37.1 Analysis of Structure
Methods of analysis as in 22 shall be used. The material strength to be assumed shall be characteristic values in the determination of elastic properties of members irrespective of the limit state being considered. Redistribution of the calculated moments may be made as given in 37.1.1.
37.1.1 Redistribution of Moments in Continuous Beams and Frames
The redistribution of moments may be carried out satisfying the following conditions:
- a) Equilibrium between the internal forces and the external loads is maintained.
- b) The ultimate moment of resistance provided at any section of a member is not less than 70 percent of the moment at that section obtained from an elastic maximum moment diagram covering all appropriate combinations of loads.
- c) The elastic moment at any section in a member due to a particular combination of loads shall
Table 18 Values of Partial Safety Factor for Loads
(Clauses 18.2.3.1, 36.4.1 and B-4.3)
| Load Combination | Limit State of Collapse | Limit States of Serviceability | ||||
|---|---|---|---|---|---|---|
| DL | IL | WL | DL | IL | WL | |
| (1) | (2) | (3) | (4) | (5) | (6) | (7) |
| DL + IL | 1.5 | 1.0 | 1.0 | 1.0 | - | |
| DL + WL | 1.5 or 0.90 | - | 1.5 | 1.0 | 1.0 | |
| DL + IL + WL | 1.2 | 1.0 | 0.8 | 0.8 | ||
NOTES
- 1 While considering earthquake effects, substitute EL for WL.
- 2 For the limit states of serviceability, the values of given in this table are applicable for short term effects. While assessing the long term effects due to creep the dead load and that part of the live load likely to be permanent may only be considered.
not be reduced by more than 30 percent of the numerically largest moment given anywhere by the elastic maximum moments diagram for the particular member, covering all appropriate combination of loads.
- d) At sections where the moment capacity after redistribution is less than that from the elastic maximum moment diagram, the following relationship shall be satisfied:
where
- = depth of neutral axis,
- effective depth, and
percentage reduction in moment.
- e) In structures in which the structural frame provides the lateral stability, the reductions in moment allowed by condition 37.1.1 (c) shall be restricted to 10 percent for structures over 4 storeys in height.
37.1.2 Analysis of Slabs Spanning in Two Directions at Right Angles
Yield line theory or any other acceptable method may be used. Alternatively the provisions given in Annex D may be followed.