Project 1_Comparative study of different storey buildings for Seismic forces
AIM: - TO STUDY AND COMPAIR THE RESULTS ON,
- Factors influencing the dynamic characteristics of different storey building for seismic force
- Factors influencing the Natural Period of different storey building for seismic force
- Factors influencing the Mode shape of oscillations of different storey building for seismic force
INTRODUCTION
- Every building offers a minimum resistance to the forces induced by the external effects like earthquake.
- The important dynamic characteristics of a building are the modes of oscillation and damping. Thus, it has effect of,
- Flexural Stiffness of Structural Elements on mode shapes
- Axial Stiffness of Vertical Members on mode shapes
- Degree of Fixity at column bases on mode shape
Data assumed are:
Material Properties
Grade of Concrete: M30
Grade of Steel Reinforcement Bars: Fe 415
Structural Element Sizes
Beams: 300 x 400 mm
Columns: (GIVEN IN TABLE) for different models
Slab: 150 mm thick
Loading
Live load on floor: 3 KN/m2
Brick wall Load on beams: 10 KN/m
Buildings are assumed to be pinned at base
PROCEDURE:
GENERAL PROCEDURE FOR DESIGNING ALL THE REQUIRED BUILDING
BUILDING: A
Go to ETABS software
start the software
Select "New Model
Select "Use the Built-in setting with”
Now grid and storey settings to be done as per required
then click "ok"
a new window with the grid and floor will open
go to: Define
again, add new material > India >Rebar > Indian > HYSD Grade FE415 > ok
Go to define tabs section properties > frame section > add new > Column (size) > M30
then again add new Beam (300*400) > M30
Go to define tab > section properties > slab section > add new > slab l50 > M30 < thick = 150mm > ok
Now by using quick draw tools add column, beam, and slab to all the floor as required
go to base plan select all the base points
Go to Assign menu > Joints > Restraints > pinned > ok
Go to define tab > Load Pattern > add loads > ok (add all the required load like dead. live, brick wall, etc.)
Go to define tab > Mass source > modify/show mass sources > specified load patterns > add loads with multiplier values > ok
To add live load and brick wall dead load
for all other floors except top, go to Assign> shell loads > uniform > lives > 3 kN/m^2 > apply > ok
Now to apply deal load of brick wall go to select tab > object type > beams > ok > close.
then go to Assign > frame loads distributed > brick wall > 10 kN/m^2 > APPLY > OK
Then Go to assign > shell > diaphragms D1> Apply > close
Now go to analyze > check model > select all > ok
now you will get a warming tab
go to analyzes > run analysis
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu).
BUILDING: B
Save the file as model-B, and continue the building B as per question,
in building-B, only increasing the storey till storey 5
Edit the number of storeys till G+5, from edit option
Assign the sell loads, from previous model to show in model-b
Now, define the diapragm, by selecting the slab
Run the model, and analyse it
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu).
Building c
Save the file as model-c, and continue the building b as per question,
Change the column sizes as (C-550x300) in building-C
And rorate the column to 90 degree in the Local axes
Now, define the diaphragm, by selecting the slab
Run the model, and analyse it
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu).
BUILDING: D
Save the file as model-D, and continue the building-D as per question,
And rorate the column to 90 degree in the Local axes
Now, define the diaphragm, by selecting the slab
Run the model, and analyse it
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu)
BUILDING: E
Save the file as model-E, and continue the building E as per question,
in building-B, only increasing the storey till storey 5
Edit the number of storeys till G+10, from edit option
Change the column sizes as (C-600x600) in building-C
Change the column sizes as (C-400x400) in building-C
Assign the different cloumn sizes after storey-6 to storey-10
Now, define the diaphragm, by selecting the slab
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu)
BUILDING: F
Save the current file as model-F, and modify the model as per question
Change the column of building, from storey-6 to storey-10 by set building view limits, as shown below figure
Define the new column size, as (C600x600) and assign it to selected storey in the building
All column are assign to be C600x600
Now, define the diaphragm, by selecting the slab
Run the model, and analyse it
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu)
BUILDING: G
Save the current file as model-G, and modify the model as per question
Edit the storey by edit stories and grid system as per the given question
Increse the number of storey till G+25
Assign the sell loads, from previous model to show in model-F
Define the new column size, as (C800x800) and assign it to selected storey in the building
By set view option deselect the beam and floor to view only the column
Change the column of building, from storey-21 to storey-25 by set building view limits, as shown below figure
Define the new column size, as (C400x400) and assign it to selected storey in the building
Change the column of building, from storey-11 to storey-20 by set building view limits, as shown below figure
Define the new column size, as (C600x600) and assign it to selected storey in the building
Now, define the diaphragm, by selecting the slab
Run the model, and analyse it
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu)
BUILDING: H
Save the current file as model-H, and modify the model as per question
By set view option deselect the beam and floor to view only the column
Define the new column size, as (C800x800) and assign it to selected storey in the building
Now, define the diaphragm, by selecting the slab
Run the model, and analyse it
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu)
BUILDING: J
Save the current file as model-j, and modify the model as per question
Select the slab from select by slab property
Change the shell load to 3.3kN/m^2
All loads is replace from 3kN/m^2 to 3.3kN/m^2 as shown below figure
Now, define the diaphragm, by selecting the slab
Run the model, and analyse it
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu)
BUILDING: K
Save the current file as model-k, and modify the model as per question
Select the sell load, and assign the new loads to 3.6kN/m^2 as 20% increse in the load
All loads is replace from 3.3kN/m^2 to 3.6kN/m^2 as shown below figure
Now, define the diaphragm, by selecting the slab
Run the model, and analyse it
now to see the results go to: Display > show tables > structure output > model Participation mass ratios (from top right corner drop down menu)
RESULTS
Extra loads to be increse in building:
BUILDING: J
In this case we need to add imposed load 10% more than that in "building case J".
