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# ETABS - Science topic

Explore the latest questions and answers in ETABS, and find ETABS experts.
Questions related to ETABS
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I need information about chord rotation . How to calculate it in etabs using time history analysis.
Drawing a fragility curve using rotation in ETABS through time history analysis involves several steps. A fragility curve represents the probability of structural damage at various ground motion intensity levels. In this case, you want to consider rotation as a measure of structural damage. Here's a simplified guide:
Create the ETABS Model:
Import or create your structural model in ETABS. Ensure that it's properly defined with materials, elements, and boundary conditions.
Define Response Spectrum Function:
In ETABS, you need to define the rotational response spectrum. Go to "Define" > "Function" > "Response Spectrum" and create a new response spectrum function for rotation.
Define Time History Analysis Parameters:
Set up your time history analysis parameters. Go to "Analysis" > "Time History Options" to define load cases, time steps, damping ratios, and other analysis settings.
Apply Ground Motions:
Import or define your ground motion records in ETABS. Go to "Define" > "Time History" and specify the ground motion records for your analysis.
Assign Ground Motions to Load Cases:
Assign the ground motions to the respective load cases for your structure.
Perform Time History Analysis:
Run the time history analysis by selecting "Run Analysis" or a similar option in ETABS.
Define Damage Thresholds:
Determine rotation thresholds that correspond to different levels of structural damage. These thresholds will be used to categorize the results.
Post-Processing:
After analysis, review the results to extract rotation values for different time steps or nodes/elements in your structure.
Create Fragility Curves:
Calculate the probability of exceeding the damage thresholds for each ground motion record. This typically involves post-processing the analysis results using scripts or custom tools.
Plot the Fragility Curve:
Use a software tool like Excel, MATLAB, or Python to plot the fragility curve. The x-axis represents ground motion intensity (e.g., spectral acceleration), and the y-axis represents the probability of exceeding the rotation threshold.
Interpret and Analyze:
Analyze the fragility curve to understand how the structure's rotation response relates to different ground motion levels.
Keep in mind that this is a high-level overview, and the exact steps may vary depending on the complexity of your structure and analysis requirements. Additionally, scripting or programming may be necessary to automate the process of extracting results and creating the fragility curve. Ensure you have a good understanding of ETABS and structural analysis principles before attempting this task.
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Hi, Can anyone give me a source where I can find detailed steps in modelling of negative stiffness isolator? Another question is, Can I use shape memory alloy as material of base isolators in ETABS? If so, what are the steps?
You can use
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I have a pressing issue with my thesis, as I need to analyze numerous 3D moment frames, but I'm running short on time. Moreover, the buildings I'm studying are symmetrical and lack torsion or disarray complexities. I wonder if it's possible to model 2D frames with properties equivalent to those of the 3D frames, and still achieve accurate results. This would significantly save me time. I'm seeking assistance on how to perform this task in ETABS. Can anyone help me with this?
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Hi
I was wondering how exactly are the pushover loads applied in FEA programs?
For instance, in SAP2000 you can apply the following load patterns
• user-defined
• modal
• accel
The first case is trivial but in modal and accleration load patterns, is th eload applied to all the elements? I.e. is it applied individually to each beam and column proportional to mass?
In MIDAS the available load patterns are similar. On their website on uniform acceleration they say the following:
Uniform Acceleration: The load is distributed relative to the inertia forces developed in the structure, which has been subject to a uniform acceleration. If the acceleration is uniform, the load pattern is determined proportionally to the mass at each story level.
Since above they mention storey levels I wonder whether the programs try to lump the forces at individual floors.
Thanks
Hi Likhon! Thanks for the reply.
In both cases, the loads are not applied individually to each element, but rather distributed based on the structure's dynamic properties. This approach allows the FEA program to account for the structural response to dynamic loads more accurately.
So if the loads are not applied individually on each element how is the analysis performed? The loads ultimatetly have to be somehow applied in the model. This can happen under the hood but there needs to be some process. Say for the uniform accelerations, we know we're carrying out a nonlinear static analysis, so the term "accelerations" is technically irrelevant. Although you could perform a quasi-static dynamic analysis. But as you said, the concept is to reproduce the dynamic properties of the structre.
My thinking is, what the program does, is to apply forces equivalent to the element mass x specified acceleration for every member. So I wonder whether this is the proces incorporated in Midas/SAP2000?
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Dear all,
I am performing Time History(Linear) in ETABS using IS 1893-2016 along with static and Response Spectrum analysis. If the downloaded TH from PEER database is in the unit of G and I am using SI system of unit then what should be scale factor?
The scale factor to be again multiplied by Ig/2R or software will automatically calculate it?
Thanks
Hi,
You should convert G to mm/sec2 (SI system). Thus, the scale factor should be 9807.
