Project 1_Comparative study of different storey buildings for Seismic forces

AIM :

• To 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?
• To Compare fundamental natural periods of buildings H, J and K. Have the buildings become more flexible or stiff due to change in mass?
• Effect of Building Height on T: How does the fundamental natural periods of Buildings A, B, F and H change with change in building height?
• Effect of Column Orientation on T: How does the fundamental natural periods of Buildings B, C and D change with change in column orientation?

GIVEN DATA :

Structural Element Sizes :

• Beams - 300 * 400 mm
• Columns - 400 * 400 mm
• Slab - 150 mm thick

Material Properties

• Grade of Concrete : M30
• Grade of Steel Reinforcement Bars : Fe 415

Loading

• Dead Load on beams from infill wall : 10 kN/m
• Live load on floor : 3 kN/m2

PROCEDURE :

• BUILDING A (G+2)
• Open etabs and set up the model,
• click on the new model option
• set up the codes and units to be used in the project
• 
• click ok to start the modelling the building (a) project.
• Setting up the grid data, you need to click on the custom grid option.
• 
• In the same menu you can fix the length, number of grids in the both orthogonal directions, spacing between the all the vertical and horizontal grids, etc.
• we have set up a 4*3 bay grid with 4m centre to centre spacing in between.
• Fixing the story data, click on custom story data option
• 
• specify the base level, plinth level, height of the floor level and the number of floors to be included in the model,
• thus we arranged a G+2 Building, with a 1.5m plinth height from the base,
• also fix the master story to the building and all the similar storys in the same menu,
• Your model is set to be executed in etabs with the grids and the storys as specified.
• DEFINING MATERIALS PROPERTIES,
• Set details of the materials you are going to use for the projects in Etabs
• we have to use M30 grade and Fe415HYSD Steel as per the specifications
• Go to define>material>properties>add new>concrete/steel>grade>ok
• 
• DEFINING THE SECTION PROPERTIES,
• We are using the rectangular concrete sections for the structural elements like beams , columns, and slabs
• 
• 
• 
• Go to define>section properties>frame sections>concrete rectangular
• specify the column / beam dimensions and the type of reinforcements to be used in the model
• define slab section, again go define>section>slab
• specify the slab thickness as 150mm and the section as the membrane.
• EXECUTE THE MODELLING,.
• We can use the commands in Etabs named quick draw tool,
• 
• 
• 
• 
• 
• as the name suggest , you can draw the beams , columns, floors, with the help of the tool
• DEFINE THE LOAD PATTERNS,
• After completing the model we need to list down the types of loads that are expected on the structure during its service period
• 
• Go to define>load patterns>add loads
• We are having the dead loads, live loads, super dead load, earthquake loads in x and y direction
• 
• also we need to define the mas source , by adding 100% of dead and super dead load as well as 25% of the imposed or live load,
• 
• GENERATE LOAD COMBINATIONS
• Go to define>load combinations>check the convertable option
• a list of load combinations will appear which you can look at and modify any time during the project if needed
• Assign load to the structural members, you can select the particular member from the model and assign it in the load taht is imposed on it
• select the beam assign a udl , of super dead load due to brick walls resting upon it
• 
• 
• 
• Thus a similar technique, is used the loads on the beams ands floors are assigned as follows
• ASSIGN THE FLOOR DIAPHRAGM
• Select teh s150 slab selection from then select option
• go to assign>shell>diaphragm
• 
• select teh default D1 diaphragm already in corporated in etabs and click ok
• you can see the center of mass of our model has been automatically calculated as we assign the floor diaphragm
• 
• SAVE THE MODEL AND RUN ANALYSIS,
• Now that everything with regards to our 1st model is complete , we can procedd to run analysis for the building

Time period for building A,

BUILDING B (G+5)

• MAKE A COPY BY Save as , from model a go to files and click on the save as option
• See the destination folder named it Model B
• The model is set for changes as per requirement for building B
• EDIT STORY DATA Go to edit > story and grid data
• Click on the modify story data option
• set the height and story you want to edit
• also set each story similar to master story A as created in model A

• CHECK THE MODEL BEFORE RUNNING ANALYSIS
• The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
• similarly you need to check the diaphragm is assigned or not, to your new model

• RUN ANALYSIS
• Now all the checks have been made and the structure is ok we can made the analysis
• and do that simply press F5 button to run the analysis
• It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.

