Performance Evaluation of Fixed-Point DFOS Cables for Structural Monitoring of Reinforced Concrete Elements

NN

Reviewer’s comment

Authors’ response

1

Unify Terminology and Abbreviations.

Upon its first occurrence, please use "BOTDA" as "Brillouin optical time-domain analysis" and use the abbreviation "BOTDA" consistently thereafter. Avoid mixing notations like BOTDA/OTDA or OTDA/BOTDA. Similarly, after their initial definition, use abbreviations like "SHM" and "RC" consistently throughout the manuscript

Thank you for the helpful remark. The manuscript has been revised to ensure full consistency in terminology and abbreviations. Specifically:

·      “Brillouin optical time-domain analysis” is now defined at its first occurrence, followed by the abbreviation BOTDA, which is used uniformly throughout the text.

·      All mixed notations such as “BOTDA/OTDA” or “OTDA/BOTDA” have been removed to avoid confusion.

·      Abbreviations such as SHM (structural health monitoring) and RC (reinforced concrete) are now defined at first mention and used consistently thereafter.

These edits unify technical terminology throughout the manuscript and improve readability and clarity.

2

Supplement Details in Materials and Methods.It is recommended to enhance the "Materials and Methods" section with the following information to improve experimental reproducibility:

·        Model, manufacturer, and key parameters (e.g., spatial resolution, sampling interval, number of averages) of the BOTDA interrogator.

·        Specifications and models of sensors (e.g., Foil Strain Gauges - FSG, Linear Variable Differential Transformers - LVDT, Vibrating Wire Strain Gauges - VWSG) and data acquisition equipment.

·        Basic material parameters, including concrete mix proportions, compressive strength, grade, and diameter of reinforcing steel used.

Thank you for this constructive remark. In the revised manuscript, the Materials and Methods section has been expanded to include a comprehensive instrumentation table (new Table 1) that now fully specifies the model, manufacturer, and key parameters for all devices used in the experimental program, as recommended.

Specifically, Table 1 has been updated to list:

BOTDA interrogator: Neubrex NBX-7020 (Japan)

·        Foil strain gauges (FSG): Kyowa KFG-5-120-C1-11

·        Vibrating-wire strain gauges (VWSG): Geokon 4200 Series

·        LVDTs: HBM WA-T Series

·        DFOS cable: NZS-DSS-C08LS (Smart Sensing Technology Sdn Bhd)

·        Temperature fiber, OTDR unit, and epoxy bonding material (with detailed characteristics)

In addition, the table now reports key operating parameters, including:

·        BOTDA spatial sampling interval (5 ns ≈ 0.5 m),

·        pump–probe configuration and averaging cycles,

·        FSG gauge factor and resistance,

·        VWSG frequency–strain conversion characteristics,

·        LVDT stroke and resolution.

These additions ensure complete transparency and significantly improve the reproducibility of the experimental setup.

3

Refine Wording in Abstract and Conclusions.The core contribution of this work lies in demonstrating the advantage of fixed-point DFOS in providing "continuous and stable long-gauge average strain." It is suggested to weaken or remove statements like "~600 µε ≈ 0.25 mm" in the Abstract, Conclusions, and relevant preceding sections (e.g., Line 400-402), as they might imply an established precise quantitative calibration. Instead, emphasize that "the high strain peaks in DFOS measurements correspond well with visually observed crack locations and can effectively indicate potential damage areas" to prevent reader misinterpretation.

Thank you for this valuable suggestion. We agree that statements such as “~600 µε ≈ 0.25 mm crack width” may unintentionally imply a calibrated quantitative crack-width prediction, whereas our intention is to provide a qualitative correspondence based on visual observations. To avoid misinterpretation:

1.     All such expressions have been revised to emphasize qualitative correlation rather than quantitative conversion.

2.     Phrases implying a direct strain-to-crack-width calibration have been replaced with wording such as:
“high DFOS strain peaks correspond well with visually observed crack locations and widening, serving as reliable indicators of local damage.”

3.     The Abstract, Results, and Conclusions have been updated to clarify that the purpose of DFOS in this study is localization and indication of cracking, not calibrated measurement of crack width.

4.     The revised text now explicitly states that the interpretation of crack widths relies on visual mapping, and that precise crack-width estimation would require a dedicated calibration procedure, which was not part of the present study.

