Modelling of 25 storey building with the specified properties using ETABS

1.Ans

AIM

To Model a 25-storey building on ETABS with structural properties as specified below and to cross check the parameters as per 1S -1893 Provisions.

PROCEDURE

STEP-1

• Go to ETABS software click on the file menu

• click on create new model option
• A new model dialogue box will be open as model initialization.
• Select Use Built in Setting with option

• select display unit as Metric SI (or as per your requirement)

Step-2

• Next a new dialogue box will appear
• select grid and storey inputs and custom story data Enter X grid Data at a distance of 4 meter and Y gird data at 4-meter distance

• Now edit the stories by using the user defined storey Input

• plinth at 1.5-meter height 25 storey with 3-meter height each. Storey, I have been labelled as master storey and all above levels are labeled similar to that.

• I have make story1 as master storey and all other story similar to story1.

Step-3

• Select material properties under the define tab

• Define the materials of concrete M30 grade and steel of transverse reinforcement as 415 grade

Step-4

• Select Section properties under the define tab

• Click on the frame section and create a new property as beam and input the values as 300x400mm.

• After the define properties for the column as 800x800 and slab thickness as 150mm

Step-5

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

• Now draw a column of size 800x800mm at the intersection of the horizontal and vertical grid and beams with quick draw tool keeping all stories on.

• Beams drawn using quick draw beam tool keeping all the stories on

• Using the quick draw floors option all the slabs have been modeled keeping similar stories ON.

• Select assign and click on joint select pinned support.
• Fix the pin supports at the base

Step-6

• Now define the load patterns: click on the define to and click on load patterns.

• Define the loads like dead load, live load brick load earth quake load in x direction and positive x and negative x and same loads in the Y direction also Mention IS codes of respective loads

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

• Do the same for all the earthquake loads.
• Assign the loads and select similar stories. Click on shell load under the assign tab.

• Click on live load and give value as 3kn/m^2.
• Click on apply.

• For the root we will take only 50% of the live load.
• Similarly add 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 go to mass source from the define tab.

• Modify the mass source and tick mark the required loads

• Add load patterns and assign to the model

Step-7

• Define the load cases

• Click on the load combinations

• Click on the add default design combos.

• Now Create Daiphagram

• go to assign tab
• select shell and click on daiphragram

• Analyze the model using analyze option then click on check model the modelled 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.

RESULT

• Now click on Display-show tables Analysis results structure output Modal Information-modal periods and frequencies.
• The time periods for fundamental mode-ly direction and fundamental Mode -1 direction are noted from the table and are as follows

• Display show tables analysis results structure output-modal information-modal participation mass ratios

• From the table the natural time period for mode-l and torsional DOF are noted as follow.
• So, from the results it is clear that the torsional time period is less than two translational time period as required by Is 1893 provision table 5
• When we add the three-mode mass ratios we get 0.90 which means first three modes of seismic oscillation contribute more than 65% of building weight as per ETABS analysis

• The storey drift for serviceability Base shear case (EQX or EQY) is tabulated from the following tool path.
• Go to display Storey response plot
• Keeping load case to EQY and switching to max story drift the maximum drift value noted is 0.004.
• So as per the clause 7.11.1.1, the maximum inter storey drift is milited to 0.004 for each storey height. But our value is 0.0020 which is within the code limits.

CONCLUSION

• Hence, the modelling is completed and analyses in ETABS
• The results are within given ranges.