Civil Engineering Association

Hello Friends,
I am new to Etabs. I have following question
1- If i want to apply seismic load some percentage of self weight. how can i do so? for example i want to apply earthquake load of 0.2g ( that is weight of each element is multiplied by 0.2 and applied at centroid of that element in global X or Y direction as required), how can i do so in Etabs??

Hi,

There are two way to do that:
1.Explicitly build FE model (with elements and joints - expl. mesh) and manually assign joint masses (calculated in advance) along each degree of freedom. This way is not practical for large models, but is suitable for comparative study.
2. More practical and fast is to use automatic mesh options for elements and program options to define mass sources:
* Firstly - Assign/ Frame (or Area)/ Automatic Frame/Line/ Automatic Frame Subdivide... . Preview and check mesh (model).
* Define /Static Load cases - one case with self weight included (with self weight multiplier or explicitly assigned as load) - e.g. LSw1
*Define/Mass Source/... From loads - define "Mass Combination" - define mass multiplier for loads - e.g. Lsw1 with multipl. =0.2.
Other two options are also possible - they are connected with mass properties - material mass and additional line and area masses.
Always check after analysis calculated masses. Above proposed way of assigning mass from loads suffer from missing info for mass in advance ( before analysis).
Regards

Try this....

First... define mass source --From Loads--Dead whit multiplier 1...
with live load aplied factor from codes from your country...

second.. for static analysis...Define-- static load cases... quake...user coeficient...and. base shear coeficient use...0.2g and ready.... remember static analysis shear V = W Cs, Cs = 0.2g your case...

regards.... sorry bad english

i need help,
in Brazil we use the NBR6118 design code of concrete, the code is very similar of Eurocode 2.

i'm try to design a model of a simply crimping beam with a uniform load.
the flexural diagrams are ok, but in the design, the midle of beam is designed with a major moment.

anyone know why?

Hi all,
Stiffness modifier can be found under "Effective Stiffness" in ATC40 or FEMA356. What I remember are 0.7 and 0.5 for flexural of column and beam, respectively, and 0.5 for shear of column/beam. However, 0.7 of flexural modifier value could produce underestimate deformation result. To approach more closely, you can use program i.e. XTRACT, RESPONSE2000 or CUMBIA (for free but Matlab script). By program you may find effective stiffness up to 0.3 for column.

Cheers
adekajeng

Did any body notice the following errors in ETABS...how to correct them!

1) if you once enabled the dynamic analysis and put the response parameters in etabs and run the analysis.....and then you want to remove the dynamic thing and want to solve it in static by removing dyanmic analysis tick mark in analysis options and deleting the response spectrum cases spec x and y and its function now u run the file and you will not see the seismic calculations in FILE>PRINT TABLES>SUMMARY....
no calculations about Time period etc...why is it so?

2)if your default units are say kip-ft....you goto FILE>PRINT TABLES>SUMMARY and u will see the seismic calculations for base shear depedent on seismic weight W in kips.....like

1) V=0.002W
2) V=0.006W
3) V=0.1W

now the interesting thing...you change your units from kip-ft and then goto the same summary...you will see that ETABS will give you wrong calculations for the base shear...lolx

Hello Friends,
I'm facing a problem in generating a trapezoidal section in etabs. The section is that of a waffle rib having web width of 8" at top and 7" at bottom. I used an SD section in etabs but that is designed only for columns. For beams, i can use this section only for analysis but it is not designed by etabs.

Waiting for help.
Thanks in advance.

Please explain the attached picture of section cut and place the moments on the structure. I dont understand the RIGHT and LEFT side and the 1,2 and z moments and forces.

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Sorry the image is here

The following are the rules for section cuts

1. For cuts in plan (slab results) the default 1 axis is in the direction of the cut and
F1 is in-plane shear
F2 is axial force
FZ is out-of-plane shear
M1 is out-of-plane moments
M2 is twisting moments
MZ is in-plane moments.

2. For horizontal cuts in elevation of XZ walls (pier results) the default 1 axis is in the X direction and
F1 is in-plane shear
F2 is out-of-plane shear
FZ is axial force
M1 is out-of-plane moments
M2 is in-plane moments
MZ is twisting moments.

3. For horizontal cuts in elevation of YZ walls (pier results) the default 1 axis is 90 degrees to X direction and
F1 is in-plane shear
F2 is out-of-plane shear
FZ is axial force
M1 is out-of-plane moments
M2 is in-plane moments
MZ is twisting moments.

4. For vertical cuts in elevation of XZ walls (spandrel results) the default 1 axis is in the X direction and
F1 is axial force
F2 is out-of-plane shear
FZ is in-plane shear
M1 is twisting moments
M2 is in-plane moments
MZ is out-of-plane moments.

5. For vertical cuts in elevation of YZ walls (spandrel results) the default 1 axis is 90 degrees to X direction and
F1 is axial force
F2 is out-of-plane shear
FZ is in-plane shear
M1 is twisting moments
M2 is in-plane moments
MZ is out-of-plane moments.

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It is simple statics. For equilibrium to exist, the difference in left and right should be almost zero. But in a finite element program, there may be slight differences.

I would suggest you to manually mesh the slab instead of using the auto mesh because it can create some differences. Also, if you can, you should use the section cut forces instead of relying on the output.

The ETABS User Manual has a good section on SECTION CUTS. I can post it here if you don't have it.

Please post the section cut documentation