Challenge

Modelling of 25 storey building with the specified properties using ETABS

ETabs modeling of 25 story building

AIM

To model and analyze a 25 story building with given specification and to cross-check the parameters as per IS 1893 provision

PROCEDURE

Choose the built-in settings option and select the display units and codes
After model initialization select the grid and story inputs from the New model quick templates dialogue box
In this dialogue choose grid spacing and custom story data which is used to provide the inputs specified above
Enter X grid data at a distance of 4meter and y grid at as 4 at a distance of 4m

Now edit the stories by using the user-defined story input, 26 stories are incorporated
Story 1 has been labeled as master story and all above levels are labeled similar to that

Select material properties under the defined tab
Define the materials of concrete M30 grade and steel of transverse of reinforcement as 415 grade and longitudinal reinforcement as 500 grade

Select section properties under the defined tab
Click on the frame section and create the new property as beam and input the values as 300*400mm

After the defined properties for the column as 800*800 and slab thickness as 150mm

Using the membrane property, slab size 150mm has been added to the list
Membrane property will help to consider only slab weight and floor weights in analysis of structure while no stiffness component of flange advantage are considered during the calculation

Now draw a column of size 800*800mm at the intersection of the horizontal and vertical grid and beam with a quick draw tool keeping all stories on

Beams drew using quickdraw beam tool keeping all the stories on
Using the quick draw floor option, all the slabs have been modeled keeping similar stories ON

Now define the load pattern: Click on the define data and click on load pattern
Define the loads like dead load, live load, brick load, earthquake load in the X direction and positive X and negative X, and the same loads in the Y direction also. Mention IS codes of respective loads

Click on modify lateral load, set range from base to 25^th stores and seismic zone factor as 0.36, importance factor 1.25, and period 0.5 seconds

Similarly, add a live load of 10KN/m^2 on all the beams
For that select all the beams from select object type beams
Go to the frame load and click on the distributed load and enter the value as 10KN/M^2

Now create the diaphragm by going to the assigned tab then shell and selecting diaphragms

Analyze the model using analyze option then click on check model, the modeled structure is verified without errors and warnings

Using analyze>run analysis, the model is analyzed and deflection patterns, BMD/SFD patterns are cross-checked logically. It is understood that the worked model provides reliable results

RESULT

Now click on Display>show tables>Analysis results>Structure out>Model information>modal periods and frequencies.
The periods for fundamental model-1Y direction and fundamental Mode-1X are noted from the table and are as follows

T*1=3.746sec and Ty1=3.913sec
Display>show tables>alaysis results>structure output>modal information>modal participation mass ratios.
From the table, the natural period for mode-1 and torsional; DOF is noted as following

T*1=3.581sec Ty1=3.3sec Txy1=2.609sec
So from the result, it is clear that the torsional period is less than two translational time periods as required by IS1893 provision table 5
When we add three-mode mass ratios we get 0.9044 which means the first three modes of seismic oscillation contribute more than 65% of building weight as per Etabs analysis
The story drift for serviceability Base shear Case is tabulated from the following tool oaty
Go to display> story response plot
Keeping load case to EQY and switching to max story drift the maximum drift value noted is 0.0020

So as per clause 7.11.1.1, the maximum inter-story drift militates to 0.004 for each story height
But our value is 0.0020 which is within the code limits
CONCLUSION- The modeling is completed and analyzed in ETabs and the results are within the given ranges

Ship work like this
in your own course.