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As part of the pounding analysis comprising a 5-story and a 3-story structure in ETABS, I have introduced gap elements between the buildings. I am currently evaluating which analysis method to employ - FNA or Direct Integration. Which of these methods would be more suitable for this scenario?
According to CSI ETABS manual and its advice you have better to use FNA methods because of its speed and accuracy in most of the cases.
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what steps should i ensure it is done correctly. do i apply it as a link or a spring
i think it should be a point spring
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I want to overlay a processed image onto an elevation view of a ETABS model using openCV and ETABS API in c# !
Professionally nobody is teaching these tools yet in our industry... but if you are willing to do that, you must learn any programming language like Python, VBA, or MATLA. Then, you can start writing the API code for the specific task you want to do. OAPI changed my life since I implemented that in my research studies. I hope this is useful.
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I'm currently doing a nonlinear model in Perform3D and I need to calculate the mode shape. I create the structure first in ETABS and import it on Perform3D but I noticed that there's a difference in the modal mass participation ratio. Therefore, I know that the story response plot that I extracted in ETABS is different from the Perform3D.
Now I don't know where to extract that data. Can anyone help me with this? For research purposes only.
Thank you.
Modal Shape Vector multiply by story mass
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I am working on a 2D frame to study the response of Base isolated structure. I did modal analysis analytically in MATLAB and tried comparing with modal analysis output of ETABS. The modal time periods obtained is not same. I choose the stiffness of isolator to obtain time period of 2.2s which is closed to ETABS result of 2.4s while I am getting period of 3.4s from MATLAB.
It would be a great help if anyone can figure out the problem. Thank you
Hossein Safar Yousefi Fard For fixed base case, the results are almost same in both ETABS and MATLAB. As of damping, I have not included them both in ETABS and MATLAB as the damping is very low and wouldn't significantly affect the modal analysis.
The link element has only been assigned with its horizontal stiffness (a very simplified modelling).
I also think the MATLAB script for isolated structure might be the problem but that is what I am getting from the literatures I referred. If you can explain a bit on the script, I might be helpful. And thank you for your effort.
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I am carrying out pushover analysis. I want to know if we design the elements using etabs and if we unlock the structure for giving nonlinear hinges will etabs consider designed area of reinforcement while assigning nonlinear hinges. or we need to give beam reinforcement overrides??
Hussam Ali Mohammed This link is not working.
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So far, ETABS doesn't open completely 8 out of 10 times. I have to close it using Task Manager. Upon debugging from the dialog box, it highlights the line 'EtabsObject.ApplicationStart' in yellow. The issue is that the same code opens the ETABS at other two times. With this uncertainty, I'm finding it difficult to continue programming. I'm attaching my VBA file.
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I have modelled a structural wall in ETABS using shell elements. I need to obtain the moment and shear force from it. How can we extract it from ETABS?
Also, can anyone suggest any another method to model the structural walls in ETABS to get the results?
To extract Moment (M) and Shear Force (V) for a structural wall in ETABS, you can follow these steps:
Open the model in ETABS and select the wall in question.
Go to the "Results" tab and select "Frame Results".
In the Frame Results window, you will be able to see the Moment and Shear Force diagrams for the wall.
To extract the specific values, you can click on the "Export" button in the Frame Results window and choose the type of file you want to export the data to (e.g. CSV, Excel, etc.).
The exported file will contain the values for Moment (M) and Shear Force (V) for each node along the wall. You can then use this data for further analysis or to generate detailed reports.
Note: It's important to make sure that you have performed a static analysis on your model before attempting to extract the Moment and Shear Force values.
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I've already calculated the blast pressure that will act on the building. However, I am not quite sure how can I apply this load to a building. Please, help me with this one. Thanks
I have the same problem. Let me know if you did it
Thanks
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I need to model about a dozen variations of a ten-story building using ETABS. I and my guide have decided to use ETABS OAPI for the purpose. Also, I'll be accessing it through Excel VBA. What would be a good way to learn it? I searched on web but there seem to be limited resources!
Aryan Shahabian Thank you very much
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I am aware of checking this value for one member for one load combination, as shown in the attached figure. However, I am looking for ways to extract all these ratios in tabular form. Did anyone encounter this before?
I am looking for ways to extract PMM ratio for 3D, which is already computed/generated by ETABS. Your excel has points plotted on 2D surface of either P-M2 or P-M3. Of course, we can write write a code to generate 3D surface of demand of column and then plot P-M2-M3 for computing ratio.
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I,m modelling the reinforcement concrete building in ETABS but i find the period very big in the first mode
Technically mode shape depends on mass and stiffness. It is not dependent on what type of nonlinear analysis type. Please check the modal load case and read the technical documentation.
Best of luck 🤞
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In his name is the judge
I want to build some parametric structures. my objects is period of first mode, eccentricity and (frequency of torsional mode/frequency of transitional mode). So I decide to use NSGAII for make my parametric structure.
