Experimental Study on the Flexural Behavior of Concrete-Filled Steel Box Slabs
Round 1
Reviewer 1 Report
Line 87: „Geometries of the seven specimens.“ should be „The main parameters of the seven specimens“.
Fix Figure 2 so that all lines would be visible.
Figure 3 should not be „Schematic diagram of .............“, but be „an inside view“
Line 100-101: Write which class concrete mixture was used and what compressive strength mortar mixture concrete was covered after two weeks and how long was the mortar mixtured hardened.
Figure 5 does not have all lines visible, change it so all lines would be visible.
Does chosen concrete class not influence the end result?
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The submitted paper deals with the flexural behaviour of the concrete-filled steel box slab. First of all, the paper summarizes actual topic-related findings from scientific papers. Afterwards, the proposed experimental investigation is described. Namely, the findings on the flexural response of different types of concrete-filled steel box slabs are presented. The obtained experimental data served for the development of an analytical relation for the calculation of the flexural capacity of similar types of members. The flexural capacity calculated by the proposed relation and other existing relations were compared and evaluated in comparison with experimental results.
As a reviewer, I have got the following questions/comments on your paper:
Introduction
The state of the art describes experimental findings on the flexural behaviour of concrete-filled steel members. However, a more comprehensive study of existing data would be beneficial. Moreover, no findings on available analytical relations for the calculation of flexural performance are presented.
Experimental data
The test specimens used for the experimental investigation are well-described. However, more comprehensive information on the studs is missing. Namely, it concerns the length of studs, surface treatment and end treatment (method of anchorage).
Figure 2 is not clear and hard to see.
There is no information on how the mechanical properties of concrete were obtained. (number of specimens, calculation of a mean value, test procedure etc. ) Only the average compressive strength is provided.
Could the authors clarify, why there are two types of steel plate thickness mentioned in table 2?
To obtain the flexural capacity of the investigated members, the types of test were used – a force-controlled test and a displacement-controlled test. Why only a displacement-controlled was not used?
Could the authors clarify why the element SBCS-1 with no studs and internal plates exhibits higher flexural capacity than most of the other elements?
Experimental Test Results and Discussions
What types of material properties (design values, characteristic values, mean values) were used for the calculation of flexural capacity by the selected relations?
What was the reason to develop a new relationship for the calculation of flexural capacity of a concrete-filled steel box slab, because, as the authors showed in the manuscript, there are relations which seem to be relatively precise (GB50936) and simple? Why the proposed formula does not contain any coefficient which would consider the effect of bond strength between steel plates and concrete (studs etc.). What was the reason not to use the stress block depth factor for concrete?
Conclusions
The conclusions presented in the manuscript are very general and predictable.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Point 2: The test specimens used for the experimental investigation are well-described. However, more comprehensive information on the studs is missing. Namely, it concerns the length of studs, surface treatment and end treatment (method of anchorage).
Response: The statement “The stud used in this study is a 50mm ribbed steel bar. The end of the stud was welded on the steel plate.” was added in Lines 101-102 of the revised manuscript.
Question: Actually, my question was related to the other end of the stud if it is free or there is some other end adjustment.
Point #4: There is no information on how the mechanical properties of concrete were obtained. (number of specimens, calculation of a mean value, test procedure etc. ) Only the average compressive strength is provided.
Response: Thank you for the comment. The manuscript was revised (Lines 110-114, Line 119 in the revised manuscript) to address this comment.
Question: Could the authors explain what they meant by saying “cured under the same condition”? Could they describe the whole process of curing?
Point 8: What types of material properties (design values, characteristic values, mean values) were used for the calculation of flexural capacity by the selected relations?
Response: The characteristic values (fy and fck) of material properties were used to calculate the flexural capacity. In the revised manuscript, formulas (1), (2) and (3) have been modified. The statement“fck=0.67fcu for normal strength concrete”was added in Line 397 of the revised version.
Question: The authors stated that they used the characteristic values of the materials to get the flexural capacity of a selected member by using the proposed formulas. Subsequently, they compared the obtained value with the value measured during the experimental test on the same member. However, in my opinion, this approach is wrong. The characteristic values (usually 5th percentile) of material properties do not describe adequately the behaviour of the materials and as consequence, it makes no sense to compare the calculated moment capacity by the proposed formulas with the value measured on a real member. In other words, the authors compared the incomparable.
Moreover, the proposed formulas should be validated first before the authors recommend them for an engineering design (conclusion).
Point 9: What was the reason to develop a new relationship for the calculation of flexural capacity of a concrete-filled steel box slab, because, as the authors showed in the manuscript, there are relations which seem to be relatively precise (GB50936) and simple? Why the proposed formula does not contain any coefficient which would consider the effect of bond strength between steel plates and concrete (studs etc.). What was the reason not to use the stress block depth factor for concrete?
Response: The flexural moment capacity formula of the concrete-filled steel box slab proposed in this paper was different from that in Chinese code GB50936 and American code AISC. The flexural moment capacity formula in GB50936 was derived based on square section members. The flexural moment capacity in AISC ignored the contribution of concrete. The flexural moment capacity formula proposed in this paper considered the contribution of steel box and concrete. It is suitable for calculating the flexural moment capacity of rectangular section member with a small height-to-width ratio. A detailed explanation can be found in Lines 340-364 of the revised manuscript.
The statement“The test results showed that the moment capacity of the specimen with stud was about 3% lower than that of the specimen without stud. The moment capacity of the specimen with stiffening plate was about 5% higher than that of the specimen without stiffening plate. Stud and stiffening plate had a little influence on the moment capacity of the concrete-filled steel box slab relative to the section size of the specimen. Therefore, the formula proposed in this paper does not consider the influence of stud and stiffening plate on the moment capacity of the specimen.”was added in Line 307-313 of the revised version. The test results showed that there was no obvious slip between the built-in concrete and the steel box, it was considered that the steel box and concrete had a good synergistic effect when the specimens were damaged. Therefore, the formula proposed in this paper did not consider the influence of stud and stiffening plate on the bond strength of steel plate and concrete. In future research, we will further study the influence of the bond strength on the flexural performance of specimen.
In the formula proposed in this paper, x was the depth factor for concrete. The caption of Figure 15 (Line 326) has been changed to “The stress blocks of the specimen.”
Question: I do not understand what you mean by “x was the depth factor for concrete”. "x" corresponds to the depth of the compression zone of concrete. In Fig. 15 the stress block is showed with no stress block depth factor which is very unusual. Therefore, I asked what was the reason not to use the stress block depth factor for concrete?
Author Response
Please see the attachment.
Author Response File: Author Response.doc
