Project 1_Comparative study of different storey buildings for Seismic forces
AIM:
The aim of this project is to compare the different story building for seismic forces as per the specification given.
INTRODUCTION:
The structural configuration of the building plays a major role in determining the overall response during an earthquake. differently when induced bt the same sesimic force.
1. Building - A (G+2)
Given date
Number of story - 02,
Structural element size:
- Column size - 400 X 400,
- Beam size - 300 X 400,
- Slab - 150mm think.
Material Properties
- Grade of concrete : M30,
- Grade of steel reinforcement Bars : Fe 415.
Loading
- Dead load on beam from infill wall :10kn/m
- Live load ion floor : 3kn/m2
Step - 1:
1. Open ETABS software,
2. Once you click on the new model, a dialogue box wii open and change set up the codes,
3. After change the setting cilck ok,
4. To set up the gird data you need to click on the custom gird option,
5. Once you do that a menu you can fix the length, numbers of the girds in both the orthogonal direction, spacing between all the vertical and horizontal girds etc
6. Follwing the same apporach we have set up a 4 X 3 bay gird with 4m center to center spacing in between
7. Similar to what we did while setting up the grids, click on the custom story data option.
8. Then specify the base level plinth level height of each floor and the number of floor to be included in the model.
9. Also you need to fix a master story and all the similar storys in the same menu
10. Once you do this your model is set to be excited in ETABS with the gird and storeys as specificed
Material Propertys:
STEP -2
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 Fe415HYSD steel as per the specifications
3. So in order to define the same go to define material properties >add new > concrete >steel >grade>ok.
Section Properties:
STEP -3
1 .We are using the rectangular concrete sections for all the structural elements like beams, columns, and slabs.
2. So, we need to define that in ETABS software so that it allows us to use these sections repeatedly throughout the project.
3. And to do so, go to define>section properties>frame sections>concrete rectangular.
4. 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.
5. So, you can define both columns and beams from the same menu.
6. Now, to define the slab section, again go to define>section>slab.
7. Again a menu will open up where you need to set the slab specifications required for the project.
8. Here, you need to specify the slab thickness as 150mm and the section as a membrane.
Quick draw Column, Beam & Slab
STEP-4
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.
Load Patterns:
STEP -5
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.
Load Combination:
STEP -6
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 :
STEP -7
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:
STEP -8
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.
STEP -9
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.
3. Then, you can simply press F5 on your keyboard or click on the arrowhead available on the ETABS screen to run the analysis for the current model.0
Modal Response for building
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:
- From model A, go to files and click on the save as option
- Set the destination folder and name it "BUILDING B"
- The model is set for changes as per the requirements of building b
Edit story Data
- From the new file, go to edit>story and grid data.
- Click on the modify story data option.
- Set the height and the number of storeys you want to add.
- In our case, we need to add 3 more floors to convert our 2 story building into a 5 story one.
- Also, make sure to make each story similar to the master story created in Model A.
Check the model before Running Analysis:
1. Now that our model is ready we need to check for two to three things before running the analysis and noting the modal period.
2.The first check is for the load assignment.
3.From the bottom ribbon in ETABS, go the show frame and shell loads one at a time.
4.This way the model will show if the corresponding load has been assigned till the top floor.
5. Similarly, you need to check if the diaphragm has been assigned to the new model or not.
6. You can check it by going to the view settings option and checking the diaphragm visibility.
7. If the diaphragm is not visible, you need to select all the floors and assign the diaphragm like we did for the first model.
Chekc for Shell Loads
Check Frame Loads
Check for Diaphragm Check:
Run Analysis:
Building "C" (G+5 with column orientation in the Y - 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:
Copy model save as:
Edit the column size and orientation:
Check for Diaphragm Check:
Check Before Running the Analysis
Model Response Building C
4. Building "D" (G+5 with column orientation in the Y - Direction)
- Select the Column Section and Bring the Orientation Back to Zero
Run the Analysis:
Model Response Building D
5.Building "E" G+10
Column Sizes for top storeys 400 X 400
Column Size for bottom 5 Storeys 600 X 600
PROCEDURE:
In this model, we don't need to alter anything other than the column orientation. The sizes of the column will remain the same however, we have to shift the column orientation from X to Y direction. So follow the same procedure as we did for the previous model and save as the C file into the D file. Then, select the column section and assign the local axes and bring the origin back to 0. This way, all the columns shall be oriented in the Y-direction. Then like usual, check for the loads and the diaphragm before running the analysis. Then, go ahead and note the modal period for building D.
So, as explained above, the model was executed for building D and the natural period was noted as inserted below:
Copy model save as:
- Add up 5 New stories and set the model for Building E
Step -1
Edit Story
- Change the view Setting of the model
- Set the building Limit, Select columns and Assign them the Required Sections
- C 400 X 400
- C 600 X 600
- Assign C 600 X 600
- Building Limit for top 5 Stories
Select the bottom 5 Story Columns
- Assign 600 X 600
Model After Assigning Different Columns for Different Floors
Check for Diaphragm Check:
Run the Analysis
Model Response For Building
6. Building "F" (G+10)
Consistent column size throughout the structural C600X600
- Adjust view option Settings
Select all the columns.
- Assign C600X600
Run the Analysis
Model Response For Building
7. Building G (G+25)
Columns for top 5 stories C 400 X 400
Columns dor middle 10 stories 600 X 600
Columns dor middle 10 stories 800 X 800
Edit the story Data and Add up 15 new stories
View Settings
Set building Limited From 1 to 10 storey
Select all the columns and Assign C 800 X 800 section
- Set Building Limit 11 -20
- Select all the columns and Assign C600 X 600 Section
- Set Building Limit 20 -25
- Select all the Columns and Assign C 400 X 400
- Run The Analysis
- Model Response For Building G
8. Buildinng "H" (G+25)
Consistent column size throughout the building C800 X 800
- View Setting to Hide Beams and Floors
- Select all the columns and Assign C 800 X 800 Section
- Run the Analysis
- Model Response for building
9. Building "J"(G+25)
10% increment thye imposed loads
- Select the S150 dlab 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 building
2. So we need ti increase that by 10% meaning we need to replace the existing imposed load with 3.3kn/m^2
- Run the Analysis
- Model Response for Buiilding J
10. Building "K" (G+25)
20% Increment in the imposed load
- Select the S150 slab section
- Assign 3.6kn/^m2 Distributed shell load for a 20% increase
- Run the Analysis
- Model Response for Building K
PHASE II: COMPRARATIVE ANALYSIS OF BUILDING PROPERTIES BASED ON THEIR STRUCTURAL OUTPUTS
As we have completed the modeling and analysis of different story building in the previous phase of the project now we are going to comprare those results and try to understand the change in behavior of building based on their structural geomentries. so a comprehensive comparative analysis of structural properties of different story building is executed in the below sections on the basis of various criteria such as stiffness, mass, building height,etc.
- Effect of stiffness on T compare fundamental natural periods of building E & F as well as G & H why is there a marginal or signification difference in the fundamental natural periods?
Comparative Table
| MODEL NAME | NO OF STOREYS | COLUMN DESIGN SPECIFICATIONS |
NATURAL PERIOD (Seconds) |
|
| BUILDING E | 10 |
upper 5 storeys : 400 X 400 Bottom 5 storeys : 600 X 600 |
1.731 | |
| BUILDING F | 10 | Consistent column size throghout :600 x 600 | 1.735 | |
| BUILDING G | 25 |
|
4.17 | |
| BUILDING H | 25 | Consistent column size throghout :800 x 800 | 4.416 |