Inputs of optimization are transitional mass, rotational mass, length and width of structure and objects are period of first mode and (frequency of torsional mode/frequency of transitional mode) and in each one I assume eccentricity constant.
So I think there is a problem. I think there is a relation between rotational mass and transitional mass with respect to length and width of structure and eccentricity of mass.
If my guess is true I have to remove rotational mass from my inputs and use the relation instead.
So my big question is
Is there any formula to evaluate rotational mass based on dimension, eccentricity and transitional mass in rectangular plan?
wish you best
Take refuge in the right.
If your structure is an 'office' or 'hospital' type building with concrete floors, so that the floors form rigid diaphragms at each storey, mass is associated with the translational response, and mass moment of inertia (MMI) is associated with the torsional response. You need to study an appropriate text on this, or an ETABS program manual, etc. Attached are formulae for calculating the MMI for typical floor shapes, including how to allow for these shapes being offset from the overall centre of mass.
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Hello, Nonlinear analysis experts.
I'm performing a static nonlinear pushover analysis of a RC shear wall as stated in the @Thomsen and @Wallace example (Thomsen, J. H., & Wallace, J. W. (2004). Displacement-based design of slender reinforced concrete structural walls—experimental verification. Journal of structural engineering. 130(4), 618-630.).
I used the ETABS 18.0.2 software to perform the analysis and construct the pushover curve. (the EDB file of the model is in the attachment field)
I used the wide-column approach to simulate the shear wall and assigned 6 fiber (auto) P-M-M hinges to account the nonlinear behavior of the wall.
More details about the shear wall are illustrated in the figure below.
Also, the material behavior was extracted using a plot digitizer tool and implemented on ETABS.
Further details about the materials are down below.
When I pushed the shear wall by a 141KN lateral force, it was expected to get a displacement of about 69.9mm, but the results were not as expected.
The last figure shows the comparison between the envelope of the experimental results and the resulted FE pushover curve.
Any suggestions?
Thanks for helping out Dr.Mahdi.
I really appreciate it.
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I am doing non linear modeling of unreinforced masonry structure using equivalent frame modeling. when i assign moment rotation hinges at the top and bottom of masonry pier ETABS gives error assigning hinges requested calculated properties are not available for material or section type. how can get away from this error.
Excuse me sir. I am having same problem. How did you solve it?
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Hello, Anyone here with a recommended experimental research paper that conducts shake table testing of reinforced concrete. I am validating my results and in order to do that I need an actual building and simulate it in ETABS to verify that the ETABS are capable to depicts the displacement response through time when conducting Non-Linear Time History Analysis.
Dear Jan Lhester Valdez Navasca;
You can verify with following reference:
1- Pinto A., Verzeletti G., Molina F.J., Varum H., Pinho R., Coelho E. [1999]. “Pseudo-Dynamic Tests on Non-Seismic Resisting RC Frames (Bare and Selective Retrofit Frames)”. EUR Report, Joint Research Centre, Ispra, Italy. 2- Carvalho E.C., Coelho E., Campos-Costa A. [1999] “Preparation of the Full-Scale Tests on Reinforced Concrete Frames. Characteristics of the Test Specimens, Materials and Testing Conditions”, ICONS Report, Innovative Seismic Design Concepts for New and Existing Structures, European TMR Network, LNEC. 3- Pinho, R. and Elnashai, A.S. [2000]. “Dynamic collapse testing of a full-scale four storey RC frame”, ISET Journal of Earthquake Technology, Paper No. 406; 37(4), pp. 143-164. 4- Varum, H. [2003]. “Seismic Assessment, Strengthening and Repair of Existing Buildings”, PhD Thesis, Department of Civil Engineering, University of Aveiro
Warm regards,
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I have modelled a 16 storey RCC building in ETABS and performed non linear static analysis. But the analysis is found unfinished. I have reduced no. of storeys and increased number of null steps. But no use. Please help me to find out the reason?
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I wanted to understand how these softwares are different in terms of the complexity of analyses and accuracy of results. I'm looking at performing Time History Analyses over a set of ground motion data and have observed slight differences in the results obtained using the mentioned software. I wish to know the reason behind this and why do we not hear about Drain 2Dx as often as SAP2000 or ETABS.
Dear Rohit,
I believe that the results of these two softwares should not be so different because these two softwares are basically similar. However, Sap is more complex and Etabs is more spedific and easier to use for small construction buildings with normal materials like concrete or steel.
Hope this helps
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initially i decided to perform non linear time history analysis on SAP 2000 but my sir suggested me to create analyze and design the model in ETABS and then export to SAP 2000, but after creating the model we are unable to import it in SAP 2000 as we are getting errors so i have decided to perform non linear time history analysis in ETABS19, so please let me know is it possible?
Yes, it is ease to perform non linear time history analysis for G+15 RCC building in ETABS 19.
