1. Solution 2 Date of assignment: 20January Date of solution: ?? January
E-Course on seismic design of tanks

2. E-Course on Seismic Design of Tanks / January 2006
Part II: True/ False
Identify the following statements as True or False
2.1) Seismic force depends on mass of structure.
True
2.2) In IS 1893(Part 1):2002, there are five seismic zones.
False
There are four zones, numbered from II to V.
2.3) In IBC 2003,response modification factor for buildings with good ductility is lower than that for elevated tanks on frame type staging
For a building with good ductility, response modification
factor, R = 8.0 as against, R = 3.0 for elevated tanks on frame staging
 Sudhir K. Jain, IIT Kanpur
E-Course on Seismic Design of Tanks / January 2006

3. Part II: True/ False (contd…)
2.4) In IS 1893:1984,performance factor, K for buildings with
Good ductility is more than that for elevated tanks
False
Performance factor, K is same (K = 1.0), for a building with
good ductility and elevated tanks.
2.5) Importance factor for tanks is higher than for buildings.
True
2.6) Damping of structure does not affect base shear coefficient.
See Table 3 of IS 1893(Part 1):2002 and Fig. 2 of IS 1893:1984
 Sudhir K. Jain, IIT Kanpur
E-Course on Seismic Design of Tanks / January 2006

4. Part II: True/ False (contd…)
2.7) In IS 1893(Part 1):2002, base shear coefficient depends on type of foundation.
False
In IS 1893(Part 1):2002, base shear coefficient does not
depend on type of foundation. Rather, in IS 1893:1984, it use to depend on type of foundation.
 Sudhir K. Jain, IIT Kanpur
E-Course on Seismic Design of Tanks / January 2006

5. E-Course on Seismic Design of Tanks / January 2006
Part III: Solutions
2.1)As per IS 1893:1984, obtain base shear coefficient for following structures using response spectrum method
(Fo = 0.4,  = 1.0; consider 5% damping)
1) A building with good ductility and time period of 1.1 sec.
2) A building with low ductility and time period of 1.1 sec.
3) An elevated tank with time period of 1.1 sec.
Solution: In response spectrum method, base shear coefficient is expressed as:
Ah = KIFoSa/g for buildings
Ah = IFoSa/g for elevated tanks
We have, Fo = 0.4,  = 1.0
 Sudhir K. Jain, IIT Kanpur
E-Course on Seismic Design of Tanks / January 2006

6. E-Course on Seismic Design of Tanks / January 2006
Part III: Solutions
All three structures have time period of 1.1 sec and damping of 5%, and hence, from Figure 2 of IS 1893:1984, Sa/g = 0.1
For building with good ductility:
K = 1.0, I = 1.0
Ah = KIFoSa/g = 1.0 x 1.0 x 1.0 x 0.4 x 0.1 = 0.04
For building low good ductility:
K = 1.6, I = 1.0
Ah = KIFoSa/g = 1.6 x 1.0 x 1.0 x 0.4 x 0.1 = 0.064
For elevated tank:
I = 1.5
Ah = IFoSa/g = 1.0 x 1.5 x 0.4 x 0.1 = 0.06
 Sudhir K. Jain, IIT Kanpur
E-Course on Seismic Design of Tanks / January 2006

7. E-Course on Seismic Design of Tanks / January 2006
Part III: Solutions
2.2) For following elevated tanks, obtain base shear coefficient as per IS 1893:1984 (Fo = 0.4,  = 1.0)
1) Time period = 0.5 sec; damping of 0%, 2% and 5%
2) Time period = 1.4 sec; damping of 0%, 2% and 5%
Solution: Base shear coefficient for tank is:
Ah = IFoSa/g
We have, Fo = 0.4,  = 1.0 and Importance factor, I = 1.5
Values of Sa/g are to be obtained from Fig. 2 of IS 1893:1984
 Sudhir K. Jain, IIT Kanpur
E-Course on Seismic Design of Tanks / January 2006

8. E-Course on Seismic Design of Tanks / January 2006
Part III: Solutions
Time period
(Sec)
Damping
(%)
Sa/g
Ah = IFoSa/g
0.5
0.50
1.0 x 1.5 x 0.4 x 0.5 = 0.300 2
0.25
1.0 x 1.5 x 0.4 x 0.25 = 0.150 5
0.16
1.0 x 1.5 x 0.4 x 0.16 = 0.096
1.4
0.15
1.0 x 1.5 x 0.4 x 0.15 = 0.090
0.12
1.0 x 1.5 x 0.4 x = 0.063
0.08
1.0 x 1.5 x 0.4 x 0.08 = 0.048
Note the effect of damping on base shear coefficient
 Sudhir K. Jain, IIT Kanpur
E-Course on Seismic Design of Tanks / January 2006