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Do the Crack Inspection Yourself: The Remote Crack-measuring System

Earthquakes frequently occur in Taiwan. Therefore, the questions as to whether cracks have appeared in residential buildings after a major earthquake, whether such cracks affect the seismic resistance of such buildings, and how the safety of such buildings can be verified must be resolved.

Due to its location on a seismic belt, Taiwan is subject to over 1,000 perceptible earthquakes every year. Cracks inevitably appear in buildings and bridges. The inspection of cracks generally involves observation and the use of measuring tools to document their width, length, position, and distribution, etc. This information is used in the initial determination of the deterioration or damage caused to a building or bridge. Thus, effective measurement of cracks and their timely repairs are of great importance to ensure the safety of people and their assets.

To help the general population and professionals rapidly and effectively measure the size of earthquake-induced cracks remotely, a “remote crack-measuring system” was invented by the interdisciplinary research centers of the National Applied Research Laboratories (NARLabs), comprising the National Center for High-Performance Computing (NCHC), National Center for Research on Earthquake Engineering (NCREE), and Instrument Technology Research Center (ITRC).

An Innovative Technology: Easy to Operate, Fast, and Inexpensive
Currently, most methods for measuring cracks in buildings use contact ways; specifically, such methods involve the use of equipments such as crack-measuring device or handset-measuring instrument available in the market, which must be placed against cracks for measurement. Although there are also imported instruments that can be used to conduct measurements at a distance, they are slow, extremely complex to operate, and highly expensive.

The remote crack-measuring system is the first independently developed technology in Taiwan that can measure cracks remotely. The system applies four focused and highly accurate laser beams1 to project a rectangle onto a crack, and then photographs the crack and four points surrounding it. Next, the captured image is analyzed and the length and width of the crack are calculated. 

The remote crack-measuring system can measure cracks at a distance of up to 50 meters (approximately 15 floors high). Three versions of this system are currently available: the smartphone version, the smart camera version, and the digital single-lens reflex camera version.

Users can download the Crackphone App, developed by NCHC, to measure cracks independently. The App records the length and width of cracks and provides this information to specialists who further examine or repair the cracks to ensure building safety. For professionals, the App enables them to effectively measure cracks of bridges and tall buildings that are far and difficult to reach, enabling them to gain information on cracks that were originally impossible to measure, thereby improving home and road safety.

Crack Data in the Cloud Enables Sending Automated Notices
Small cracks are often inconspicuous at first; after accumulating over time, they can endanger building safety. Considering this problem, NCHC is prepared to further develop this system in the cloud, helping users keep track of each crack over a long period and automatically compare and analyze data, with automated notices sent to users when the system detects abnormal changes in one or more cracks.

NCHC aims to integrate this system with Taiwan’s geographic information system in the future and document changes in each crack along with cracks of nearby locations. This will enable the diagnosis and analysis of large or small regions and help related departments gain information on numerous cracks and the complex changes they undergo, thereby facilitating the enactment of precautionary measures in response.

Both the Practical and Academic Value of Ensuring Living Safety Have Been Recognized
The remote crack-measuring system has gained recognition and support from NCREE in academia as well as T.Y. LIN International Taiwan, CECI Engineering Consultants Inc., Taiwan, and Resources Engineering Services Inc. in industrial sector. NCREE has already announced plans to implement this crack-measuring system as a crack-inspection module in its bridge-disaster prevention and management system, rendering it a mandatory tool for bridge inspection. 

The Meinong earthquake that occurred in February 2016 devastated Taiwan, and the earthquakes in Japan and Ecuador in April 2016 caused the collapse of numerous buildings as well. The Taiwanese government launched a home safety program and began actively carrying out inspections of buildings older than 20 years. President Tsai Ing-wen also indicated that all old buildings in Taiwan must be inspected to ensure their safety. However, more than 750,000 buildings and 27,000 bridges in Taiwan fall under this category. The remote crack-measuring system is particularly beneficial in such situations. It enables the public to measure cracks in their homes without further assistance and helps to protect their own homes, together making Taiwan a safer society.

Note 1: How to measure cracks at a distance
Two conditions must be satisfied to measure the length and width of cracks: The camera must be vertical to the wall and a reference scale must be employed.

Figure 1. In the remote crack-measuring system, lasers used for positioning are installed on the four corners of the rectangular case of a mobile phone or camera. 

A laser can maintain a concentrated beam over a long distance, and a rectangle (Figure 1, blue rectangle) can be maintained. However, in reality, the wall is not exactly perpendicular to the photographer, and the actual laser beams on the wall form a parallelogram (Figure 1, red parallelogram) (when the crack is observed from a position perpendicular to the wall). Before the crack is photographed, the mobile phone or camera must first be placed perpendicular to the wall to reset, after which the mobile phone or camera records the starting angle for photographing the wall. When the mobile phone or camera is turned to photograph the crack, the change in angle is recorded, and the blue rectangle is calibrated into the red parallelogram when placed perpendicular to the wall. The image of the crack is also adjusted to the image captured perpendicular to the wall, which is the real image of the crack.

When the crack is being photographed, the crack and all four points of the lasers must be in the picture; the red parallelogram formed by the four laser beams serves as the reference scale, and the mobile phone or camera compares the image of the crack with the red parallelogram, enabling it to calculate the real length and width of the crack.

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