Project 1_Comparative study of different storey buildings for Seismic forces

                               

                                Comparative Study of Different Story 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.

INTRODUCTION :-

• The overall response to an earthquake is significantly influenced by the structural design of the building.
• When the same seismic forces are applied, different building geometries respond differently.
• For a safer design approach, it is crucial to comprehend how buildings respond in relation to their structural configurations.
• As a result, we used ETABS to model various buildings with various geometries for this project.
• Additionally, the software is used to analyze their responses, and the outcomes are then contrasted in order to gain a better understanding of the structural behavior of buildings with various storeys.

DETAILED PROCEDURE :-

• For simplicity, this project is divided into two parts. The first phase dealt with modeling buildings, which entails building structures from the ground up while adhering to predetermined geometrical and structural constraints.
• The first phase itself also includes conducting the analysis and creating the structural output for each building.
• A comparison analysis of the structural findings obtained in the first half is also included in the project's second phase.
• Based on the comparison results, it is concluded that the structural characteristics of the structures relate to their seismic reaction.

 PHASE ONE :- Modeling the Buildings and Generating their Respective Structural Outputs using ETABS 

• This project consists of a total of 10 buildings to provide a more thorough analysis.
• Beginning with A and ending with K, the buildings are arranged alphabetically. Here is a thorough explanation of a step-by-step process for modeling any building and providing the corresponding structural outputs:

1. BUILDING "A" (G+2)

 Open ETABS and Set up the Model

1. Use the desktop shortcut or the start menu search to launch ETABS.
2. Once the software is operational, select "new model" from the menu.
3. A dialogue box where you can configure the codes and units to be used in your project will appear after you click on the new model.
4. Consequently, make the necessary adjustments and press OK to begin modeling the first building in this project.

•  Setting up the Grid Data

1. You must select the custom grid option in order to configure the grid data.
2. Following that, a menu containing all the grid settings will appear.
3. You can adjust the length, the number of orthogonal grids in both directions, the distance between each vertical and horizontal grid, and other options in the same menu.
4. Thus, by employing the same strategy, we have created a 4 x 3 bay grid with an interspace of 4 meters.

•  Fixing the Story Data

1. Click on the custom story data option, just as we did when setting up the grids.
2. Next, indicate the model's base level, plinth level, height of each floor, and total number of floors.
3. As a result, we have planned a G+2 structure with a plinth height of 1.5 meters.
4. Also, you need to fix a master story and all the similar storeys in the same menu.
5. And for our project, story one is the master and all other remaining floors are similar storeys.
6. Once, you do this, your model is set to be executed in E - TABS with the grid and storeys as specified.

•  Defining the Material Properties

1. It is crucial to enter information about the supplies you'll be using for the project in E-TABS.
2. Additionally, in accordance with the specifications, we must use Fe415 HYSD steel and concrete of the M30 grade for our model.
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 use rectangular concrete sections for all the beams, columns, and slabs that make up the structure.
2. So that we can use these sections repeatedly throughout the project, we must define that in the ETABS software.
3. Go to define > section properties > frame sections > concrete rectangular to do this.
4. The dimensions of the column/beam and the type of reinforcement (HYSD415) to be used in the model can then be entered in the dialogue box that then appears on your ETABS screen.
5. As a result, you can define beams and columns from the same menu.
6. Go back to define>section>slab to define the slab section now.
7. Once more, a menu will appear where you can enter the project's slab requirements.
8. Here, you need to specify the slab thickness as 150mm and the section as a membrane.

* B300X400

 * C400X400

           

* S150

         

•  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. so, the same approach was followed and the following beams, floors, and slabs were drawn in our ETABS model.
3. And in order to do that, we can employ the quick draw tool commands in ETABS.
4. With the aid of this tool, you can draw every beam, floor, and column, as the name suggests.
5. Simply choose the appropriate tool, such as quick draw columns for drawing columns, and vice versa. then pick the appropriate section from the drop-down menu.
6. After that, all you have to do is open the plan view grid system and begin clicking on the grid locations where you want to place these structural components.
7. The following beams, floors, and slabs were thus drawn in our ETABS model using the same methodology.