IF incase, you are looking for importing model to SAP or ETABS - use the following links. Check the version's of your current software.
Thank you.
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I need to study the effects of tuning liquid damper on some building, so I search about the method of modeling TLDs on SAP2000 or etabs or RSA.
Greetings Nayer Nassef ,
Such devices may require coding the structure and the device in MATLAB, Python or in a second degree the modelling of the structure and the device in Opensees or ABAQUS or ANSYS.
Regards.
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i am working on wall slab precast connection.
But whether that spring on node will act as connection in precast or steel structure? Or it ll act as a foundation spring?
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Anything related to seismic design or 3DCP, I would appreciate a lot. I know grasshoper, karamba, sap2000, etabs, autocad, revit, matlab and have experiencia in buildings. I am so sorry if this bother someone.
Dear Mr. Mauricio Ballesteros,
I have an anti-seismic method which I would like to examine in detail. If you are interested in cooperation, send me a personal message
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In ACI318-19 section R6.3.1 and its commentary, "member stiffness GJ should be reflected the degree of cracking and inelastic action that has occurred along each member before yielding".
On table 6.6.3.1.1(a) the value for I-cracked for each member is recommended. However, I cannot find any recommendation for cracked torsional stiffness.
I am analyzing the structure subjected to gravity, wind, and earthquake load according to ACI using ETABS, and I am struggling about this issue
Please explain what is the best practice for applying cracking stiffness modifiers for torsion in
beams (Torsional constant, J),
columns (Torsional constant, J),
walls (in-plane f12), and
slab sections (m12).
It would be really appreciated if supportive reasons are provided.
Thank you.
Correction factor of torsional stiffness of concrete beams
A very common case in reinforced concrete buildings is the placement of side beams on the main beams. The problem that designers face in this situation is that the beams turn red due to excessive twisting. In these conditions, the solution is not to increase the cross-sectional dimensions, but to consider the torsional stiffness correction coefficients in them.
According to the philosophy of applying stiffness correction coefficients, which we examined in the previous article of stiffness coefficients of beams and columns, in the current situation, due to torsional cracks, the main beam rotates and its torsional stiffness decreases. Therefore, a coefficient should be considered to correct the torsional stiffness of these beams.
Unlike the flexural stiffness correction coefficients of beams and columns, the ninth section does not specify a specific number for the torsional stiffness correction factor; instead, it clearly states that the torsional stiffness of cracked members must be properly calculated and considered in structural analysis. Therefore, the process of determining the torsional stiffness correction factor is opposite to the computational flexural stiffness correction factor.
In cases where it is possible to reduce the torsional anchor by replaying the internal anchors to a member of an indeterminate structure, the Tu value can be reduced to 0.67Tcr.
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Hi everyone,
I'm making a time history analysis in abaqus, I have defined material Rayleight damping as for etabs as for abaqus, but when comparing modal shapes I found out that although the two first modal shapes are similar, from the third one they change (because abaqus show an axial modal shape while etabs never shows it), then it takes me to different results when making a time history analysis and compare it to Etabs Results.
PD: I put a point mass in abaqus and etabs but still not sure if it is considered in the analysis.
I'm adding files for some of you to help me.
Thank you.
There is big difference but to be specific in Abaqus
~In modelling material non linearity there is different material model like concrete damage plasticity and smeared cracking model
~In modelling geometric non linearity.
~In modelling compressive and tensile behaviour of concrete especially in Abaqus for tensile behaviour depending on the type of the problem we may use stress~displacement or stress~strain.
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I'm working on behavior of base isolated frame in SAP2000.
For modeling Lead Rubber Bearings, we should use Link Element with nonlinear properties. One the properties we need is Effective Damping Coefficient. for example if the manufacturer of the device has been said that effective damping ratio is equal to 19%, i want to know how should i convert it to effective damping coefficient?
As I think this reference will be helpful
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How to Control Punching Shear of Flat Plate without increasing Thickness and Providing Capital and Drop Panel?
I need help regarding ETABS 19 also. Any researcher here who can help me out?
Shear reinforcement is the answer, but it has to be a special kind. Because flat slabs are so thin, not only are conventional stirrups difficult to place, they are very poor because of the slip involved - slip at the corner bends. The answer is 'headed studs', in the form of pre-fabricated stud rails. The studs have large heads (more than conventional shear studs used for steel beam - slab composite action), to reduce bearing stress. These studs are very efficient shear reinforcement, with low slip. If you web-search for 'stud rail reinforcement' or the like, you will find a lot of manufacturers and plenty of pictures. They are widely used in seismic areas of North America (for both prestressed and reinforced slabs), because even flat slabs laterally braced by seismic frames, walls or bracing can suffer cyclic earthquake induced cracking and punching failure around the columns. Amin Ghali of the University of Calgary published quite a few papers on the subject in the 1990s.
