Modelling of 25 storey building with the specified properties using ETABS

CHALLENGE 6

Aim: The main aim of this challenge is to gain the knowledge about the concept of modelling of a multi – storey building with the use of ETABS software and also about how to extract the time period and the mass participation ratio results from the software. The codal provisions that are to be satisfied for a building while designing is also learnt.

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.

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 in view of parapet)
• Live load on floor : 3 kN/m2 (Let us assume the same for roof floor)

1. a) Buildings are assumed to be pinned at the base
2. b) All columns in all storey are of the same size
3. c) All beams in all storeys are of the same size
4. d) Building is located on Soil type-II and in Zone-III. Assume other factors if required.

Carry out the following exercises:

Check if the translational fundamental natural period of vibration in both the x and y direction is approximately: T_x1= 4.4 second and T_y1= 4.2 second.

This check will help confirm if modelling is done correctly. Some deviations from the above values is 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 satisfied:

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

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 provision on inter-storey drift limitations in clause 7.11.1.1 satisfied. Please note that this check is for Serviceability Limit State and hence is for situation when stucture is subjected to unfactored seismic base shear.

CRITERIA		DESIRABLE SOLUTION	EXERCISE RESULT
Fundamental Translational Natural period	X - Direction	4.4 seconds	4.416 seconds
	Y - Direction	4.2 seconds	4.22 seconds
Torsional irregularity	IS 1893 – 2016 (part 1) Table 5	Torsional mode Time period  should be lesser than X and Y direction time period	Yes
Vertical irregularity	IS 1893 – 2016 (part 1) Table 6 clause 7	First three modes together should contribute at least 65% in mass participation factor in each principal direction	Yes
		Fundamental lateral natural periods in two principal plane direction are away from each other by at least 10%	No
Inter – storey drift	IS 1893 – 2016 (part 1) clause 7.11.1.1	Storey drift shall not exceed 0.004 times the storey height for base shear eith no load factors (4*10^-3)	Yes

Images of the modelling procedure:

DEFINING OF GRIDS

DEFINING OF STOREYS

DEFINING OF BEAM PROPERTIES

DEFINING OF COLUMN PROPERTIES

DEFINING OF CONCRETE MATERIAL PROPERTY

DEFINING OF REBAR MATERIAL PROPERTY

DEFINING OF LOADS

DEFINING OF EARTHQUAKE LOADS ALONG X - DIRECTION

DEFINING OF MASS SOURCE

DEFINING LOAD COMBINATIONS

ASSIGINING OF DIAPHRAGM

3 - D VIEW OF THE MODEL

RESULTS:

MODAL TIME PERIOD

MASS PARTICIPATION RATIOS

STOREY DRIFT ALONG EQX

STOREY DRIFT ALONG EQY

Conclusion:

From the challenge carried out it can be concluded that the concept of modelling of a multi – storey building with the use of ETABS software and also about how to extract the time period and the mass participation ratio results from the software. The codal provisions that are to be satisfied for a building while designing is also learnt.

Vijayalakshmi S H