Damage Analyses of Replaceable Links in Eccentrically Braced Frame (EBF) Subject to Cyclic Loading

Round 1

Reviewer 1 Report

The paper investigates the influence of weldings and number of stiffenings in the shear response of links. The paper is very interesting and deserves to be published in Applied Science if the following issues are correctly addressed:

1) In the paper, the term "fuse" and "link" are used alternatively. Please use one of this terms. It is maybe better to use the term "link" it makes the subject more immediately recognizable.

2) Is this kind of link suitable for both horizontal links EBFs and Vertical link EBFs? In the authors opinion, is there any difference between the behaviour of replaceable links for horizontal and vertical EBFs configurations? Please explain.

3) How much is the overstrength exhibited by the links?

Author Response

Dear Reviewer,

Thanks very much for your hard work. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are clearly highlighted in the paper. Thank you very much for all your help and looking forward to hearing from you soon.

Best regards

Sincerely yours

We submit here the revised manuscript as well as a list of changes:

Response to the reviewer’s comments:
Comment 1: In the paper, the term "fuse" and "link" are used alternatively. Please use one of this terms. It is maybe better to use the term "link" it makes the subject more immediately recognizable.
Response: In this paper, the links are characterized as “fuse” function to protect other members. We are very sorry for our negligence of alternate use of the terms "fuse" and "link". To make the subject more immediately recognizable, we have made correction according to reviewer’s comments.

Comment 2: Is this kind of link suitable for both horizontal links EBFs and Vertical link EBFs? In the authors opinion, is there any difference between the behavior of replaceable links for horizontal and vertical EBFs configurations? Please explain.

Response: We deeply appreciate your asking about the applicability of this kind of link to horizontal links EBFs and vertical link EBFs and Vertical link EBFs, and we have reviewed a lot of related literature carefully. This study had shown that links possess excellent ductile, energy-dissipating behavior which can be applicable to the horizontal links EBFs. Although both the horizontal link and the vertical links are used as the main energy-dissipating elements to prevent inelastic deformation of other components, there are differences between the horizontal and vertical links which can be drawn:

Horizontal links are separated from the floor beam and then were bolted together by the end-plate. This will not only realize independent control of required strength, ductility and structure stiffness, but also quick inspect and replace yielded and damaged links following a major earthquake.  However, vertical links are connected between the floor beam and the braces by bolts or welds. This cannot realize independent control of required strength, ductility and structure stiffness, and cannot replace yielded and damaged links following a major earthquake.

In addition, it attempts to design vertical shear links according to horizontal links using some modification factors. For horizontal links EBFs, the drift angle of the frame, θ, can then be written in terms of the link rotation angle, γ, as:

θ_p=γ_p·e/L

However, the equations about the calculation of the link rotation in vertical links EBFs should be modified because the connections of vertical links and horizontal links are different. Therefore, it will be presented that in the vertical links, the ultimate state of the shear and bending moment capacities reached values different from 1.5 Vp and 1.2Mp for horizontal shear links. Besides, the link length limitation for designing other elements outside the vertical links should be modified. As a future work, we will study the behavior of vertical links EBFs and examine the applicability of this kind of links.

Comment 3: How much is the overstrength exhibited by the links?

Response: It is really true as Reviewer suggested that the overstrength factor of a link is an important parameter for capacity design of its adjacent elements and connections. The nominal value of plastic strength (V_pn) was calculated as 0.6f_yA_w or 2M_p/e per the AISC 341-10 provisions, using the nominal yield strength of the steel and nominal dimensions, while the measured value of plastic strength (V_p) was based on the actual measured yield strength of the steel and actual measured dimensions. Table 1 lists the measured value of plastic shear strength (V_p) and maximum shear strength V_pn of the specimens. The overstrength factor of the shear link, is defined as the ratio V_pn/V_p.

Table1. The Overstrength Factor of Specimens..

We tried our best to improve the manuscript and made some changes in the manuscript.  These changes will not influence the content and framework of the paper. We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.
Once again, thank you very much for your comments and suggestions.

Reviewer 2 Report

attached

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,
Thanks very much for your hard work. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are clearly highlighted in the paper. Thank you very much for all your help and looking forward to hearing from you soon.

Best regards

Sincerely yours

We submit here the revised manuscript as well as a list of changes:

Response to the reviewer’s comments:

Comment 1: There are some phrases that are seen exactly the same in other papers. The phrases “This often results in oversized link elements” and “the beams are expected to sustain significant damage” are seen repetitively in other references. The authors do need to search out the paper and see if there is such a replication. They need to paraphrase and also cite to respect the academic integrity; otherwise it is a clear plagiarism.

