Review Reports

Round 1

Reviewer 1 Report

The paper assesses the design methods in ACI 318, EC2 and MC2010 for punching shear at eccentrically loaded internal, edge and corner column connections. The databases for edge and corner columns are rather limited and do not include all the available tests. References to previous evaluations of the EC2 and MC2010 evaluations of punching resistance at edge columns are missing. I have reviewed the spreadsheet used to calculate punching resistances at edge and corner columns to EC2 and I believe there to be significant errors. For example, for edge columns subject to inwards eccentricity the punching resistance should be calculated with the reduced perimeter U1* shown in Fig 6b of the paper and described in the paper. This approach is not used in the spreadsheet (ref 25) where beta is calculated in terms of W1 which is inconsistent with the text. For corner columns, an error is made in the calculation of the design shear stress which should equal VEd/(U1*.d) or (U1/U1*)VEd/(U1.d) where beta = U1/U1*. In the paper the spreadsheet the shear stress is calculated as (U1/U1*)VEd/(U1*.d). This explains the very conservative results obtained with EC2. The presentation of results can also be improved. For example, Fig 15 does not provide any clear evidence that the shear resistance is best related to sqrt(fc). Nowhere in the charts is the influence of loading eccentricity on shear resistance assessed even though this is the subject of the paper. The procedure adopted in the SCIA analysis requires more explanation.

Author Response

Please see the attached file with the item-by-item responses

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper deals with eccentric punching shear in concrete slab-column connections. This is a typical situation in edge and corner columns and is a common practical case. The paper presents a database of eighty-eight experiments of flat slabs under eccentric punching shear, moreover, a linear finite element analysis of all the specimens is included. The ultimate shear stresses are compared to the shear capacities determined with international codes to highlight the inconsistencies of the design methods.

The research topic is of great importance for the civil engineering community and could be within the scope of the journal, but the paper requires major revisions before it can be published in the journal.

English is good, nevertheless there are some refuses or grammatical errors or repetitions (e.g. line 47 “were developed for the development”; line 79 “stress” should be “stresses”; line 87 “in” should be “is”; line 166 “using the equation Eq. (16)” should be “using Eq. (16)”; line 234 “any other relevant nonlinear effects” should be “any other relevant nonlinear effect”; line 515 “err” should be “are”; etc.)

 

In the abstract, line 13, use “deal with” instead of “are”.

 

The introduction could be enlarged to include some bibliographical references to papers dealing with eccentric punching; f.i.

“Eccentric punching strength of continuous flat slabs—Analysis of different experimental setups”, Structural Concrete, Volume 22, Issue 2, Pages 1183 – 1204, April 2021

“Eccentric Punching Shear of Waffle Slab”, ACI Structural Journal, Volume 115, Issue 1, Pages 163-173

 “Comparison of recent code provisions for punching shear capacity of R/C slabs without shear reinforcement”, Lecture Notes in Civil Engineering, Volume 10, Pages 113 – 1322018

 

“Eccentric punching tests on column bases - Influence of column geometry”, https://doi.org/10.1002/suco.202100744

Line 39: Use “people” instead of “men”

Line 55: Correct “Model Code 2019” into “Model Code 2010”

Line 100: check the symbol alfa,s

Line 110: why the equation (12) is taken among equations 10, 11 and 12? The authors should specify.

Line 116: The authors refer to the Dutch version of EC2; nevertheless, to make the work more general, the authors are invited to consider values recommended in EC2 for NDPs, therefore the Eurocode should be cited as “EN1992-1-1:2004”.

Lines 118-120: the concrete contribution has the same expression for one-way shear and two-way shear, but some parameters have different values; please, specify those parameters and correct the sentence.

For the sake of completeness, in section 2.1.2 the authors should precise that EC2 also requires the verification around the perimeter of the column or loaded area.

Line 293: The percentage values are in the range 1.3 – 1.5, looking at Figure 14b.

Line 330: In figure 16b the influence of the longitudinal steel ratio is not so evident as the authors assert; also the influence of the effective depth is not so relevant, too. The values in the three diagrams of figure 16 are all very dispersed. The authors are invited to revise the text.

Line 347, 350: Please dot not use the first plural person (“We compared”).

