Seismic Performance of Fully Prefabricated L-Shaped Shear Walls with Grouted Sleeve Lapping Connectors under High Axial Compression Ratio

Round 1

Reviewer 1 Report

Authors carry out an extensive research work. Please consider the following before the paper can be considered for publication

·         The introduction section is too lengthy and needs to be summarized, please include only relevant literature

·         Please discuss in details your research gap, research problem and objectives at the end of the introduction section

·         The conclusion need to be shortened

·         Please compare your results with previous study

Author Response

Response to Reviewer 1 Comments

Point 1: The introduction section is too lengthy and needs to be summarized, please include only relevant literature;

Response 1: First of all, many thanks to the expert for valuable suggestions on this study. The author has summarized the introduction carefully and the references have been rearranged. The revised content in the introduction is shown in the red font in the article.

Point 2: Please discuss in details your research gap, research problem and objectives at the end of the introduction section;

Response 2: In the last two paragraphs of the introduction, the author introduces the research gaps and research objectives of this paper. The additions are as follows:

However, the research on its application performance in actual structural components is still insufficient.

At present, the research on prefabricated walls mainly focused on the straight shear walls [10,14-18]. However, in order to meet the requirements of building functions, L-shaped shear walls are often used in practical projects. Due to the asymmetric geometry of L-shaped shear walls, the wall body is susceptible to eccentric lateral force. It is apparent that L-shaped shear walls have higher requirements for joint connections. Therefore, the reliability of L-shaped shear walls connected by APC connectors needs to be evaluated urgently. Besides, previous studies have focused on the effects of low axial compression, i.e., axial compression ratio less than 0.3 on the seismic performance of prefabricated components [10,14,16,25,26]. In practical projects, both large structural dead weight and insufficient concrete strength will cause large axial compression ratio, which is a great challenge to the seismic performance of the structure. Furthermore, with the increase of axial compression ratio, the ductility and energy dissipation of the specimen decreased obviously [15,27]. Therefore, it is necessary to investigate whether the prefabricated specimen can achieve the seismic performance equivalent to the cast-in-place specimen under high axial compression ratio [26]. According to reference [26], the axial compression ratio of 0.5 was selected for this test.

To study the seismic performance of fully prefabricated L-shaped shear wall connected by APC connectors under high axial compression ratio, three full-scale L-shaped shear walls, including a cast-in-place wall and two prefabricated walls connected by type-I and type-II APC connectors, were designed for a quasi-static test, and the failure modes, bearing capacity, stiffness, deformation, and energy dissipation of the specimens under the axial compression ratio of 0.5 were comparatively studied.

Point 3: The conclusion need to be shortened;

Response 3: The author has summarized the conclusion carefully. The modification content is as follows:

1. The final crack distribution and failure modes of the L-shaped prefabricated walls were basically the same as those of the cast-in-place wall, and all the specimens have suffered bending-shear failure. The difference was that the failure of the cast-in-place specimen occurred at the root of the wall limb, while the failure of the prefabricated specimen occurred at the top of the sleeve due to the constraints of the sleeve.
2. At the ultimate state, a horizontal through crack was formed between the upper surface of the grouting joint and the prefabricated wall. Although the wall did not undergo obvious shear slip due to the action of the occlusal teeth at the joint, accumulated damage occurred in the out-of-plane displacement of the specimen.

3.The bearing capacity, stiffness, ductility and energy dissipation capacity of the prefabricated specimen connected by type-I sleeve were comparable to those of the cast-in-place wall, while the prefabricated wall connected by type-II sleeve showed greater bearing capacity and stiffness, as well as better ductility and energy dissipation capacity.

4. Types-I and type-II APC sleeves could effectively transfer reinforcement stress in L-shaped shear walls, and the prefabricated specimens basically met the assumption of plane section before yielding, and the sleeves were not significantly damaged during the whole loading process.
5. Out-of-plane torsion occurred in both cast-in-place and prefabricated walls, but the maximum absolute value of out-of-plane displacement and oblique deformation for prefabricated walls was smaller due to its high stiffness.

Point 4: Please compare your results with previous study;

Response 4: In recent years, the authors have studied frame columns and straight shear walls connected with APC connectors. Combined with the previous research and the study of this experiment, the design recommendations for precast components connected with APC connectors were summarized in Section 4.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper points out the progress and shortcomings of previous research on sleeve connection of prefabricated concrete members. Pseudo-static tests were conducted to investigate seismic performances of three L-shaped shear walls with different manufacturing methods. The research methods, test contents and result analysis of the manuscript are described in detail.

It is recommended to consider different axial compression ratios for performance analysis.

