Evaluation of the Structural Health Monitoring Results of the Applied Fiber Optics in the Pile-Raft Foundations of a High-Rise Building
Round 1
Reviewer 1 Report
In the paper, the authors demostrated an practical application of fiber-optic sensor in the SHM of a building. Generally, the design and arrangement of the experiment has been clearly explained. However, the motivation of the work is not well presented. And the context does not well support the conclusion part.
In the abstract and introduction, it says that the "Fiber optics performance results differ significantly from simulation models, as they represent the results of deformations (settlement) in the vertical plane, while fiber optic transmits actual strains in the horizontal plane along the length of the cable." However, I does not seen the simulation part in the manuscript. The authors do cited the previous works about the simulation. But in this paper, the simulation should also be explained in details.
Additionlly, the direction of the results from simulation and fiber sensor highly depends on how the sensors were installed and how the simulation model was built. If there are fiber sensors installed vertically, the vertical strain information should also be obtained. Thus, the authors must explain why the sensors were all installed in a horizontal plane while they only simulated the vertical deformations.
Author Response
The group of authors thanks Reviewer for the important comments and tried to correct all the flaws in the revised article as much as possible. The structure of the paper was improved, the introduction part was mainly re-written, to present the obtained research results to the reader as clearly as possible.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Summary: The respected authors presented and monitored the results of structural health of embedded fiber optics in the upper layer of the raft pile over the entire area of a high-rise building and performed the analysis of compression and tensile strains. They found with an increased deflection of the raft under the application of a concentrated load (columns). They also found that fiber optic arrangement in and around the building transmitted the actual strains in the horizontal plane along the length of the cable.
Comments:
1. Please try to improve the introduction section by inserting few more references regarding application of fiber optics sensors like FBGs into the structural health monitoring especially high-rise buildings along with the necessity of it.
2. If possible, try inserting the geological profiles of the area under building to identify the response of strains on the type of layers inside.
3. Try to insert some mathematical relations relating the compressive and tensile strains desired for the analysis of the results.
4. Try inserting the contours of basement deformation analyzed by FEM model.
5. Try inserting the color maps of temperature and strain field distribution while monitoring FBGs.
Author Response
The group of authors thanks Reviewer for the essential notes that helped to restructure the introduction and presentation of the problem, although connect with simulation methods, previously mentioned for the first time only in the discussion part.
Author Response File: Author Response.docx
Reviewer 3 Report
The importance of fiber optic sensors to monitor structural health has been emphasized in various research works. The present work is an experimental demonstration of the structural health monitoring over the entire area of a high-rise building 16 in Nur-Sultan. The strain imposed on the buildings are monitored using fiber-optic strain sensors. A complete practical demonstration of fiber optic strain sensor on a real construction field may draw attention from the researchers in this field. The manuscript needs to be revised in some points to improve the quality of the manuscript before publication.
The author’s address is incomplete with no country defined. Again, the country of the place where the experiment was performed is not given in the abstract.
The operating principles of fiber optic strain sensor employed in this work should be commented in the abstract.
What does the “continuity of concreate over time” means at line 63, page 2? Do you mean the durability of concreate?
Figure 4 is unclear to read the contents included, and the letters are invisible.
Instead of current Figure 5, a picture of installment of fiber optic sensor on the concreate surface would be much more interesting.
Figure 8 has very small fonts which is very hard to read. What is the “Corrugated flexible conduit”? Can this affect the strain application on the fiber?
It seems like -20-40 me should be read as -20 to 40 me. If it is right, it should be corrected in the manuscript.
The fiber-optic sensor measures the strain along the surface, and as you mentioned this strain values does not directly give the vertical settlement distribution resulted from the load from upper floors. However, if you have strain distribution due to the vertical loading, it should be possible to find the vertical displacement of the fiber sensor. I like to recommend the authors to work on this analysis.
Author Response
The team of authors thanks the Reviewer for the efforts and valuable comments.