MODEL RESPONSE FOR BUILDING B

BUILDING C (G+5 WITH COLUMN ORIENTATION IN X DIRECTION)

• Create a copy model by save as
• choose the appropriate location for save as
• Now model is set to be edited as svae model
• EDIT THE COLUMN SIZE&ORIENTATION
• Go to define>section properties >frame section
• click on modify show properties option
• Rename the column as we needed in model c 550*300

• Then edit the breadth and length by entering the values in the box
• we need to orient 550 in the x direction
• select the column section>go to asiign local axis>rotate >90degrees

• CHECK THE MODEL BEFORE RUNNING ANALYSIS
• The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
• similarly you need to check the diaphragm is assigned or not, to your new model

• RUN ANALYSIS
• Now all the checks have been made and the structure is ok we can made the analysis
• and do that simply press F5 button to run the analysis
• It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.

MODEL RESPONSE FOR BUILDING C

BUILDING D (G+5 WITH COLUMN ORIENTATION IN Y DIRECTION)

• We have to shift the column orientation from x to y direction
• so follow the same procedure,as we did for the previous model and save as model d
• select column section assign the local axis and bring the origin to 0
• Thus columns should oriented in y direction.

SELECT COLUMN SECTION BRING BACK TO ORIENTATION:

• we need to orient 550 in the Y direction
• select the column section>go to asiign local axis>rotate >0degrees

• CHECK THE MODEL BEFORE RUNNING ANALYSIS
• The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
• similarly you need to check the diaphragm is assigned or not, to your new model

• RUN ANALYSIS
• Now all the checks have been made and the structure is ok we can made the analysis
• and do that simply press F5 button to run the analysis
• It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.

MODEL RESPONSE FOR BUILDING D

BUILDING E (G+10)

Column sizes for top 5 storys = 400*400

Column sizes for bottom 5 storys = 600*600

ADD UP 5 NEW STORYS AND SET THE MODEL FOR BUILDING E,

• Change the view settings of the model,
• You can go view option settings and uncheck the structural members taht you want to hide currently for modelling purposes
• so we to tools and uncheck the beams and floors in order to make only columns are visible.
• set the building limits select columns and assign them the required sections
• since, we need differrent columns for top 5 floors and bottom five floors

• first we need to set the limits bottom 5 floors and then viceversa
• you can go to edit>set the building limits
• hence first set the limits to bottom 5 >select all columns by holding the left click making the box around the entire model >go to assign and assign them to required column section

• Repaet the same procedure for remaining top 5 columns

• CHECK THE MODEL BEFORE RUNNING ANALYSIS
• The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
• similarly you need to check the diaphragm is assigned or not, to your new model
• 

• RUN ANALYSIS
• Now all the checks have been made and the structure is ok we can made the analysis
• and do that simply press F5 button to run the analysis
• It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.

MODEL RESPONSE FOR BUILDING E

BUILDING F(G+10)

Consistent column structure throughout the structure C 600*600

• The building has same columns for entire structure , so we need to adjust the view settings >hide beams and floors >select all the columns >assign them the frame section properties c 600*600
  • CHECK THE MODEL BEFORE RUNNING ANALYSIS
  • The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
  • similarly you need to check the diaphragm is assigned or not, to your new model
  • RUN ANALYSIS
  • Now all the checks have been made and the structure is ok we can made the analysis
  • and do that simply press F5 button to run the analysis
  • It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.

• 

  MODEL RESPONSE FOR BUILDING F

BUILDING G (G+25)

Top 5 storys - C 400*400

Middle 10 storys - C 600*600

bottom 10 storys - C 800*800

Edit story data add up 5 new storys

• view edit settings
• set building limit 1-10
• select all the columns assigns C 800*800 section
• 
• Set limit 11-20
• select all the columns assigns C 600*600 section

• set building limit 20 -25
• select all the columns assigns C 400*400 section
• CHECK THE MODEL BEFORE RUNNING ANALYSIS
• The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
• similarly you need to check the diaphragm is assigned or not, to your new model
• RUN Analysis,
• Now all the checks have been made and the structure is ok we can made the analysis
• and do that simply press F5 button to run the analysis
• It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.
• 

