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.

1. BUILDING "A" (G+2)

Open ETABS and Set up the Model

Open ETABS from the desktop shortcut or by searching for it from the start menu.

Once the software is up and running, click on the new model option.

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.

Thus, do the needful settings and click ok to start modeling the first building in this project.

Fixing the Story Data

Similar to what we did while setting up the grids, click on the custom story data option.

Then, specify the base level, plinth level, height of each floor, and the number of floors to be included in the model.

Thus, we have arranged for a G+2 building with a 1.5m plinth height from the base.

Also, you need to fix a master story and all the similar storeys in the same menu.

And for our project, story one is the master and all other remaining floors are similar storeys.

Once, you do this, your model is set to be executed in ETABS with the grid and storeys as specified.

Defining the Material Properties

It is important to set details of the materials you are going to use for the project in ETABS.

And for our model, we have to use the M30 grade concrete and Fe415 HYSD steel as per the specifications.

So, in order to define the same, go to define>material>properties>add new> concrete/steel> grade> ok.

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

We are using the rectangular concrete sections for all the structural elements like beams, columns, and slabs.

So, we need to define that in ETABS software so that it allows us to use these sections repeatedly throughout the project.

And to do so, go to define>section properties>frame sections>concrete rectangular.

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.

So, you can define both columns and beams from the same menu.

Now, to define the slab section, again go to define>section>slab.

Again a menu will open up where you need to set the slab specifications required for the project.

Here, you need to specify the slab thickness as 150mm and the section as a membrane.

Execute the Modeling

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.

And to do that, we can use the commands in ETABS named quick draw tool.

As the name suggests, you can draw all the beams, floors, and columns with the help of this tool.

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.

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.

So, the same approach was followed and the following beams, floors, and slabs were drawn in our ETABS model.

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

Check the Model before Running Analysis

Now that our model is ready we need to check for two to three things before running the analysis and noting the modal period.

The first check is for the load assignment.

From the bottom ribbon in ETABS, go the show frame and shell loads one at a time.

This way the model will show if the corresponding load has been assigned till the top floor.

Similarly, you need to check if the diaphragm has been assigned to the new model or not.

You can check it by going to the view settings option and checking the diaphragm visibility.

If the diaphragm is not visible, you need to select all the floors and assign the diaphragm like we did for the first model.

Check for Shell Loads

Run the Analysis

Now that all the checks have been made and the structure is ok, we can run the analysis.

And to do that simply press the F5 button on your keyboard or click on the arrowhead available at the bottom ribbon in ETABS.

It will take a few seconds and the deflected shape of the building will appear indicating that the analysis has been completed.

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

Like we did for building B, now do it for building C through building B.

Choose the appropriate location and save the file as building c.

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

Edit the Column Size and Orientation

To edit the column section, go to define>section properties>frame section.

Now, select the previously created column for building A and B.

Click on the modify/show properties option.

Rename the column as needed which in our case is 550x300.

Then, edit the length and breadth by entering the values in the box.

Now, we need to orient the 550mm in the X-direction.

So, select the column section then go to assign>local axis>rotate>90 degrees.

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

Run the Analysis

Hit the F5 button on your keyboard and ETABS will automatically run the analysis for you.

You can display the modal table when the analysis is complete and the deflected shape of the model is visible on your screen.