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Reviewer's note |
Author’s report |
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1 |
The author’s address is incomplete with no country defined. Again, the country of the place where the experiment was performed is not given in the abstract. |
Thanks a lot. Line 17 adds country information. Moreover, our capital was renamed a couple of days ago. Now it is the city of Astana. Corrections have been made throughout the manuscript. |
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2 |
The operating principles of fiber optic strain sensor employed in this work should be commented in the abstract. |
Thank you. The operating principles of fiber optic strain sensor were added in Lines 17-18. |
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3 |
What does the “continuity of concreate over time” means at line 63, page 2? Do you mean the durability of concreate? |
Yes, it was a direct translation from the local language, though meant to be cracks durability. Corrected to durability of concrete over time. |
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4 |
Figure 4 is unclear to read the contents included, and the letters are invisible. |
Thank you for your comment. When generating the PDF format in MDPI submission system, the resolution of the photo from AutoCAD was lost, although the quality is good in Word. Now I have inserted the pictures as JPG or PNG format. In any case, there are original drawing files that I will provide in any required format. |
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5 |
Instead of current Figure 5, a picture of installment of fiber optic sensor on the concreate surface would be much more interesting. |
Thank you. Figure 5 was removed. A photo of the cable laying in the trench under the cover drain, which carries more information about the FO cable installment, and one more photo showing the layering on the concrete surface have been added to Figure 7. Installment of fiber optic sensor on the concreate surface. |
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6 |
Figure 8 has very small fonts which is very hard to read. What is the “Corrugated flexible conduit”? Can this affect the strain application on the fiber? |
Figure 7 (Previously Figure 8) has been amended with large font size. Corrugated flexible conduit can not affect the tension or compaction strain along the cable. It is only for cable protection from external damages. |
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7 |
It seems like -20-40 me should be read as -20 to 40 me. If it is right, it should be corrected in the manuscript. |
Thank you very much for your note. It has been changed to “from -20 to -40 µɛ”. |
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8 |
The fiber-optic sensor measures the strain along the surface, and as you mentioned this strain values does not directly give the vertical settlement distribution resulted from the load from upper floors. However, if you have strain distribution due to the vertical loading, it should be possible to find the vertical displacement of the fiber sensor. I like to recommend the authors to work on this analysis. |
The team of authors thanks Reviewer for the comment. We will work in this direction. We have obtained the distribution of strains along the raft plane and see the places of compression or tension. At the moment, the building is at the final stage of construction, when shopping malls on the 1st and 2nd floors have been put into operation, underground parking lots and car washes are loaded, but the live load of the upper floors has not yet been applied, as finishing work is underway. It is a bit difficult to estimate all the loads, as the design loads on the columns are not yet fully applied. We took the first measurements of fiber optics strains and already see an uneven pattern of strains. It's also a bit difficult to determine if there is a static load on the raft, or if it's a dynamic load from the cars in the parking lot. However, work in this direction is underway and I think in 2 years it will be possible to connect the obtained strains patterns with the coordinates of the loads in the raft plane. |
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Thank you for answering the concerns in the previous review. However, I still do not see the point to compare the simulation and fiber-optic sensor obtained results.
Yes, It is clear that in the simulation the deformation of the plane was obtained and the fiber sensor was measuring the in-plane strain and stress. But, can you simulate the in-plane stain/stress and compare with the fiber senor? Or, can you calculate the deformation from the fiber sensor obtained strain/stress distribution and compare with the simualtion?The conclusions in the paper made me believe that the simulation and experments are independent, which is not true. The correlations between them was not clearly shown.
Author Response
Thank you very much for your comment.
The simulation results from the referenced literature cannot be compared with the results from monitoring with fiber optic cable, embedded as the measuring body in-plane the foundation raft. Simulation is a preliminary assessment of the settlement of the building made before the construction of the building and it is the results of the simulation that helped determine the location of the fiber optic cable in the building plan, and to cover areas with expected increased settlement. (Lines 57-62).
The purpose of monitoring with the use of fiber optics was to observe the continuity of concrete over time since the depth of the pit was significantly lower than the groundwater level and the formation of cracks would allow water to penetrate into them. (Lines 61-65).
Theoretically, it is possible to calculate the vertical deformation within a gauge length.
An unbonded length of FO cable between two adjacent points of fixture, which is called a gauge length, has been taken to be 2 meters. That is, every 1 με=∆l/l of relative elongation/shortening equal to 2mm, if l=2m. Then the leg, or vertical deformation, will be equal to 0.089165mm at 1 με. But we do not know whether this deformation will accumulate in the form of settlement, or the slope might be refracted upward and restored in height.
Therefore, the monitoring of vertical settlement will be carried out by a team of surveyors according to the results of fiber optics.
The team of authors understood the issue that simulation results from the referenced literature cannot be compared with the fiber optic and placed clarification in Discussion (Lines 259-262, 290-297).
The following outputs have been added in the conclusion:
- The excess of deformations of 600 με or 0.6 mm m⁻¹ or 0.3 mm for change in crack width are exceeded, requires a local diagnostic examination with concrete sampling and testing for strength characteristics as part of the diagnostic survey.
- When a strain above 1000 με (0.1%) occurs, a basic structural analysis is recommended, above 1500 με a detailed structural analysis is required.
- Fiber optic monitoring results at the time of testing did not exceed the permitted values for high-rise building operation; however, they characterized the general picture of the strain in the raft plane and make it possible to determine the initiation of cracks in concrete at an early stage.
Author Response File: Author Response.docx
