Aspects of Vibration-Based Methods for the Prestressing Estimate in Concrete Beams with Internal Bonded or Unbonded Tendons
Round 1
Reviewer 1 Report
This article proposes a method on the feasibility of a hybrid approach based on dynamic identification and the knowledge of the elastic modulus. Some comments are exposed as followings:
(1) In Eq.(5)，why didn’t use L+△L?
(2) In part 7, the paper states that ’Regrettably, the outcomes of the method are not reliable; the estimated values enormously exceed the expected prestressing.’ Thus, what’s the paper’s highlights and the practical point?
Author Response
The author appreciates the positive evaluation of the reviewer.
This article proposes a method on the feasibility of a hybrid approach based on dynamic identification and the knowledge of the elastic modulus. Some comments are exposed as follows:
- In Eq.(5)，why didn’t use L+△L?
Corrected. It was an evident typo.
- In part 7, the paper states that ’Regrettably, the outcomes of the method are not reliable; the estimated values enormously exceed the expected prestressing.’ Thus, what’s the paper’s highlights and the practical point?
The paper shows that vibration-based methods are not sensitive to the effect of prestressing. The derivation of the formulation of the proposed approach is promising. However, in the formulation of axial force estimation or prestress state, the estimates of concrete elastic modulus, experimental frequency, etc have high uncertainty, which adversely affects the final estimation. The author shows that the vibration-based method could not give reliable prestress estimation, even if the effect of mass variation is considered.
Reviewer 2 Report
The theme of the manuscript is interesting and appropriate to the scope of publication of this journal, however there are serious problems, such as:
a) The general structure of the paper is very bad, there is confusion between the parties and how the author chooses to divide their sections;
b) Innovation and scientific prominence are not shown properly, in many parts of the text it seems to me to be a technical report !!
c) In some sentences there is an excess of unnecessary citations, on the other hand, in general the text needs more current and important references, there are very old citations !!!
For these reasons, at this point I suggest the rejection of the manuscript, but in the future after the adjustments the authors could resubmit and be considered for publication again.
Author Response
The theme of the manuscript is interesting and appropriate to the scope of publication of this journal, however, there are serious problems, such as:
a) The general structure of the paper is very bad, there is confusion between the parties and how the author chooses to divide their sections;
The author re-organized the paper into two main parts. In the first part, the author presents a discussion on the effects of prestressing in the dominant frequencies of beams. He formalized the frequency of the beam with and without prestressing and evaluate the difference numerically. In the second part, the authors presented the test results of seven prestressed beams, nominally identical with the same prestressing force, used for the method discussion. He evaluated the level of the prestressing losses which is less than 30% for each beam.
b) Innovation and scientific prominence are not shown properly, in many parts of the text it seems to me to be a technical report !!
Unfortunately, the tables and details which resemble a technical report were included in the manuscript by mistake. The editorial office transformed the manuscript in the MDPI format and included in the text details which were after \end{document} in the latex source file. The author is sorry for this mistake and hopes that the reviewer will give a milder judgement about this research effort.
c) In some sentences there is an excess of unnecessary citations, on the other hand, in general, the text needs more current and important references, there are very old citations !!!
The author updated the reference adding the most important and recent ones.
Reviewer 3 Report
The article can be divided into four parts. The first part (Chapter 1) is a general description of the role of prestressing reinforcement in RC structures. The second part (chapter 2) provides an overview of the research on the effect of prestressing on the natural frequency of the structure. The third part (chapter 3) contains a mathematical description of the influence of the prestressing force on the natural frequency. The fourth part (chapter 3 and chapter 4) presents the analysis of the influence of the change of prestressing force on the vibration frequency of the system.
The first part is limited to basic information about prestressed structures. No literature was cited in this section. Due to the very general nature of the information contained in this chapter, no reference to the position of literature is allowed. However, this is unusual in the case of an introductory chapter to the discussed issues.
In the second part of the paper there is luck of theoretical information on the influence of axial force on the frequency of vibrations occurring in the transverse direction. For example, the information that the vibration frequency decreases with increasing axial force acting in one direction has not been mentioned. When the axial force acting in one direction reaches a critical value, the vibrations stop. On the other hand, when the axial force acts perpendicularly to the cross-section and the cross-section experiences rotation with the force, the frequency of vibrations increases with the increase of force. It needs to be highlighted that in this second, mentioned above case, the axial force changes direction during vibration due to the rotation of the cross-section.
The third part, where the research problem was formulated, was presented clearly and does not require any supplements. Each dependencies follow from the previous ones.
The fourth part (Chapter 4 - Method and Chapter 5 - Testing of the procedure on a real case problem) is, in the opinion of the reviewer, presented in a too general manner and too many threads have been explored. The relationships (15) and (16) are too general and it is impossible to follow the method of minimizing the error described by the equation (15). The fact that the presentation of the problems is too general is evidenced by the fact that text contained between the lines 182 - 236 (only 1.5 pages) contain a description of the analysis of the test results of 7 bridges of different spans (from 4 to 12 - Table 2). On the other hand, the analysis concerns objects with a constant span of 40 (table 1). By minimizing the relationship (15), it is not stated for how many forms it is minimized.