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I have understood the meaning of F11,F12, F22, V13, V23, M11, M22, etc but am still confused which one to use to check my shell forces. Please suggest some tutorial video if available
Shell/Plate Element Force Analysis | F11 F22 M11 M22 V13 V23 Explained | ETABS SAP2000
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Sir,
I have performed time history analysis in ETABS. The size of the files after analysis is very large. I have extracted my results for my research paper.
Now, I want to store my data and free some space for other analyses.
How and where should store the analyzed file without losing the analysis results (without unlocking them)?
I am confused because if I copy the file it will unlock the model automatically.
Thank you.
The seismic response of a structure under dynamic loading of a typical earthquake is determined using time history analysis (Wilkinson and Hiley, 2006)
Remove any Null Objects, Lines, and Properties from your Model. All unneeded lines and attributes in the ETABS model contribute to the poor operating performance. Because ETABS also provides time to study the aforementioned lines. As a result, removing it and cleaning the model can help to minimize the model's slowness.
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Should I use ETABS or Perform 3D for IDA analysis?
Does Perform 3D provide more functions for IDA?
Yes. You can perform IDA in Perform-3D. However, it does appear that Perform-3D is not well suited for analysis of very large drifts (i.e. P-delta collapse). This thing you need to check. On the other hand, You may use SAP or E-Tabs.
Regards,
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I am modeling a steel braced frame in ETABS. I want to model the panel zone.
Please suggest how to do this.
Or share any document related to this.
Thanks.
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In general, if we want to use the auto assign hinge in SAP2000 or ETABS, in the box shown in the second figure, what load combination or load case should be used for time history analysis?
Thanks
Since we cant take axial load (P) variation in auto hinges, we take constant P from gravity load case. And V is the shear demand at yielding corresponding to the same load combination of P ( as mentioned in later versions of SAP2000 )
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Dear all,
Am doing validation on a 3-D model of a 30 storey building on Etabs 2016 by a non-linear time history method with El Centro ground acceleration and the parameter that I used is nonlinear fluid viscous damper and lead rubber isolation after running the analysis fundamental period is ok but why storey displacement is so far different?
The following tutorial helps you:
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Problem: I want to model the glass fiber in concrete beam in ETABS 2019 but there is no option in ETABS 2019 about modeling of glass fiber for concrete beam.
How to Model GFRP in ETABS? The fiber reinforced polymers use ACI 440.1R-15 which is the most updated code I found. And there is no option in ETABS 2019
I would be happy to hear from you,
Thank you!
yes
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i am trying to simulate the flat slab with equivalent frame method with ETABS software to conduct the pushover analysis, for modeling the rigid torsional member I adjust the torsional constant modifier to a very high value (1+e15). am I correct? if not what is the suitable way to simulate the rigid torsional member?. Thanks in advance.
Do you want to eliminate the torsion effects of slabs on beams? You can define a weightless rigid diaphragm (slab) and apply its weight manually on all beams.
If this is not the case you are looking for, please elaborate more.
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Hello Dear Researchers,
Should designers of earthquake-resistant buildings compare the period obtained by numerical analysis software (SAP, ETABS...), with the empirical period, and what is the relationship between these two periods, if any?
Thank you for explaining this to us.
Best regards.
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Hello
Recently I have heard that just SAP should be used for dynamic analysis of building and the results of ETABS are not valid for nonlinear dynamic analysis. I have done nonlinear dynamic analysis with Etabs software. Are the results acceptable?
Is there any evidence for this?
Both programs that you mentioned, could able to nonlinear analysis based on plastic Hinge, and both results are accepted. But you must notice that the operation that SAP2000 use to run nonlinear analysis is faster that ETABS and I strongly recommended that if you want to do nonlinear analysis for a frame structure use SAP2000 or higher programs such as PERFORM 3D instead of ETABS, especially if you want to do nonlinear analysis for your articles.
Best Regards
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how the shear force or bending moment diagrams are helpful for us for the design of structures in etabs? by just looking at these diagrams what do we get?
Using these diagrams lets you easily design your "element" for bending and shear forces applied to the element. However, Etabs do the design for you if you want.
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Which is better in your opinion ETABS - SAP2000 - SAFE
For analysis and design Steel and Concrete structure
All of my respected researcher - This area is not my specialisation but on the ground of learning material of construction software - https://wiki.csiamerica.com/display/etabs/Home
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I am performing nonlinear pushover analysis of RC building structure by auto hinges in ETABS and during analysis it shows, 'maximum number of total steps reached, subsequent results will not be available.'
How to resolve this issue. ?
What should be the value of target displacement to be used in the software?
Usually, after the "maximum number of total steps" sentence, the error states the sentence starts with "case: ....".
Could you tell us what it says after "case:"?
