Project 1_Comparative study of different storey buildings for Seismic forces

COMPARATIVE STUDY OF DIFFERENT STOREY BUILDING FOR SEISMIC FORCES.

AIM:

To study the comparative study of different storey building for seismic forces.

INTRODUCTION:

ETABS is an engineering software product that caters to multi-storey building analysis and design. Modeling tools and templates, code-based load perscriptions, analysis methods, and solution techniques, all coordinates with the grid-like geometry unique to this class of structure. We all know that earthquake is a devastating disaster on planet earth. Earthquake codes are revised period by period and updated improvements in the representation of ground motion, soils, and structure. Moreover, these revisions have been made in recent years. The Indian Standards Codes (IS 1893:2016(part 1)) was also revised in 2001 and has been effect since 2002. Most recent data of earthquake show that the irregular distribution of mass, stiffness and strengths may cause serious damage to structural systems.

OBJECTIVES:

• Know how to extract different seismic reasponses for a structure.
• How to easily alter certain properties in an ETABS model.
• Know the factors influencing the dynamic characteristics of building.
• Know the factors influencing the time period of building.
• Know the factors influencing mode shape of building.

1. Building A

Step1-

• Open ETABS 2020 and set up the model.
• Open ETABS from the window shhortcut or by searching for it from the start menu.
• Once the software is open, click on the new model option.
• Once you click on the new model, a dialouge box will open where you can set up the codes and units to be used according to our project.
• Thus, the needful settings is done now click ok to start modeling the first building in this project.

Step2-

• Setting up the grid data and story data.
• To set same menu, you can need to click on the custom grid option and then edit the grid data.
• In the same menu, you can fix the length, number of grids in both directions, spacing between all the vertical and horizontal grids, etc.
• So, by following the same approch, we have set up a 4X3 bay grid with 4m center to center spacing in between.

Step3-

• 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 stories 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.

Step4-

• Defining the "material properties".
• It is important to set details of the materials you are going to use for the project in the ETABS.
• And for model, as given in the project 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>concrete/steel>grade>ok.

Step5-

• Defining section properties.
• We are using the rectangular concrete section 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>concrete rectangular.
• Then, a dialouge box will appear ob 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 requierd for the project.
• Here, you need to specify the slab thickness as 150mm and the section as a membrane.

B300X400

C400X400

S150

Step7-

• Execute the modeling.
• Now that we have defined everything from materials to beams, columns, and slabs to be needed for iur 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 vise 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 this structural elements.
• So, the same approch was followed and the following beams, floors, and slabs were drawn in our Etabs model.

Quick Draw Columns

Quick Draw Beams

Quick Draw FLoors

Complete Model in 3D

Step8-

• Define the load patterns.
• After completeing the model, now we need to list down the type of loads that are expected on the structure during its service period.
• And to do so, go to define>load pattern> add loads.
• Here, you can add all the loads and for our project, we are having the dead laod, super dead load (Brick wall load), live load, and the earthquake load in x and y directions.
• 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.

Step9-

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

Step10-

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

10 KN/m brick wall load on beams

3KN/m^2 live load on slab

Step11-

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

Step 13-

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

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::

Step1-

• 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.

Step2-

• Edit story data.
• Form the new file, go to edit>story and grid data.
• Click on the modify story data option.
• Then, right-click on the top story and select the add story option.
• Set the height and the number of storys 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.

Converted 5 story model

Step3-

• Prior to conducting an analysis, check the model.
• We need to make sure of two or three things after our model is complete before executing the analysis and determining the modal period.
  The load assignment is checked first.
• One by one, the show frame and shell loads move up from the bottom ribbon in ETABS.
  In this manner, the model will indicate whether or not the matching load has been allocated to the top floor.
• In a similar vein, you must verify whether the diaphragm is associated with the new model or not.
• By selecting the view settings option and examining the diaphragm visibility, you can verify it.
• You must choose every floor and allocate the diaphragm as we did if it is not visible.

