Failure Analysis of a Concrete Anchor under Severe Seismic Action

Round 1

Reviewer 1 Report

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Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Reviewer Comments

Manuscript number: applsci-1418984

Full Title: Failure Analysis for Concrete Anchor Behavior Under Severe Seismic Action

The study deals with the design methods and failure mechanisms of concrete anchor systems. In particular, the study is focused on the new Korean guidelines for seismic design of electric power transmission/distribution facilities.

The presented work is interesting, however, some minor revisions should be addressed before acceptance.

• English should be improved in all text. For example:

Abstract:

remove “that” in “This paper explored and evaluated that how different…”

remove “in” in “reduced the seismic demands in quite efficiently.”

Introduction:

“The guidelines….have been updated” or “The guideline….. has been updated.”

Try to reformulate the phrase: “The large stress redistribution on the plate-to-plate contact zone due to the huge seismic event, East-Japan earthquake has still developed.” It is not very clear.

What do the authors intend with: “…seismic tension option include anchor design…”

Similar issues should be checked in all the sections of the paper.

• The introduction should give a broader overview of the research state of the art on the topic. For now, it is limited only to the updates of the Korean guidelines.
• In Eq. 3 variables should be the same as the ones mentioned in the explanation text above.
• Check the phrase: “…by multiplying the displacement amplification factor by the displacement amplification”. (is the use of “displacement amplification” twice correct?)
• The inelastic energy absorption factor is once referred to as Rµ and then Fµ. Is it a type or they are two different factors?
• The study is focused on the anchor system and carries out some numerical analysis (both static and dynamic non-linear) on one specific case study with a base steel plate anchored with four anchor bolts. However, the authors should spend some more words on how the “upper” structure can affect the overall performance of the joint (i.e the presence or not of bracings, presence of stiffening plates in the joint, flexural stiffness of the base plate, etc).
• For the time-history analysis some more results (as base shear-lateral displacement should be given. Also the position of the lumped mass along the z (vertical) axis, in the FE model for dynamic time-history analysis, is not clear in Figure 14.
• Do the authors think if any experimental work is needed in this field? Or are there any experimental investigations already available in the literature and how are your numerical results compared to those experimental ones?

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The reviewed paper deals with the response modification factor, overstrength factor in terms of brittle and ductile failure of anchor system. Also, the parametric studies for tension and shear behaviors of anchor system has been conducted for the elastic design and ductile design under earthquake motion was compared.

The topic is very actual and useful. Capacity based design for the mechanical and electrical installations and structures for this application is very useful and research on the subject should be encouraged. Also, the detail numerical model in Abaqus is used, and the static and dynamic analysis are conducted.

Also, the paper is well structured, and the authors have clearly emphasized the main contributions and conclusions of the study.

In the reviewer’s opinion, this paper is good and valuable study.  The paper can be accepted for publishing after some corrections and explanations. The reviewer has some comments and recommendations for the authors.

• the state of the art and previous research is not described in detail.The regulation is mentioned, but research by various authors on the subject is not included.Also, in the civil engineering, this type of connection of steel column and concrete foundation is quite well elaborated and there are many tests for it.
• I may have missed, but in Equation 1 the meaning of parameter I is not described
• can the authors explain the claim “The earthquake hazard map in Korea shows the maximum ground acceleration equivalent to 10% of the excess probability for 100, 250, and 500 years in the form of an equidistant line. This period and the over-probability mean the same as the return period of 1,000, 2,400 and 4,800 years.” The 10% of the exceedance in 500 years is usually for limit state of significant damage.
• Can the authors explain the observed limit states? Only the limit state near collapse is observed, but with such equipment and facility the limit state of usability and the limit state of significant damage are very important.
• can the authors explain the sentence “The base shear force refers to the total amount of seismic load that acts on the top of the structure when the seismic load is converted into an equivalent static load…”. Base shear is shear force at the bottom of the structure, near the fundation (not on the top).
• The sentence “As the lateral force gradually increases, the structure moves out of elastic range and can resist the formation of plastic hinges” is unclear. It is not necessary that plastic joints can be formed and that the structure can move into the plastic region. Rephrase the sentence a little more clearly.
• How did the parameters change to make the scenario happen to each failure mechanism? It remains unclear whether in the numerical model the failure mechanisms are independent and observed separately or are they within the same model? The difference is because there is often an interaction of various failure mechanisms and it is difficult to observe them independently.
• It is necessary to describe in more detail the numerical model in Abaqus. What failure criterion was used with what parameters? What is the interaction failure surface between stresses? also, what parameters of strength and stiffness degradation were used in the dynamic analysis?
• The anchoring of the steel anchor to the concrete foundation was modeled. What is the interaction property between concrete and anchor and how is it modeled in abaqus? Is this consistent with the pull out test?
• Only in the concrete foundation there are more failure mechanisms. In addition to the anchors, the reinforcement to which the stresses are transmitted is almost always placed in the foundation block. Is the reinforcement modeled in concrete? Because it has a big impact on the concrete breakage mechanism.
• If I understood correctly, the construction for dynamic analysis is absolutely rigid except for the anchoring details. Thus, the acceleration of the construction approaches the values of PGA for a period equal to zero. This is not realistic to expect due to flexibility of structure, so it is possible that the results are not very reliable. Can the authors explain this assumption?
• why is a dynamic analysis conducted with only one record? for the convenient results, at least 7 motion records are required and the mean value of the results should be taken. It is possible that the particular record did not excite the construction or underestimated its response at dominant periods.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper has been clearly improved and can be published.

Reviewer 3 Report

The authors answered questions asked by the reviewer and improved the work. All questions have been explained and I agree that the paper can be published.