Comparative study of different storey buildings for Seismic forces

QUESTION:-

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?

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

ANSWER:-

Aim:- To compare,

1) Fundamental natural periods of buildings E & F as well as G & H. And the significant difference in the fundamental natural periods.

2) Fundamental natural periods of buildings H, J and K. Have the buildings become more flexible or stiff due to change in mass.

3) Fundamental natural periods of Buildings A, B, F and H with change in building height.

4) Fundamental natural periods of Buildings B, C and D with change in column orientation.

Introduction:-

• Buildings oscillate during earthquake shaking. The oscillation causes inertia force to be induced in the building.
• The intensity and duration of oscillation, and the amount of inertia force induced in a building depend on features of buildings, called their dynamic characteristics, in addition to the characteristics of the earthquake shaking (beyond the control of an engineer) itself.
• The important dynamic characteristics of buildings are modes of oscillation and damping (assumed constant in most practical cases).
• A mode of oscillation of a building is defined by associated Natural Period and Deformed Shape in which it oscillates.
• Every building has a number of natural frequencies, at which it offers minimum resistance to shaking induced by external effects (like earthquakes and wind) and internal effects (like motors fixed on it).
• Each of these natural frequencies and the associated deformation shape of a building constitute a Natural Mode of Oscillation.
• The mode of oscillation with the smallest natural frequency (and largest natural period) is called the Fundamental Mode, the associated natural period is called the Fundamental Natural Period.

Procedure:-

1)Fundamental natural periods of buildings E & F as well as G & H. And the significant difference in the fundamental natural periods.

Step:-1

Building E

• First we have to open the etabs software and create the new model and add the 10 storey in the story data as shown below.
• Next we put the story1 and Story6 as Master Story, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to bottom 5 storeys with the size of (600X600)mm, and add columns to top 5 storeys with the size of (400X400)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs with the thickness of 150mm from 1st storey to 10th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-2

Building F

• First we have to open the etabs software and create the new model and add the 10 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (600X600)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs with the thickness of 150mm from 1st storey to 10th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-3

Building G

• First we have to open the etabs software and create the new model and add the 25 storey in the story data as shown below.
• Next we put the story1, Story11, and Storey21 as Master Storeys, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to bottom 10 storeys with the size of (800X800)mm,

• Next assign the columns to middle 10 storeys with the size of (600X600)mm

• Next we assign the columns to top 5 storeys with the size of (400X400)mm.

• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs with the thickness of 150mm from 1st storey to 25th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-4

Building H

• First we have to open the etabs software and create the new model and add the 25 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (800X800)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.

• Next we assign the slabs with the thickness of 150mm from 1st storey to 25th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Result:-

• The fundamental natural period of Building E is T=1.561 sec.
• The fundamental natural period of Building F is T=1.557 sec.
• The fundamental natural period of Building G is T=3.618 sec.
• The fundamental natural period of Building H is T=4.412 sec.
• In the Building E we use two different column sizes, one has been assigned to top 5 storeys and another one to the bottom 5 storey. But in building F there is only one column size we use for the entire building, thats why there is a significant difference in the fundamental natural periods.
• Similarly we use three different column sizes for building G, and one column size for building H.
• Hence there is a significant difference in the fundamental natural periods.

2)Fundamental natural periods of buildings H, J and K. Have the buildings become more flexible or stiff due to change in mass.

Step:-1

Building H

• First we have to open the etabs software and create the new model and add the 25 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (800X800)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs with the thickness of 150mm from 1st storey to 25th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-2

Building J

• First we have to open the etabs software and create the new model and add the 25 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below.
• Next we put all the storeys similar to storey1, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (800X800)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs with the thickness of 150mm from 1st storey to 25th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.
• Here we have to increase the mass by 10% compared to building H.
• To increase the mass by 10% we need to add live load of 30kN/`m^2` for every storey, as shown below.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-3

Building K

• First we have to open the etabs software and create the new model and add the 25 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below.
• Next we put all the storeys similar to storey1, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (800X800)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs with the thickness of 150mm from 1st storey to 25th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.
• Here we have to increase the mass by 20% compared to building H.
• To increase the mass by 20% we need to add live load of 60kN/`m^2` for every storey, as shown below.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Result:-

• The fundamental natural period of Building H is T=4.412 sec.
• The fundamental natural period of Building J is T=4.617 sec.
• The fundamental natural period of Building K is T=5.288 sec.
• When the mass of the building is increases, then the natural period of the building also increases.
• When the mass of the building J increased by 10% compared to Building H, the Building J is more flexible than the building H.
• When the mass of the building K increased by 20% compared to Building H, the Building K is more flexible than the building J and building H.
• Finally when the weight of the building increases, the buildings become more flexible.

3)Fundamental natural periods of Buildings A, B, F and H with change in building height.

Step:-1

Building A

• First we have to open the etabs software and create the new model and add the 2 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below.
• The height of the building is 7.5m, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (400X400)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs to the 1st storey and 2nd storey with the thickness of 150mm, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-2

Building B

• First we have to open the etabs software and create the new model and add the 5 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below
• The height of the building is 16.5m, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (400X400)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs from 1st storey to 5th storey with the thickness of 150mm, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-3

Building F

• First we have to open the etabs software and create the new model and add the 10 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below
• The height of the building is 31.5m, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (600X600)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs with the thickness of 150mm from 1st storey to 10th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-4

Building H

• First we have to open the etabs software and create the new model and add the 25 storey in the story data as shown below.
• Next we put the story1 as Master Story, and the height of the building is 76.5m, as shown below.

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (800X800)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs with the thickness of 150mm from 1st storey to 25th storey, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Result:-

• The fundamental natural period of Building A is T=0.5 sec.
• The fundamental natural period of Building B is T=1.036 sec.
• The fundamental natural period of Building F is T=1.557 sec.
• The fundamental natural period of Building H is T=4.412 sec.
• When the height of the buildings increases, the natural periods of buildings also increases.

4)Fundamental natural periods of Buildings B, C and D with change in column orientation.

Step:-1

Building B

• First we have to open the etabs software and create the new model and add the 5 storey in the story data as shown below.
• Next we put the story1 as Master Story, as shown below

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (400X400)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs from 1st storey to 5th storey with the thickness of 150mm, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.

• Now we need to change the column orientation to the X direction.
• We go to the Assign and select frame option, and in that we select the Local axes option, as shown below.

• After selecting the local axes option the new tab appears, in that we put Rotate by Angle as 90 degrees, as shown below.

• The column orientation has been changed to X direction with the angle of 90 degrees, as shown below.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-2

Building C

• First we have to open the etabs software and create the new model and add the 5 storey in the story data as shown below.
• Next we put the story1 as Master Story, and the height of the building is 16.5m, as shown below

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (550X300)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs from 1st storey to 5th storey with the thickness of 150mm, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.
• Now we need to change the column orientation to the X direction.
• We go to the Assign and select frame option, and in that we select the Local axes option, as shown below.

• After selecting the local axes option the new tab appears, In that we put the Rotate by Angle as 90 degrees, as shown below.

• The column orientation has been changed to X direction with the angle of 90 degrees, as shown below.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Step:-3

Building D

• First we have to open the etabs software and create the new model and add the 5 storey in the story data as shown below.
• Next we put the story1 as Master Story, and the height of the building is 16.5m, as shown below

• Next we have to set the material properties and section properties.
• We assign the columns to all the storeys with the size of (300X550)mm.
• Next we assign the beams to all the storeys with the size of (300X400)mm.
• Next we assign the slabs from 1st storey to 5th storey with the thickness of 150mm, as shown below.
• Next we have to assign all the loads such as live load, dead load, brickwall load and seismic loads etc,.
• Now we need to change the column orientation to the Y direction.
• We go to the Assign and select frame option, and in that we select the Local axes option, as shown below.

• After selecting the local axes option the new tab appears, In that we put the Rotate by Angle as 90 degrees, as shown below

• The column orientation has been changed to Y direction with the angle of 90 degrees, as shown below.

• After assigning all the loads, we have to check the model and the model shows no error.
• After checking the model, then click on the run analysis.
• Finally the run analysis has been finished, then the deformed shape of the model will appears, as shown below.

• Next we have to click on the Display option and then select the show table option.
• After selecting the show table option, then we need to select the Modal Participating Mass Ratios from the Structure output.
• Then after the Modal Participating Mass Ratios table will appear, as shown below.

Result:-

• The fundamental natural period of Building B is T=0.972 sec.
• The fundamental natural period of Building C is T=1.086 sec.
• The fundamental natural period of Building D is T=1.067 sec.
• Here the natural periods of buildings shall be increased due to the change in column orientation.

Final Result:-

1) Fundamental natural periods of buildings E & F as well as G & H. And the significant difference in the fundamental natural periods.

• The fundamental natural period of Building E is T=1.561 sec.
• The fundamental natural period of Building F is T=1.557 sec.
• The fundamental natural period of Building G is T=3.618 sec.
• The fundamental natural period of Building H is T=4.412 sec.
• In the Building E we use two different column sizes, one has been assigned to top 5 storeys and another one to the bottom 5 storey. But in building F there is only one column size we use for the entire building, thats why there is a significant difference in the fundamental natural periods.
• Similarly we use three different column sizes for building G, and one column size for building H.
• Hence there is a significant difference in the fundamental natural periods.

2) 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 T=4.412 sec.
• The fundamental natural period of Building J is T=4.617 sec.
• The fundamental natural period of Building K is T=5.288 sec.
• When the mass of the building is increases, then the natural period of the building also increases.
• When the mass of the building J increased by 10% compared to Building H, the Building J is more flexible than the building H.
• When the mass of the building K increased by 20% compared to Building H, the Building K is more flexible than the building J and building H.
• Finally when the weight of the building increases, the buildings become more flexible.

3) Fundamental natural periods of Buildings A, B, F and H with change in building height.

• The fundamental natural period of Building A is T=0.5 sec.
• The fundamental natural period of Building B is T=1.036 sec.
• The fundamental natural period of Building F is T=1.557 sec.
• The fundamental natural period of Building H is T=4.412 sec.
• When the height of the buildings increases, the natural periods of buildings also increases.

4) Fundamental natural periods of Buildings B, C and D with change in column orientation.

• The fundamental natural period of Building B is T=0.972 sec.
• The fundamental natural period of Building C is T=1.086 sec.
• The fundamental natural period of Building D is T=1.067 sec.
• Here the natural periods of buildings shall be increased due to the change in column orientation.