Modelling of 25 storey building with the specified properties using ETABS
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
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.
Carry out the following exercises:
Check if the translational fundamental natural period of vibration in both the x and y direction is approximately: Tx1= 4.4 second and Ty1= 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 EXERCISE
SOLUTION RESULT
Fundamental.
X direction 4.4sec 4.41 sec
Translational
Natural period. 4.2sec. 4.22sec
Y direction
Torsional irregularity. Torsional mode
IS 1893 – 2016. time period
(part 1)Table 5. Should be less YES
Than X and Y
Direction time
Period
First three modes
Together should
Contribute at least YES
65% in mass
participation factor in each principle direction together should
Vertical irregularity. Fundamenta
IS 1893 – 2016 lateral natural
(part 1) Table 6 periods in two
clause 7 principle plane NO
Direction are away
from each other
by atleast 10%
Inter – storey
drift IS 1893 – 2016 storey drift shall
(part 1) clause 7.11.1.1 not exceed 0.004
time to story height YES
for base shear either
no load factors
(4x10^ -3)
RESULT:
From this 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.