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hello all
I have to define a correctly nonlinear property for steel. what I must do for filing out the parts that I show in the picture?
dear @Alaa Taha Al-Najjar
You are right, thank you. I did the same
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hello everyone, i'm trying to model a 3D one story buiding with mass IIrregularity, the model has 4 elastic columns and rigid diaphragm. the model has no beam, so i used rigid diaphragm to equal dof of top nodes of columns. i use a model from a reasercher's article, he note that the modal frequences of first three mode is 1.16 , 1.96 , 2.37 HZ respectively. i builded the model in etabs and can verify my model with 0.33% error, but i couldn't verify model in opensees. i trying almost everythings to verify it but Unfortunately all my work was unsuccsesfull. in my reaserch i found that mass moment of inertia is principle parameter in model with mass IIrregularity, so i try figure out how modal analysis run in etabs and opensees and what difference between them. i found that etabs centeralized all masses in center of mass and then make mass matrix with 3 parameters like that [mass in x direction 0 0 0 mass in y direction 0 0 0 mass moment of inertia about hight axis ] but i wondering opensees generate mass matix for each node(also we can use center of mass for assigne mass) and also mass matrix for 6 dof model with 3 limited dofs (dofs limited in z direction and rotation about x ,y axis) is 6*6, so i'm confused to understad how opensees derrive mass matix and calculate modal frequences. i try both assigning mass to nodes and center of mass. in first condition i assigned mass moment of inertia like that mass n "mass in x direction" "mass in y direction" 0. 0. 0. "mass moment of inertia about height axis" etabs calculate mass moment of inertia with multiple each mass of nodes by distance of node from center of mass then sum these valus and attain mass moment of inertia abuot height axis. also we can use another formula for it. i try all patterns i found but i can't verify my model because i can't understand how opensees run modal analysis and make eigen values. for best understanding i upload my model in opensees and etabs. I'm so thankful if you can help me. with best regard
I hope my research will be of use to you
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Asslam-o-alaikum everyone,
The time for a building comes out to be 0.79 sec in ETABS, 0.822 sec in Perform 3d Software and by manual calculation it comes out to be 0.922 sec for the 1st mode using the modal mass of the building using the equation of simple harmonic motion. Why there is difference and are these values in acceptable range?
Thank you
Dear Hamza Cheema,
Period of vibrations of the considered building cannot be different from each other and it does not depend on which program for analysis you are using. The matter is that different programs are using the various factors in the design models to describe the behavior of the building under horizontal loading. You must consider this and bring the design models to the same conditions for any program. In this case the period will have the same value.
Best regards,
Prof. Dr. Mikayel Melkumyan (Armenia)
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Among all the softwares for analysis and design. Which is best for design of ribbed slabs and also raft foundations. I tried etabs but failed to get the results
SAFE is the ultimate tool for designing concrete floor and foundation systems
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Hello dears
Do I have to adjust the non-linear specifications of the steel property in ETABS manually? how can I do it correctly?
thanks
Dear Ali,
Greetings.
That depends on how you want to consider nonlinearity in your structure and the type of hinge you will use to capture P-M interaction. If you use fiber elements, material properties must be indicated carefully since all the stiffness (or flexibility) matrices result from integrating the material tangent stiffness over the element cross-section.
In the case of concentrated plasticity models, it is a little bit more complicated. When assigning P-M hinges, the software asks for how you want to define the yield (interaction) surface (yield surface is needed to relate the axial force and flexural moment to axial and rotational plastic deformation of hinges). If you choose to use the pre-prepared yield surfaces such as those introduced in AISC 360 or ASCE 41, you do not need to assign any material. However, if you chose the software itself calculates the yield surface, you need to assign the material properties accurately (for P-M-M is also the same).
Regarding the type of hardening, beams and columns are usually modeled following the kinematic hardening rule because they often show little cyclic hardening at the small cycles and considerable degradation in larger ones. Although components such as panel zones or EBF shear links show stable cycles with noticeable cyclic hardening (isotropic), for convenience, they are also modeled with the kinematic hardening rule.
I hope this could help.
BR.
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Dear all
I have a 2D steel frame that is subjected to nonlinear time history analysis.
7 acceleration records have been selected from the PEER and scaled to normal (1g) and then used for the analysis.
But unfortunately, no significant yielding has occurred in the frame's plastic hinges.
I am thinking that the PGA of my scaled record must not be sufficient to enforce hinges to yield.
A friend says that I have to multiply another g (=9.81) in my function.
Would you please teach me what is the right way?
Scaling the records should be in accordance with the target hazard level. If the hazard level of interest is the spectral acceleration at the fundamental period, Sa(T1), which is equal to 1g (for example), then scale your records so that they have the same value at T1.
Regarding the units of the time history, it must be in m/s2, so after scaling you need to multiple by 9.81 if the record is originally given in g units.
I hope this helps
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HI,
can anyone explain me how to get modal mass coefficient and modal participation factor as per ATC 40 from SAP 2000?
