Modelling of 25 storey building with the specified properties using ETABS

CHALLENGE-6:

Modelling of 25 storeys building with the specified properties using ETABS

AIM:

Modelling of 25 storeys building with the specified properties using ETABS

INTRODUCTION:

ETABS is a structural analysis program that deals with multi-storey buildings analysis and design. The software has a friendly graphic user interface. It helps in 3D modelling and analysing building structures, saving significant time and effort. Basic or advanced systems under static or dynamic conditions may be evaluated using ETABS. Easy to create the modelling 25 storeys building with the specified properties using ETABS.

QUESTION:

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 the roof floor in view of the 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 storeys 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.

Carry out the following exercises:

• Check if the translational fundamental natural period of vibration in both the x and y direction is approximate: Tx1">Tx1y1= 4.4 second Ty1">Ty1x1= 4.2 second

This check will help confirm if the 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 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 structure is subjected to unfactored seismic base shear

PROCEDURE:

1. Open the ETABS software and open to the New model.

2. Now select units like metric units, India, steel(IS 800) and concrete(IS 456) code books.

3. Now select the custom grid spacing and custom story data.

4. Now create the 25 storeys data, plinth height is considered as 1.5 m and all 25 floors are similar to the Storey1 and click ok.

5. Now Go to Define to add the materials Grade of concrete M30 and Fe415 steel.

6. Now Go to section properties, Select frame sections and create a Beam of size 300mmx400mm, Columns 800mmx800mm and slab 150mm thickness.

7. Now select a Slab section 150mm thickness considered as a membrane.

8. Now go to load patterns and created loads.

9. Now Mass source and mentioned the mass multipliers for load patterns as per code.

10. Now check for Load cases as all loads are mentioned or not.

11. Now create Load combinations for the concrete frames for the user-defined interface.

12. Now modelling all elements. Go to the quick column tool and choose the property to ensure with all storeys option at the bottom.

13. Go to the quick beam tool and choose the property to ensure with all storeys option at the bottom.

14. Now create the slab at 150mm thick, select storey1 and ensure with similar stories.

15. After that select the frame properties to select all beams and assign the Frame loads to distribution frame loads with a wall of 10KN/M.

16. Now Select all slabs and assign the live loads 3 Kn/m2.

17. Now again select all slabs to assign all diaphragms. It is useful for lateral calculations.

18. After that save the model and analyze it.

RESULTS:

CHECKING:

Criteria		Desirable Solution	Results
Fundamental Translational natural period	X-direction Y-direction	4.4 seconds 4.2 seconds	4.41 seconds 4.22 seconds
Torsional irregularity	IS 1893-2016(Part-1)	Time period should be lesser than X and Y direction time periods	Yes
Vertical irregularity	IS 1893-2016(Part-1) Table-6 Clause-7	The first three modes together should contribute at least 65% in the mass participation factor in each principal direction	Yes
		Fundamental lateral natural periods in two principal plane directions 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 with no load factors (4x10-3)	Yes

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