Project 1_Comparative study of different storey buildings for Seismic forces

 PROJECT:-  Comparative Study of Different Story Buildings for Seismic Forces

 AIM:- To Model and Analyze Multiple Buildings With different floor levels and design parametrs using ETABS software and compare the result to understand their overall seismic behaviors 

 

INTRODUCTION:

• The structural configuration of the building plays a major role in determining the overall response during an earthquake. Different building geometries behave differently when induced by the same seismic forces. Hence, it is very important to properly understand the response of buildings related to their structural configurations for a safer design approach.
• Therefore in this project, we have modeled different buildings with varying geometries using ETABS. Furthermore, their responses are analyzed with the help of the software and the results are then compared to grasp an understanding of the structural behavior of buildings with different storeys.

 

 

PROCEDURE:-

1. BUILDING  A (G+2):-

• Open the ETABS software.
• Click on New model to create new model

• After choosing a new model a dialogue box will appear as model intialization.
• Choose the built-in settings option and select the display units and codes as below;

 

• In the "New model quick templete" select the "custom grid spacing'  as below 
• Make  X grid data at a distance of 4 metre and Y grid data as 4 at a distance of 4 metres

• Then in same dialog box itself click on  "custom story data "
• Then make make first level after base as "plinth" level from 1.5 m from the base 
• Rest take as its in height prespective 
• Click on the "FLOOR 3" and add 22 stories to make 25 storey building and name it all sties after plinth as the  STOREY 1,2 And click OK 

• After the our ETABS screen appear as below;

DEFINING MATERIAL PROPERTY:-

• Now , click on define choose "material properties."
• To create material like concrete and steel to be used in the model.
• Define the materials of concrete M30 grade and steel Rebar reinforcement as 415 grade

• Now we successfully added the material properties as below;

DEFINING BEAMS AND COLUMNS:-

• Select "Section properties" under the" define" tab.
• Click on the "frame section' and add new property as beam and input the values as 300*400
• Go to the "reinforcement"  and give design type and rebars as below
• Also look at the property modifier if we work in as ultimate project (make inertia for 0.35 for beam)

• Similarly add the colums as beams
• Define properties for the  column as 400*400 

• Now we successfully added the frames i.e columns and beams

DEFINING SLAB:-

• Now select "Section Properties" under "Define" Tab.
• Select "Slab Sections".
• Select Add new properties in Slab Properties.
• (make modelling type as membrane)

• Now we successfully added the slab

LOAD PATTERN:-

• Now we are adding "load pattern"
• go to the "define" click on "load pattern "
• Add the load as per below showing ;
• Make sure the give direction and eccentricity to the Eqx and EqY loads 

MASS SOURCE:-

• Mass should be considered for seismic lateral movement
• Go to "define" tab select mass source
• Select modify/show "mass source"
• Slect speified load patterns
• Considered deal load as 100%, LL-25%, wall load or super DL-100% as per code

LOAD CASES AND LOAD COMBINATIONS:-

• Check for "load cases" as we assign properly or not, go to "define" tab and select "load cases"
• Go to "define" tab and  select "load combinations"
• Select add default design combo
• Select following properties and press ok

 PLACING THE BEAMS AND COLUMNS:-

• Select quick draw column from left side column
• At bottom left properties object will open 
• Make sure Select all stories from the bottom
• Select property-Column 400*400
• And draw column on grid points 

• Similarly, now select quick beam drawn option
• From properties object  select property- Beam 300*400
• Select all stories
• Place the beam on the grids one by one

 PLACING OF SLAB:-

• Select the slab icon tp draw the slab on similar stories 
• Make sure select similar story not all stories
• Draw the slabs one by one by clicking the middle of the slabs drawn portion 

APPLIYNG LOADS:-

load on frame;

• Now go to select tab in which  select properties and then select frame section and select B300*400
• After selecting beams go to assign tab , select frame loads and  select distributed
• Load pattern name - Type wall, uniform load - type 10KN/m as given 

 Applying Load on slab:-

• Now select slab sections apply the Live load 
• go to select tab and  select properties  in that  select slab section i.e select SLAB 150
• Then go to assign tab  and select shell loads in which  select uniform loading
• load pattern name-  select live, select load -3kn/m^2

• Similarly appling load on the diaphragm of the slab 
• Select slab section again
• Similarly, go to select tab and  select properties  in that  select slab section i.e select SLAB 150
• Go to assign tab and click on  shell and select diaphragms then select D1 from the dialog box and click ok to aply it

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL A

• The analysis model appeared like this as shown below;

 

Modal Response for MODEL A

 

 2. BULDING-B(G+5):-

Save as the MODEL B to start from that and make only changes in the stories

• In this model we need to increase the number of storey i.e 5 number of storeys.
• Now to model building B, we need not create a new ETABS file from scratch. just copy the buiding-A file using save as options and do the alteration as needed.
• Go to file then click on the  save as  and select destination folder and save as  MODEL-B