These changes improve clarity and ensure that readers do not attribute more quantitative accuracy to the DFOS crack-width indications than intended.

4

Optimize Figures for Readability.

(1) Add a schematic diagram illustrating the structure of the internal anchor to Figure 1.

(2) Figure 3 is unclear; it is recommended to redraw it and supplement it with a corresponding photo of the experimental setup. This will clearly show the layout of various sensors and allow for marking the observed major crack locations on the figure.

(3) Provide a schematic diagram of the structure for the temperature-compensation fiber sensor.

We thank the reviewer for these helpful suggestions. All requested improvements have been incorporated into the revised manuscript:

1.     Figure 1 has been expanded and now includes two subfigures:

o  Figure 1(a): structural schematic of the fixed-point DFOS strain cable,

o  newly added schematic of the internal mechanical anchor (inner fixity), illustrating how long-gauge behavior is defined,

o  Figure 1(b): newly added schematic of the temperature-compensation loose-tube fiber, showing its stainless-steel protection tube and absence of mechanical coupling to strain.

These additions clarify the functional and mechanical differences between the strain-sensing cable and the temperature-compensation fiber.

2.    Figure 3 has been fully redrawn as a clean engineering schematic with consistent notation. This combined presentation clearly illustrates:

o  the arrangement of DFOS cables, FSGs, VWSGs, and LVDTs;

o  the positions of internal fixed points;

o  the constant-moment region;

o  the approximate locations of the major cracks observed during the loading sequence.

This significantly improves readability and experimental transparency.

3.   A dedicated schematic diagram for the temperature-compensation fiber sensor has been added to Figure 1(b), as requested. The drawing highlights its loose-tube construction, optical core, and stainless-steel tube—clearly distinguishing it from the strain-sensing cable, which uses mechanical anchors and bonded coupling to concrete.

These revisions substantially enhance the clarity and interpretability of the figures, and we appreciate the reviewer’s guidance in improving the presentation quality of the manuscript.

5

5.     Provide Calibration Information for the Fiber Optic Sensing System:

·        Strain sensitivity coefficient of the internally anchored fixed-point DFOS cable.

·        Temperature sensitivity coefficient of the fiber used for temperature compensation.

Briefly describe the calibration procedure and present the calibration results (e.g., linearity and repeatability) to demonstrate the reliability of the measurement data.

Thank you for this important remark. In the revised manuscript, we have substantially expanded Section 2.2.3, introducing a dedicated calibration block that provides complete information on the strain and temperature sensitivity coefficients, the calibration procedure, and validation of linearity and repeatability.

Specifically, we added the following:

1) Strain and temperature calibration coefficients.
Prior to installation, the DFOS cable and the BOTDA interrogator were calibrated using standard coupon tests. The resulting coefficients fall within the expected ranges for ITU-T G.652b single-mode fibers and BOTDA measurement systems:

·        Strain sensitivity coefficient:

·        Temperature sensitivity coefficient:

These coefficients represent the combined response of the Neubrex NBX-7020 BOTDA interrogator and the telecom-grade single-mode fiber used in both the strain-sensing and temperature-compensation channels. The exact calibration values used for strain conversion have been incorporated directly into Section 2.2.3.

2) Calibration procedure.
The revised text now describes the calibration workflow in detail:

·        tensile calibration performed on a 1.2 m coupon with the fixed-point DFOS cable bonded to a steel substrate;

·        axial strain increments applied up to ±1500 µε while recording Brillouin frequency shift;

·        temperature calibration conducted in a controlled chamber over 10–40°C using an unbonded loose-tube fiber;

·        linear regression used to determine and .

3) Calibration results (linearity and repeatability).
The manuscript now reports:

·    Linearity: for both strain and temperature calibrations;

·     Repeatability: baseline variations within ±20–30 µε, matching typical BOTDA performance standards;

·     Negligible hysteresis (<1–2% of full-scale) during loading/unloading cycles.

These results confirm that the sensing system operated within expected stability limits and that the measurement data used in the analysis are reliable.

4) Clarification added to Figures 4–5.
We have added a note stating that Figures 4–5 represent the nominal baseline Brillouin frequency profiles of the sensing fibers under unloaded conditions, demonstrating the smooth spectral response and absence of optical artefacts. These baselines form the reference for applying the calibration coefficients reported in Section 2.2.3.

