Modelling of 25 storey building with the specified properties using ETABS

Aim: ETABS modelling of a 25 storey building

Procedure:

Step 1: Analysis of Model.

a. Material Data:

• Concrete Grade: M30
• Grade of Steel: Fe415

b. Properties:

• Beam: 300 x 400 mm
• Column: 800 x 800 mm
• Slab: 150 mm

1. Create a Model with following initialization:

1. Display Unit: Metric SI
2. Steel Section Database: Indian
3. Steel Design Basecode: IS 800:2007
4. Concrete Design Code: IS 456:2000

2. Specify the following in model:

a. Grid Spacing:

• Number Grid Lines in X-Direction: 5
• Number Grid Lines in Y-Direction: 4
• Spacing of Grid in X-Direction: 4
• Spacing of Grid in Y-Direction: 4
• Number of Stories: 26
• Typical Story Height: 3
• Bottom Story Height:1.5

3. Define the properties:

• Go to Define -> Material Properties -> Add new material.
• Create the matrial for concrete as shown in figure.
• Add the grade of Concrete as M30. Click Ok.

• Repeat the same Go to Define -> Material Properties -> Add new material.
• Create the matrial for Steel as Rebar HYSD 415 as shown in figure. Click Ok.

4. Add section properties:

• Go to Define -> Section Properties -> Frame Section -> Add new Property.
• Select Concrete Rectangular Shape.
• In the Frame section property data

1. Property Name: Beam
2. Material: M30
3. Section Dimension: Depth=400mm, Width=300mm.

• Repeat the same to define section property for column as follows.

1. Property Name: Column
2. Material: M30
3. Section Dimension: Depth=800mm, Width=800mm.

• Define -> Section Properties -> Slab Section -> Add new property.
• In slab property data set the following.

• Property Name: Slab
• Material: M30
• Section Dimension: 150mm.

5. Go to View Menu -> Set Plan View

6. Go to Draw Menu -> Draw Beam/Columns/Brace Objects -> Quick Draw Columns.

• In the properties of the Object, Set the property as Column.
• Using select object cursor, drag windows in such a way it is not creating the column in the bottom right corner of the model.

7. Go to Draw Menu -> Draw Beam/Columns/Brace Objects -> Quick Draw Beam/Columns.

• In the properties of the Object, Set the property as Beam.
• Using select object cursor, drag windows in such a way it is not creating the column in the bottom right corner of the model.

8. Go to Draw Menu -> Draw Floor/Walls Objects -> Quick Draw Draw Floor/Walls.

• In the properties of the Object, Set the property as Slab.
• Using select object cursor, drag windows in such a way it is not creating the column in the bottom right corner of the model.
• The slab object is automatically modeled.

9. Select Bottom joints.

• Go to Assign -> Joints -> Restrains.
• Select and apply pinned restrains.

10. Define Load Patterns:

• Go to define -> Load Patterns -> Dead Load & Live Load.
• Create a Wall Load as Super Dead Load.
• Create a Seismic load in X & Y Direction. Provide IS Code 1893.

• Select X Direction Seismic load & go to Modify Load.

1. Provide Direction & Eccentricity on X Direction.
2. Zone Factor: 0.16
3. Story Range: Bast to 25 Story.
4. Response Reduction Factor: 5
5. Importance Factor: 1.
6. Time Period: Pragrame calculated.

• Select Y Direction Seismic load & go to Modify Load.

1. Provide Direction & Eccentricity on Y Direction.
2. Zone Factor: 0.16
3. Story Range: Bast to 25 Story.
4. Response Reduction Factor: 5
5. Importance Factor: 1.
6. Time Period: Pragrame calculated.

• We have to define the mass sourse data in Seismic load with respect to Dead, Live & SuperDead Load.
• Go to Define -> Mass Source Data -> Modify data.

1. Mass Source: Specified load pattern.
2. Add Mass multiplier for Load pattern: Dead Load=1, Wall Load=1 & Live load= 0.25.

Step 2: Assigning of Load:

1. Live Load on Floors= 3kN/m.

• To select all the floors & types go to select -> Object type -> Floors.

• Go to Assign -> Shell Load -> uniform.
• Load pattern Name: Live
• Uniform Load: 3
• Direction: Gravity.

• The floor load of 3kN/sq.m is added on all floors.

2. Dead Load on Beams= 10kN/m.

• To select all the beams & types go to select -> Object type -> Beam.

• Go to Assign -> Frame Load -> Distributed.
• Load pattern Name: Wall
• Load Type Specification: Force
• Direction: Gravity.
• Uniform Load: 10.

• The Beam load of 10kN/m is added on all Beams.

Step 3: Add diaphragms.

• Go to assign-> shell -> Diaphragms.
• Select the D1 and diaphragms will be added on the all floors.

Generate Check model:

• Go to Analyze -> check model.

Go to Analyze -> Run Analysis.

Results:

• Go to model Explorer Display>show tables>Analysis results>Structure ouput>Modal information>modal periods and frequencies.
• The time periods for fundamental mode-1Y direction and findamental Mode -1X direction are noted from the table and are as follows:

• Tx1=4.416 seconds and Ty1=4.222 seconds

• Display>show tables>analysis results>structure output>modal information>modal participation mass ratios.
• From the table the natural time period for mode-1 and torsional DOF are noted as follow:
• Tx1=4.694 seconds Ty1=4.488 seconds Txy1=3.489 seconds
• So from the results it is clear that the torsional time period is less than two translational time period as required by IS 1893 provision table 5.
• When we add the three mode mass ratios we get 0.9044 which menas first three modes of seismic oscillation contribute more than 65% of building weight as per ETABS anaysis.

• The storey drift for serviceability Base shear case(EQX or EQY) is tabulated from the following tool path.
• Go to display>Storey response plot
• Keeping load case to EQY and switching to max story drift the maximum drift value noted is 0.0000072.

• So as per the clause 7.11.1.1,the maximum inter storey drift is milited to 0.004 for each storey height.But our value is 0.0020 which is within the code limits.