A written description of the cyclic load has been existed in Section 2.3, but the displacement and time curve can be more intuitive to reflect.

It is recommended to add a table in Section 2.1 to intuitively reflect the parameter differences of each test model.

The reasons of the designment of components LAPC-1 and LAPC-2 should be more clarified. 

There are no references about Equation 3 - 5. Please add them.

"Figure X" of all picture captions should be bold.

The advantages and disadvantages of this study are not specified in the conclusion.

Author Response

Many thanks to the expert for valuable suggestions on this study, and detailed responses can be found on the first page of the document.

Author Response File: Author Response.docx

Reviewer 3 Report

This paper presents an experimental study on a cast in-place wall and two fully prefabricated walls connected with two types of Grouted sleeve lapping connectors (APC). A similar failure mode was captured in both prefabricated walls and the cast-in-place wall, where flexural damage as well as development of cracks were observed. With respect to the location of the failure, the cast-in-place wall failed at the root of the wall limb while the failure of the prefabricated wall happened at the top of the sleeve due to the constraints of the sleeve. The structural response parameters of the tested walls, including strength, stiffness, ductility and damping coefficients, were compared and the differences were discussed in detail. The paper is well-written and well organised and the scope of this study is worthy of investigation. While this paper is appropriate for publication in Applied Sciences, the reviewer has some minor comments to be addressed as follows:

1) “the seismic performance of the prefabricated wall connected by type-II sleeve was superior to that of the cast-in-place wall” (Abstract). What performance was specifically found to be superior? Strength? Stiffness? Ductility? ... Please be specific.

2) It is suggested to include the following relevant publication on the behaviour of shear wall panels in the Introduction and briefly explain the effects of axial compressive load on the wall.

Behaviour and performance of OSB-sheathed cold-formed steel stud wall panels under combined vertical and seismic loading. Thin-Walled Structures 183, 110419.

3) A new figure should be added showing the cyclic loading protocol applied during experimental tests.

4) Please clarify whether any LVDTs were used in the experimental test setup and their locations.

5) The hysteretic responses of the walls showed drops after their peak loads in the negative displacements (Figure 8) while there is no softening branch within the positive displacements of the hysteretic curves. What is the reason? It would be great to add a discussion on this. 

Author Response

Many thanks to the expert for valuable suggestions on this study, and detailed responses can be found on the first page of the document.

Author Response File: Author Response.docx

Reviewer 4 Report

The topic addressed in the article is interesting, but it is very much covered in the research, not making it clear what its objective is, so it is not possible to assess whether these objectives have been achieved. In addition, there are definitions that need to be clarified, as well as the essential justifications and clarifications, which are detailed below:

SUMMARY: reorder the structure, presents the description, there are no objectives and there is a large description of the results.

INTRODUCTION: there are gaps in the argumentation, errors in the references and the objective of the research is not stated.

The references cited [8-11] do not indicate what they contribute to the research.

References [15-16] are two, and authors are indicated.

On the other hand, there are references in this field that have not been considered such as:

Study of effects of sleeve grouting defects on the seismic performance of precast concrete shear walls. Xiao, S (Xiao, Shun) [1] ; Wang, ZL (Wang, Zhuolin) [1] ; Li, XM (Li, Xiangmin) [1] ; Harries, KA (Harries, Kent A.) [2] ; Xu, QF (Xu, Qingfeng) [1] ; Gao, RD (Gao, Rundong) [1]

Experimental investigation on connection performance of fully-grouted sleeve connectors with various grouting defects. Guo, T (Guo, Tong) [1] ; Yang, J (Yang, Jun) [2] ; Wang, W (Wang, Wei) [1] ; Li, C (Li, Chuan) [3]

Seismic Behavior of Innovative Precast Superimposed Concrete Shear Walls with Spiral Hoop and Bolted Steel Connections. Wu, X (Wu, Xi) [1] , [2] ; Wang, MF (Wang, Meng-fu) [1] , [2] ; Liu, ZL (Liu, Ze-long) [1] , [2]

From row 112 onwards, there is no numbering, which makes it difficult to indicate specific points in the article.

On that page, the statement after references [24-25] "However, there are few studies on the applicable component types for APC connector, and the research on its application performance in actual structural components is still insufficient". Given its importance for research, it requires justification or references to support it.

The statement "Therefore, the reliability of L-shaped short-leg shear walls connected by APC connectors needs to be evaluated urgently, especially at high axial compression ratios". It should be justified if there are already references that have addressed this issue. Which ratios have been studied and which ones consider high axial compression ratios?

Why are L-shaped walls studied?

The last paragraph I think should be part of point 2.

