ETABS_Errors Indication

Microsoft Word - ETABS Tips, Tricks and Model Checking

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ETABS TIPS, TRICKS and MODEL CHECKING [By coolest bliss] [ www.coolestbliss363.blogspot.com

] [forum.civilea.com[

I-STABILITY ERRORS 1‐LAST ANALYSIS RUN LOG After running your model, please always check your analysis log for global errors. These errors should be of magnitude 10e-10 or smaller. If you find larger errors, please unlock your model and check your model.

2‐CHECK MODEL Another very important tool in ETABS for model checking is found under Analyze menu and that is “Check Model” option. These checks are:i-

Line checks

ii-

Point checks

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Area checks

iv-

Loading and mesh checks There is also an option to enter tolerance value for these checks to be performed. Be default the value is 0.001m or 1mm. You can go as far as 0.025m or 25mm, if you are having real

http://dc300.4shared.com/doc/MSQpZq68/preview.html

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trouble in your model. Line, point and area checks verify for overlaps and any area or line not connected to points or nodes. Sometimes area overlap problem arises when you model has curves. To save time and to work with each check efficiently, you can check your model for each check separately.

After pressing “OK” button, ETABS will start to check your model and then it will display a windows showing you the list of all the errors. This report will also be saved as a te t file in your model folder. If there is no error, you are lucky, ETABS will display “Model has been checked. No warning Messages”. You should always check your whole model, not ust the selected ob ects.

An important tip here is after closing the warning window, the BAD ELEMENTS will be selected by ETABS automatically. Do not click anywhere, ust go to ASSIGN menu Group and assign these BAD ELEMENTS a group for selection. Now work on these errors by any mean you want. After you are done select the same group and check the model only for the selected group selection. In this way you will save time on model checking option. If you get warnings again which will of course be less than previous warnings unless you made some blunder assign them again the group and so on until you have zero warnings. Then check the model as whole for the final time.

3 ‐SUPPORT YOUR A B SE


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Always make sure, your model base has supports, pinned, fi ed etc, otherwise your model is obviously unstable. When you run the analysis and find that the warning is related to negative stiffness values found in model, base support could be one of the problems, ust unlock the model, provide base supports and re-run.

ETABS does not check the supports for your model. If for e ample you have applied the supports for the base of model but have also drawn some lines in space with no supports, Checking the model will not return any errors, rather it will say there are no errors unless you have other errors, like overlapping etc.

Now, you have run the analysis and found that it displays warnings as shown here:-


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These errors are about negative stiffness and loss of accuracy. Loss of accuracy error is okay, but if the no. of digits lost e ceeds 11, ETABS stops the analysis process. Your model deformed shape will also be affected. It will only show the animation of the BAD ELEMENTS, because ETABS tries to give the deformed animation of all the model elements. Now if some element is ill conditioned and deforming like infinity then obviously other GOOD ELEMENTS deformation small as compared with infinity will be very negligible as compared to these BAD ELEMENTS deformation. So there is something wrong with your model. PRO IDE S PPORTS.

II-CON IG RATION/CONCEPT AL ERRORS 1‐FRAME OUTPUT STATIONS rame output stations is a useful command and it basically allows you to enter no. of segments or spacing of segments of a frame section beam, column etc at which you want the output shear, moment, steel etc. . By default, there are 3 stations start, mid and end of a frame section. As you increase the no. of segments or decrease the spacing of segments, there will be obviously more and


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more calculations and your model run time will be increased. or a refine model, enter ma imum spacing to be 150mm or 6”.

2‐FRAME RELEASES rame releases is a special tool for releasing the frame for torsion, moment, shear, load etc. There is a limit on the combination and you must check this in ETABS help file. or e ample, only moments can be released on both ends, all other options a ial load, shear and torsion can be only be released at only one end. It will now allow you to release on both the ends. Try changing shear force 2 and moment 3. Select the desired releases and press “OK”, or select “No releases” option to unselect all. You will see 2 green dots and either ends of frame for which you have released the shear, moments etc. This option is generally applied to a secondary beam resting on another primary beam. You can release both moments for this beam on both ends.


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3‐ANALYSIS OPTIONS

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ETABS_Errors Indication

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