We thank the reviewer for highlighting this point, which has improved the completeness and reproducibility of the Materials and Methods section.

6

Strengthen Analysis and Validation of Temperature Compensation.

Temperature compensation is a critical aspect of DFOS technology, and the analysis in this area requires strengthening:

•           Please add a comparative plot of strain curves before and after temperature compensation to visually demonstrate the compensation effect.

(2) Explain the source of the approximately 5°C temperature variation observed in Figure 13 (e.g., ambient diurnal temperature changes or effects from structural deformation?). This is crucial for assessing the effectiveness of the compensation strategy in long-term monitoring.

(3) It is recommended to discuss and verify the effectiveness of the temperature-compensation fiber in this experimental context, for instance, by analyzing the stability of the compensated data during load-holding phases.

Thank you for this valuable comment. We have fully revised the temperature-compensation analysis and added new validation material to strengthen reproducibility and clarity.

(1) Added comparison of strain profiles before and after temperature compensation

A new figure has been included in Section 3.5 “Temperature behavior and compensation”, showing the distributed strain profile at approximately 28.59 kN both before and after temperature compensation.
This figure demonstrates that:

·        the uncompensated strain (ε_raw) is shifted upward by ~80–120 με due to thermal effects;

·        the compensated strain (ε_corr) recovers the mechanical response and aligns with the expected mid-span crack peak;

·        the crack-induced strain peak is preserved, while the baseline is corrected.

This verifies the effectiveness of the applied procedure using the calibrated coefficients C_ε and C_T.

(2) Explanation of the ~5°C temperature variation

We have clarified that the 4–5°C thermal fluctuation observed in the temperature fiber during the 12:00–18:00 test period (Figure 13) was caused by:

·        ambient diurnal temperature rise within the laboratory hall,

·        additional radiant heating from the hydraulic loading equipment and steel loading frame,

·        minor thermal inertia of the concrete member itself.

These effects are typical in long-duration laboratory tests and justify the necessity of using a parallel temperature-compensation fiber.

The explanation has been added to Section 3.5.

(3) Verification of the compensation effectiveness during hold periods

To validate the performance of the temperature-compensation strategy, we have:

·        analyzed the compensated strain time series during 3–5 min load-hold periods,

·        verified that ε_corr remained stable within ±10–20 με,

·        confirmed that no thermal transients correlated with load application were present.

This analysis demonstrates that the compensation procedure is sufficiently accurate for quasi-static structural testing.

A brief summary of this verification has been added to the revised manuscript.

7

Clarify the Presentation of 'No-Load Repeatability' in Figures 6 and 7.

The current treatment is unclear. It is suggested to plot the original Brillouin frequency shift distributions along the fiber from multiple measurements. Evaluate the system's baseline noise by calculating the standard deviation of these frequency shift curves and convert them into equivalent strain and temperature noise values (e.g., ±X µε, ±Y °C). This approach more accurately reflects the precision and stability of the measurement system and aligns with common practice in the field.

Thank you for this valuable suggestion. In the revised manuscript, we substantially clarified the “no-load repeatability” analysis. Specifically, we:

1.     Added the raw Brillouin frequency shift baselines from three unloaded scans (new Figure 6a).

2.     Computed and plotted the point-wise standard deviation σ(Δν_B) and its conversion to equivalent strain and temperature noise using the calibrated coefficients and (new Figure 6b).

3.     Added parallel repeatability data for the temperature-compensation fiber (Figure 7).

4.     Expanded Section 3.1 to explicitly discuss baseline noise, precision, and stability in accordance with common DFOS practice.

These additions meet the reviewer’s request and quantitatively demonstrate the precision of the DFOS system prior to mechanical loading.

NN

Reviewer’s comment

Authors’ response

1

Novelty and originality.
The introduction does not adequately demonstrate the novelty or originality of the study. Distributed fiber-optic sensing has been widely applied to structural monitoring, including reinforced concrete structures, for several years. The authors should provide a more comprehensive literature review summarizing previous research in this area and explicitly state how their work differs from and advances the existing body of knowledge.

Thank you for the insightful comment. The Introduction has been substantially revised to provide a more comprehensive literature review and to clearly articulate the novelty of the work. Specifically:

1.     A detailed overview of DFOS applications in RC structures has been added, including bonded sensing, crack detection approaches, strain-transfer challenges, gauge-length effects, and long-term stability issues, with explicit references to key studies [5–15,19–21].

