A Discussion about the Rod Position in the Splitting Tensile Tests on Hollow Concrete Blocks

Round 1

Reviewer 1 Report

The authors have done a very good amount of review work on "An overview about the splitting tensile test in hollow concrete blocks". Manuscript can be accepted in present form..

 

Author Response

Muchas gracias por tus comentarios.

Reviewer 2 Report

Generally, this research is relevant, showing an interesting relationship between load location and tensile strength results, however, it must be kept in mind that it involves only one type of hollow blocks. This unfortunately makes the conclusions very limited - which must be written in section Conclusions. I think that the authors should have examined at least two different masonry units and then we can talk about some trend in the behavior of hollow blocks. Now there is only random information, without universal significance.  Such studies, describing identical blocks with a higher compressive strength are already published by the authors, so the novelty of this research is questionable.

Additionally, I think that the authors have divided the information on the results of their research too much, which results in presenting very small amount of information in this paper. This is probably due to the desire to do a large number of articles, but this is not a good policy. In my opinion the analysis of the effect of rod flexability on the obtained results should be presented here, because it is here that the authors show the obtained results of the research. So comparing it here is entirely reasonable. The method to use a supplementary file for information shown in another article - to avoid self-plagiarism - is not good tendency. Please consider this issue.

The main issues to be completed and improved

1)    Please indicate the practicality of using the various loading schemes analyzed here in determining the tensile strength of masonry units and relate this to the tensile strength of whole masonry walls.

2)    Rows 32-34 and also 42-43. Please briefly discuss the research already available in the literature, including primarily the cited [11-18]. This way of citing the literature is inappropriate, the authors need to show the most important information - including the types of masonry units tested - regarding the main assumptions of the studies presented there.

3)    Rows 34-36 - please discuss this statement in more detail and present explicitly where the tensile strength of masonry units can used (see the point 1).

4)    The authors made marginal reference in the text to Figure 2 (in addition, there is nothing before the figure appears), please expand/discuss this with reference to the stresses shown there, the partial dimensions (a1, b1,...) and the surfaces indicated.

5)    Fig. 3b: please provide an identical graph for the value of compressive strength over gross area.

6)    Table 2: If 'L' given in formula (1) - split length - should be taken according to the Fig. 4 - so the value of 'L' is different in each case. However, in the Table 2 as 'L' we have the dimension of the entire block. So, please provide the correct value of 'L' (the numerical value) which is inserted each time in formula (1). Please do not use the same letter designation for quantities having different values. The consistency in the markings between Fig. 2 and Fig. 4 should be provided.

7)    It is entirely appropriate to compare tensile strength obtained during the tests with the value determined in direct tensile test, but please explain the purpose of comparing the tensile strength values obtained to each other (the second part of the Table 3).

8)    Rows 292-293: what do the authors mean by statement " that the splitting test over the gross area gave better results"? - relating this to Fig. 7 greater values of tensile strength are obtained for the net area.

Author Response

Thank you very much for your comments.

The main aim of this research is to evaluate by experimentation, the influence of the rod position in the tensile strength estimation of the HCBs by applying the splitting test from ASTM C-1006.

It is known that the tensile strength of HCBs controls the masonry wall behavior to resist the first slope cracking (diagonal tension) under lateral loads. In that sense, obtaining reliably the tensile strength of the HCBs becomes a major issue.

Unfortunately, there are no international standards that determine a procedure to find the direct tensile strength of masonry units. Therefore, in the previous research of the authors [1], an experimental methodology was developed to obtain the direct tensile strength of HCBs.

On the other hand, a few experimental tests of HCB from splitting tests [2-8] have been reported in the specialized literature. Moreover, a question exists among the researchers about the best way of placing the rod (over the net area or gross area) for the estimation of the splitting tensile strength (Figure 1a, gross area; Figure 1b, net area).

Thus, the splitting strength over the gross area has been computed in the following works [12,11,14]; and over the net area in the following references [9,10]. There are even authors that applied the load over the gross area and computed the strength over the net area [16,17]. The last one, in the authors' opinion is not a good strategy.

It is true that in this research we only used one type of HCB with different compressive strength; however, in table 4, results of other authors are incorporated and an experimental tendency is obtained.

1-The practicality of using the various loading schemes is to answer to the question about how to place the rod in the splitting strength estimation by applying the ASTM standard.