Check for shell loads

Check for frame loads

Diaphragm check

Step4-

• Conduct Analysis
• Now that all the necessary checks have been made and the structure is sound, we can conduct the analysis.
• To do this, simply hit the F5 key on your keyboard or click the arrowhead that is accessible at the bottom ribbon in ETABS.
• After a short while, the deflected shape of the building will show that the analysis is finished.

Model response for Building B

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

Building C's story and grid data won't change. But, we must resize the columns and align them in the X direction. Thus, the full sequential process for the same is covered in detail below:

Step1-

• Save As to Make a Copy of the Model
  Now use the same procedure for building C through building B as we did for building B.
• After deciding on the proper place, save the file as building c.
• The model can now be altered as needed.
  
  

Step2-

• Modify the Column Orientation and Size.
• Go to define>section properties>frame section to change the column section.
• Select the building A and building B column that you already made.
• Select the option to change or display properties.
  As needed, rename the column (in this case, 550x300).
• Next, adjust the breadth and length by typing the values in the corresponding boxes.
• The 550mm needs to be oriented in the X direction at this point.
• To rotate 90 degrees, choose the column segment and then assign>local axis>rotate.
• By laying down 550mm in the X direction, all of the columns will be orientated in the X-direction in this manner.

Required column section


Step3-

• Check before running the analysis.
• Like we did 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

Step4-

• Execute the Analysis.
• Press the F5 key on your keyboard, and ETABS will carry out the analysis automatically.
• When the analysis is finished and the model's deflected shape appears 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)

The column orientation is the only thing that needs to be changed in this model. The columns will stay the same size, but we need to change their orientation from the X to the Y direction. So save as the C file into the D file, following the identical steps as we did for the prior model. Next, pick the column segment, set the local axes, and reset the origin to zero. In this manner, the Y-direction will be the orientation of every column.

As a result, as previously mentioned, the model was run for block D, and the natural period was recorded as follows:

Step1-

Select the column section and bring the orientation back to zero

Run analysis

Model Response for building D

5. Building "E" (G+10)

Column size for top 5 storeys: 400X400

Column size for bottom 5 storeys: 600X600

Prcedure:

We must include five additional stories in this model. Furthermore, we must designate various column diameters for various floors. And in order to accomplish so, we will first save the building D ETABS file as a new model for the building E. Next, make changes to the story data in ETABS, just as we have done with our earlier models. Next, we must include two more column sections with the necessary instructions and place them in our model at the proper floors.

Therefore, the following is the step-by-step process for creating new columns and placing them on necessary floors:

Add up 5 new stories and set the model for building E

Change the view settings of the model.

• Users can view the only objects that need to be worked on right now and modify the model using an option in ETABS.
• The see option settings tool is what it's named. It is conveniently located on the ETABS front tool ribbon.
• For modelling purposes, you can uncheck the structural members that you wish to hide at this time by going to the display option settings.

Set the building limit, select columns, and assign them the required sections

• Given that the top five stories require distinct columns and the bottom five floors require different columns.
• As a result, we must edit the top five stories first, then the lowest five.
• Consequently, we must first configure the building limitations to include the lowest five stories and then the opposite.
• You can go to edit>set building restrictions to accomplish that.
• With ETABS, you can view just the floors you need to work on by selecting the set building limit option.
• Therefore, first set the limit to the lowest five. Then, pick every column by constructing a box around the complete model with a left-click. Finally, assign the necessary column section to them.
• For the remaining top columns, repeat the process, and finish with the model.

Building limits

Run analysis

Model Response for building E

6. Building "F" (G+10)

Consistent column size throught the structure: C600X600

Procedure:

The columns of this building are consistent throughout. Consequently, there isn't much sectional editing that has to be done. All we have to do is change the view settings, conceal the floors and beams, pick every column, and give each one the C600x600 frame section attributes.

Adjust view option settings

Select the columns

Assign C600X600

Model Response for building F

7.Building G (G+25)

Columns for the top 5stories: C400X400

Columns for middle 10 stories: C600X600

Columns size for 10 stories: C800X800

Procedure:

We must add fifteen more levels to this model and designate varying column diameters for each floor. By altering block F, we may design this model just as it was previously presented for the prior project. The following talks about the same:

Edit the storey data and add uo 15 new stories

8. Building "H" (G+25)

Consistent column size throughout the building : C800X800

Procedure:

The model before it is the same as this one. To assign the column section for the entire structure, all we have to do is select all the columns, go to assign, select C800x800, click OK, and we're done. Thus, for easier comprehension, the same process is detailed below.

