Analysis of Bearing Strength of Post-Tensioning Anchorage Zone with Respect to Relative Bearing Area and Lateral Confinement Design

Round 1

Reviewer 1 Report

The paper presents an experimental study on eleven specimens with the aim of evaluating the bearing strength of the post-tensioning anchorage zone with respect to the relative bearing area and lateral confinement design of spiral and stirrup rebars. Load transfer tests were performed, and the bearing strength, load-displacement curves, and fracture modes of the post-tensioning anchorage zones were analysed.

Thus, in general, the paper presents some interesting results and can be transformed into a paper worth publishing. However, several points need to be addressed before the paper can be accepted for publication.

In all, the information presented is useful and of interest to the readers of International Journal of Applied Sciences. However, several topics discussed in this review should be addressed. Comments below are subdivided into two main parts: (A) General comments and (B) Specific comments (by line number)

• GENERAL COMMENTS:

In page 1, line 38-39, the authors state that “The strands are inserted into the ducts after concrete hardening”. This sentence should be amended as this is not always the case. When, at one end of the tendon, there is a dead-end anchorage or an intermediate anchorage (or coupler), the strands must be placed before concrete casting.

Also in line 39, the sentence “then tensioned and anchored to prestress the concrete” should be reformulated, since the concrete is prestressed simultaneously with the tensioning of the tendon. The anchorage just prevents the strands from re-entering the duct and losing their tension.

In page 2, line 56, the authors state that the proposed design model “increased the bearing strength of the anchorage zone”. This sentence should be reformulated since the design model doesn't increase the bearing strength, but the design model allows to consider the favorable effect of the confinement, thus the estimated bearing strength is higher.

Regarding research with advanced concrete material (UHPC, HPFRC, etc.), there are relevant research works in the area that could be referred:

• Marchão, C., Lúcio, V., Ganz, H. R. (2017): Optimization of anchorage corner blisters for post-tensioning tendons. Structural Concrete. 2017; 18(2):334–348. https://doi.org/10.1002/suco.201600057).

Regarding research in local anchorage zone confinement, there are also relevant works that should be referred:

• Bonetti R, Roberts-Wollmann C and Santos J (2014) Bearing strength of confined concrete. ACI Structural Journal 111(6): 1317–1324
• Marchão, C., Lúcio, V., Ganz, H. R. (2019): Efficiency of the confinement reinforcement in anchorage zones of post-tensioning tendons. Structural Concrete. 2019; 20(3):1182-1198. https://doi.org/10.1002/suco.201800238
• Rebelo, J., Marchão, C., Lúcio, V. (2019): The efficiency of confinement reinforcement in post-tensioning anchorage zones. Magazine of Concrete Research. 2021; 73(6), pp. 271–287. https://doi.org/10.1680/jmacr.19.00050

Regarding reference [22], there is a more recent version of PTI (6^th Edition, 2006), which includes the design model by Wollmann and Roberts-Wollmann, so Eq.(3) is out of date.

In page 5, in Fig. 2, the duct diameter is dimensioned. However, the caption only refers the lateral confinement and anchorage device.

In page 6, lines 195-196, the authors stated that “Even though the contribution of lateral reinforcement (Ps) is based on the assumption that the anchorage device does not have cone and ribs (…) in general, special anchorage bearing plates with cones and ribs, as shown in Fig. 2(a), are used”. This sentence should be clarified/reformulated since the the contribution of lateral reinforcement (Ps) is included in the design model of Wollmann and Roberts-Wollmann, which is part of the chapter 3.3 on “Special Bearing Devices” of PTI (6^th Edition, 2006), where in Fig. VIII-8 it is shown a typical test block for special bearing plate and illustrates an anchorage with cone and ribs.

According to the authors, the average concrete strength at the date of the tests was determined using cylindrical specimens with 100 mm diameter and 200 mm height (lines 226-227). It should be noted that, according to Eurocode 2, the compressive cylinder strength of concrete should be determined using cylindrical specimens with 150 mm diameter and 300 mm height. The use of smaller cylinders leads to higher compressive strengths. This should be taken into account on the determination of the bearing strength.

The loading procedure of the load transfer test specified by EAD 160004-00-0301 consists of a cyclic loading between 0,8 Fpk and 0,12 Fpk, as the authors refer, but the number of cycles depends on the stabilization of strain readings and crack widths, with a minimum of ten. Was this factor considered? How were the concrete strain and crack openings read? The test monitoring equipment should be described in more detail. Besides strain readings and crack widths, the values of the upper and lower loads of the cycles must be specified in the paper.

Also with regard to the load transfer test, the acceptance criteria does not only depend on the failure load, but also on the values of the crack widths for certain predefined points of the cycles. Was this taken into account?

In Tables 2, 3 and 5, the units of the values presented in the last column (“Confinement by surround-ing concrete outside spiral”) must be provided.

The authors should present a list of notation.

• SPECIFIC COMMENTS:

1. Page 2, Line 49 – Consider changing “strengthening” to “confining”.
2. Page 3, Lines 103 to 105 – Revise the sentence.
3. Page 4, Lines 62 – Change “???(?) is the concrete strength at the time of tensioning” to “???(?) is the characteristic compressive cylinder strength of concrete at the time of tensioning.
4. Page 6, Lines 220 – Change “Table 2” to “Table 1”
5. Page 9, Line 313 – Change “as well wide cracks on the top surface” to “as well as wide cracks on the top surface”
6. Page 13, Line 350 – Consider changing “rebar” to “reinforcement”

Author Response

Dear Reviewer1,

thank you very much for your useful comments on our paper. 
We have carefully considered all your comments, and the revised manuscript is now attached for your reconsideration. 
We really appreciate the opportunity to resubmit. 
Also, we would like to thank you for your excellent comments which significantly improved the quality of our paper.

Best regards,
Jun-Mo Yang

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript "Analysis of bearing strength of post-tensioning anchorage zone with respect to relative bearing area and lateral confinement design" reports adherence composting and is very interesting to potential readers, however the authors should make some corrections to the text:

a) The abstract should include some quantitatively highlighted results in the conclusions, in addition to scientific innovations that should be highlighted;

b) The manuscript as a whole has few references, so the state of the art presented in the introduction is limited, I suggest the introduction of some works such as: 10.1186/s40069-020-00448-3; 10.1016/j.istruc.2021.07.051; 10.3390/polym12081776; 10.1061/(ASCE)BE.1943-5592.0001750.

c) In Fig. 5a and 12, the information presented is confusing and difficult to read, look for another way to present them;

d) Present future perspectives of this research in the conclusions.

Author Response

Dear Reviewer2,

thank you very much for your useful comments on our paper. 
We have carefully considered all your comments, and the revised manuscript is now attached for your reconsideration. 
We really appreciate the opportunity to resubmit. 
Also, we would like to thank you for your excellent comments which significantly improved the quality of our paper.

Best regards,
Jun-Mo Yang

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper was improved based on the suggestions/comments previously made.

This reviewer has just one more suggestion: in page 3, lines 112-113, consider changing the sentence “So the most researches investigated the strength rather than strain nor crack opening” to “So most research investigated strength rather than strain or crack opening”

Author Response

Dear Reviewer 1,

Thank you very much for your useful comments on our paper.

The sentence was changed as you suggested.

Best regards,

Jun-Mo Yang

Author Response File: Author Response.docx