EXPERIMENTAL PROGRAMME

Acronyms are used without indicating their meaning, if they do not have one, e.g. LSW or LAPC. They are also referred to in relation to figure 2. Description of figure 2 is mixed with information from figure 3.

What is the justification for the combination of Type I and Type II connectors in the same section? Why are the connectors distributed in this way?

In the prefabricated model elevations there are reinforcements with an anchorage length of 775 mm which are not in the in-situ model and therefore cannot be compared. Furthermore, these reinforcements are not shown in the floor plan. As they are prefabricated elements, how are these rebars connected? The use of reinforcement with connectors distorts the concept of connection with connectors. These questions must be justified in detail.

In table 1, the reinforcement of diameter 8 has a lower value than the prescribed value of 400 and on the other hand, diameter 14 has a much higher value. How does the elastic limit of the steel influence the behaviour of the connection, is there a guarantee that the quality of the steel of the reinforcement is the same as that tested?

When it is indicated that the concrete is C40, the resistance value is for cubic or cylindrical specimen.

When it is stated that "it can be calculated that the axial compressive strength of C40 concrete is 32.2 MPa," is this value deduced from the standard or is the application of a formula to go from cubic to cylindrical specimen, is it a characteristic value or an average value? Please explain.

Where it says "It can be calculated that axial force N of all specimens is 2865kN", could you please indicate which values of A and fc apply?

RESULTS: it is necessary to indicate whether the values used in formula (2) are characteristic or calculation values, indicating also which values are applied for each of the specimens.

Figure 9.a shows high gradation values for low displacement in the case of LAPC-2, what is the justification for this?

In the case of figure 9.b there are values with a degradation higher than 1, what does it mean to have a degradation higher than 1, what is its justification?

Points 4 and 5 are also results.

When in point 4 it says "The force-strain curves of the outermost longitudinal rebars of the edge members of the specimens" are the 8 mm horizontal bars or the 14 vertical bars.

The sentence "It is apparent from Figure 12 that the load- strain curves of the outermost rebars of the edge members of the specimens LAPC-1 and LSW-1 were in good agreement, indicating that the stress conditions of the rebars of the edge members of the two specimens were basically the same" requires justification. The same applies to the explanation in figure 13. How do you quantify good agreement or similar?

Figure 14 requires further analysis, as well as justification of the values in figure 14.a.

Although point 3 refers to results and discussion, there is no discussion of results in relation to previous research. The discussion is fundamental to demonstrate that there is progress on existing research and to justify what the research assumes to be progress.

The conclusions cannot be generalised, as only one type of wall has been tested with one type of reinforcement diameter; there is no indication of how the behaviour would be depending on the amount of reinforcement. The same applies to the anchorage dimension, with the study carried out, it can only be validated for the length tested and with the filler mortar used, as the influence of this on the behaviour has been verified.

It is stated that "When the stirrups and horizontal distribution of reinforcements at the bottom of the prefabricated specimens and the cast-in-place specimen were densified" how many tests have been carried out, how has this densification been assessed in the tests?

Minor:

There are spelling mistakes with capital letters without full stops in several sections of the article.

Author Response

Many thanks to the expert for valuable suggestions on this study, and detailed responses can be found on the first page of the document.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors have successfully addressed all my comments

Author Response

Point 1: Please compare your results with previous study.

Response 1: First of all, many thanks to the expert for valuable suggestions on this study. In terms of failure phenomena, deformation capacity and energy dissipation, the author compared and analyzed the results of previous studies on prefabricated walls. The details are outlined in red in Sections 3.1, 3.6, and 3.7.

Sections 3.1:

Similarly, reference [25] showed that concrete damage of straight prefabricated shear walls was mainly concentrated in the range from the bottom of the wall to 300 mm higher than the top of the sleeve, indicating that this range was the weak part of the prefabricated specimen. It can be seen from Figure 7 (a) that the spalling of the concrete outside the sleeve was more serious at the limit state. This was mainly due to the manufacturing error, which made the spacing of stirrups within the height range of the sleeve locally larger, and the deformation capacity of the outer concrete was poor. Compared with this test, in the reference [25], stirrups with a spacing of 50 mm were arranged within the height range of the sleeve in the prefabricated wall, and the concrete outside the sleeve was only partially damaged at the limit state. Therefore, proper densification of stirrups within the height range of the sleeve can effectively improve the bonding performance of the external concrete.

