# Distributed fiber optic sensor data of the openLAB loading test on 2025-05-06


## Abstract

Between 2025-05-05 and 2025-05-07, extensive experiments were carried out on the openLAB research bridge.
The test program was structured as follows:

- Day 1 (2025-05-05): Static and dynamic measurements in the reference state
- Day 2 (2025-05-06): Loading of the bridge with hydraulic jacks up to the ultimate limit state
- Day 3 (2025-05-07): Local damage to the prestressing tendons (cutting wires at several locations)

This dataset contains distributed fiber optic strain sensing (DFOSS) data measured during the load test conducted on day 2.
The load was applied locally to PE 2.1 (span 2, PE axis 1) using two hydraulic jacks and increased in steps up to a total of 400 kN.

Related ressources:

- Digital documents of the openLAB and BIM models: [Digitale Unterlagen der openLAB Versuchsbrücke (Stand 2025-11-29)](https://doi.org/10.25532/OPARA-1010)
- Experimental regime and environmental data: [Experimental procedure for the tests on the openLAB from 2025-05-05 to 2025-05-07](https:doi/org/doi.org/ https://doi.org/10.25532/OPARA-1012) 
- Load and deflection: [Monitoring Data of the openLAB Research Bridge – Load Test on PE 2.1](https://doi.org/10.25532/OPARA-852).
- Crack pictures and surface crack widths: [Photographic documentation of crack development on the openLAB during the loading test on 2025-05-06](https:doi/org/doi.org/10.25532/OPARA-898)

All timestamps are given in UTC+0.


## Repository Structure

To make the data consumable, it is split into several archives, each of which contains this same README.


### 📁 Documents 

The archive `Documents` contains:

- A spreadsheet file `Channeltable.xlsx` with a spreadsheet for each interrogator showing which sensors were connected to it. All spreadsheets are additionally exported to UTF-8 plain text files, in which the columns are separated by tabs.
- A spreadsheet with information on the sensors' properties and purposes, installation methods and connector positions in the openLAB. A PDF version is attached. More information can be found in [Digitale Unterlagen der openLAB Versuchsbrücke (Stand 2025-11-29)](https://doi.org/10.25532/OPARA-1010).


### 📁 fibrisTerre

`fibrisTerre` contains the measurements files of the fTB 5020 connected to the DFOS integrated in the prestressing strands of PE 2.1 in both the proprietary binary format and an exported version of the strain measurement.
The proprietary binary raw measurement files reside in the subdirectory `Raw_data`.
The exported strain data files reside in the subdirectory `Exported`: a separate UTF-8 encoded tab-separated text file for each day.
Time stamps are given in UTC+0 in ISO 8601 format.
On the 2025-05-05 and 2025-05-06, three sensing segments were connected by patchcords: sg_1 (the first strand in the parabolic tendon), sg_2 (the second strand in the parabolic tendon), and sv (the strand in direct bond).
The following table shows the positions of the beginning and the end of the sensing segments.
From the start (s) and end (e), the direction of the segments can be inferred.
The middle (m) is calculated by applying offsets on both ends of the girder from the technical drawings.
The sensor position is the length along the sensor and the openLAB position is the distance to axis 10.
On the 2025-05-07, only sg_1 was connected, but the coordinates are still valid.

| Gage name | Sensor position | openLAB position (x) | Notes                                   |
| : ------- | :-------------- | :------------------- | :-------------------------------------- |
| sg_1s     | 10.92           |                      | Tendon, strand 1, axis 30               |
| sg_1m     | 18.255          | 22.5                 | Tendon, strand 1, middle of PE 2.1      |
| sg_1e     | 25.50           |                      | Tendon, strand 1, axis 20               |
| sg_2s     | 37.70           |                      | Tendon, strand 2, axis 20               |
| sg_2m     | 44.955          | 22.5                 | Tendon, strand 2, middle of PE 2.1      |
| sg_2e     | 52.30           |                      | Tendon, strand 2, axis 30               |
| sv_s      | 64.40           |                      | Strand in direct bond, axis 30          |
| sv_m      | 71.49           | 22.5                 | Strand in direct bond, middle of PE 2.1 |
| sv_e      | 78.50           |                      | Strand in direct bond, axis 20          |

