Project 1_Comparative study of different storey buildings for Seismic forces

AIM:- to do a comparative study of 10 different buildings for the following aspects

• factors influencing the dynamic characteristics of the building
• factors influencing the natural period of a building
• factors influencing the mode shape of oscillations

GIVEN DATA:-

• height of the story as 3m
• height of the plinth as 1.5m
• dead load on the beam from wall infill is 10KN/m
• live load is taken as 3kn/m^2
• the thickness of the slab as 150mm
• the base of the structure is pinned
• grade of the concrete as M30
• grade of the reinforcement as Fe415

• DETAILS OF EACH BUILDING ARE GIVEN AS FOLLOWS

step 1:- to create grid and story data

• open etabs> new model
• give the input as per the Indian standards
• go to custom grid data
• and modify the parameters
• go to custom story data and modify the parameters

step 2:- define material properties

• go to define the menu
• click on material properties
• add concrete and reinforcement details as given in the question

step 3:- to add details of structural elements

• go to define
• Click on section properties> frame sections
• then click on add new properties
• add size and shape of beams and columns

• go to define
• Click on section properties > slab sections
• add the slab element with a thickness of 150mm

step 4:- to add loads and load cases

• Go to define
• click on load patterns
• add new loads cases
• modify the lateral loading parameters add a zone, influence factor for the seismic loading
• Click on OK

• add load combinations
• go to define
• select load combinations
• click on add default design combinations
• select load combination as concrete fame design

STEP 5:- to model the structure

STEP 6:- To assign loads

• select the elements for which loads should be assigned
• go to select> properties
• frame sections> beams
• then go to assign
• frame loads
• then give the input as 10kn/m as wall dead load
• then click on ok

• select all the slab elements
• go to assign
• click on shell loads> uniformly distributed loads
• give the input for the live load as 3
• then click on ok

• then assign mass source for the structure
• select all the slab elements
• go to assign a tab
• click on shells
• select diaphragms

then click on run analysis to get the mode points, time periods, and deformations under the assigned loads

RESULTS:-

• modal periods and frequencies table

• modal mass participating ratio table

MODEL B

• given size of the beam 300 x 400
• size of the column 400 x 400
• no of storey 5
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

• modal periods and frequencies table

• modal mass participating ratio table

MODEL C

• given size of the beam 300 x 400
• size of the column 550 x 300(rectangular column oriented along X-axis)
• no of storey 5
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

• To orient the columns along x-axis
• select all the columns
• go to assign
• frame> local axes
• given the angle as 90

• then assign the diaphragm loads and run analysis to check the deformations

• modal periods and frequencies table

• modal mass participating ratio table

MODEL D

• given size of the beam 300 x 400
• size of the column 550 x 300(rectangular column oriented along X-axis)
• no of storey 5
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

DEFORMED SHAPE OF THE STRUCTURE

• modal periods and frequencies table

• modal mass participating ratio table

MODEL E

• given size of the beam 300 x 400
• size of the column 600 X 600 (from base to story 5)
• size of the column400 x 400 (from story 6 to story 5)
• no of storey 10
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

TO ASSIGN DIFFERENT COLUMN SIZES AT DIFFERENT LEVELS

• firstly assign the column sizes as 600x600 for all storys
• then go to view
• select set building view limits from story6 to story 10

• then select all the columns
• go to assign >frame sections
• select the column size as 400x400
• click on OK

• modal periods and frequencies table

• modal mass participating ratio table

MODEL F

• given size of the beam 300 x 400
• size of the column 600 X 600
• no of storey 10
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

• modal periods and frequencies table

• modal mass participating ratio table

MODEL G

• given size of the beam 300 x 400
• size of the column 800 X 800 (from base to story 10)
• size of the column 600 x 600 (from story11 to story 20)
• size of the column 400 x 400 (from story21 to story 25)
• no of storey 25
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

firstly create a 25 story model with column size as 800 x 800 at all levels

• select set building view limits from story11 to story 20

• then select all the columns
• go to assign >frame sections
• select the column size as 600x600
• click on OK

• similarly assign the column size as 400 x 400 for the top 5 storeys

• ensure that the live loads and dead loads are assigned
• then select all the slab elements
• go to assign
• select shell> diaphragm
• then click on OK
• then save the model and run analysis to view the deformations

• modal periods and frequencies table

• modal mass participating ratio table

MODEL H

• given size of the beam 300 x 400
• size of the column 800 X 800
• no of storey 25
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

• modal periods and frequencies table

• modal mass participating ratio table

MODEL J

• given size of the beam 300 x 400
• size of the column 800 X 800
• no of storey 25 with imposed mass 10% larger than the model H
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

• modal periods and frequencies table

• modal mass participating ratio table

MODEL k

• given size of the beam 300 x 400
• size of the column 800 X 800
• no of storey 25 with imposed mass 20% larger than the model H
• height of the storey 3m
• height of the plinth 1.5m
• similar to the model A construct a structure as per the given data
• and run analysis to view the deformations

• modal periods and frequencies table

• modal mass participating ratio table

RESULTS:-

• EFFECT OF STIFFNESS ON TIME PERIOD

time period of building E with uniform column size is 1.208sec

time period of building F with varying column size is 1.25sec

Conclusion:- comparaing the time period of building E and F we can conclude that there is no effect of stiffnesss on time period

• EFFECT OF BUILDING HEIGHT ON TIME PERIOD

time period of the building A with 2 storey is 0.345s

time period of the building B with 5 storey is 0.714s

time period of the building F with 10 storey is 1.255s

time period of the building H with 25 storey is 3.37s

CONCLUSION:- we know that the height of the building is directly proportional to time period we can conclude that if height of the building increases time period also increases

• EFFECT OF COLUMN ORIENTATION ON TIME PERIOD

time period of the building B with column size 400 x 400 is 0.714S

time period of the building C with column size 550 x 300 is 0.789s

time period of the building D with column size 300 x 550 is 0.772s

CONCLUSION:- we can conclude that oientation of the columns influence the magnitude of lateral deformation

• EFFECT OF FLEXURAL STIFFNESS OF STRUCTURAL ELEMENTS ON MODE SHAPES(considering the building B)

flexural stiffness of the beams close to zero inertia (considering 5% of inertia) is 2.482s

flexural stiffness of the beams with 100% of inertia is 0.741s

CONCLUSION:- inertia of the beams which influences the stiffness of the beam increases the time period

• EFFECT OF AXIAL STIFFNESS OF VERTICAL MEMBERS ON MODE SHAPES
  

consideing the building H for example

time period of the building H (regular) is 3.37s

time period of the building H (with zero axial area) is 6.23s

EFFECT OF BASE OF FOUNDATION ON TIME PERIOD

time peroid of building B with pinned supports is 0.741s

time period of the building B with fixed supports is 0.648s

CONCLUSION:- we can conclude that if the base of the structure is restrained the effect of time period on the mode point will be less