SHM System Performance and Distribution

The FCB SHM software, Master FCB SHM System.vi, is installed as a service on the local

computer at the US 30 bridge. By operating as a service, the program is able to restart if there is a power outage at the bridge site. Every time the program starts, it pauses for two minutes to

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allow the si425-500 to initialize, and then the monitoring process automatically begins. When the subVI, Synchronized Evaluation and Report Generation.vi, is called to evaluate a data file, it

checks for the existence of the needed text files. If the files do not exist, the subVI assumes that the SHM system has just started the monitoring process, and thus, autonomously creates the files. If the files already exist, information is retrieved from the files to determine the point from which to resume in the evaluation and report generation process. With this configuration, the SHM system is able to resume from any intentional or unintentional system shut down.

Typical statistics for the FCB SHM system at the US 30 bridge during 33 weeks of operation are as follows:

• Raw strain data are saved in approximately one MB file sizes, and approximately 3.4 gigabytes (GB) of raw strain data are collected in 24 hours.

• The average time that is required to complete phases 2–6 of the reduction and evaluation process for each data file has been approximately 1.68 seconds. The time ranges from one to seven seconds, depending on the number of extrema that are extracted from within the data file.

• The average time that is required to generate a daily report from a RPP data file is has been approximately 8.7 seconds. The time required to generate a report has been observed to be essentially independent of the day of week for which it is being created.

• The extrema that are extracted from the data files and evaluated to assess the

structural behavior of the bridge constitute, on average, 0.13% of the raw data that are collected. Percentages range from 0.01% to 0.38%, depending on the number of extrema that are extracted from within the data file.

• Matched extrema are saved following evaluation, but raw data files are deleted. The matched extrema files that are saved constitute approximately 5.5% of the

uncompressed data size.

Based on the time requirements to perform each of the operations, the processing of one data file and potential report generation thereafter should always be finished before a new data file is created. The success of this rapid evaluation can be attributed to the fact that only the event extrema are being evaluated, rather than the entire data set. However, if there is unexpected overlap with processing and file creation, the software is designed to allow for file backup in the intermediate save directory until the normal one-to-one sequencing resumes.

As illustrated in Figure 5.24b, controls are set in the US 30 SHM system to save only the matched extrema and not the raw data. With this storage format, the available storage space on the local computer system is extended by approximately 94.5%. This option was included to address the data management and storage criticism of SHM, which was previously mentioned in Section 2.4.

The SHM system software, Master FCB SHM System.vi, performs as one system, but as

previously presented, it is essentially composed of two components. The first component is the software that communicates with the data acquisition equipment to collect and store data, which is usually supplied by the equipment manufacturer. The second component is the subVI,

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Synchronized Evaluation and Report Generation.vi, which is called by the data collection

component to reduce and evaluate a data file after it has been created. In addition, all programs that are used to train the SHM system were designed to be independent of the hardware that collects the data. With this software design, the VIs and subVIs that were developed in this research are usable with any data acquisition system and software as long as they are programmed to autonomously perform the following:

• Save continuous strain data in files with specified sizes

• Save data files in columns with tab delimited format, where the column zero is the timestamp, column one is the buffer, and all remaining columns compose the sensor array

• Use the subVI, Create File Name.vi, to name the saved data files, or develop code to

name that data files in a format that is identical to that which is created by Create File Name.vi

• Be able to call the subVI, Synchronized Evaluation and Report Generation.vi, to

perform the data reduction, evaluation, and report generation procedures after a data file has been saved.

Since the subVI, Remove Zero Flicker.vi, was specifically created to address filtering needs in

the data collection utility of the si425-500 for this project, it is recommended that this subVI be removed from the SHM system software if it is used with other data acquisition systems.