Hi
Modal analysis outputs can be found in the SM toolbox 6.0.4 instructions in the following sections:
74.30. ModalParticipatingMassRatios
74.31. ModalParticipationFactors
74.32. ModalPeriod
74.33. ModeShape
Best regards
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I am analyzing an existing steel structure with viscous dampers. However, when I performed a FNA analysis, the period of my first mode is excessively large, it's not realistic. Clearly, I have some error in modelling, but I can't pinpoint em out.
I have attached the modal period with their corresponding participating mass ratio.
Dear Kay Guanlao,
Pinpointing these errors can be really hard in some situations. First the model should be checked which will pinpoint any error based on connection between elements as Pouya Amirchoupani mentioned above. If that does not help your cause, you can try by animating the structure in that particular mode and see for any irrelevant deformed shape.
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I want to assign panel zones in my model. I am confused about how to assign it properly. I do not how to fill the P/Py for columns. Do I need to assign individually for each joint?
Thank you very much Amir Shirkhani sir for the pdf.
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Hello everyone,
I have imported the structure into perform 3d from etabs version 19 and assign the nonlinear properties at material or cross section level. When i tried to run the analysis, it says that structure is poorly conditioned or unstable but in the Etabs the structure looks fine and it is already designed building. Can anybody tell me how to solve this issue?
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This is the response spectrum that I have defined. I have chosen zone III f . and then I want to go for pushover analysis and see the pushover curve.. and see the Vy value generated for Zone III that I have chosen.
Now here Spectrum Source = Defined function (RS IS, that I have defined, ) But what to put at SF (m/sec2) ?? The value that is being displayed is by default. But what I have to put ?? I have to put something right ?? Please help.
It depends on I importance factor and R response reduction factor as well. i.e. (I*g)/R.
If you take I=1 and R=1.Then you have to use 9810 to convert units.
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Aslam-o-alaikum,
Hello everyone, i don't know why my monotonic pushover curve is not reaching the target displacement without any warning errors (but it reaches by enhancing tolerance) and why my different cases of cyclic pushover curve (with even enhanced tolerance) terminate without any prior error messages in ETABS? I am so fed up with it. Any help would be appreciated.
you can follow these steps :
1. increase the maximum null (zero) step per stage.
2. increase the maximum total step per stage.
3. Use event-to-even stepping: NO.
4. Decrease the convergence tolerance (relative).
why don't you use SAP2000?
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Hi guys. Just a question.
I am modelling my columns and beams in section designer. I noticed that in SAP2000, Mander's ( confined) can be modified inside Section designer including the ties spacing which can affect the stress-strain curve of the concrete.
But in ETABS, as I model the columns in section designer, I noticed that I cannot modify ttie spacing. Also, I dont know if nonlinear properties of concrete are already incorporated in the model automatically.
thoughts?
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Good day Sir/Ma'am, anyone here knows how to extract data from structural analysis software specifically from ETABS to MS Excel. Thank you and God bless!
Mehran Shahpari thanks, but I want to make a program that can easily check the analyzed structures without exporting the data to excel manually.
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Why Moment Resisting Frame Drift is more than Shear Wall Frame Drift, if they are in the same Seismic zone and the same quantity of material?
• Analyzing two Models ( Moment Resisting Frame and Shear Wall Frame) by Etabs.
• The same property and the same quantity of materials.
• Analyzing both Models in the same Seismic Zones.
• Both Models are the same geometry, the same height and Floors.
My question is:
Why Base Shear and Drift in Model of Moment resisting frame provided more than in Shear Wall Frame?
Due to the difference in the response modification factor, the base shear of both structures will not be the same.
Moment-resisting frames are more flexible than the shear wall; don't you think this is one of the reasons for the difference in the amount of allowable drift in these two systems?
Also, drift computations include the fundamental period, scaling modal drift obtained from modal response spectrum analysis, the seismic design base shear, torsional irregularities in structures, and the significance of P-delta effects.
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I have to do push over analysis on a 10 storey composite frame consisting of WPB steel embedded composite column. Since automatic hinge application is available only for steel and concrete members in Etabs. The only option is to apply a user defined hinge to the composite column. But while giving user defined hinges the input parameters while defining hinge should be consistent with my composite section. It would be helpful if anyone has idea on user defined hinges. I have attached the error message shown by Etabs.
@Amirhossein Heidari sir thank you for your response. Let me try it.
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I created Fiber P-M-M hinge where I pasted the fiber layout generated by section designer. I assigned it at the support of my column. However, I came accross this error once I run the program. It says it cannot generate fiber hinge data. Any ideas?
I tried the same procedure in ETABS but the analysis commenced.
Amir Shirkhani Thanks. apparently, the error came from my fiber data that are undefined. The first line is fixed to zero when I manually paste the fiber data. I deleted it and the model run without warning.
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While running non-linear analysis in ETABS I am getting the following error.