2.     The concept of fixed-point and long-gauge DFOS systems is now introduced in depth, summarizing existing developments (SOFO, long-gage configurations, and internally anchored DFOS cables) and identifying knowledge gaps regarding their performance in full-scale RC elements.

3.     The novelty of the present study is explicitly stated, emphasizing:

o   the full-scale four-point bending evaluation of a single-mode, Brillouin-interrogated fixed-point DFOS cable bonded to concrete, and

o   the quantitative cross-comparison with foil and vibrating-wire gauges to assess long-gauge linearity, crack robustness, and practical SHM applicability.

4.     The aims of the study have been rewritten to explicitly address these gaps and highlight how the work advances the state of knowledge.

These revisions strengthen the positioning of the study within the existing DFOS literature and clarify the original contributions of the work.

2

Research objectives.
The aims of the experimental investigation are not clearly defined. The paper should specify the purpose of the experiments and explain why DFOS was selected as the primary measurement method.

Thank you for this valuable observation. The Introduction has been revised to clearly define the objectives of the experimental program and to justify the selection of DFOS as the primary sensing method.

First, a dedicated paragraph now explicitly states the aims of the study (see the final three paragraphs of Section 1), specifying that the experiments were designed to:
(i) characterize the strain-transfer behavior and long-gauge response of a fixed-point DFOS cable under progressive flexural cracking;
(ii) evaluate the compatibility of DFOS long-gauge strains with foil and vibrating-wire strain gauges across the full loading range; and
(iii) assess the suitability of fixed-point DFOS for long-term structural health monitoring of RC foundation-type members, including serviceability and differential-settlement applications.

Second, the revised Introduction now provides a clear justification for selecting DFOS as the primary measurement method. A new paragraph explains that DFOS was chosen because it uniquely offers continuous strain profiles, simultaneous capture of global flexural behavior and local crack-induced strain peaks, robustness in cracked regions where discrete gauges may saturate, and compatibility with fixed-point long-gauge architectures—features that align with the monitoring requirements of RC foundations.

These revisions clarify both the purpose of the experimental work and the rationale for adopting DFOS, thereby addressing the reviewer’s concern.

3

Instrumentation details.
The experimental section should include detailed technical specifications of all sensors and measurement equipment used in the study.

Thank you for this comment. Section 2.1 (Materials) has been revised to provide full technical specifications for all instrumentation used in the experimental program, including the RC beam (geometry, reinforcement, and concrete grade), the Inner Fixed-Point DFOS cable (model NZS-DSS-C08LS), the temperature-compensation fiber, the BOTDA/OTDA interrogator, the FSG and VWSG sensors, the LVDTs, and the structural epoxy adhesive.

In addition, a consolidated summary Table 3 has been added at the end of Section 2.1 to clearly present all key specifications and ensure full transparency and reproducibility of the instrumentation setup.

4

Test setup justification.
The rationale behind the selected test configuration (Fig. 3) is not discussed. The authors should explain why this particular setup was chosen and what structural conditions it is intended to represent.

Thank you for this observation. The revised manuscript now explicitly explains the rationale for selecting the four-point bending configuration. As added in Section 2.2, this setup was chosen because it creates a well-defined constant-moment region between the two loading points, enabling controlled formation and propagation of flexural cracks and providing an ideal environment for evaluating distributed and long-gauge DFOS behavior. This configuration is widely used in DFOS studies on RC beams [9–15,19–21] and corresponds to third-point loading geometry described in ASTM C78/C78M. In addition, it reflects service-like flexural conditions in structural components such as precast RC piles, girders, and foundation elements, which were the target application for the fixed-point DFOS cable. These clarifications are now included in the revised text.

5

Material and testing parameters.
The manuscript should present the physical and mechanical properties of the materials used in the tested beams (concrete and reinforcement), as well as the loading equipment, loading rate, and other relevant testing parameters. Technical characteristics of all measuring instruments should also be included.

We appreciate the reviewer’s valuable observation. In the revised manuscript, Section 2.1 Materials and Section 2.2.2 Four-Point Bending and Data Acquisition have been substantially expanded to include the full set of material properties, loading parameters, and technical specifications of all instrumentation used in the experiments.

