measurement system. The PSD converts the laser spot position into electrical signals that directly represent displacement, providing a straightforward measurement chain that avoids the errors inherent in integrating accelerometer data twice.
2Reliability
If accelerometers are used for earthquake monitoring, then the system can operate dynamically, but frequency bandwidth limitations prevent accurate reproduction of permanent displacements associated with inelastic building behavior
Solution Approach 1:
The patent replaces dynamic accelerometer systems with a static optical measurement system. The laser-PSD configuration provides a direct geometric measurement of displacement that is not constrained by frequency bandwidth limitations. This allows accurate capture of both dynamic and permanent displacements, including those from inelastic building behavior, without the frequency response constraints of accelerometer-based systems.
3Measurement precision
If traditional engineering inspection procedures are used after a major earthquake, then thorough assessment can be performed, but the process is time consuming and constrained by lack of available qualified structural engineers
Solution Approach 1:
The patent enables buildings to self-report their structural response through the optical measurement system. The laser-PSD system continuously monitors floor displacements and automatically records interstory drift values, eliminating the need for manual inspection by structural engineers. This allows rapid assessment of building integrity immediately after earthquakes without requiring available qualified personnel.
Solution Approach 2:
The patent implements continuous monitoring of interstory drift values before earthquakes occur. The system maintains records of baseline drift measurements, allowing immediate comparison with post-earthquake readings. This preliminary action enables rapid assessment of building damage by comparing current measurements against historical data, significantly speeding up the evaluation process after seismic events.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid and accurate assessment of building damage post-earthquake by providing direct measurements of interstory drift, overcoming limitations of accelerometer-based systems, and allowing for immediate post-event readouts, thus enhancing safety and operational efficiency in urban environments.
Implementation Method 1
a diffracted laser beam source and a position sensitive detector array adapted to receive the diffracted laser beam and indicate the range of movement of the building caused by an earthquake
Data Source
Figure 1A
Figure 1B~1C
Figure 2
AI summary
A sensor system provides measurement of building interstory drift based on a laser beam impinging on a discrete diode sensor array. The diode sensor array determines the location at which a projected laser bean strikes the array, which provides a direct measurement of interstory drift. The diode sensor array is a two dimensional array of discrete diodes that allow the location of an impinging laser beam to be very accurately tracked as the beam moves back-and-forth across the diode array. Local rotations of the laser source that result from rotations of structural members (e.g. floor beam rotation) are appropriately corrected for. This allows accurate, dynamic measurements of the interstory drift between two floor levels of a shaking building.