On the Residual Static and Impact Capacity of Shear-Reinforced Concrete Beams Subjected to an Initial Impact

Round 1

Reviewer 1 Report

In this manuscript, a high-velocity initial impact test first initiated severe shear damage on RC beams. The beams were after tested quasi-statically for their residual static capacity and by sequential impact tests for the residual impact capacity. This research has practical engineering significance and this manuscript is well written. However, there are still some small problems to be solved before this manuscript is accepted:

(1)    The summary is too long, please simplify it appropriately.

(2)    In line 49-51: ‘While local and global shear damage modes during impact loads have been investigated extensively , there is not much research about their effect on the residual static and dynamic shear capacity.’ Why did predecessors seldom carry out this research?

(3)    In line 124: ‘the mid-point displacement using digital image correlation (DIC).’ The DIC method used for laboratory measurement is a highlight. However, the test accuracy must be specified when using this method, otherwise the reliability of the test data cannot be guaranteed. Please refer to the following documents for details:

Shape characteristics of coral sand from South China Sea. Journal of Marine Science and Engineering. 2020, 8(10): 803. DOI:10.3390/jmse8100803.

Experimental study on mesoscopic shear behavior of calcareous sand material with digital imaging approach. Advance in Civil Engineering. 2020, 8881264. DOI:10.1155/2020/8881264.

(4)    In line 318-319:‘It can be seen that Beam D1 failed by shear, as shown by the brittle response, although it contained the largest amount of shear einforcement.’ Why does D1 contained the largest amount of sheet einforcement shown the brittle response?

(5)    The conclusion is too long, please state only the important test results.

Author Response

Thank you for taking your valuable time and reading my article. I hope that you found it interesting.

(1) I shortened the abstract by removing the part discussing the local damage as it may not be an as important result. I agree that it previously was too long!

(2) For structural elements sustaining the amount of damage observed after the initial impact, you would seldom use the element even though residual capacity is there for civilian structures. For this reason, I think the residual capacity may not be that interesting outside research. However, while this is true for civilian structures, my research topic is protective structures which means that it is of interest to us as the total deformation capacity is often used for fortification design.

We also had a secondary aim to collect a lot of data for the dynamic response, which is why sequential impact testing was used. 

(3) We verified the DIC analysis by applying the procedure to the piston in the same picture as the beam and compared the DIC results against the displacement measured from the MTS machine. They agreed almost perfectly!

I, therefore, added on rows 125-126 of the newly uploaded version: "The results using DIC were validated by applying the procedure on the piston of the MTS machine in the pictures taken. The results using DIC showed to converge well with the displacement measured by the MTS machine."

(4) This was explained in rows 335-336 of the peer-reviewed version. The steep diagonal cracks opened during the initial impact resulted in a low static shear capacity.

(5) I reduced the conclusions by about 30% to only show what was important.

Hope this was enough for your doubts of the article. Thanks for helping me improve it.

With kind regards,

Viktor Peterson

Reviewer 2 Report

The article contains interesting laboratory tests for concrete beams subjected to dynamic loading. The presented results may be helpful at the design stage of reinforced concreto beams exposed to fast-changing loads. Below are some comments and suggestions:

1. In the introduction, it should be mentioned that the construction materials from which reinforced concrete is made are tested as independent elements and cooperating with each other. The influence of the fast-changing load on the stress-strain characteristics of building materials differs from static loads, causing an increase in the load taken over (doi:10.3390/ en14051483).

2. In the subsection 2.1, it is necessary to write what was the difference in the load rate in static and quasi-static tests.

3. In the subsection 2.4 it should be written why the impact load of 60 kg has been chosen, whether it results from some standard or geometric model corresponding to industrial conditions.

4. For Figure 8, it should be written what method was used to measure the crack angles in the concrete beams.

5. In the subsection 3.2, one stress-strain characteristic with mean values ​​from Figure 15 would be useful. In addition, it should be added formulas by which to calculate the shear stress and the corresponding strain.

6. Applications are well written and cover the scope of the research.

Author Response

Thank you for taking your valuable time and reading my article! I sincerely hope it was interesting.

(1, 2) The standards that I have referred to which were used for material testing only tests properties by quasi-static loads. If these are then used in a numerical model they would have to be recalculated using dynamic increase factors. The rates and procedures are described in the standards referred to, so I don't think I have to repeat them again as the interested reader can download the standard. This saves some space and makes it easier to focus on the research itself in my opinion.

(3) I described this in rows 134-146. The mass and drop height were determined by updating them in a model until a final displacement which was larger than the displacement capacity of the beams. 

I added the italic text to make it clearer: "The mass and drop height of the striker was updated until a final displacement after retardation of about 9 mm using the rigid-plastic model."

(4) This was described in rows 206-207. A secant line was drawn between a start and end of the crack and its angle was determined in the drawing software automatically.

(5) We mainly want to focus on the experimental results for this paper and work on analyzing them properly later on. This is a fantastic idea for future analysis in the coming work!

Thank you for your valuable comments. They helped with improving the paper!

With kind regards,

Viktor Peterson