Select all the columns and assign C800X800 section

Run analysis

Modal Response for building H

9. Building "J" (G+25)

10% increment in the imposed loads

Procedure:

There is nothing to modify in terms of modelling because Building J is a perfect replica of Model H. Nonetheless, we must raise the building's applied load by 10%, or 3KN/m2, for each of the building's slabs. Therefore, the steps to follow are mentioned below:

Select the S150 Slab Section

• Navigate to Uniform>Assign>Shell loads>ten percent more of it.
• We have applied an imposed load of 3KN/m^2 to every slab in all of our prior constructions.
• Therefore, we must raise that by 10%, which means we must substitute 3.3 KN/m2 for the current imposed load.

Run the analysis

Modal Response for building J

10. Building "K" (G+25)

20% increment in the imposed loads

Procedure:

We may use the same process that we used for building j for this model. But instead of increasing it by 10%, we need to increase it by 20% this time. Thus, the sequential process is enumerated 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

Task2: COMPARATIVE ANALYSIS OF BUILDING PROPERTIES ON THEIR STRUCTURAL OUTPUTS

After finishing the modelling and analysis of various story buildings in the earlier project phase, we will now compare the findings and attempt to comprehend how building behaviour varies depending on their structural geometry. As a result, a thorough comparison of the structural characteristics of several story structures is carried out in the parts that follow, taking into account a number of different factors such mass, stiffness, and building height.

Comparison of the fundamental natural periods of buildings E and F and G and H reveals the effect of stiffness on T. Why do the fundamental natural periods differ, either somewhat or significantly?

Comparative Table

Conclusion:

Because buildings E and F only have five stories, different column designs don't really affect them. But as we can see, the uniform column size throughout the structure of buildings G and H results in a more natural era. Thus, it can be deduced that giving tall buildings bigger foundation columns and smaller top floor columns helps regulate the natural period 'T'.

Compare the fundamental natural periods of buildings H, J, and K to see how mass affects T. Has the shift in mass made the buildings stiffer or more flexible?

Comparative Table

Conclusion:

The table illustrates that the natural period of tall buildings is closely correlated with the imposed mass of the structure.

Building Height's Effect on T: How does a change in building height affect Buildings A, B, F, and H's fundamental natural periods?

Comparative Table

Conclusion:

The natural period 'T' is likewise precisely proportional to the building height, as the preceding table shows.

Effect of Column Orientation on T: What effects does a change in column orientation have on the fundamental natural periods of Buildings B, C, and D?

Conclusion:

There is minimal difference in the lateral displacement in both orthogonal directions when the column cross-section is square. The lateral displacement in one direction—X or Y—will, however, be less than that in the other direction, which has a shorter column length, when the column is oriented in that direction.

Impact of Flexural Stiffness of Structural Elements on Mode Shapes: Examine Building B's fundamental mode form in two scenarios: one in which the beams' flexural stiffness in relation to the adjacent columns' is very tiny, and the other in which it is large.

Comparative Table

Conclusion

It should go without saying that reducing a beam's flexural stiffness will also decrease the beam's overall flexural strength, which will cause the basic natural period to increase.

Axial stiffness of vertical members' effects on mode shapes: Examine Building H's fundamental mode form in two different scenarios: one in which the axial cross-sectional area of the columns is very small, and the other in which it is substantial.

Conclusion

Regardless of the structural design of the building, the fundamental natural period increases as the axial stiffness of the columns diminishes.

Impact of Degree of Fixity at Column Bases on Mode Shape: Examine Building B's Fundamental Mode Shape under Two Conditions: One in which the column bases are fixed, and the other in which they are pinned.

Conclusion

It is clear that pinned support provides less constraints than fixed support, allowing for greater movement and an extension of the natural period. Therefore, it can be said that having a fixed support will allow you to have more control over a building's fundamental natural period.