Modelling of 25 storey building with the specified properties using ETABS

AIM-

Model a 25 storey building on ETABS

with structural properties as specified

below. Ground floor or plinth floor level

can be taken at a height of 1.5 metres

from the base. Each of the successive

25 storeys has a storey height of 3 metres.

INTRODUCTION -

ETAB OR ETABS they meaning are same .

it is extendended 3d analysis of building

system.

it is engineering software product .

-that caters to multistorey building

design and analysis .

-ETabs offers single user interface.

-to perform modelling .

analysis , design , and reporting .

PROCEDURE -

-STEP :1

-Open etabs

-click on new mode l

and choose use built in setting with option .

-set display unit is metric SI as per

requirement .

-then click ok .

-new dialouge box will apper .

-select custom grid spacing and

then select edit grid data

-new dialouge box will appear

then enter x grid data at a distance

of 4 meter distance .

-

-click ok

-then select custom story data

and select edit story data .

-add story up to 25

and give input plinth height is 1.5 m .

-and all other story height as 3m .

-

-then make story 1 as master stroy

and all other storey similar to 1

-then our building model is generated .

-

STEP -2

Select material properties

select define from that select

material properties .

-new window will apeear and

from that select add new new material.

-

-new windows will appear now

define materiakl type concerete

and grade M30 .

-Similar define rebar property .

-

go to define tab , select section properties

and from that select frame properties .

-new window will appear , in that

select add new property .

-then select rectangular concerete

section , rename it as B 300X400

-Change the property as M30

AND changed the size as B 300 X 400

-Similar add column section properties .

-then go to define select section property .

from that select slab section .

-new windows appear

rename it slab 150 , modelling type

as membrane and changed thickness

as 150mm .

-Draw structural members .

for frist select mode as all stories

at right bottom corner .

-then select quick draw column

and changed property as C 800X800

-Place the column at every intersection

of grid

-then select quick draw column /beam.

-changed property as B 300X400

-PLACE beam at all grids .

-now we need to changed mode as similar

stories at bottom of window .

-in order to avoid slab placement

in plinth level .

-

-select quick draw floor /slab and

draw slab sections

-select assign and click on joint select

pinned support

-fix pin support at base .

CLICK on define from that select

the load pattern .

-define load like dead load , live load

brick wall load and earthquake load

in x direction and eccentric earthquake

load in position x and -x and

same load in y direction also

mention is code of respective load .

-click on modify lateral load

set range from base to 25th

storey , changed direction

and eccentricity , seismic zone

factor as 1.25 and time period

as .5 sec .

-do same for all earthquake loads .

STEP

ASSIGN LOADS

-to assign loads , select similar stories

at bottom of windows

-then select members .

-after go to assign tab > shell load .>

uniform

-A new window will appear in that

select live load and give value as 3 kn/m^2

-click on apply

--then select all story at the bottom

of the windows and select all beam

under select tab .

-after that do assign tab > frame load

.distributed .

-enter value 10 kn/m2

-go to mass source from define tab.

modify mass source and check specified

load pattern .

-add load pattern and assign the model.

ok .

STEP

DEFINE LOAD CASES .

-Click ok .

-go to define >load combination .

-click on add default design combos

and select conecrete frame design .

ok.

-frist select slab .

then go assign tab ,select shell

and click on diaframe created sucessfully .

-check model , modelled structure varified

without warning and errors .

-then go analysis tab and run analysis .

RESULT -

MODAL 1 TIME PERIOD =4.435 SEC.

MODEL 2 TIME PERODE =4.408

• Display--> show tables-->analysis result-->structure output >modal information > modal participation mass ratios
• From the table the natural time period for mode 1 and torsional DOF are noted as follows

• Tx1= 4.435 seconds, Ty1=4.408 seconds= and Txy1=3.303 seconds
• So from the results it is clear that the torsional time period is less than two translational 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 0.8042 which means the first three modes of
• seismic oscillation contribute more than 65% of building weight as per ETABS analysis
• The storey drift for seviceability base shear case (EQxor EQy) is tabulated from the following tool path
• Then go to display-->story response plot
• keeping load case to EQy and switching to max story drift the maximum drift value is noted as 0.0016
• Keeping load case for EQx and switching to max story drift the maximum drift value noted is 0.001492

• so as per the clause 7.11.1, the maximum inter storey drift is limited to 0.004 for each story height.
• But our value is is within the code limits