Projefct 1_Comparative study of different storey buildings for Seismic forces

Ouestion:

Task:

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

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?

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?

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?

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.

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.

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.

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

Datas assumed are:

o Material Properties

• Grade of Concrete: M30

• Grade of Steel Reinforcement Bars: Fe 415

o Structural Element Sizes

• Beams: 300 x 400 mm

• Columns: (GIVEN IN TABLE)

• Slab: 150 mm thick

o Loading

• Live load on floor: 3 kN/m2

• Brick wall Load on beams: 10 kN/m

o Buildings are assumed to be pinned at base

PROCEDURE:

GENERAL PROCEDURE FOR DESIGNING ALL THE REQUIRED BUILDING

• Go to ETABS software
• start the software

• Select "New Model"
• Select "Use the Built in setting With:"

• Now grid and stroy 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 tab< section properties < frame section < add new < Column (size)< M30
• the again < add new < Beam (300*400)< M30

• Go to define tab< section properties < slab section < add new < slab150 < M30< thick = 150< 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 th Assign menu< Joint< Restraints< pinned< ok

• Go to define tab< Load Pattern< add load< ok (add all the required load like dead, live, brick wall, etc.)

• Go to define tab< Mass source< modify/show mass source< specified load patterns< add loads with multiplier value< ok

• To add live load and brick wall dead load.
• for all other floors except top, go to Assign< shell loads< uniform< live< 3 kn/m^2 < apply < ok
• for top floor go to Assign< shell loads< uniform< live< 1.5 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< distrubuted < brick wall< 10 kn/m^2 < APPLY < OK

• Then Go to assign < shell< diaphragms< D1< Apply< close.

• Now go to analyze < check model< sellect all< ok .
• qow you will get a warrnig tab.
• go to analyze< run analysis
• now to see the results go to : Display< show tabels< structure output< model Participation mass ratios (from top right corner drop down menu).

RESULTs:

BUILDING: A

BUILDING: B

BUILDING: C

BUILDING: D

BUILDING: E

BUILDING: F

BUILDING: G

BUILDING: H

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 privious building was 3 Kn/m^2
• 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 privious 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 :

A. 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?

1. The fundamental Natural period of building E is 2.689 sec
2. The fundamental Natural period of building F is 1.46 sec
3. The fundamental Natural period of building G is 3.514 sec
4. The fundamental Natural period of building H is 2.878 sec

Reason:

• On compairing E and F, The significant changes in the time period is caused because we used Two diffrent type of column sizes in Building E and only One type of column in F building.
  
  
• On compairing G and H, The significant changes in the time period is caused because we used three diffrent type of column sizes in Building G and only One type of column in H building.

B. 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?

1. The fundamental Natural period of building H is 2.8 sec
2. The fundamental Natural period of building J is 3.7 sec
3. The fundamental Natural period of building K is 3.8 sec

Reason:

• On ccompairing the fundamental natural periods of buildings H, J and K we can see a slight chnage in time period of H compairing to J and K, as well as the time period is constant in J and K. this small chnages happened because of bit incriment 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 praportional to the flexibility of the struccture.

C. 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?

1. The fundamental Natural period of building A is 0.534 sec
2. The fundamental Natural period of building B is 0.928 sec
3. The fundamental Natural period of building F is 1.46 sec
4. The fundamental Natural period of building H is 2.878 sec

Reason:

• On compairing A, B, F, & H: we can say that as the height of the building gets increased, the time perod of the building also increases.
  
  
• so, time period is directly proporstional to Height of building.

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

1. The fundamental Natural period of building B is 0.928 sec
2. The fundamental Natural period of building C is 1.057 sec
3. The fundamental Natural period of building D is 1.047 sec

Reason:

• On compairing B, C, & D: we can see that the time period of C is more that D which inturn is more than B.
  
  
• So, the siffness of building is more if the columns are oriented in longer length direction.

E. 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 columns:

Mode : 1

Mode : 2

Mode : 3

All Modes

• For situation when flexural stiffness of beams is larger than adjoining columns::

Mode : 1

Mode : 2

Mode : 3

All Modes

F. 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:

Mode : 1

Mode : 2

Mode : 3

All Modes

• For situation when axial cross-sectional area of columns is very large:

Mode : 1

Mode : 2

Mode : 3

All Modes

G. 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:

Mode 1

Mode 2

Mode 3

All modes

• For situation when base of column is fixed:

Mode 1

Mode 2

Mode 3

All modes