Modelling of 25 storey building with the specified properties using ETABS

1.

Aim

To draw a 25 storey building by using Etabs with given structural properties. Also to check the arrived results is satisfying the IS 1893 2016 part 1

To Check the translational fundamental time period of vibration.

To Check torsional Irregularity

To check Vertical Irregularity

To check Inter storey drift

Procedure

• Open Etabs software.
• Then give the Indian settings and Code books.
• Then give grids and storey heights as required.
• Create material properties for concrete and steel.
• Then create section properties for beam and column section.
• Then create slab properties.
• Then provide load pattern as dead load, live load, wall load, earthquake load etc.
• Give mass source and dead load as 100%, Wall load as 100% and Live load as 25%.
• Then create load combinations.
• Use quick columns commends and select the column size and place it on the grids. Check all storey is selected.
• Then use quick beam commend and select the beam section and click on each grid the beams will be created. Check all storey are selected.
• Then give slab properties for similar selection.
• Then select beams and assign uniform wall load of 10kN.
• Then select slab and assign uniform live load as 3kN
• Then assign diaphragm for the structure.
• Once everything is assigned, then save and run analysis.

Output

Result

To check Fundamental Natural Period of Vibration

Direction Given Analysis Result

X axis 4.4 sec 4.41 sec

Y axis 4.2 sec 4.22 sec

Torsional Irregularity

As per IS 1893 2016 Part 1 of Table 5,

The torsional mode time period is lesser than X and Y direction time period.

In this case mode 1 and 2 is higher than mode 3 hence it satisfies the torsional irregularity.

Vertical Irregularity

First three modes should contribute at least 65% of mass participation factor in each principal plan direction.

In this case the mode 1 contributes 80% and mode 2 contributes 80% hence it is satisfied.

Fundamental natural periods in two principal directions are away from each other by at least 10% .

In our case the mode 1 is 4.41 and the mode 2 is 4.22,

For 10% away the minimum value is 3.959 but the mode 2 is 4.22 which not away from the X direction.

Inter storey drift

As per IS 1893 2016 Claus 7.11.1.1, storey drift shall not exceed 0.004 time the storey height for base shear with no load factor 4x10-3

In our case the base shear with no loads is 1.60x10-3. Hence it satisfies the inter storey drift.