Modelling of 25 storey building with the specified properties using ETABS
Modelling of 25 storey building with the specified properties using ETABS
AIM -
TO STUDY HOW TO MODEL A 25 storey building with the specified properties using ETABS
OBJECTIVE -
- To know the model of a high-rise building in ETABS software
- To verify the seismic code requirements from the ETABS analysis
Model a 25-story building on ETABS with structural properties as specified below. The ground floor or plinth floor level can be taken at a height of 1.5 meters from the base. Each of the successive 25 stories has a story height of 3 meters.
Structural Element Sizes
- Beams: 300 × 400 mm
- Columns: 800 × 800 mm
- Slab: 150 mm thick
Material Properties
- Grade of Concrete: M30
- Grade of Steel Reinforcement Bars: Fe 415
Loading
- Dead Load on beams from infill wall: 10 kN/m (Let us assume the same for the roof floor given the parapet)
- Live load on the floor : 3 kN/m2 (Let us assume the same for the roof floor)
a) Buildings are assumed to be pinned at the base
b) All columns in all stories are of the same size
c) All beams in all stories are of the same size
d) Building is located on Soil type II and in Zone III. Assume other factors if required.
PROCEDURE -
STEP 1 -
- Start the ETABS software from the desktop shortcut or by searching in the start menu.
- Then, the ETABS intro page will be displayed on your screen. Look for the new model option present on the left side of the screen.
- Once you click on the new model option, you will be required to set up some basic details per about the project.
- You can fix the standard codes you will be using for the design from the dropdown list that pops up when you create a new model in ETABS.
- So, the same was done and the new model for our 25-story tower was initiated as inserted below:
STEP 2 -
- Setting up the Grid and Story Data for the Project
- After starting a new model in the software, you can set up the grid locations as per the Architectural drawings received.
- And in our case, we have been given a 5x4 grid system with 4-meter Uniform spacing in between.
- So, select the custom grid option and specify the number of grids with the total relevant spacing in-between and form a grid system for the ETABS model.
- Similarly, go to custom story data and insert the total 25 stories as required for our project with each story height of 3 meters.
- Also, set up the plinth from the base at a height of 1.5m.
- And, make the thirst floor the master story and all remaining floors similar floors to that of the first story.
STEP 3 -
- Define Material Properties
- After setting the grid and storing data and before executing the modeling part, we need to specify the Material properties we will be needing for our project.
- And as specified in the question, we need M3M30-grade concrete and FE415 steel for this model.
- So, go to define>material properties > add new material.
- Now from the dropdown menu, select India as the region, concrete as the material type, and, Indian standard with M30 grade.
- Follow the same procedure and define the HYSD 415 steel.
STEP 4 -
- Define Section Properties
- After defining the materials, we now need to go ahead and set the details for beam and column sections as well as the slab we need for our 225-story model.
- And to do that, again go to define then select section properties and choose frame sections.
- Then, select the concrete rectangular section from the list of different section shapes.
- Now, set up the grade as M30 and give column dimensions as 800 x 800.
- Similarly for beams, enter the dimensions as 300 x 400 as specified in the question.
- Then, go to reinforcement details and set up the stud reinforcement for beams and columns.
- Now, again go to the define>section properties and select slab sections.
- label, choose the label type as membrane and specify the thickness as 150mm as specified in the question.
BEAM MATERIAL PROPERTY
COLUMN MATERIAL PROPERTY -
SLAB MATERIAL PROPERTY -
STEP 5 -
- Execute the Modelling
- Now that we have specified the sizes and types of frames and slabS to be used for our project, we can start the modeling phase in ETABS.
- So, there are several ways ETABS allows you to model the structural element for your project.
- One of the ways is called the quick draw tool. This tool allows you to quickly draw beams/columns and floors at specified locations on your grid system.
- Therefore, the same tool is used and all the beams, columns, and slabs are modeled as per our grid system.
- Also, make sure to use proper one-story, similar-story, or all stories options available at the right-hand side bottom of your ETABS screen while modeling the structural elements.
- For example, columns will be modeled at all stories while slabs shall be done for similar stories as there's no slab at the base of the plinth of the building.
- Thus, all the beams, columns, and floors were drawn and the following model was prepared in ETABS.
Columns Modelling
BEAMS
SLABS
STEP 6 -
- Defining Load Patterns
- After completing the modeling part, now it's time to define all the loads that our Model is expected to Encounter.
- So, go to define>load patterns and a dialogue box will open up that will contain all the load cases that you can define for your project.
- From the same menu, choose the dead load, super dead load (Brick wall load), and the earthquake load in both the orthogonal directions.
STEP 7 -
- Define Mass Source
- To run the seismic analysis for a building, we need to define the relative seismic weight of the building which is also known as the mass source.
- So, to define mass source in ETABS, go to define> mass source.
- Now, modify the mass source and add up the values to be included in the seismic weight of the structure.
- And according to the codes, the total seismic mass of the building includes 100% of dead load, super dead load, and 25% of the live load present on the structure.
STEP 8 -
- Generate Load Combinaitons
- To generate load combinations, go to define>load combinations.
- Then, select add default design combos.
- Check the concrete frame design and click on the ok button to generate the default load combos.
STEP 9 -
- Assign the Frame and Shell Loads
- To assign loads, we first need to select the section on which we are assigning the loads.
- So, go to select>section>B300x400 to assign super dead load as specified in the question.
- After selecting the beam section, go to assign then frame loads.
- A dialogue box will open where you can specify the type and intensity of loading.
- And as given in the question, beam sections are subjected to a uniform loading of 10 KN/m due to the super-dead load imposed by the brick walls.
- Similarly, a uniform shell load of 3 KN/m^2 is to be assigned for all the slab sections.
STEP 10 -
- Assign the Diaphragm
- After selecting the slab, go to assign and click on the diaphragm.
- Now, select from the diaphragm list.
- The center of mass for our building will be automatically generated after assigning the floor diaphragm.
STEP 11 -
- Run the Analysis
- You can go to the Analysis tab and run it from there or either you can simply press F5 on your keyboard and the ETABS will run the analysis for you.
- Wait for the analysis to complete and for the building to take the deflected shape.
STEP 12 -
- Generate the Output
- Now after successfully running the analysis, go to display and show table.
- A list in a tree format will appear from where you can generate the results of your choice as per the analysis.
- So, go to the structural output>modal information>modal periods and frequencies.
- Similarly, do it for the modal participation ratio and the maximum inter-story drift.
RESULT -
ETABS model was completed and analysed.