MODEL RESPONSE FOR G

BUILDING H (G+25)

• Column size through out the building C 800*800
• 
• entire structure which can be done by simply selecting all the columns >go to assign>select c 800*800>click ok
• view settings to hide beams and floors
• select all the columns assign C 800*800 section
• CHECK THE MODEL BEFORE RUNNING ANALYSIS
• The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
• similarly you need to check the diaphragm is assigned or not, to your new model
• RUN Analysis
• Now all the checks have been made and the structure is ok we can made the analysis
• and do that simply press F5 button to run the analysis
• It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.

MODEL RESPONSE FOR BUILDING H

BUILDING J (G+25)

10% Increment in the imposed loads,

• Building j is exact copy of model h,
• we dont need to alter anything, related to modelling
• We need to increased the imposed loads by 10% which is assigned as 3kn/m^2 on all slabs of the buildings
• select the s150 slab section
• Go to assign>shell loads>uniform increase it by 10%
• replace imposed load with 3.3kn/m^2
• CHECK THE MODEL BEFORE RUNNING ANALYSIS
• The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
• similarly you need to check the diaphragm is assigned or not, to your new model
• Run analysis
• Now all the checks have been made and the structure is ok we can made the analysis
• and do that simply press F5 button to run the analysis
• It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.

MODEL RESPONSE FOR BUILDING J

BUILDING K (G+25)

20% Increment in the imposed loads,

• Building j is exact copy of model h,
• we dont need to alter anything, related to modelling
• We need to increased the imposed loads by 20% which is assigned as 3kn/m^2 on all slabs of the buildings
• select the s150 slab section
• Go to assign>shell loads>uniform increase it by 20%
• replace imposed load with 3.6kn/m^2
• CHECK THE MODEL BEFORE RUNNING ANALYSIS
• The first check is for load assignment , from bottom ribbon in etabs ,go to show frame shell loads one at a time
• similarly you need to check the diaphragm is assigned or not, to your new model
• Run analysis
• Now all the checks have been made and the structure is ok we can made the analysis
• and do that simply press F5 button to run the analysis
• It will take few seconds to show in deflected shape of the building will appear indicating that the analysis has been completed.

MODEL RESPONSE FOR BUILDING K

RESULTS :

• 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?

MODEL NAME	NO OF STOREYS	PERCENTAGE INCREASE IN MASS	NATURAL PERIOD (SECONDS)
BUILDING H	25	Regular mass with no increament	3.259
BUILDING J	25	10% increament	3.259
BUILDING K	25	20% increament	3.259

i have done the mistake , which makes an error ,

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

MODEL NAME	NO OF STOREYS	TOTAL BUILDING IN HEIGHT (M)	NATURAL PERIOD (SECONDS)
BUILDING A	2	7.5	0.34
BUILDING B	5	16.5	0.714
BUILDING F	10	31.5	1.136
BUILDING H	25	76.5	3.259

CONCLUSION:

As indicated in above T is directly proportional to building height.

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

MODEL NAME	NO OF STOREYS	COLUMN ORIENTATION	MAXIMUM STORY DRIFT (MM) EQX EQY
BUILDING B	5	EQUAL IN BOTH DIRECTION	2.25 2.30
BUILDING C	5	X DIRECTION	2.10 2.50
BUILDING D	5	Y DIRECTION	2.45 2.15

When column sross section is square there's not much difference between lateral displacement in both orthogonal direction.

• 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?

MODEL NAME	FLEXURAL STIFFNESS ON BEAMS	NATURAL PERIOD
BUILDING B	100% 10%	1.036 2.627

If you decrease the flexural strength of the beam, overall flexural strength of the beam also going to reduce and consequently fundamental natural period will shoot up

MODEL NAME	AXIAL STIFFNESS ON COLUMNS	NATURAL PERIOD
BUILDING H	100% 10%	4.416 5.991

An axial stiffness of columns decreases the fundamental natural period of building increases of its structural geometry

MODEL NAME	NO OF STOREYS	FIXITY AT BASE	NATURAL PERIOD
BUILDING B	5	PINNED FIXED	1.036 0.941

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