The lower surface of the joint of the prefabricated wall and the interface of the bottom of the cast-in-place wall (both of which have been chiseled) did not have obvious cracks, indicating that the chisel can effectively improve the bonding strength between the grouting material and the concrete. Similarly, the surface of the concrete at the joint was chiseled to effectively avoid premature cracking of the joint surface in straight prefabricated walls [25]. In addition, the rebar in the sleeve was not pulled out at the limit state, and the sleeve had no obvious deformation, indicating that the sleeve had good mechanical properties.

Sections 3.6:

The ductility coefficient of each specimen was greater than 2, and the ductility coefficient of the prefabricated wall was higher than that of the cast-in-place wall, which indicates that the deformation capacity of the prefabricated wall was better than that of the cast-in-place wall. However, in reference [10,16], the deformation capacity of the prefabricated walls connected with traditional grouted splice connectors were lower than that of the cast-in-place wall due to the weak constraint of the region near the sleeve. The reason was that the APC sleeve and stirrups enhanced the confinement of the concrete at the bottom of the prefabricated specimen, and type-II sleeve had stronger constraint ability due to its larger size, which made the bearing capacity decrease more slowly and the ultimate displacement was larger under the ultimate load.

Sections 3.7:

The energy dissipation capacity of the specimen was evaluated by the equivalent viscous damping coefficient  [31], which can be calculated as follows:

Where S_ABCD is the area of the hysteresis loop, and S_OBE and S_ODF represent the area of the triangle in Figure 11. Among the loading levels of the three cycles, the specimen had damage accumulation in the second and third loading cycles, so only the first loading cycle was considered in the calculation. The relationship between the equivalent viscous damping coefficient  of the specimen and the horizontal displacement is shown in Figure 11.

Figure 11. Equivalent viscous damping coefficient -displacement curve of specimens.

In the previous research on the prefabricated wall connected with traditional grouted splice connectors [16], the equivalent viscous damping coefficient of the prefabricated wall was lower than that of the cast-in-place wall at the later stage of test due to the slip of the connecting reinforcements and the larger crack width of the post cast joint. In this test, it can be seen from Figure 11 that the equivalent viscous damping coefficient of the all specimens increased with the increase of the horizontal displacement after the reinforcement yielded, and the equivalent viscous damping coefficient-horizontal displacement curve of LAPC-1 was similar to that of LSW. However, the equivalent viscous damping coefficient of the specimen LAPC-2 was smaller than that of other specimens at the later loading stage. This was mainly due to the larger crack width at the grouting joint during the failure of the specimen LAPC-2, which led to the reduction of the energy dissipation capacity of the specimen to a certain extent. Therefore, to improve the bonding property of the surface of the grouting joint, it is recommended that the bottom of the prefabricated specimen and the top surface of the foundation should be properly chiseled.

In reference [25], the spacing of stirrups and horizontally distributed reinforcements at the bottom of prefabricated walls was 50mm, while that of cast-in-place wall was 100mm. The results showed that the energy dissipation capacity of straight prefabricated walls connected with APC connectors was better than that of cast-in-place wall. Similarly, in practical projects, the spacing of stirrups and horizontally distributed reinforcements at the bottom of cast-in-place wall were not encrypted. However, in this test, in order to compare with the prefabricated wall, the stirrups and horizontally distributed reinforcements at the bottom of the cast-in-place wall was encrypted with a spacing of 50 mm, which resulted in the higher energy dissipation capacity of the cast-in-place wall to some extent. The equivalent viscous damping coefficient  of each specimen at different stages are shown in Table 4. It can be seen from Table 4 that, at the same loading stage, the viscous damping coefficient of all specimens were basically the same before the failure of specimens, which indicates that they had similar energy dissipation capacity on the whole.

Author Response File: Author Response.docx

Reviewer 2 Report

• All comments have been answered accurately, accept in the present form.

Author Response

Thank you very much for the reviewer's advice. I sincerely wish you good health and success in your work.

Reviewer 4 Report

No se ha realizado una discusión de los resultados relacionándola con anteriores estudios que demuestren el avance respecto de la brecha indicada en la introducción.

Translate to English：
There has been no discussion of the results in relation to previous studies demonstrating progress on the gap indicated in the introduction.

Author Response

Point 1: There has been no discussion of the results in relation to previous studies demonstrating progress on the gap indicated in the introduction.

Response 1: First of all, many thanks to the expert for valuable suggestions on this study. In past studies of traditional sleeve grout connectors, the results showed that the ductility and energy dissipation capacity of prefabricated  walls are lower than those of cast-in-place walls. Therefore, in terms of failure phenomena, deformation capacity and energy dissipation, the author compared and analyzed the results of previous studies on prefabricated walls. In addition, the authors also describe previous studies on the energy dissipation capacity of straight prefabricated walls connected with APC connectors. The details are outlined in red in Sections 3.1, 3.6, and 3.7.