* Quick Draw Columns

           

* Quick Draw Beams

            

* Quik Draw Floors

          

* Complete Model in 3D

                 

• 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. A specific structural member can be chosen from the model, and the load placed on it can be assigned.
2. Consider choosing the beam and placing a super dead load on it because brick walls are supporting it.
3. As a result, a similar technique is employed, and the following loads are placed on the beams and slabs:

* 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 :-

• Now that everything related to our first model is finished, we can proceed with running the analysis for this building.
• Please save our project in the location of your system's choice before we can proceed with the analysis.
• The analysis for the current model can then be run by simply pressing F5 on your keyboard or by clicking the arrowhead present on the ETABS screen

 * Modal Response for Building A

           

 2. BUILDING "B" (G+5) 

• Now to model building B, we need not create a new ETABS file from scratch.
• Rather we will save a copy of the building A file and do the alterations needed for building B. For example, we can increase the number of stories to 5 by editing the story data within the copied file. So, the complete procedure to do so in ETABS is discussed below :-

• Make a Copy by "Save as"

1. From model A, go to files and click on the save as option.
2. Set the destination folder and name it "BUILDING B".
3. The model is set for changes as per the requirements of building b

•  Edit Story Data

1. Go to edit > story and grid data from the new file.
2. Select "Modify Story Data" from the menu.
3. Then, choose Add Story from the context menu when you right-click on the top story.
4. Decide on the height and number of additional stories you want.
5. In our situation, we must add 3 more floors to turn our 2-story structure into a 5-story structure.
6. Additionally, make sure that each tale resembles the grand narrative produced in Model A.

* Converted 5 Story Model

                 

•  Check the Model before Running Analysis

1. Our model is now ready, but before we run the analysis and note the modal period, we need to make sure of two or three things.
2. The load assignment is the first thing to be checked.
3. Go to the show frame and shell loads one at a time from the bottom ribbon in ETABS.
4. The model will then display whether the appropriate load has been assigned up to the top floor in this manner.
5. The diaphragm must also be verified to see if it has been assigned to the new model or not.
6. By selecting the view settings option and examining the diaphragm visibility, you can verify it.
7. You must select every floor and assign the diaphragm, just as we did for the first model, if the diaphragm is not visible.

* Check for Shell Loads

          

* Check for the Frame Loads

           

* Diaphragm Check

           

•  Run the Analysis

1. Now that all the checks have been made and the structure is ok, we can run the analysis.
2. And to do that simply press the F5 button on your keyboard or click on the arrowhead available at the bottom ribbon in E-TABS.
3. It will take a few seconds and the deflected shape of the building will appear indicating that the analysis has been completed.

* 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.
• So, the complete stepwise procedure for the same is discussed in detail below:

• 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.
3. Now, the model is set to be edited as needed.

•  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.
8. This way, all the columns shall be oriented in the X-direction meaning 550mm laying down in the x direction.

* Required Column Section

          

• 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.

Check for the Frame loads

          

* Check for the Shell Loads

                

* Diaphragm Check

              

•  Run the Analysis

1. When you press the F5 key on your keyboard, ETABS will carry out the analysis for you automatically.
2. When the analysis is finished and the model's deflected shape is visible on your screen, you can display the modal table.

* Modal Response for Building C

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

• Nothing else in this model needs to be changed besides the direction of the columns.
• We must switch the column's direction from X to Y even though the column sizes won't change.
• Save the C file as the D file by following the same procedures we used for the previous model.
• Select the column section next, then alter the local axes and origin to 0.
• This will cause all of the columns to be oriented in the Y direction.
• Following the customary checks for loads and the diaphragm, the analysis should be carried out.
• Next, note the modal period of building D.

* So, as explained above, the model was executed for building D and the natural period was noted as inserted below :-

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

(The detailed procedure to do it has already been discussed for the previous model)

               

* Required Column Section

            

* 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

PROCEDURE :-

• In this model, we need to add up 5 more storeys to our model.
• In addition, we also need to assign different column sizes on different floors. And to do that, we'll first save the ETABS file for building D as a new model for building E.
• Then, edit the story data as we have done for our previous models in ETABS.
• Then, we need to add two new column sections with the required directions and assign them at appropriate floors in our model as specified.

* So, the stepwise procedure to create new columns and locate them on required floors is explained below :-

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

           

•  Change the View Settings of the Model

1. Users can modify the model and view the only objects that need to be worked on right now using an option in ETABS.
2. The instrument is known as view option settings. It is conveniently reachable from ETABS's front tool ribbon.
3. So you can uncheck the structural members that you currently want to hide for modeling purposes in view option settings.
4. We don't need to view beams and slabs right now because we need to assign different column sizes in our model.
5. In order to make the only columns visible for editing, we go to the tool and uncheck the boxes for beams and floors.

•  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. So, we need first set the building limits up to the bottom five floors and then vice versa.
4. And to do that, you can go to edit > set building limits.
5. The set building limit option in ETABS allows you to view only the floors that you need to work on.
6. 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.
7. Repeat the procedure for the remaining top columns and complete with the model.

