Modelling of 25 storey building with the specified properties using ETABS

ANSWER

1. Model creation

The structure is created as per the question.

2. Material definition

Materials are defined as M30 and Fe415.

3. Section properties

Beam section, Column section and Slab section properties are added here.

• Beam section = 300x400mm.
• Column section = 800x800mm
• Slab is 150mm thick.

Beam

Column

Slab

4. Load patterns & Combinations

Dead load, Live load, Wall load and Seismic loads are added.

Seismic loads

Seismic Zone factor is 0.16 from IS 1893:2016.

EQX and EQY are defined as follows.

5. Mass source

6. Drawing Beams, Columns & Supports

Columns

Columns are drawn from the 'Quick draw' option.

Beams

Beams are drawn from the 'Quick draw' option.

Slabs

Slab is created by selecting 'Quick draw' option by setting to 'Similar stories'. Because in base and plinth, there are no slabs.

Supports

Base storey is selected and Pin joint is assigned at all nodes.

7. Load assignment

Wall load

Select all beams and assign wall load as 10kN/m.

Live load

Select all slabs and Shell load-Distributed. The select Live load as 3kN/m. Diaphram load is also assigned.

8. Analysis

After all these steps above, Model is analysed.

RESULTS

1. Fundamental Translational Natural period

2. Torsional Irregularity

As per IS 1893-2016 (Part I) Table 5,

Torsional mode time period should be lesser than X & Y direction time periods. From the result above,

Torsional mode time period = 3.31s, which is less than X & Y modes.

3. Vertical Irregularity

a) As per IS 1893-2016 (Part I) Table 6, Cl. 7,

First 3 modes together should contribute at least 65% in the Mass participation factor in each principal direction.

Here, from the above result, The 1st mode itself is participating 80% in Mass participation.

b) As per IS 1893-2016 (Part I) Table 6, Cl. 7,

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

Here,

Mode 1 Time period = 4.416s

Mode 2 Time period = 4.222s

ie,

Mode 2 should be at least 3.97s. So it isn't satisfying here.

4. Inter-storey drift

Max. Storey drift for EQX and EQY are given below.

Criteria		Desirable solution	Exercise result
Fundamental Translational Natural period	X- direction	4.4s	4.416s
	Y-direction	4.2s	4.222s
Torsional Irregularity	IS 1893-2016 (Part I) Table 5	Torsional mode time period should be lesser than X & Y direction time periods	Yes. ie, 3.31s<4.4s, 3.31s<4.2s
Vertical Irregularity	IS 1893-2016 (Part I) Table 6, Cl. 7	First 3 modes together should contribute at least 65% in mass participation factor in each principal direction	Yes. Mode 1 = 80.42% & Mode 2 = 80.84%
		Fundamental natural time periods in two principal plane directions are away from each other by at least 10%	No
Inter-storey drift	IS 1893-2016 (Part I), Cl. 7.11.1.1	Storey drift shalln't exceed 0.004 times the storey height for base shear with no load factors	Yes.