Sections 3.1:

Similarly, reference [25] showed that concrete damage of straight prefabricated shear walls was mainly concentrated in the range from the bottom of the wall to 300 mm higher than the top of the sleeve, indicating that this range was the weak part of the prefabricated specimen. It can be seen from Figure 7 (a) that the spalling of the concrete outside the sleeve was more serious at the limit state. This was mainly due to the manufacturing error, which made the spacing of stirrups within the height range of the sleeve locally larger, and the deformation capacity of the outer concrete was poor. Compared with this test, in the reference [25], stirrups with a spacing of 50 mm were arranged within the height range of the sleeve in the prefabricated wall, and the concrete outside the sleeve was only partially damaged at the limit state. Therefore, proper densification of stirrups within the height range of the sleeve can effectively improve the bonding performance of the external concrete.

The lower surface of the joint of the prefabricated wall and the interface of the bottom of the cast-in-place wall (both of which have been chiseled) did not have obvious cracks, indicating that the chisel can effectively improve the bonding strength between the grouting material and the concrete. Similarly, the surface of the concrete at the joint was chiseled to effectively avoid premature cracking of the joint surface in straight prefabricated walls [25]. In addition, the rebar in the sleeve was not pulled out at the limit state, and the sleeve had no obvious deformation, indicating that the sleeve had good mechanical properties.

Sections 3.6:

The ductility coefficient of each specimen was greater than 2, and the ductility coefficient of the prefabricated wall was higher than that of the cast-in-place wall, which indicates that the deformation capacity of the prefabricated wall was better than that of the cast-in-place wall. However, in reference [10,16], the deformation capacity of the prefabricated walls connected with traditional grouted splice connectors were lower than that of the cast-in-place wall due to the weak constraint of the region near the sleeve. The reason was that the APC sleeve and stirrups enhanced the confinement of the concrete at the bottom of the prefabricated specimen, and type-II sleeve had stronger constraint ability due to its larger size, which made the bearing capacity decrease more slowly and the ultimate displacement was larger under the ultimate load.

Sections 3.7:

The energy dissipation capacity of the specimen was evaluated by the equivalent viscous damping coefficient  [31], which can be calculated as follows:

Where S_ABCD is the area of the hysteresis loop, and S_OBE and S_ODF represent the area of the triangle in Figure 11. Among the loading levels of the three cycles, the specimen had damage accumulation in the second and third loading cycles, so only the first loading cycle was considered in the calculation. The relationship between the equivalent viscous damping coefficient  of the specimen and the horizontal displacement is shown in Figure 11.

Figure 11. Equivalent viscous damping coefficient -displacement curve of specimens.

In the previous research on the prefabricated wall connected with traditional grouted splice connectors [16], the equivalent viscous damping coefficient of the prefabricated wall was lower than that of the cast-in-place wall at the later stage of test due to the slip of the connecting reinforcements and the larger crack width of the post cast joint. In this test, it can be seen from Figure 11 that the equivalent viscous damping coefficient of the all specimens increased with the increase of the horizontal displacement after the reinforcement yielded, and the equivalent viscous damping coefficient-horizontal displacement curve of LAPC-1 was similar to that of LSW. However, the equivalent viscous damping coefficient of the specimen LAPC-2 was smaller than that of other specimens at the later loading stage. This was mainly due to the larger crack width at the grouting joint during the failure of the specimen LAPC-2, which led to the reduction of the energy dissipation capacity of the specimen to a certain extent. Therefore, to improve the bonding property of the surface of the grouting joint, it is recommended that the bottom of the prefabricated specimen and the top surface of the foundation should be properly chiseled.

In reference [25], the spacing of stirrups and horizontally distributed reinforcements at the bottom of prefabricated walls was 50mm, while that of cast-in-place wall was 100mm. The results showed that the energy dissipation capacity of straight prefabricated walls connected with APC connectors was better than that of cast-in-place wall. Similarly, in practical projects, the spacing of stirrups and horizontally distributed reinforcements at the bottom of cast-in-place wall were not encrypted. However, in this test, in order to compare with the prefabricated wall, the stirrups and horizontally distributed reinforcements at the bottom of the cast-in-place wall was encrypted with a spacing of 50 mm, which resulted in the higher energy dissipation capacity of the cast-in-place wall to some extent. The equivalent viscous damping coefficient  of each specimen at different stages are shown in Table 4. It can be seen from Table 4 that, at the same loading stage, the viscous damping coefficient of all specimens were basically the same before the failure of specimens, which indicates that they had similar energy dissipation capacity on the whole.

Author Response File: Author Response.docx