The authors are invited to add at least some proposals (not necessarily new formulations) about the improvements that could be introduced in the current design formulations, using results of the comparison they have made and based on that they should also revise the last sentence of the abstract.

After revising the paper according to above comments, in the revised version resubmitted, not only have the conclusions to be sound and justified, but above all they must follow logically from experimental and numerical results.

Author Response

Please see the attached file with the item-by-item responses

Author Response File: Author Response.pdf

Reviewer 3 Report

 The paper deals with the punching shear failure in reinforced concrete flat slabs, around columns placed in the edge or in the corners of the slab. In these cases, due to the unbalance moments around the column, the maximum shear stresses around the column are higher than in interior columns subjected to axisymmetric loading, resulting more critical.  However, much less experimental campaigns have been that are  out on edge or corner columns and, consequently, there are still aspects of the punching shear behavior related to the resistant mechanisms and failure modes not yet well understood.

In the submitted paper, a data base of 88 experiments on flat slabs under eccentric punching shear reported in the literature is presented, including a summary of the testing procedure of each reference and a description of the slab specimens. In addition, a parametric study analyzing the influence of several variables on the punching shear strength is performed.  A comparison of the predictions of the tests results using different design codes provisions has also been made, drawing conclusions about their accuracy. Another aspect of the study is highly appreciated: the analysis by means of a linear finite model, to provide some forces acting on the critical section of the tests performed.

 

The subject is of great scientific and technical interest because the presented database will be very useful for understanding the physics of the problem, that will help to develop and verify theoretical models based on the structural mechanics, to calibrate numerical models and to design more safe and economical structures.

 

The manuscript is very well organized and written, the objectives are clear, the methodology correct, the data base is very clear and complete and the conclusions are very clear and important. Therefore, this reviewer considers that this is a very good paper that can be accepted for publication after minor changes. In the following, several comments and suggestions are made that may help to improve the quality of the paper. They are:

 

1.     In page 21, lines 330-333,  and in the firs conclusion it is said: “Larger reinforcement ratios result in larger shear capacities, as expected. As more tension reinforcement is provided, the contribution of dowel action to the shear capacity increases, as reflected by the results from the database”. This reviewer agrees with this statement, however he considers that the effect of larger a longitudinal reinforcement ratio is not only to increase the dowel action, but also the aggregate interlock (due to a reduction of crack width) and the contribution of the uncracked concrete zone, (due to a increment of the flexural compression block depth).

 

In fact, some of the punching shear strength available models are based mainly on the contribution of the uncracked compression zone, highly affected by the longitudinal The tensile strength used is the reinforcement ratio.  It is suggested to include the two above mentioned effects.  

 

2.     In page 15, it is said that, for those tests that the tensile strength is not provided, the value proposed by  Sarverghadi [22] fct=0.76 sqr(fc)  was used.  Is there any reason to adopt this value in front of that proposed in EC2 or MC2010?. If other value for fct was used, could it have a large influence in the results of the predictions?

 

3.     I consider that the contents of table 2 and table 3 should be better explained in the table caption.

 

4.     In relation to the final evaluation of the results of the predictions using the codes, this reviewer considers that more emphasis should be made on the fact that the results are generally unsatisfactory. Altogether there are 88 experiments, and at best the coefficient of variation is 28%, which is quite high. The situation can be considered even worst when the different cases are studied separately (interior, edge or corner columns),where there is no more than 41 tests in each block and the scatter is similar to that of the total tests.

 

5.     The comparison between the results obtained by ACI, EC2 and MC2010, codes can be considerably affected by the different number of tests predictions made in each case, since the higher number of tests, the higher is the scatter, in general. The ideal would be to compare results of the same number of tests.

 

In the case of the total specimens, 88 predictions were made with ACI (CoV=34.52%), 68 with EC2 (CoV=44.09%) and 55 with MC2020 (CoV=27.96). If we divide the result of the CoV by the number of tests , we would obtain ACI=44.09/88=0.392, EC2=44.09/68=0.648 and MC2020=27.96/55=0.508. This numbers give us an approximate idea of the influence of the size of the sample on the scatter.