imposed load in other way is said to be Live load, so the live load added in previous building was 3 KN/m2
Hence, the 10% live load in this case is added to be 3.3 kN/m^2
BUILDING: K
In this case we need to add imposed load 20% more than that in "building case J".
imposed load in other way is said to be Live load, so the live load added in previous building was 3 kN/m^2
Hence, the 20% live load in this case is added to be 3.6 kN/m^2
COMPAIRING RESULTS ON THE BASIS OF GIVEN TASK
1. 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?
The fundamental Natural period of building E is 1.323 sec
The fundamental Natural period of building F is 1.256 sec
The fundamental Natural period of building G is 3.192 sec
The fundamental Natural period of building H is 3.372 sec
Reason:
On comparing E and F, the significant changes in the time period is caused because we used Two different type of column sizes in Building E and only One type of column in F building.
on comparing G and H. The significant changes in the time period are caused because we used three different type of column sizes In Building & and only one type of column in H building.
2. 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?
- The fundamental Natural period of building H is 3.372 sec
- The fundamental Natural period of building J is 3.372 sec
- The fundamental Natural period of building K is 3.372 sec
Reason:
On comparing the fundamental natural periods of buildings H, J and K we can see a no change in time period of H comparing to J and K, as well as the time period is constant in J and K. these small changes happened because of bit increment in live load.
From this we can say that, as the stiffness, mass, storeys of building increases natural period increases.
Also the weight of building is directly proportional to the flexibility of the structure.
3. 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?
- The fundamental Natural period of building A is 0.518 sec
- The fundamental Natural period of building B is 1.073 sec
- The fundamental Natural period of building F is 1.256 sec
- The fundamental Natural period of building H is 3.372 sec
Reason:
On comparing A, B, F. & H: we can say that as the height of the building gets increased, the time period of the building also increases.
so, time period is directly proportional to Height of building
4. Effect of Column Orientation on T: How does the fundamental natural periods of Buildings B, C and D change with change in column orientation?
- The fundamental Natural period of building B is 0.518 sec
- The fundamental Natural period of building C is 1.173 sec
- The fundamental Natural period of building D is 1.173 sec
Reason:
On comparing B, C, & D: we can see that the time period of C is equal to D which Intern is more than B
So, the stiffness of building is more if the columns are oriented in longer length direction.
5. Effect of Flexural Stiffness of Structural Elements on mode shapes: Compare fundamental mode shape of Building B in two situations when flexural stiffness of beams relative to that of adjoining columns is very small versus when it is large.
- On Comparing fundamental mode shape of Building B in two situations when flexural stiffness of beams relative to that of adjoining columns is very small versus when it is large.
- For situation when flexural stiffness of beams is smaller than adjoining column:
6. Effect of Axial Stiffness of Vertical Members on mode shapes: Compare fundamental mode shape of Building H in two situations when axial cross-sectional area of columns is very small versus when it is large.
- On Comparing fundamental mode shape of Building H in two situations when axial cross-sectional area of columns is very small versus when it is large.
- For situation when axial cross-sectional area of columns is very small
7. Effect of Degree of Fixity at column bases on mode shape: Compare fundamental mode shape of Building B in two situations when base of columns is pinned versus when it is fixed.
- On Comparing fundamental mode shape of Building B in two situations when base of columns is pinned versus when it is fixed.
For situation when base of column is pinned