2-A paragraph was added to the introduction, lines 39-49, with a discussion based on the references [11-18]. (reference was updated [10-17])

 … “Mojsilović, N. [10] performed direct tensile tests in two series of hollow clay blocks (x and y directions) (Figure 1), while in a previous research, the authors [11] also carried out direct tensile tests in the x and y directions but for HCBs. Haach, V.G et al. [12] developed an indirect test to determine the tensile strength, but their results were compared with another indirect tensile test. Almeida, J.C et al. [13, 14] obtained the softening behavior of different clay blocks by applying an indirect tensile test. Santhakumar, A.R. and S. Ashok [15], suggested an experimental method to test tensile strength of brick masonry. McBur-ney, J.W [16], also, obtained the tensile strength of bricks. On the other hand, Barbosa, C.S. and J.B. Hanai [17] tested hollow concrete blocks and cylinders made with the block material in order to obtain the mechanical properties and structural behavior in compression and tension.”. …

 In none of the previous research background, the influence of the rod position has been evaluated in the splitting tensile strength estimation by applying the ASTM standard.

3-This sentence was improved. A paragraph was also added before Figure 2, explaining the importance of tensile strength in masonry.

Lines 49-50: … “In some studies [1, 4, 10, 12, 18], where various masonry elements like prisms, and walletes were tested, the tensile strength of masonry units could be a decisive parameter to describe its behavior under several loading conditions..” …

 Lines 85-99: … “It is known that the tensile strength of the HCB controls the behavior of a masonry wall before the first diagonal cracking occurs, under lateral loads. The vertical cracking failure mode of prisms and wallettes under axial compression is the principal failure mode of the HCB masonry (Figure 2 a). The vertical cracking, in general, is controlled by the tensile strength of the units (HCB). Due to the different stress-strain properties of the HCB and the mortar, an interaction between both materials is exhibited when they are subjected to the same stress. This interaction makes that the less deformable material, typically the HCB, restricts the transversal strain of the most deformable material (mortar), inducing compression stresses in the mortar and tension stresses in the HCB (Figure 2 b). Thus, obtaining a reliable tensile strength of the HCB becomes a major issue. Therefore, the main aim of this research is to evaluate the influence of the rod position in the estimation of tensile strength, through experimentation, by applying the Splitting test from ASTM C-1006-13 standard on HCBs. Figure 2 c and 2 d, show the principal dimensions of blocks used in the current research, the mean values of the dimensions illustrated in figure 2 d, are indicated in Table 2” …

4-Figure 2 was improved. In addition, a paragraph was added before Figure 2, explaining the stress states and the importance of tensile strength in masonry. The partial dimensions are shown in Table 2, which was also indicated in the text and in the figure.

Lines 85-99

5-Figure 3 was improved, and the graph for the values of compressive stresses over the gross area was provided, additionally, the interest areas of that figure were highlighted.

6-The letter designation was changed in figure 2 and in table 2. The nomenclature of figure 2 was homogenized with that of figure 4.

7-The purpose of comparing the tensile strength values obtained with the splitting tests is that the readers appreciate the differences for the same block, when different rod positions are used in the splitting tests.

8-The authors want to express with that statement, is that the values obtained with the rod placed over the gross area are closer to the values obtained with the direct tensile test than those obtained with the rod placed over the net area.

 

Reviewer 3 Report

The manuscript entitled "An overview of the splitting tensile test in hollow concrete blocks" presents an interesting study conducted on the relevance of splitting test direction for estimation of the tensile strength of concrete blocks. However, the introduction section includes multiple references cited in bulk format, and the abstract doesn’t include the necessary information to make it suitable for separate publication. The paper needs minor revisions before it is processed further. Some comments follow:

Title: The title can be improved; maybe the authors can introduce a formulation related to the "relationship between splitting test setup and the tensile strength of hollow blocks."

 

Abstract

Please highlight the novelty of the study.

Please replace the majority of the qualitative statements with quantified result comparisons. This sentence should be improved. "One of the main results was that the 16-splitting test over the net area in the x-direction can overestimate the tensile strength of the blocks." Also, new sentences should be included to present the results of the research.

Please remove the following sentence. "Results obtained from this research are of great importance in specific loading conditions like differential displacement or seismic loads." since this is only a claim without a proper scientific background.

This section must be suitable for separate presentations (independent of the manuscript text body).

 

Introduction section

The introduction section should be significantly improved. Please conduct a comprehensive and exhaustive study of the previous literature. Please clearly highlight the pros and cons of previous results and justify the need for the current research. Currently, the introduction section presents references to literature in bulk format [11–18], [11–18], etc., without a clear relation between the presented data and the cited literature. Please discuss the highlights individually and assure a clear correspondence between the affirmations from the manuscript and those from the cited papers.

The sentence that should include the novelty and aim of this study is missing from the introduction section. Please introduce a paragraph at the end of the introduction in which you present the novelty and aim of this study in relation to the current state of the literature and research.

