Modelling of 25 storey building with the specified properties using ETABS
ANSWERS
- AIM & INTRODUCTION:
- To Know modelling of a high rise building in ETABS software.
- To verify the seismic code requirements as per IS Code 1893 from ETAB analysis.
I am modelling a 25-storey building on ETABS with structural properties as Structural element of Sizes :
- Beams: 300 × 400 mm
- Columns: 800 × 800 mm
- Slab: 150 mm thick
Material Property as
- 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)
- PROCEDURE
- Modelling by grid method.
- Define
- Materials (Concrete-M30,Rebar-Fe415) and sections (Beam, Column & Slab).
- Add/draw column, beam and slab in Model.
- Assign load in beams, slabs.
- Add load patterns.
- Add load weightage in mass source.
- Do load combinations.
- Assign base (foundation) as pin joint.
- Check model for frame joints & connections.
- Run Analysis.
- RESULT
|
Criteria |
Desirable solution |
Exercise result |
|
|
Translational fundamental natural period of vibration |
X-direction |
4.4 |
4.416 |
|
Y-direction |
4.2 |
4.222 |
|
|
Torsional irregularity |
Table 5 of IS 1893 (part 1) – 2016 |
Torsional mode time period should be lesser than X and Y direction time periods. |
Yes, less than 4.416 & 4.222 |
|
Vertical irregularity |
Table 6 of IS 1893 (part 1) – 2016, |
First three modes together should contribute at least 65% in mass participation factor in each principal direction. |
Obtained as shown in below Table 2 |
|
Fundamental lateral natural periods in two directions are away from each other by at least 10%. |
Not obtained. Ie 4.416 x 0.90 = 3.97, but it is 4.222 as shown in Table – 1. |
||
|
Inter-storey Drift |
Limitations in clause 7.11.1.1 of IS 1893 (part 1) – 2016, |
Storey drift shall not exceed 0.004 times the storey, height for base shear with no load factors. |
Yes |
Table - 1
|
Case |
Mode |
Period |
Frequency |
CircFreq |
Eigenvalue |
|
sec |
cyc/sec |
rad/sec |
rad²/sec² |
||
|
Modal |
1 |
4.416 |
0.226 |
1.423 |
2.025 |
|
Modal |
2 |
4.222 |
0.237 |
1.488 |
2.215 |
|
Modal |
3 |
3.311 |
0.302 |
1.898 |
3.602 |
|
Modal |
4 |
1.404 |
0.712 |
4.475 |
20.030 |
|
Modal |
5 |
1.349 |
0.741 |
4.659 |
21.704 |
|
Modal |
6 |
1.071 |
0.934 |
5.867 |
34.423 |
|
Modal |
7 |
0.759 |
1.318 |
8.281 |
68.577 |
|
Modal |
8 |
0.738 |
1.356 |
8.518 |
72.550 |
|
Modal |
9 |
0.607 |
1.647 |
10.350 |
107.123 |
|
Modal |
10 |
0.492 |
2.031 |
12.762 |
162.859 |
|
Modal |
11 |
0.481 |
2.079 |
13.060 |
170.564 |
|
Modal |
12 |
0.404 |
2.477 |
15.565 |
242.257 |
Table - 2
|
TABLE: Modal Participating Mass Ratios |
||||||||||||||
|
Case |
Mode |
Period |
UX |
UY |
UZ |
Sum UX |
Sum UY |
Sum UZ |
RX |
RY |
RZ |
Sum RX |
SumRY |
SumRZ |
|
sec |
||||||||||||||
|
Modal |
1 |
4.416 |
0.000 |
0.804 |
0.000 |
0.000 |
0.804 |
0.000 |
0.195 |
0.000 |
0.000 |
0.195 |
0.000 |
0.000 |
|
Modal |
2 |
4.222 |
0.808 |
0.000 |
0.000 |
0.808 |
0.804 |
0.000 |
0.000 |
0.190 |
0.000 |
0.195 |
0.190 |
0.000 |
|
Modal |
3 |
3.311 |
0.000 |
0.000 |
0.000 |
0.808 |
0.804 |
0.000 |
0.000 |
0.000 |
0.826 |
0.195 |
0.190 |
0.826 |
|
Modal |
4 |
1.404 |
0.000 |
0.104 |
0.000 |
0.808 |
0.908 |
0.000 |
0.546 |
0.000 |
0.000 |
0.741 |
0.190 |
0.826 |
|
Modal |
5 |
1.349 |
0.100 |
0.000 |
0.000 |
0.909 |
0.908 |
0.000 |
0.000 |
0.552 |
0.000 |
0.741 |
0.743 |
0.826 |
|
Modal |
6 |
1.071 |
0.000 |
0.000 |
0.000 |
0.909 |
0.908 |
0.000 |
0.000 |
0.000 |
0.089 |
0.741 |
0.743 |
0.915 |
|
Modal |
7 |
0.759 |
0.000 |
0.033 |
0.000 |
0.909 |
0.941 |
0.000 |
0.066 |
0.000 |
0.000 |
0.807 |
0.743 |
0.915 |
|
Modal |
8 |
0.738 |
0.033 |
0.000 |
0.000 |
0.942 |
0.941 |
0.000 |
0.000 |
0.064 |
0.000 |
0.807 |
0.806 |
0.915 |
|
Modal |
9 |
0.607 |
0.000 |
0.000 |
0.000 |
0.942 |
0.941 |
0.000 |
0.000 |
0.000 |
0.030 |
0.807 |
0.806 |
0.946 |
|
Modal |
10 |
0.492 |
0.000 |
0.017 |
0.000 |
0.942 |
0.958 |
0.000 |
0.065 |
0.000 |
0.000 |
0.872 |
0.806 |
0.946 |
|
Modal |
11 |
0.481 |
0.016 |
0.000 |
0.000 |
0.958 |
0.958 |
0.000 |
0.000 |
0.066 |
0.000 |
0.872 |
0.872 |
0.946 |
|
Modal |
12 |
0.404 |
0.000 |
0.000 |
0.000 |
0.958 |
0.958 |
0.000 |
0.000 |
0.000 |
0.015 |
0.872 |
0.872 |
0.960 |