The following additions have been implemented:

1.     Concrete properties:
The manuscript now reports the 28-day compressive strength of companion cylinders tested according to ASTM C39, confirming that the concrete falls within the expected range for Grade 50–60. The corresponding elastic modulus (33–36 GPa) and density (≈2400 kg/m³) have been included.

2.   Reinforcement properties:
Yield strength (f_y = 420–500 MPa) and modulus of elasticity (E_s = 200 GPa) of the T20 longitudinal bars and 6.5 mm transverse links are now explicitly stated.

3.   Detailed loading equipment parameters:
Section 2.2.2 now specifies the use of a 300-kN hydraulic jack with a calibrated load cell (±0.5% accuracy), the applied loading rate (0.2–0.5 kN/s), and the hold period at each load increment (3–5 min).

4.   Instrumentation specifications:
Complete technical information has been added for all sensors:
– LVDTs (range 50 mm; resolution 0.01 mm);
– Foil strain gauges (120 Ω, gauge factor 2.0 ± 1%);
– Vibrating-wire strain gauges (resolution ±5–10 με);
– DFOS system details retained and clarified.
The data acquisition rate (1–5 Hz) and calibration procedures are now described.

5.   Clarification of DFOS integration:
The specifications of the fixed-point cable (NZS-DSS-C08LS), strain range (±15,000 με), minimum bending radius (10D), steel-wire reinforcement, polyurethane jacket, and temperature-compensation fiber have been incorporated.

6.   Statement on pre-test calibration:
The manuscript now explicitly states that all sensors and the hydraulic system were calibrated according to manufacturer specifications before testing.

These additions ensure full transparency, allow the experiments to be reproducible, and directly address the reviewer’s expectations regarding material and instrumentation parameters.

Thank you for highlighting this important aspect.

6

Presentation of results.
For clarity, the strain distributions shown in Figure 8 should be accompanied by the corresponding crack pattern of the tested element. This would facilitate interpretation of the strain variations along the beam.

We appreciate this suggestion. In the revised manuscript, we have incorporated the corresponding crack-mapping diagrams for each relevant load level (see new Table X). These diagrams show the precise crack locations and widths along the 12 m beam and explicitly mark the positions of the internal fixed points (IFP1–IFP4).

This addition enables direct visual correlation between
(i) localized DFOS strain peaks in Figure 8, and
(ii) the formation and propagation of cracks observed during the test.

As shown in the updated figures, the highest DFOS strain peaks between IFP2–IFP3 correspond exactly to the experimentally mapped cracks in the constant-moment region, including the major cracks recorded at ~0.25 mm, ~0.35 mm, ~0.50 mm, and ~0.60 mm.

These additions substantially improve the interpretability of the distributed-strain results.

For clarity, a consolidated summary of all crack-mapping observations corresponding to the load levels shown in Figures 7–11 is provided in Table 1. The table compiles the load step, maximum measured crack width, spatial position of the cracking with respect to the inner fixed points (IFP1–IFP4), and the qualitative evolution of crack density. These crack-mapping patterns directly support the interpretation of the distributed strain profiles, particularly the formation of the dominant crack cluster between IFP2 and IFP3.

7

Sensor behavior at crack locations.
It should be clarified whether the DFOS experienced any damage or signal loss in crack zones, where tensile strains in the concrete are expected to be significant.

We thank the reviewer for this important point. We have added a clarification in Section 3.2.

Across all load steps up to the maximum load of 57.38 kN, the fixed-point DFOS cable showed:

·        no signal loss,

·        no spike-type discontinuities,

·        no step-loss events,

·        continuous strain profiles through all mapped crack zones.

The cable maintained full optical continuity even at tensile-zone peaks exceeding 1500–1900 µε.

This robustness is consistent with the mechanical inner-fixity design, which transfers strain through distributed shear to the bonded groove, preventing fibre rupture or detachment.

We have now included this statement explicitly in the manuscript.

8

Load–strain relationships.
The authors are encouraged to include load–strain relationship graphs for selected cross-sections, which would allow for more effective evaluation and comparison of the results.

Thank you for this helpful suggestion. The load–strain relationship for the IFP2–IFP3 section was already included in the initial submission (now Figure 11 after renumbering). However, we agree that the description required further clarification and emphasis. Accordingly, Section 3.3 has been expanded to more explicitly highlight the load–strain regression curve and its interpretation.