* * * W A R N I N G * * *
THE P-M-M INTERACTION SURFACE IS NOT CONVEX,
HINGE PROPERTY: C3H2,
RELATIVE ERROR = 0.010275, THE SURFACE WAS ABLE TO BE ADJUSTED
Can anyone of you who have faced a similar problem can share the reason or solution to fix this error?
Kay Guanlao Go through steps
1. Model your section using section designer
2.In Define > Define fibre layout > choose the number of fibres that you need based on your section > Check the box calculate moment-curvature using the fibres > click ok > then a pop up window comes with all the fibre data generated.
3. Ctrl+A to select the data of all the fibres ( remember the number of fibres) and ctrl+c to copy the data.
4. Go to define hinges - fibre-P-M2-M3 hinge
and follow the images as attached.
The images are named in the sequence, I didn't have a proper writing tool
hope it will help everyone.
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I want to nonlinear static analysis according to FEMA 440. But in etabs the only option available for the plastic hinge is by using ASCE 41-17 code.
Please let me know how to assign the hinge according to FEMA 440
You have to assign user defined hinges. And under the values of moment and rotation as per fema 440. Hope this can help you.
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Please compare various common programs, e.g., ETABS, TEKLA, etc. as well as the new generation of parametric ones, e.g., Karamba, Kangaroo, etc.
In my opinion, ETABS and SAP2000 are good for structural analysis and design and ABAQUS is a good software for research.
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According to the FEMA356 and ASCE41-17 (3.3.3.2), we have to push the structure 150 percent greater than the target displacement!
In this case, controlling the performance level of plastic hinge seems uneconomical. Why do the CODES refer to this paragraph at all?
Dear Mehran,
This criterion is to provide enough safety margin between the target performance point and the incipient collapse level of the whole structure. But why? here I try to mention primary explanations for such a regulation briefly:
1. As you certainly know, the procedure for calculating the target displacement of the structures is somehow inaccurate. It only gives an estimate of the experienced displacement by the system during an actual earthquake. You can quickly come to this conclusion from looking at the assumptions behind calculating the effective period (Te), modification factors (c0, c1, and c2), and see how simple and applicably-limited they are.
2. A nonlinear static analysis, what ASCE 41 calls NSP, is supposed to simulate the performance of structures during real earthquakes. However, in an actual earthquake, the structure may experience multiple cycles of inelastic deformation, which cause deterioration and degradation both in element and system scales that subsequently diminish the system's capacity. Therefore, the cumulative deformation (inelastic) experienced by a system, which is the primary source of damage, can be significantly more than its maximum one.
3. During a severe ground excitation, structures may experience dynamic instability, which is the consequence of softening the whole system. At this point, the structure becomes so soft that it can not withstand its own weight and start to deform laterally due to P-Delta forces without any external forces. Nonlinear static algorithms, both force-control, and displacement-control cannot capture such a phenomenon when evaluating the whole structure. Even if they could, the unpredictability and uncertainty in the parameters affecting the softening branch of the system performance (dynamic properties of the systems, soil property, hinge property, e.t.c.) still are too high that the code simply prefers to push this point farther to the systems performance level.
4. And more importantly, to encourage engineers to do nonlinear dynamic analysis (NDP).
These are a few reasons for increasing the target displacement when evaluation the seismic response of structures using NSP.
BR,
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I have performed a nonlinear static analysis in etabs for a steel braced frame. The pushover curve is linear and the model has shown any yielding. But the analysis has stopped before reaching the target displacement. I do not know why?
Please suggest what to do. Why the analysis is stopping if there is no plastic hinge formed before reaching the target displacement?
Complementing Karim Aljawhari 's comment, this problem may be related to numerical convergence issues (assuming the nonlinear hinges were assigned properly). When I performed pushover analysis in ETABS, I found out that if the target displacement is unrealistic big the software stops running before hinges are formed. My suggestion is to reduce the target displacement and check if the software will at least run until the target is reached. If the software still stops prematurely, then it probably means that you have to change some of the nonlinear analysis parameters.
I hope this helps :) Good luck
Rafaela
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Can ETABS design a non-prismatic concrete section?
I have been trying to make non-prismatic beam design in ETABS, but every time I try to run the concrete design module, an error shows.
I would really appreciate any tips or suggestions
Thank you very much in advance
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I want to perform wind analysis in ETABS for 30+ storey building and i am in confusion for what type of analysis should i prefer for exact answer?
I mean Linear analysis or Non linear analysis for Wind analysis?
Linear and Non linear analysis is used for earthquake but can we use it for Wind analysis?
I have wind Tunnel Test data available with me.
You can do non-linear analysis if you want, but it totally depends on your aims. According to some CODEs, you can do linear analysis for up to 50 story buildings.
Thus, specify the purpose of the design and refer to the restrictions of your country's CODEs.
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In your opinion which is the best software to analyse a 3D frame: