Project 1_Comparative study of different storey buildings for Seismic forces

Project 1

Comparative study of different storey buildings for Seismic forces.

AIM: TO MODEL AND ANALYZE MULTIPLE BUILDINGS WITH DIFFERENT FLOOR LEVELS AND DESIGN PARAMETERS USING ETABS SOFTWARE AND COMPARE THE RESULTS TO UNDERSTAND THEIR OVERALL SEISMIC BEHAVIOUR.

ANS:-

Procedure:

1. BUILDING "A" (G+2)

• Open ETABS and Set up the Model

1. Open ETABS from the desktop shortcut or by searching for it from the start menu.
2. click on the new model option.
3. Once you click on the new model, a dialogue box will pop up where you can set up the codes and units to be used in your project.
4. Thus, do the needful settings and click ok to start modeling the first building in this project.

• Setting up the Grid Data

1. To set up the grid data, you need to click on the custom grid option.
2. Once you do that, a menu with all the grid settings will open up.
3. In the same menu, you can fix the length, numbers of grids in both the orthogonal directions, spacing between all the vertical and horizontal grids, etc.
4. So, by following the same approach, we have set up a 4 x 3 bay grid with 4m center to center spacing in-between.

• Fixing the Story Data

1. Similar to what we did while setting up the grids, click on the custom story data option.
2. Then, specify the base level, plinth level, height of each floor, and the number of floors to be included in the model.
3. Thus, we have arranged for a G+5 building with a 1.5m plinth height from the base.
4. Also, you need to fix a master story and all the similar storeys in the same menu.

• Defining the Material Properties

1. It is important to set details of the materials you are going to use for the project in ETABS.
2. And for our model, we have to use the M30 grade concrete and Fe415 HYSD steel as per the specifications.
3. So, in order to define the same, go to define>material>properties>add new> concrete/steel> grade> ok.
4. However, since we have already specified the Indian Standard Codes of practices, the M30 concrete and 450 steel is added by default into the project

• Defining Section Properties

1. We are using the rectangular concrete sections for all the structural elements like beams, columns, and slabs.
2. go to define>section properties>frame sections>concrete rectangular.
3. Then, a dialogue box will appear on your ETABS screen where you can specify the column/beam dimensions and the type of reinforcement (HYSD415) to be used in the model.
4. Now, to define the slab section, again go to define>section>slab.
5. Here, you need to specify the slab thickness as 150mm and the section as a membrane.

• Execute the Modeling

1. Now that we have defined everything from materials to beams, columns, and slabs to be needed for our structure, we can go ahead and draw each structural element as per the specifications.
2. And to do that, we can use the commands in ETABS named quick draw tool.
3. As the name suggests, you can draw all the beams, floors, and columns with the help of this tool.
4. All you need to do is select the relative tool that is quick draw columns for drawing columns and vice versa. Then choose the section from the dropdown list.
5. Then, simply go to the grid system in plan view and start clicking on the grid locations where you want to build these structural elements.
6. So, the same approach was followed and the following beams, floors, and slabs were drawn in our ETABS model.

• Define the Load Patterns

1. After completing the model, now we need to list down the types of loads that are expected on the structure during its service period.
2. And to do so, go to define>load patterns>add loads.
3. Here, you can add all the loads and for our project, we are having the dead load, super dead load (Brick wall load), live load, and the earthquake load in x and y directions.
4. Also, you need to define the mass source by adding 100% of dead and super dead load as well as 25% of the imposed or live load.

• Generate Load Combinations

1. Go to define>load combinations>default combinations>check the convertible option.
2. A list of load combinations will appear which you can look at and modify anytime during the project if needed.

• Assign Loads to the Structural Members

1. You can select a particular structural member from the model and assign it the load that is imposed on it.
2. For example, select the beam and assign a udl of super dead load due to the brick walls resting upon it.
3. Thus, a similar technique is used and the loads on beams and slabs are assigned as follows:

10 KN/m brick Wall Load on Beams

3 KN/m^2 Live Load on Slabs

• Assign the Floor Diaphragm

1. Select the S150 slab section from the select option.
2. Go to assign>shell>diaphragm.
3. Select the default D1 diaphragm already incorporated in ETABS and press ok.
4. It is now done, and you can see the center of mass for our model has been automatically calculated as we assigned the floor diaphragm.

• Save the Model and Run Analysis

1. Now that everything with regards to our first model is complete, we can proceed to run the analysis for this building.
2. But we'll have to first save our project before running the analysis so do it at the preferred location within your system.

Modal Response for Building A

2. BUILDING "B" (G+5)

• Create a Copy Model by Save As

1. Like we did for building A, now do it for building B through building A.
2. Choose the appropriate location and save the file as building B.

• Fixing the Story Data

1. go to edit tab
2. add 3more stories

• Checks Before Running the Analysis

1. Like we did for building A, checks for the frame and shell loads are to be made.
2. Also, make sure the floor diaphragm has also been assigned before going ahead with the analysis.

• Assign the Floor Diaphragm

1. Select the S150 slab section from the select option.
2. Go to assign>shell>diaphragm.
3. Select the default D1 diaphragm already incorporated in ETABS and press ok.

• Run Analysis

go to left top,showing run analysis (play symbol) then click it.

Modal Response for Building B

3. BUILDING "C" (G+5 with column orientation in X-direction)

The story and grid data for building c will remain still. However, we need to change the column size and orient the same in the X-direction.

• Create a Copy Model by Save As

1. Like we did for building B, now do it for building C through building B.
2. Choose the appropriate location and save the file as building c.

• Edit the Column Size and Orientation

1. To edit the column section, go to define>section properties>frame section.
2. Now, select the previously created column for building A and B.
3. Click on the modify/show properties option.
4. Rename the column as needed which in our case is 550x300.
5. Then, edit the length and breadth by entering the values in the box.
6. Now, we need to orient the 550mm in the X-direction.
7. So, select the column section then go to assign>local axis>rotate>90 degrees.

• Checks Before Running the Analysis

1. Like we did for building B, checks for the frame and shell loads are to be made.
2. Also, make sure the floor diaphragm has also been assigned before going ahead with the analysis.

• Run Analysis

go to left top,showing run analysis (play symbol) then click it.

Modal Response for Building C

4. BUILDING "D" (G+5 WITH COLUMN ORIENTATION IN THE Y-DIRECTION)

• Create a Copy Model by Save As

1. Like we did for building C, now do it for building D through building C.
2. Choose the appropriate location and save the file as building D.

• Select the Column Section and Bring the Orientation Back to Zero
• 

Run the Analysis

Modal Response for Building D

5. BUILDING "E" (G+10)

Column sizes for top 5 storeys: 400x400

Column sizes for bottom 5 storeys: 600x600

• Create a Copy Model by Save As

1. Like we did for building C, now do it for building D through building C.
2. Choose the appropriate location and save the file as building D.

• Add 5 New Stories and Set the Model for Building E

• Change the View Settings of the Model

1. There's an option in ETABS that allows users to adjust the model and view the only objects that are needed to be worked on currently.
2. The tool is called view option settings. It is easily accessible from the front tool ribbon of ETABS.
3. So, you can go to view option settings and uncheck the structural members that you want to hide currently for modeling purposes.
4. Since we need to assign different column sizes in our model, we don't need to view beams and slabs currently.

• Set the Building Limit, Select Columns, and Assign them the Required Sections

1. Now, since we need different columns for the top 5 floors and different columns for the bottom five.
2. Therefore, we need to edit the top 5 and bottom 5 stories one after the other.
3. go to edit>set building limits.
4. The set building limit option in ETABS allows you to view only the floors that you need to work on.
5. Hence, first set the limit to bottom 5>select all columns by holding the left-click and making the box around the entire model>go to assign and assign them the required column section.
6. Repeat the procedure for the remaining top columns and complete with the model.

Select all columns,

• C400X400

Run the Analysis

Modal Response for Building E

6. BUILDING "F" (G+10)

Consistent Column size throughout the structure: C600X600

• Create a Copy Model by Save As

1. Like we did for building E, now do it for building F through building E.
2. Choose the appropriate location and save the file as building F.

• Adjust View Option Settings

• Assign Column600X600

• Run the Analysis

• Modal Response for Building F

7. BUILDING G (G+25)

Columns for top 5 stories: C400X400

Columns for middle 10 stories: C600x600

Columns for bottom 10 stories: C800x800

• Create a Copy Model by Save As

1. Like we did for building C, now do it for building D through building C.
2. Choose the appropriate location and save the file as building D.

• Edit the Story Data and Add up 15 New Stories

• View Settings

• Set Building Limit from 21-25

Select all the Columns and Assign C400x400

• Set Building Limit 11-20

• Select all the Columns and Assign C600x600 Section

Set Building Limit from 1-10

• Select all the Columns and Assign Column800x800 Section

• Run the Analysis
• Modal Response for Building G

8. BUILDING "H" (G+25)

Consistent column size throughout the building: C800X800

• View Settings to Hide Beams and Floors

• Select All the Columns and Assign C800x800 Section

• Run the Analysis

• Modal Response for Building H

9. BUILDING "J" (G+25)

10% increment in the imposed loads

• Create a Copy Model by Save As

• Select the S150 Slab Section
• Go to Assign>Shell loads>Uniform>increase it by 10%

1. We have assigned a 3KN/m^2 imposed load on all slabs for all of our previous buildings.
2. So, we need to increase that by 10% meaning we need to replace the existing imposed load with 3.3 KN/m^2

• Run the Analysis

• Modal Response for Building J

10. BUILDING "K" (G+25)

20% increment in the imposed loads

• Create a Copy Model by Save As

• Select the S150 Slab section
• Assign 3.6 KN/m^2 distributed shell load for a 20% increase

• Run the Analysis

Modal Response for Building k

RESULTS:-

• 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?
• 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?

• 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
• 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?

• 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.
• 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.
• 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.