Response: We greatly appreciate your valuable and very helpful comments. We have carefully reviewed the article again and there is no such duplication. Considering your comments, the sentence of “This often results in oversized link elements, which leads to over-designed structures and foundations” were changed to “This causes the design of cross-sectional dimensions of links to be enlarged, resulting in over-designed structures and foundations, and increasing the cost of the overall structure” and the sentence of “the beams are expected to sustain significant damage” were changed to “the beams are forecast to sustain sever damage”. We uphold scientific ethics and respect the academic integrity, and object to plagiarism and falsification undoubtedly. As a future work, we will try our best to improve English expression skills.

Once again, special thanks to you for your good comments and reminders.

Comment 2: Revise: ..of the overall structures [35], and L3~L5.

Response: It is really true as Reviewer suggested that some mistakes we made in writing and editing our paper. We have made correction according to the Reviewer’s comments.

Comment 3: The introduction needs to compare the reinforcing schemes such as corrugation with the stiffening used in the paper in terms of the dissipation of energy and the increase percentage comparing with the plain specimens. This can be found in: NUMERICAL STUDY ON STEEL SHEAR WALLS WITH SINUSOIDAL CORRUGATED PLATES. Also the authors need to point out the experimental results of the elastic bracing used in doi.org/10.1016/j.jcsr.2012.05.008  as opposed to the bracing scheme of the present study, although the application may be somewhat different.

Response: We strongly agree with your suggestion, and have added this literature to our paper, by comparing the reinforcing schemes such as corrugation with the stiffening used in the paper in terms of the dissipation of energy and the increase percentage comparing with the plain specimens. The content specifically as follows: “Kalali and Ghazijahani [15]presented an investigation into the cyclic behavior of corrugated steel plate shear walls （SPSWs）, it was shown that energy dissipation capacity of specimens with the angle of 60°are approximately 6% larger than specimens with the angle of 45°while the specimens with the same number of corrugation and wall thickness.” We have studied experimental results of the elastic bracing used in doi.org/10.1016/j.jcsr.2012.05.008 and added this literature to the Introduction. The content specifically as follows: “Previous investigations [42] have shown that elastically braced can solve the problem of the lateral bracing of structural members and further research need to discuss the applicable to EBFs.” was added (line 46-51) .

References

15.Hamed, K.; Ghanbari, G.T.; Mohammad, H. Numerical study on steel shear walls with sinusoidal corrugated plates. Latin American J. Sol. Struct. 2016, 13, 2802-2814.

42.Showkati, H.; Ghazijahani, T.G.; Noori, A. Experiments on elastically braced castellated beams. J. Constr. Steel Res. 2012, 77, 163-172.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript proposes an improved EBF for Fuses systems. The paper is interesting and includes experimental work and discussion / evaluation of the experiments. I have some comments and improvement proposals:

I propose to change Cyclic Excitation to Cyclic loading in title

In introduction, you are writing that steel moment frames experienced buckling, but also the experienced brittle fracture of moment connections in past earthquake events

In introduction, extend your state of the art part, include more literature of fuses systems and other systems for energy dissipation or systems with different way of energy dissipation like RBS/RWS which form plastic hinges in specific areas

I propose to remove Fig. 6, it is not making any sence

Explain how the rollers (Fig.3(b)) are not affecting the transfered moment. The system looks

to me that it is too wide and so it affects the tranfered moment. Further, please explain how it is not perform energy dissipation via friction.

6. Compare your results with similar tests from literature, in order to show that your element is improved compared with other systems, discuss the comparison

7. Proof read your manuscript and -if possible- ask a native English language speaking person to read and edit your manuscript. Generally English language is fine, but it can be improved in several sentences.

Author Response

Dear Reviewer,

Thanks very much for your hard work. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are clearly highlighted in the paper. Thank you very much for all your help and looking forward to hearing from you soon.

Best regards

Sincerely yours

We submit here the revised manuscript as well as a list of changes:

Response to the reviewer’s comments:
Comment 1: I propose to change Cyclic Excitation to Cyclic loading in title.

Response: It is really true as Reviewer suggested that “Cyclic Excitation” should be changed to “Cyclic loading” in title which is more in line with the theme of our experimental research without doubt. We have made correction according to the Reviewer’s comments in our paper.

Comment 2: In introduction, you are writing that steel moment frames experienced buckling, but also the experienced brittle fracture of moment connections in past earthquake events.