 

Increasing the storey

• Go to edit then "select edit stories and grid systems "and  modify show story data
• So we ahve already 2 storey in model for 5 storey we need to increase 3 more storey 
• So type 3 in number of storey  added 

 check the model before run analysis

• Check for live load, wall load etc.
• Check for diaphragms also
• Now go to run analysis
• It will take few seconds to obtain resultS
• Check weather the shell loads are visible once

check for shell loads 

 

 

 

 check for frame loads 

 

 

 diaphragms check

 

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL B

Modal Response for MODEL B

 

 

3 . Building-C (G+5, rectangular columns oriented along x-direction) :-

 

• In this model we need to change column size as 550*300 and orient the same in x-direction.
• Story and grid data will remain same.
• Go to file then click on  save as then go to  select destination folder saveas  the model-C

Edit the column size and orientation 

• Go to define > section properties > frame section
• change the property name as required and provide depth and width of column
• we need to orient the 550 in x-direction
• go to assign > frame >local axes > angle as 90degree > press apply and o

 

• Our plan is look like as follows;

 Check for loading 

• check for shell load, frame loads and diphragms as we did in previous model

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL C

Modal Response for MODEL C

 

 

 4. Building-D (rectangular column oriented along-y direction ):-

• In this model we dont need to alter anything rather than column orientation
• So follow the same procedure as we did in previous model
• Save as file with name model-D
• Go to assign thengo to  frame click on local axesand  make angle as 0 degree

Check for loading 

• check for shell load, frame loads and diphragms as we did in previous model

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL D

Modal Response for MODEL D

 

 

 5. Building-E:-

• Number of storey-10
• Upper 5 storey column size 400x400
• Bottom 5 storey column size 600x600
• Using save as save the file in destination folder with name model-E

 

  

Add stories in modelling ; 

• Go to edit and  edit stories and grid system and click on modify/show storey data and add storey 5
• We ahve already 5 store model so add just 5 storey

• Now check the loading ;

Adding and modifying the columns:

• First  we modified the existing column COLUMN 550*300 TO COLUMN 600*600

• Now we have to add the column COLUMN 400*400

• We successfully modified and add the columns;

change the view setting of the model :

• First we need to hide beams and floors to modify the column
• Go to view and  set display option from the ribbon and  uncheck beams and floors and apply  

 Set the building limits, select columns, assign them the required sections :

• We need to modify column sizes for top 5  i.e storey 6 to 10 storey
• Go to view then go to  set building view limits make top storey as 10 and bottom as 6
• The set building limits option allows you to view only the floors that you need to work on
• Select all columns from the 3D view and  go to assign and assign them the COLUMN 400*400 as below;

 

• The view after assigning the COLUMN 400*400 to storey 6 to 10 is as below;

 

Check for loading 

• check for shell load, frame loads and diphragms as we did in previous model

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL E

 Modal Response for MODEL E

 

6. Building-F:-

save as the model E as F to start from model E scratch 

• Make all column size through out the structure COLUMN 600*600
• The building has same columns for entire structure. therefore,so go to the set building view limits and select storey 6 to 10 and select them from the 3d view and assign them the COLUMN 600*600 in the place of 400*400 

Check for loading 

• check for shell load, frame loads and diphragms as we did in previous model

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL F

 Modal Response for MODEL F

 

 

7.Building G (G+25):-

• Column for top 5 stories : COLOUM 400*400
• Column for middle 10 stories :COLUMN 600*600
• Columns for bottom 10 storeis : COLUMN 800*800
• For this model we need to add 15 new stories and assign different column sizes on different floors. we can follow the exact procedure that has already been explained for the previous project to create this model by editing building F. the same is discussed below.

• Add COLUMN 800*800 to existing tally of columns

 

• We successfully add the column to the tally

• Now deslect the slab and beams to assigning the column sizes 

• For upmost 5 floors i.e storey 21 to storey 25 , assign the column as COLUMN 400*400

• For middle 10 floors i.e storey 11 to storey 20 , assign the column as COLUMN 600*600

 

• And in this model bottom 10 floor already has as COLUMN 800*800 from the scratch model F 

Check for loading 

• check for shell load, frame loads and diphragms as we did in previous model

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL G

 

  Modal Response for MODEL G

 

8. Building H (G+25):-

• Consistent column size throughout the building: COLUMN 800*800
• This is the same model as the previous one.all we need to do is assign the column section as C800x800 for the entire structure which can be done by simmply selecting all the columns > go to assign > select C800x800 > click ok. thus the same procedure is listed down below for better understanding. 

