Partial safety factor
To account for the different conditions like for material strength, load etc. Different partial factors are used for material and load. M indicate safety factor for material & for load
Design strength = Characteristic strength / rm
Design Load = rf x Characteristic load
As per clause 36.4.2 page 68 of IS 456, ?m= 1.5 for concrete and ?m =1.15 for steel. Similarly clause 36.4.1 page 68 of code gives ?f in table 18 for different values for different load combinations and different limit states.
IS 456 - 2000 Recomendations
(i)Partial safety factors for materials to be multiplied with characteristic strength is given below.
(ii)The code has suggested effective span to effective depth ratios as given below
(iii)The code has suggested effective span to effective depth ratios as given below
Basic effective span to effective depth ratio (l/l) basic
The above values are to be modified for (i) the type and amount of tension steel (Fig 4 page 38 of T5456-2000)
(ii) The amount of compression steel (Fig 5 page 39 of I5456-2000)
The type of beam ie flanged beams etc (Fig 6 page 39 of I5456 - 2000).
For slabs spanning in two directions, the l/d ratio is given below.
For slabs spanning in two directions, the l/d ratio is given below