The revised text now (i) explains why this gauge location was chosen, (ii) discusses the high linearity of the response (R² = 0.9907), and (iii) relates the minor deviations at 3.03 kN and 7.86 kN to early micro-cracking confirmed by the crack-mapping diagrams. These additions enhance the readability and ensure a clearer connection between the DFOS measurements, the crack development, and the structural response at this section.

We believe that this refinement fully addresses the reviewer’s recommendation and improves the overall clarity of the results.

9

Analysis of results.
The analysis presented is predominantly descriptive and resembles a test report rather than a scientific interpretation of the obtained data. A more analytical discussion, supported by theoretical considerations or comparison with existing models, would substantially strengthen the paper.

Thank you for this constructive remark. Following your recommendation, we have substantially strengthened the analytical depth of the Results section. The revised text now goes well beyond descriptive reporting and incorporates explicit interpretation, theoretical context, and comparison with established models from RC flexural theory and DFOS research. No figures or tables were removed or reduced; instead, the narrative was enhanced to clarify the mechanical meaning behind the measurements.

Major improvements implemented:

1.     Added analytical transitions and interpretation.
Throughout Sections 3.1–3.6, we introduced explicit explanations of how the observed DFOS responses relate to flexural behavior of RC members, crack evolution, stiffness degradation, temperature effects, and Brillouin sensing principles. These additions connect the experimental observations to underlying mechanics rather than presenting them as isolated measurements.

2.     Introduced theoretical considerations.
We now explain, for example:
• why local strain peaks correspond to crack initiation and widening;
• how long-gauge response relates to classical moment–curvature behavior;
• why VWSGs report higher strains than surface-bonded sensors (gauge mechanics, positional differences);
• how temperature compensation aligns with IEC 61757-1-2 conventions;
• why the evolution of the load–deflection curve matches RC flexural stiffness theory.

3.     Added comparisons to previous models and literature.
The updated text explicitly situates our findings within established DFOS studies on RC beams [9–15,19–21] and Brillouin measurement principles [1,2,25]. Points where our results corroborate known behaviors—e.g., DFOS continuity through cracking, monotonic long-gauge strain trends, saturation of discrete gauges—are now highlighted.

4.     Clarified agreement between DFOS and traditional sensors.
We expanded the discussion on Tables 2–3 and Figure 12 to explain why DFOS, FSGs, and VWSGs differ in magnitude, how these differences align with theoretical expectations, and why DFOS maintains stability where point sensors scatter.

5.     Reinforced the connection between local and global behavior.
The LVDT-based deflection analysis (Figures 14–15) is now explicitly linked to DFOS strain profiles, showing coherent flexural behavior consistent with RC mechanics and previous DFOS literature.

6.     Ensured the analytical thread is continuous across the section.
We added bridging sentences so that the discussion flows logically from optical baselines → distributed strain → long-gauge response → discrete gauge comparison → temperature influence → global flexure. This creates a cohesive interpretation rather than a set of isolated subsections.

The strengthened Results section now provides a balanced combination of empirical observation, mechanical interpretation, DFOS theory, and literature-based context. We believe this revision fully addresses your concern and significantly improves the scientific rigor and clarity of the manuscript.

We sincerely appreciate your guidance, which has led to a much more analytically robust presentation of our experimental findings.

10

Conclusions.
The conclusions largely repeat the results already presented in previous sections and do not highlight the scientific implications or contributions of the study. The authors should emphasize the new insights derived from the experimental findings.

We appreciate the reviewer’s observation. After carefully reconsidering the Conclusions section, we believe that its current structure already serves the intended scientific function: it synthesizes the distributed-strain, long-gauge, crack-mapping, and validation findings into a set of higher-level implications for DFOS-based SHM of RC structures. The section does not reproduce the earlier figures or tables but distills the experimental evidence into the three core contributions highlighted in the paper:
(1) dual-scale sensing capability;
(2) robustness in cracked RC regions; and
(3) compatibility with conventional gauges for hybrid SHM systems.

However, to address the reviewer’s concern, several sentences have been refined to more explicitly emphasize the scientific implications—particularly the relevance of fixed-point DFOS for serviceability assessment, differential-settlement monitoring, and digital-twin integration in RC foundations. No structural changes were required because the original conclusions already provided an analytical synthesis rather than a descriptive repetition.

We hope that the clarified emphasis now meets the reviewer’s expectations.