 

Base on this , it is suggested to slightly modify the conclusion related to the scatter of the different predictions with the codes provisions, which says:  “Evaluating all experiments, the coefficient of variation of the tested to predicted shear capacities is lower for the expressions of the Model Code 2010 518 [9], based on the Critical Shear Crack Theory, than for the empirical expressions from NEN-EN 1992-1-1:2005 [8] and ACI 318-19 [7]. “ It is proposed to mention the fact that it must be taken into account, though,  that the number of tests predicted is different for each code.

 

Author Response

Please see the attached file with the item-by-item responses

Author Response File: Author Response.pdf

Reviewer 4 Report

The subject of this manuscript is well framed in the scientific domain of the “buildings”. Although several works have been published in this domain, this is still an up-to-date topic that deserves further research. The authors developed experimental literature database on the eccentric punching shear in concrete slab-column connections to compare the experimental ultimate shear strength with multiple design codes. The collected data was also used to develop a linear finite element model in order to predict the shear forces and moments in the sections.

Generally, the manuscript is well written and present a satisfactory work. While the study results and explanation presented in this manuscript could add value in understanding the limitations of the experimental work and design codes, there could be more rigorous interpretation and scientific explanations of the mechanisms behind the observed trends. So, it is recommended to elaborate more on the results.

Keywords must indicate the main materials, tests, and methodology used in the study.

In the Abstract; Lines 11-12: Authors stated that “Typically, this situation results in edge and corner columns and is thus a common practical case.” This sentence does not make sense. Please rewrite it.

In the Abstract; Lines 20-22: “It can be concluded that this study represents the inconsistencies of the currently used design methods and the lack of experimental information.” The inconsistencies of the currently used design methods and the lack of experimental information should not be the conclusion of this study. So what? Do the authors have any suggestions? What are the future research needs? Also, reporting the results in the abstract could be helpful for the readers.

Introduction is poor (incomplete) given the scope of this study. It must be rewritten to provide an overview of the current knowledge and the existing gap in the literature.

In Lines 184 and 186: “Figure 9” should be replaced by “Figure 7.”

Tables A and B in the appendix: I think it is better to have the references on the far left or right column of the tables. The current format is confusing.

Page 17: I think it will be helpful if you can add mean, median, and standard deviation of the parameters in Table 1.

The quality of Figures 14, 15, and 16 must be improved.

Conclusions: I want to restate that “a lack of experiments in eccentric punching shear” cannot be a conclusion of this study. More rigorous interpretation and scientific explanations of the mechanisms behind the observed trends must be provided in this manuscript. Also, please provide more discussions on the future possible research needs. Authors tried to discuss future needs as follows: “A better understanding of eccentric punching shear and further experiments on deeper slabs and slabs with high-strength concrete are necessary to obtain safe designs, optimize the design of building floors, and develop better tools for the assessment of existing building slabs.” However, this is still too general and vague.

Author Response

Please see the attached file with the item-by-item responses

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In figures like 17 & 18 please distinguish between edge, corner and internal columns.

Please clarify what Level of Approximation was used in the MC2010 predictions presented in the paper.

Please provide a figure showing typical shear stress distributions obtained around the considered control perimeter with FEA for eccentrically loaded internal edge and corner columns.  

The following sentence is confusing "As can be observed in Figure 18 and Table 5, the ACI 318-19 [7] assumption of a linear elastic model distribution leads to an overestimation of the real performance of the specimens. Replacing the shear stresses calculated assuming the linear stress distribution by 461 the average values for the SCIA Engineer [31] FEM results in the comparison to the shear 462 capacity from ACI 318-19 (see Table 5) results in larger (i.e. more overly conservative) 463 values for the tested to predicted shear.".  It is unclear why replacing a linear stress distribution with an average one should lead to more conservative strength predictions. I would expect the opposite. Please explain how the average FEA stress is calculated and provide an explanation for Vtest/Vpredicted increasing when average values are used.

Please note that as explained in the fib text book the aim of using the reduced control perimeter u1* in EC2 and limiting the column transfer moment as described in Annex I of the code is to give a safe design. see page 209 fib text book Bulletin 2

Also note that the EC2 shear force distribution under eccentric loading at internal columns is based on elastic analysis by Mast (see fib text book Bulletin 2 page 207. 

 

Author Response

Please find our replies to the comments of reviewer 1 in the attached file

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have addressed all the comments and suggestions made by this reviewer and adequate changes have been made. 

Author Response

we would like to thank the reviewer for the thoughtful comments.