In addition, there are editorial errors:
- force is given in tons instead of newtons,
- the stress is given in Mpa instead of MPa,
- the weight is given in Kg instead of kg (e.g. table 1)
- in the description under Figure 7, the frequency is given in tones,
- there are no references in the text of the manuscript to tables 4-10 following the list of references.
Author Response
The author thanks the reviewer for the careful revision. The first part is a short introductory part highlighting the general problem. The author believes that it might be helpful for better understanding the physical problem, despite it being a well-known formulation. Concerning the second part, the author agrees with the reviewer and added the suggested critical remarks.
The third part did not receive corrections, as suggested by the reviewer. The fourth part was corrected. Unfortunately, the tables and details which resemble a technical report were included in the manuscript by mistake. The editorial office transformed the manuscript in the MDPI format and included in the text details, which were after \end{document} in the latex source file. The author is sorry for this mistake and hopes that the reviewer will give a milder judgement about this research effort. The fourth part is now consistent with the previous one and addresses the practical applicability of the procedure using real-case bridges. The editorial errors have been all correct.
Reviewer 4 Report
This paper examines the feasibility of a hybrid approach based on dynamic identification and the knowledge of the elastic modulus. Specifically, the author consider the effect of the axial deformation on the beam length and the weight per unit of volume.
- The analyzed problem has a scientific and technical interest for the field of materials, engineering and environmental sustainability. The manuscript can be published in this journal if the following points are fully addressed in a revised version.
- - General comment
The authors should improve the introduction and the bibliography citing other recent and relevant research papers presented in international journals dealing with this topic.
See for example:
- Overview on the prestress loss evaluation in concrete beams. In Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations(pp. 117-122). CRC Press, 2021
- On the forced vibration test by vibrodyne. In COMPDYN 2015 conference proceedings(pp. 25-27). 2015.
- - Minor points:
- Please change “Mpa” in “MPa” throughout the manuscript;
- Please change the list style: use the semicolon instead of the full stop at the end of every list point, except for the last point where is correct the use of the full stop;
- In line 231 please correct the line spacing;
- To uniform the paper and remove disparities, please add spaces before the unit of measurements and the percentage throughout the manuscript;
- Please check the font of the tables. Smaller fonts may be used, but no less than 8 pt. in size;
- To make a clearer reading of the paper please put the words “Figure” and “Table” in text in bold style;
- Please check the references, in particular for the journals. They should be described as follows:
- Author 1, A.B.; Author 2, C.D. Title of the article. Abbreviated Journal NameYear, Volume, page range.
Author Response
The author thank the reviewer for the careful revision. The references have been expanded and the minor points addressed.
Round 2
Reviewer 2 Report
Indeed, the authors were careful to review and reformulate their paper, improving its quality. However, I still have some minor corrections:
a) The abstract needs to be improved, the authors must emphasize their main quantitative results and the innovation of their research to the readers;
b) In the introduction, add a topic or paragraph about reinforced composite materials, and their definitions, this will help contextualize your research, I suggest the following papers: 10.1016 / j.cscm.2020.e00406; 10.1016 / j.jobe.2021.102483; 10.1016 / j.jobe.2021.102491. Consider these roles.
c) There are spaces between the figures that must be revised, and formatting errors in the text, observe the rules of this magazine;
d) At the conclusion, some future suggestions should be inserted.
I believe that if all these corrections are accepted by the authors, the paper may be published.
Author Response
Rev 1
Indeed, the authors were careful to review and reformulate their paper, improving its quality. However, I still have some minor corrections:
The author thanks the reviewer for the appreciative comments on the paper.
- The abstract needs to be improved, the authors must emphasize their main quantitative results and the innovation of their research to the readers;
The following sentence was added in the abstract: The author found that the uncertainty in estimating the natural frequencies and elastic modulus significantly prejudice a reliable estimate of the prestressing state.
b) In the introduction, add a topic or paragraph about reinforced composite materials, and their definitions, this will help contextualize your research, I suggest the following papers: 10.1016 / j.cscm.2020.e00406; 10.1016 / j.jobe.2021.102483; 10.1016 / j.jobe.2021.102491. Consider these roles.
The suggested references were considered in the new manuscript.
c) There are spaces between the figures that must be revised, and formatting errors in the text, observe the rules of this magazine;
This aspect will be fixed by the editorial office. The spaces between figures depend on the Latex code.
d) At the conclusion, some future suggestions should be inserted.
The following sentence was added in the conclusions: “The authors aim at testing the effect of the prestressing state on the elastic modulus of concrete via extensive experimental tests and detailed modeling of the concrete nonlinear constitutive behavior.”
I believe that if all these corrections are accepted by the authors, the paper may be published.
