Modelling of 25 storey building with the specified properties using ETABS

AIM: Model a 25-storey building on ETABS with structural properties as specified below. Ground floor or plinth floor level can be taken at a height of 1.5 metres from the base. Each of the successive 25 storeys has a storey height of 3 metres.

GIVEN DATA:

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 roof floor given 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 storey are of the same size

c) All beams in all storeys are of the same size

d) Building is located on Soil type-II and in Zone-III. Assume other factors if required.

EXERCISES:

Carry out the following exercises:

• Check if the translational fundamental natural period of vibration in both the x and y direction is approximate: Tx1">Tx1Tx1= 4.4 seconds Ty1">Ty1Ty1= 4.2 seconds

This check will help confirm if modelling is done correctly. Some deviations from the above values are possible (± 2%). But any major deviation will suggest an error in modelling.

• Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity is satisfied:

The natural period corresponding to the torsional mode of oscillation must be less than the two fundamental translational modes of oscillation along with each principal plan direction.

• Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied

• Check if the provision on inter-storey drift limitations in clause 7.11.1.1 is satisfied. Please note that this check is for Serviceability Limit State and hence is for situations when the structure is subjected to unfactored seismic base shear

PROCEDURE:

• Open the ETABS software.
• Create a new file.
• A dialog box appears.
• Click the use built-in options and set the parameters.
• Now add the grids as mentioned in the question.
• Create the number of storeys.
• All the 25 storeys are similar, so set it similar to storey 1, where storey 1 is the parent storey.
• Now click on the OK and the screen with the model and plan view appears.
  

  

  

  

  

  

  

  

  
  
  
  
  

• Now go to the material properties of the define tab, and add rebars of Fe 415 HYSD.
• Similarly, add M30 grade concrete.
• Now again go to the define tab and then select section properties.
• Add the section of the beam as 400 x 300 mm.
• Add the section of the columns as 800 x 800 mm.
• Now again go to the design tab and add the shell properties.
• Create the property of a slab with a thickness of 150mm.
  

  

  

  

  

  

  

  

  

  
  
  
  
  

• Now go to the define tab again and add the load cases and load combinations.
• Define the load patterns as well.
  

  

  

  

  

  
  
  
  
  

• Once all the components are created, now start adding them to form the structure.
• From the bottom right corner, choose the option as all storey.
• Now click on the quick draw columns.
• Drag the cursor to the grid intersection and click to create a column.
• Similarly, once all the columns are created, the beams and the slab are created.
• Take a note that slabs will only be on the 25 storeys, not on the plinth and the base level.
  

  

  

  

  

  

  

  
  
  
  
  

• Now from the menu bar, select the select tab and then select the properties, and then select the frame properties.
• Select all the beams.
• Now go to the assigned tab and assign the wall load of 10 KN/m² on each beam.
• Similarly, select all the slabs and assign a live load of 3 KN/m² on each slab.
• Then again go to the assigned tab and then click on the shell.
• Now clock on the diaphragm and add the diaphragm to all the storeys
  

  

  

  

  

  

  

  

  
  
  
  

• Now once the loads are assigned, click on the triangular shape button on the top menu section, to run the analysis.
• Save the project and then go to the analysis tables.
• Check all the exercises which were required in the question.
  

  

  

  

  

  

  

  

RESULTS:

• Check if the translational fundamental natural period of vibration in both the x and y direction is approximate: Tx1Tx1= 4.4 seconds Ty1Ty1= 4.2 seconds. This check will help confirm if modelling is done correctly. Some deviations from the above values are possible (± 2%). But any major deviation will suggest an error in modelling.
  • The time period of the modes M1 and M2 can be given as
    T1 = 2.954s < 4.4s
    T2 = 2.759s < 4.2s
    Thus, it doesn't satisfy the exercise as was asked in the question
    
    
• Check if the following provision in Table 5 of IS 1893 (part 1) – 2016, on torsional irregularity is satisfied. The natural period corresponding to the torsional mode of oscillation must be less than the two fundamental translational modes of oscillation along with each principal plan direction.
  • 2.209 < 2.759 < 2.954
    THEREFORE, T3<T2<T1
    [OK]
  • Thus satisfies.
    
    
• Check if the two provisions of clause 7 in Table 6 (shown below) of IS 1893 (part 1) – 2016, regarding vertical irregularity is satisfied
  
  • Only the value of M1 is almost 80%, thus the total will surely be above 65%.
  • Thus satisfies.
    
    
• Check if the provision on inter-storey drift limitations in clause 7.11.1.1 is satisfied. Please note that this check is for Serviceability Limit State and hence is for situations when the structure is subjected to unfactored seismic base shear
  • YES