What is Load Combinations

As per IS 1893 (Part 1): 2002 Clause no. 6.3.1.2,
the following load cases have to be considered for
analysis:
1.5 (DL + IL)<>
1.2 (DL + IL ± EL)<>
1.5 (DL ± EL)<>
0.9 DL ± 1.5 EL<>
Earthquake load must be considered for +X, -X,
+Z and –Z directions. Moreover, accidental
eccentricity can be such that it causes clockwise
or anticlockwise moments. Thus, ±EL above
implies 8 cases, and in all, 25 cases as per Table 3
must be considered. It is possible to reduce the
load combinations to 13 instead of 25 by not
using negative torsion considering the symmetry
of the building. Since large amount of data is
difficult to handle manually, all 25-load
combinations are analysed using software.
For design of various building elements (beams or
columns), the design data may be collected from
computer output. Important design forces for
selected beams will be tabulated and shown
diagrammatically where needed. . In load
combinations involving Imposed Loads (IL), IS
1893 (Part 1): 2002 recommends 50% of the
imposed load to be considered for seismic weight
calculations. However, the authors are of the
opinion that the relaxation in the imposed load is
en conservative. This example therefore, considers
100% imposed loads in load combinations.
For above load combinations, analysis is
performed and results of deflections in each
storey and forces in various elements are
obtained.