Projefct 1_Comparative study of different storey buildings for Seismic forces

Aim - To model and analyse the different kinds of buildings and conduct a comparitive analysis between the models based on different factors.

Introduction - Buildings oscillate during earthquakes whoch causes inertia forces to be developed in the building.

The intensity and duration of oscillation and the amount of inertia force depends on the features of the building which is called dynamic characteristics of the building.

Every building has a number of natural frequencies at which it offers minimum resistance to shaking induced by external effects and internal effects. These natural frequencies and asssociated deformation shape of a building constitue a natural mode of oscialltion.

The mode of oscillation with the smallest frequency is called fundamental mode.

These are the buildings which have to be modeled and analysed

Step 1 - Modelling building A

1 open ETABS and change the settings for model initialization as follows

Press OK and then select CUSTOM GRID SPACING option.

Custom grid spacing will be provided as follows

Press ok and select CUSTOM STORY DATA option to edit storys and input the following details

Grids have been created

In story 1, material properties will be edited as follows. First will be M30 grade concrete.

We need to add rebar for longitudnal reinforcement as follows

we need to add rebars again for shear reinforcement

Materials have been added. we need to add sizes of beams, columns, slabs whoch will be done from the define tab.

Column size 400x400 has been added

column reinforcement data will be as follows

Beam data needs to be added as follows

reinforcement data will be added as follows.

slab will be added from defin tab by selecting slab sections and giving it the following properties

columns have been added using quick draw columns command

beams are added using quick draw beam command

going to story 1 from plan option and keeping similar stories option on slabs have been created on story 1 and rood

go to base plan option, slect one story option

select all the joints

from assign tab the restraints will be added as PINNED

the load patterns will be added from the define tab in the following way

we will also be modifying the lateral loads of the seismic forces which will be done from the modify lateral load button

EQ x load is modified in the following way and chaging the criteria as follows

similar criteria will be addded for all the remaining earthquake loads

we need to assign the live loads which will be done from the assign tab

by keeping the plan on story 1 and keeping similar stories option on, live load is added from the assign tab as follows

live load has been added

the dead load hsa to be applied on the beams which will be done by selecting them from the SELECTtab and then selecting OBJECT TYPE option

from assign tab, we will select FRAME LOADS and then DISTRUBUTED

the load has been addded

the MASS SOURCE will be modified from the define tab as follows

we need to add load combinations which will be added from the define tab as follows

the combinations have been generated

we will add diaphgrams by selecting the floor from select tab

the from assign tab we will select shell option which wil open diaphgram dialog box as follows

after selecting the D option, we will press apply

diaphgram has been added

from the analyze tab we will select, check model option and select all the options as follows

model has been checked

we need to run analysis on the model by hitting F5 or selecting the run analysis option

select show deformed shape option the following dialog box will open

for eq x

mode case option selection

from the display tab, select show tables option select the following options

modal mass participating ratio for building A is ready

Modelling for building B

unlock the model and edit the story data option as follows

new model has been checked

model is ready for analysis

analysis has been done

modal mass participating ratio for building B

Modelling for building C

unlock building B

from section properties we will change the column size

from the select tab we will select the columns and from assign tab we will change the columns to 300x550 size

we will analyze the mode now. it gives the following results.

after running the analysis it gives the following results

model mass participation for building C

Modelling for building D

unlock building C

select the columns from select tab

from assign tab, we will assign the local axes as follows

columns are oriented as follows

after analyzing the model the following message appears

the model has been analysed

model mass participating ratio for building D

Model for building E

copy building model A

open the edit grid and story data window

edit the info in the following way

we'll create copy of column 400x400 from define tab and give new properties as column 600x600

from view tab we will set building limits as follows

building view limit has been set

from set view option we will switch off beams, joints, floors so only columns will be visible as follows

from select tab, select all the columns

from assign tab and selecting setion properties, we ill assign column size as 600x600

we will switch on the closed view data the result is as follows

analyze the model

after running analysis

model mass participating ratios

modelling for building F

copy model E, unlock it

from edit tab then view tab

edit building views limit as follows

select all the columns

from the assign tab assign the columns as Column 600x600

go to view tab then building views limit

select show all and go to set diplay option

switch on beams joints floors

analyze the model it will give the following message

we will run analysis on the model

mass participating ratio for building F

Model for Building G

copy building model F

unlock it and make the changes to storys from edit tab

we will modify story data as follows

from define tab section properties

select the Column 800x800 section and copy it

make the changes as shown below

from view tab, building views limit will be set as follows

slect the columns from select tab

assign the section properties as C 800x800

it will be applied from base upto 10th floor

from view tab, building views will be set as follows

select the columns from select tab

from the assign tab, section C 400x400 properties will be applied

column will be applied from 21st story upto roof

from building views limit, show all option will be enabled

beams joints and floors will be switched on now

check model

from the analyze tab it will show the following results

analysis will be run on the model

modal mass participating ratio

Model for building H

copy building model G

unlock the model

from view tab, building views limit will be set as follows

columns will be selected from select tab

and from assign tab select column 800x800

it wil be applied from 11th storey upto roof

select building views lmit

select show all

it will give the following results

the model will be analyzed

it gives the following result

run analysis on the model

Modal mass participating ratio for building H

model for building J

copy building model H

unloack the model

select object type, select floors, hit close

we have to imposed load 10% greater than building H

go to assign, shell loads, select uniform and change data as follows

the imposed mass has been increased by 10%

we will analyze the model

model is ready for analysis

the modal mass participating ratio for building J is as follows

model for building K

we will follow same procedure for modeling new building and make some changes like assigning imposed mass 20% greater than building H

from shell loads, select uniform

and make changes as follows

click ok and imposed mass has been increased by 20%

analyze the model

modal mass participating ratios for building K

Effect of stiffness on T

	Building E	Building F
T(X1)	1.097	1.735
T(Y1)	1.064	1.678

	Building G	Building H
T(X1)	4.17	4.416
T(Y1)	3.988	4.222

time period of building F and h is greater tham E and G because because of column uniformity in buildings F and H

effect of mass on T

comparison of natural period of building H,J and K

	H	J	K
T(X1)	4.416	4.425	4.435
T(Y1)	4.222	4.231	4.240

all the above buildings arehigh rise building. the only difference is that J and K has 10% and 20% more mass than building H

time period is directly proportional to mass so in J and K mass has increased

Effect of building height on T

	A	B	F	H
T(x1)	0.5	1.036	1.735	4.416
T(Y1)	0.488	1.01	1.678	4.222

as building height increases mass increases but overall stiffness remains same

Effect of column orientation on T

	B	C	D
T(X1)	1.036	1.145	1.12
T(Y1)	1.01	0.929	0.953

Factors influencing mode shape of oscillations