Structural Modelling using Etabs 2018

AIM:

• To conceptualize a framing plan layout and then model the building in Etabs.
• To design the structural model in compliance with provisions of IS 1893 and IS 13920.
• To run a modal response spectrum analysis and check analysis results of the etabs model for inter-storey drift requirements, vertical & planar irregularities, minimum shear wall requirements,maximum axial load ratio for column and shear walls, effective moment of inertia for beams and columns etc.

PROCEDURE:

STEP 1:

• Open the Etabs software.
• In the Start page select New model option.
• In the dialogue box that appears select the Use built in settings option.
• Change all the fields as required.
• Click on OK.

STEP 2:

• In the dialogue box select Custom Grid spacing-> Edit Grid data.
• As per the specifications provide Grid data.
• Click on OK.

• In the dialogue box select Custom Story data-> Edit Story data.
• As per the specifications provide the height and elevations.
• Rename the stories as necessary.
• Set the Story 1 as master story.
• Set the other stories as Similiar to the Master story.

STEP 3:

• To create the concrete material.
• Select Define-> Section Properties-> Frame sections.
• In the Define material dialogue box select Add new material option.
• Fill in the required fields as the following.
• Click on OK

• Follow the same procedure to create rebar material.
• The required materials have been created.

STEP 4:

• To create the beams.
• Select Define-> Section Properties-> Frame sections.
• In the Define material dialogue box select Add new material option.
• Select Concrete rectangular option.
• Modify its properties as required.

STEP 5:

• To create the columns.
• Select Define-> Section Properties-> Frame sections.
• In the Define material dialogue box select Add new material option.
• Select Concrete rectangular option.
• Select the Modify/ Show rebar option.
• Modify its properties as shown below to create the columns

Beams and Columns are defined.

STEP 6:

• To create the shear walls.
• Select Define-> Section Properties-> Wall sections.
• In the Define material dialogue box select Add new material option.
• Provide required properties as shown below to create the shear walls.

STEP 7:

• Select Define-> Load patterns.
• Add the following Load patterns.

• For the loads EQX and EQY select Modify Lateral load.
• In Direction and Eccentricity panel check only X dir for EQX and uncheck the other boxes.
• Select only Y dir and unchech other boxes for EQY.

• Click on OK.

STEP 8:

• Select Define-> Mass Source.
• In the dialogue box that appears select Modify Mass source.
• In Mass source panel select specified load patterns and unselect others.
• Add the Load patterns and their multipliers as per Code as shown below.
• CLick on OK.

STEP 9:

• To add load combinations select Define-> Load combinations-> Add default design combos.
• Check the Concrete Frame design box .
• Check the Convert to user combinaations box.
• Click on OK

• The Load combinations have been generated.
• Click on OK.

STEP 10:

MODELLING:

• Using Quick Draw columns, Quick Draw beams, Quick Draw Floors icon columns, beams and slabs will be drawn.
• In the Properties of object window change the Property to the appropriate one.
• Set the Working plane as All stories.
• Model the Properties as required.
• Place the Shear walls and then edit the Grid as per the Floor plan.
• Edit the Model as per required for the Parking floor and mumty level.

STEP 11:

• To assign loads to the frames go to Select-> Properties-> Frame sections.
• Select the created Beams.
• Go to Assign-> Frame loads-> Distributed
• Change the required fields as shown below.
• Click on APPLY and OK.

• To assign loads to the slabs go to Select-> Properties-> Slab sections.
• Select the created slabs.
• Go to Assign-> Shell loads-> Uniform
• Change the required fields as shown below.
• Click on APPLY and OK

STEP 12:

• To assign diaphragm selet Assign-> Shell-> Diaphragms-> D1.
• Click on APPLY and OK.
• The centre of mass is now automatically calculated.

STEP 13:

• Click on Run analysis icon.
• Once the analysis is complete click on Save icon to save the file.

ANALYSIS RESULTS:

Modal mass participation for first 3 modes dominates atleast 65% in both X and Y axis - Achieved

Mode 1 and 2 differ by 10% minimum - Achieved

Principal Modes greater than Torsion mode - Achieved

Inter Storey drift ratio less than 0.004 - Achieved

Base shear share between column and shear walls- Not dual system

Axial stress in column and shear wall - Achieved.