PSI - Issue 14

Siva Naveen E et al. / Procedia Structural Integrity 14 (2019) 806–819 Siva Naveen E, Nimmy Mariam Abraham, Anitha Kumari S D / Structural Integrity Procedia 00 (2018) 000–000

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5. Results and discussion The results obtained from the analysis of frames having single and combination of irregularities are plotted and compared with that of a regular frame.

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1 2 3 4 5 6 7 8 9

8

7

6

5

Level

Level

4

3

2

1

0

5

10

15

0

5

10

15

20

Storey Drift(mm)

Displacement(mm)

R

MI-1 SI-1 SI-5 SI-9

MI-2 SI-2 SI-6 SI-10

MI-3 SI-3 SI-7

R

MI-1 SI-1 SI-5 SI-9

MI-2 SI-2 SI-6 SI-10

MI-3 SI-3 SI-7

MI-4 SI-4 SI-8

MI-4 SI-4 SI-8

Fig.3. Displacement response and storey drift for MI & SI cases.

Figure 3 represents the displacement response and storey drift of MI and SI cases. Maximum storey displacement and storey drift among mass irregularity cases is observed for case MI-3, where the magnitude of mass was doubled at 2nd and 7th floor levels. Compared to the regular structure, an increase of 23% is observed in maximum floor displacement for MI-3. For SI-1, a reduction in stiffness by 43% has shown an increase of 21% in the displacement response compared to the regular one. For SI-2 and SI-3, a reduction in stiffness by 87.5% has increased the maximum storey displacement by 71% and 44% respectively with respect to the regular one. It is observed that for the same amount of reduction in stiffness, SI-2 has displayed more response than SI-3. This indicates that the seismic response of structure depends on the location of irregularity. For SI-4 and SI-5, the location of reduction in stiffness is kept same (5th floor). However, due to the amount of reduction in stiffness by 72% for SI-4 and 39% for SI-5, maximum storey displacement has increased by 38% for SI-4 and 8% for SI-5 compared to the regular frame. It is observed that for SI-3, SI-4 and SI-5, the displacement response showed an abrupt increase near the location of irregularity (i.e. change in storey height). For SI-6, the cross sectional area of columns for all the floors are almost equal but, the cross sectional shape of first two storeys (circular) differs from the remaining floors (rectangular). Thus, a reduction in stiffness by 30% is seen which is due to the cross sectional shape. It has reduced the displacement response by 20% than the regular one. In SI-7, the first two floors have circular columns and in SI-8 the first two floors have rectangular columns. However, the cross sectional area for both the shapes is kept same. Also, for both the cases, the first two floors have more cross sectional area than the remaining floors. Thus, for SI-7 and SI-8, due to the increased cross sectional area, the displacement response is reduced by 13.4% for SI-7 and 14.4% for SI-8. With the same cross sectional area, the structure with circular columns (SI-7) displaces more than SI-8. Even though circular columns have larger moment of inertia, it displaces more than that of rectangle columns as the moment carrying capacity for rectangular columns is more than the circular one. Hence, from SI-6, SI-7 and SI-8 it is observed that, with the introduction of circular columns the displacement response decreases. For SI-9 and