Response: As Reviewer suggested that our statements in the introduction regarding the investigations of the brittle fracture of moment connections in past earthquakes involved less. In conjunction with Reviewer’s comment 3, we have added relevant statements in this section to the article:

Line 44-61, “In Northridge’s damaged structures, there was only rare evidence that plastic zones actually were formed. Instead, the seismic energy was transmitted directly to the connection, overloading it and causing it to brittle fracture [7]. For the connection to be employed in seismic resistant frames, it is important to examine its ductility and energy dissipation capacity. Previous investigations [8-9] indicated that the column panel zone (PZ) ductility can considerably influence the failure mode of the beams with reduced beam section (RBS) moment connections, which the beam to- column joints with weak PZs resulting in brittle fracture within the weld connecting the beam flange to the column face. Subsequently, test by Naeim [10] have shown that the RBS usually experiences web local buckling first, followed by lateral torsional buckling and finally flange local buckling. Shervin and Maryam [11] introduced a hybrid connection named Slotted-Web–Reduced-Flange (SWRF), which consists of RBS and Slotted Beam Web (SBW). This connection is modeled by directly attaching the beam flanges to the column without any slots in the web or cuts in the flanges. The pre- Northridge connection experiences nearly double the maximum stresses of the SWRF connection at 0.04 rad of rotation. Therefore, Rao and Kumar [12] have studied a connection with rectangular hole in the web, entitled Rectangular Hollow Sections (RHS). According to this research, the connection moment–rotation behavior is represented by three parameters, namely, initial connection stiffness, ultimate moment capacity and the shape parameter. However, the shear links have different energy dissipation ways from these systems.” was added. 

7.          Miller, D.K. Lessons learned from the Northridge earthquake. Eng. Struct. 1998, 20, 249-260.

8.          Krawinkler, H. Shear in beam–column joints in seismic design of steel frames. AISC Eng. J. 1978, 3, 82–91.

9.          Popov, E.P. Panel zone flexibility in seismic moment joints. J. Constr. Steel Res. 1987, 8, 91-118.

10.       Naeim, F. The seismic design handbook, Van Nostrand Reinhold, 1989.

11.       Maleki, S.; Tabbakhha, M. Numerical study of Slotted-Web–Reduced-Flange moment connection. J. Constr. Steel Res. 2012, 69, 1-7.

12.       Rao, D.V.; Kumar, S.R. RHS beam-to-column connection with web opening—parametric study and design guidelines. J. Constr. Steel Res. 2006, 62, 747-756.

Comment 3: In introduction, extend your state of the art part, include more literature of fuses systems and other systems for energy dissipation or systems with different way of energy dissipation like RBS/RWS which form plastic hinges in specific areas.

Response: We are very sorry for our negligence of state of other systems for energy dissipation or systems with different way of energy dissipation which form plastic hinges in specific areas. Consider Reviewer’s suggestion, we have re-written this part and added it to our paper (see Response to comment 2).

Comment 4: I propose to remove Fig. 6, it is not making any sense.

Response: We are very sorry for our incorrect putting Fig. 6 in our paper. It is really true as Reviewer suggested that Fig. 6, is not making any sense, and we have deleted it.

Comment 5: Explain how the rollers (Fig.3(b)) are not affecting the transferred moment. The system looks to me that it is too wide and so it affects the transferred moment. Further, please explain how it is not perform energy dissipation via friction.

Response: We greatly appreciate your valuable and very helpful comments for our experimental device. A row of horizontally slidable rollers is added to the bottom of the lower frame beam to facilitate the installation of the lower frame beam. After the installation of the device, it was clearly found that all the rollers are not in full contact with the lower frame beam and can be easily pulled out while the self-weight load of the beam members are all borne by the supports. During the test, only one roller was involved in the sliding could be found, which may be due to deformation of the shear link resulting in a slight lowering of the lower frame beam. At the same time, in order to prevent the friction between rollers and the beam members from adversely affecting the test results, lubricating oil is applied between the roller, the frame beam and the tripod coupling beam.

Comment 6:  Compare your results with similar tests from literature, in order to show that your element is improved compared with other systems, discuss the comparison.

Response: Considering the Reviewer’s suggestion, we have studied related literature carefully and compared our study with similar tests by other researchers, and some conclusions could be drawn:

At first, our test was conducted in a pure shear device based on eccentrically braced frame to stimulate actual force of shear links. Therefore, the design of energy-dissipating shear link is separated from frame beam, which allowed more choices in determining the cross-sectional dimensions of links. Also, the connection consists of a plate welded to the end of link bolted to the frame beam, which allowed for easy replacement. Besides, the welding access hole can effectively improve links’ ductility and energy dissipation capacity. Owing to the welding access hole adopted in links, stress distribution of web was more uniform, the failure modes of specimens were ductile failure.

Comment 7: Proof read your manuscript and -if possible- ask a native English language speaking person to read and edit your manuscript. Generally English language is fine, but it can be improved in several sentences.

Response: Thanks very much for the suggestions from the Reviewer, which are very helpful for us to improve the manuscript, and our language should be improved. After carefully check, we found some grammar and sentence errors, and have modified the manuscript accordingly. And we hope the revised paper will be more clear and accurate on expressions.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All the corrections have bene made. The paper can be accepted in the present form. 

Reviewer 3 Report

All comments have been considered, so it can be accepted as it is