 

Materials and methods section

The dimensions from Figure 2.c are missing. Please provide the values of the walls' thickness.

Figure 3.a: Please introduce figure labels to highlight the areas of interest for the readers.

 

Author Response

Thank you very much for your comments.

References cited in bulk format were deleted and the introduction section was improved as we commented below. The importance of the tensile strength in masonry walls was added before figure 2 (lines 85-99).

… “It is known that the tensile strength of the HCB controls the behavior of a masonry wall before the first diagonal cracking occurs, under lateral loads. The vertical cracking failure mode of prisms and wallettes under axial compression is the principal failure mode of the HCB masonry (Figure 2 a). The vertical cracking, in general, is controlled by the tensile strength of the units (HCB). Due to the different stress-strain properties of the HCB and the mortar, an interaction between both materials is exhibited when they are subjected to the same stress. This interaction makes that the less deformable material, typically the HCB, restricts the transversal strain of the most deformable material (mortar), inducing compression stresses in the mortar and tension stresses in the HCB (Figure 2 b). Thus, obtaining a reliable tensile strength of the HCB becomes a major issue. Therefore, the main aim of this research is to evaluate the influence of the rod position in the estimation of tensile strength, through experimentation, by applying the Splitting test from ASTM C-1006-13 standard on HCBs. Figure 2 c and 2 d, show the principal dimensions of blocks used in the current research, the mean values of the dimensions illustrated in figure 2 d, are indicated in Table 2.” …

Title: The title was changed to “A discussion about the rod position in the splitting tensile tests on hollow concrete blocks”

Abstract: The abstract was improved:

… “Different loading conditions cause different tensile stress patterns in masonry structures. Several studies related to masonry behavior use indirect tensile tests to obtain that value, where the splitting test from ASTM-C-1006 is usually employed. In this paper, an experimental analysis of the tensile strength of hollow concrete blocks is reported. Different locations of the rod from the ASTM-C-1006 splitting test were analyzed. The tensile strength was evaluated in 4 different ways: 1) placing the rod in the transversal-direction over the gross area, 2) in the transversal-direction over the net area, 3) in the longitudinal-direction, and 4) 200 mm from the central region of the block in the longitudinal-direction. The obtained results were compared with the tensile strength values measured from the direct tensile test in the longitudinal-direction. In addition, an axial compressive test was performed to characterize the blocks, and a discussion about the tensile/compression ratio is shown. The experimental results from the splitting tests show that for each configuration setup, the tensile stress is different. The main result was that the splitting test over the net area with the rod positioned in the longitudinal-direction can overestimate the tensile strength more than 21% of the one over the gross area…

Introduction section: A paragraph was added to the introduction, lines 39-49, where a discussion was made from the references [11-18] ….(reference was updated [10-17])

… “Mojsilović, N. [10] performed direct tensile tests in two series of hollow clay blocks (x and y directions) (Figure 1), while in a previous research, the authors [11] also carried out direct tensile tests in the x and y directions but for HCBs. Haach, V.G et al. [12] developed an indirect test to determine the tensile strength, but their results were compared with another indirect tensile test. Almeida, J.C et al. [13, 14] obtained the softening behavior of different clay blocks by applying an indirect tensile test. Santhakumar, A.R. and S. Ashok [15], suggested an experimental method to test tensile strength of brick masonry. McBur-ney, J.W [16], also, obtained the tensile strength of bricks. On the other hand, Barbosa, C.S. and J.B. Hanai [17] tested hollow concrete blocks and cylinders made with the block material in order to obtain the mechanical properties and structural behavior in compression and tension.” …

The novelty and the aim were placed before figure 2 (lines 85-99)

 

Materials and methods section: The dimensions from figure 2c are in table 2. A note was added in the figure caption.

Figure 3 was improved, and the graph for the values of compressive stress over the gross area was provided. Additionally, the areas of interest of that figure were highlighted.

Round 2

Reviewer 2 Report

I thank the authors for the corrections and clarifications. 

Please insert in subsection 3.3 an explanation of the statement: "that the splitting test over the gross area gave better results" (explanation given in the authors' response).

Author Response

Thank you very much for your comment to improve the text, the explanation was added to the text

Lines: 330-334

… “Additionally, it is observed in Figure 7 that the splitting test over the gross area gave better results than over the net area (see Figure 4), i.e., the values obtained with the rod placed over the gross area are closer to the values obtained with the direct tensile test than those obtained with the rod placed over the net area. Considering that only one compressive strength is included in this study, thus this observation is limited to HCBs with two holes and a compressive strength of 11.62MPa on the net area”…