• Building Limits

                  

•  C400X400

                    

•  C600X600

      

•  Select Bottom 5 Story Columns

             

•  Assign C600x600

              

•  Building Limit for Top 5 Stories

             

•  Select All Columns and Assign them C400x400 Section

            

•  Model After Assigning Different Columns for Different Floors

           

•  Run the Analysis

           

•  Modal Response for Building E

            

 6. BUILDING "F" (G+10)

• Consistent Column size throughout the structure : C600X600

PROCEDURE :-

• The columns in this building are consistent throughout.
• As a result, there isn't much sectional editing required.
• Simply change the view settings, hide the floors and beams, select all of the columns, and give them C600x600 frame section properties.

• Adjust View Option Settings

• Select all the Columns

               

•  Assign C600X600

              

•  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

PROCEDURE :- 

• For this model, we need to add 15 new stories and assign different column sizes on different floors.
• We can follow the exact procedure that has already been explained for the previous project to create this model by editing building F.
• The same is discussed below :-

• Edit the Story Data and Add up 15 New Stories

       

•  View Settings

•  Set Building Limit from 1-10

            

•  Select all the Columns and Assign C800x800 Section

            

•  Set Building Limit 11-20

                

•  Select all the Columns and Assign C600x600 Section

          

•  Set Building Limit 20-25

               

•  Select all the Columns and Assign C400x400

              

•  Run the Analysis

               

•  Modal Response for Building G

          

 8. BUILDING "H" (G+25)

• Consistent column size throughout the building : C800X800

PROCEDURE :- 

1. The previous model is the same as this one.
2. All that needs to be done is to select all of the columns, go to assign, select C800x800, click OK, and          the column section will be set to C800x800 for the entire structure.
3. The same process is therefore listed below for your convenience.

• 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

PROCEDURE :- 

• Building J is the exact copy of the model H and we don't need to alter anything related to the modeling.
• However, we need to increase the imposed load on the building by 10% which is assigned as 3KN/m^2 on all slabs of the building.
• So, the procedure to do the same is listed down below :-

• 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

PROCEDURE :-

• We can use the same process we used to build j for this model.
  
• But this time, instead of 10%, we need to increase the live load by 20%.
  
• Therefore, the detailed process is listed below:
• 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

                

 PHASE II :- COMPARATIVE ANALYSIS OF BUILDING PROPERTIES BASED ON THEIR STRUCTURAL OUTPUTS

• As part of this project's previous phase, we finished modeling and analyzing buildings with varying numbers of stories. Now, we're going to compare those results and work to understand how buildings' behaviors change depending on their structural geometries.
• As a result, the structural characteristics of various story buildings are thoroughly compared in the sections below based on a number of factors, including stiffness, mass, building height, etc.

* 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 ? 

Comparative Table :-

             

 Conclusion :-

• Because there are only five stories in buildings E and F, different column designs don't make a significant difference.
• But as we can see, the consistent column size throughout the structure results in a more natural period for buildings G and H.
• Therefore, it can be concluded that providing larger columns at the base and then decreasing their size on top floors aids in controlling the natural period 'T' for tall buildings.

* 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 ? 

 

Comparative Table :-

     

 Conclusion :-

• As seen from the table, the natural period for the tall buildings is directly proportional to the imposed mass of the building.

* 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?

Comparative Table :-

          

 Conclusion :-

•  As indicated in the above table, the natural period 'T' is also directly proportional to the 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 ?

           

 Conclusion :-

When the column cross-section is square, the lateral displacement in the two orthogonal directions is not significantly different. The lateral displacement in that specific direction, whether it be X or Y, will, however, be less than that in the other direction because the latter has a shorter column length.

 * Effect of Flexural Stiffness of Structural Elements on mode shapes :-

• Compare the fundamental mode form of Building B in two instances where the flexural stiffness of the beams in relation to the adjacent columns is very minimal versus when it is significant.

Comparative Table :-

           

 Conclusion :-

• It goes without saying that reducing the flexural stiffness of beams will also reduce their overall flexural strength, which will cause the fundamental natural period to increase.

* 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. 

           

 Conclusion :-

• Regardless of the structural geometry of the building, the fundamental natural period of the structure increases as the axial stiffness of the columns decreases.

* 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.

            

 Conclusion :-

• It is obvious that pinned supports provide fewer restrictions than fixed ones, permitting more movement and, as a result, a longer natural period.
  It can be said that the fixed support will give you more control over the fundamental natural period of buildings.