### 📁 ODA … 📁 ODF

The archives `ODA` through `ODF` contain measument data of the Luna ODiSIs.
The acronyms denotes the interrogator device.

| Acronym | Model | Channels | Owner       |
|:------- | :---- | :------: | :---------- |
| ODA     | 6104  | 4        | Hentschke   |
| ODB     | 6108  | 8        | TU Dresden  |
| ODC     | 6108  | 8        | TU Dresden  |
| ODD     | 6108  | 8        | TU Dresden  |
| ODE     | 6104  | 4        | AIT         |
| ODF     | 7108  | 8        | MFPA Weimar |

The data is given in the native format written by the ODiSI, which is essentially JSON.
Although this data file structure is not officially documented, you may find some similarity with the ODiSI streaming protocol documented in the manual (`./Documents/LunaInnovationsInc._2020_ODiSI6.pdf`).
One measurement consists of a header file `<measurement name>_<datetime>_hdr.dat`, which contains metadata, such as information on the device itself, channel allocation with sensor information, measurement settings, tara values and an index of the the actual measurement files (used to navigate the measurement files quickly).
The `<measurement name>` is provided by the operator.
The `<datetime>` is the date and time in ISO 8601 format (UTC+0) when the measurement was started, i.e., the ODiSI was set to the armed state.
The header file is accompanied by a directory named `.<measurement name>_<datetime>.dir` which contains the actual measurement data files named `<measurement name>_<datetime>_<number>.dat`.
The leading dot is a convention on unixoid operating systems (e.g., Linux) to hide the file in file browsers by default.
For quick navigation, the ODiSI splits the measurement files into chunks of <0.5 GB and increments `<number>` starting from `0`.
The ODiSI cycles the channels in ascending order when measuring.
Hence, the readings are written cycling through the sensors and each line is a reading of one sensor formatted in JSON.

Note that ODiSI measures with an accuracy of 0.1 µm/m.
With file version 9 and up, the ODiSI stores the strain readings as integers to reduce the file size.
To retain the accuracy of 0.1 µm/m, the measured value is multiplied by 10 before it is written to the file.


### 📁 SensorKeys

The archive `SensorKeys` contains the so called "keys" of the DFOS sensors.
A key file called `*.od6pck` is a `zip` archive with renamed file extension and contains:

- The fingerprint of the optical fiber in the file `*.od6ref`, which is the reference state used by the ODiSI to identify the specific sensor and derive the measurements.
- Tare information (named readings, documenting specific reference states) wihch are subtracted from the actual measurement before displaying and storing.
- Metadata on the sensor with calibration coefficients, name, type, length, ect.

ODiSI sensor keys are best managed with the free open source software [`fosKeyMan`](https://github.com/TUD-IMB/fosKeyMan).


## Availability, Copyright and Funding

This dataset is available as open data.

**Authors:** Richter, Bertram and Ulbrich, Lisa Collin, Fabian and Kielreiter, Anett and Dunkel, Stephan and Kirchner, Andreas and Ganß, Martin and Wittmann, Stefan and Nöther, Nils  
**DOI:** [10.25532/OPARA-1011](https:doi/org/doi.org/10.25532/OPARA-1011)  
**Licence:** Creative Commons Attribution Share Alike 4.0 (CC-BY-SA 4.0)  
**Date:** 2025-**05**  

This dataset is result of the research projects IDA-KI ("Automated assessment of monitoring data for infrastructure constructions using AI and IoT"; funding reference: 19FV2013A-D) and FOSsure ("Fiber optic sensors for reliable condition assessment of concrete bridges"; funding reference: 01FV2075A), which were funded by the Federal Ministry of Transport, Germany, within the innovation program mFUND.