 

Check for loading 

• check for shell load, frame loads and diphragms as we did in previous model

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL H

 

  Modal Response for MODEL H

 

9. Building J(G+25) :-

• We have to 10% increment in the imposed loads.
• Building J is the exact copy of the model H and we dont need to alter  anything related to the modelling. however we need to increase the imposed load on the building by 10% which is assigned as 3kn/m^2 on all slabs of the building. so the procedure to do the same is listed down below. 

• Select SLAB 150 slab section
• Assign 3.3 kn/m^2 distributed shell loads for a 10% increase 

Check for loading 

• check for shell load, frame loads and diphragms as we did in previous model

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL J

 Modal Response for MODEL J

 

10. Building-K (G+25):-

• We have to make 20% Increment in the imposed loads.
• For this model, we can follow exact procedure as we did for a building J. however this time we need to increase th live load by 20% as opposed to 10%

• Select SLAB 150 slab section
• Assign 3.6kn/m^2 distributed shell loads for a 20% increase 

Check for loading 

• check for shell load, frame loads and diphragms as we did in previous model

ANALYSIS RUN:-

• Go to run analysis which is in below the menu tab and click it to  run analysis
• Save the file in your computer as MODEL K

 Modal Response for MODEL K

 

 

 

PART II:

COMPARATIVE ANALYSIS OF BUILDING PROPERTIES BASED ON THEIR STRUCTURAL OUTPUTS

 

• As we have completed the modeling and analysis of different story buildings in the previous phase of this project, now we are going to compare those results and try to understand the change in behavior of buildings based on their structural geometries. So, a comprehensive comparative analysis of structural properties of different story buildings is executed in the below sections on the basis of various criteria such as stiffness, mass, building height, etc.

 

 Effect of stiffness on T: Compare fundamental natural periods of buildings E & F as well as G & H. Why is there a marginal or significant difference in the fundamental natural periods? 

 

 

Comparative Table:-

 

 Conclusion:

                       For buildings E and F, varying column design doesn't make a big difference as there are only five stories. However, we can see that for buildings G and H, the consistent column size throughout the structure causes a more natural period. Therefore, it can be concluded that providing larger columns at the base and then reducing the size on top floors helps control the natural period 'T' for tall buildings.

 

 

•  Effect of mass on T: Compare fundamental natural periods of buildings H, J and K. Have the buildings become more flexible or stiff due to change in mass? 

 

 

Comparative Table:-

 Conclusion:

                     As seen from the table, the natural period for the tall buildings is directly proportional to the imposed mass of the building.

 

 

• Effect of Building Height on T: How do the fundamental natural periods of Buildings A, B, F, and H change with a change in building height?

 

 

Comparative Table

 Conclusion:

                   As indicated in the above table, the natural period 'T' is also directly proportional to the building height.

 

• Effect of Column Orientation on T: How do the fundamental natural periods of Buildings B, C, and D change with a change in column orientation?

 

 Conclusion:

                   When the column cross-section is square, there's not much difference between the lateral displacement in both the orthogonal directions. However, when you orient the column in a particular direction be it X or Y, the lateral displacement in that particular direction will be less than that in the other direction which has a lesser column length.

 

 

 

•  Effect of Flexural Stiffness of Structural Elements on mode shapes: Compare fundamental mode shape of Building B in two situations when the flexural stiffness of beams relative to that of adjoining columns is very small versus when it is large.

 

Comparative Table

(MOMENT OF INERTIA 10%) i.e BUILDING B (CHANGE INERTIA OF FRAMES)

 Conclusion:

                   It is pretty obvious that if you decrease the flexural stiffness of beams, the overall flexural strength of the beam is also going to reduce, and consequently, the fundamental natural period will shoot up.

 

• Effect of Axial Stiffness of Vertical Members on mode shapes: Compare the fundamental mode shape of Building H in two situations when the axial cross-sectional area of columns is very small versus when it is large. 

(BELOW IS THE SNAPS OF MODEL H WITH ONLY CHNAGING THE AXIAL AREA 10%)

 

 Conclusion:-

 As the axial stiffness of columns decreases, the fundamental natural period of the building increases regardless of its structural geometry.

•  Effect of Degree of Fixity at column bases on mode shape: Compare the fundamental mode shape of Building B in two situations when the base of columns is pinned versus when it is fixed.

(BELOW IS THE TABLE OF MODAL PERIOD OF BUILDING B WITH FIXED SUPPORT AT THE BASE)

 Conclusion:-

• It is evident that pinned support offers fewer restraints compared to the fixed one which leads to more movement and thus increased natural period. As a result, it can be concluded that the fixed support will give you better control over the fundamental natural period of buildings.

 

RESULT:-

We succesfully model and Analyze Multiple Buildings With different floor levels and design parametrs using ETABS software and compare the result to understand their overall seismic behaviors