Limit state method is based on statistical concepts. Strength of materials and loads are highly variable in a range of values.
Characteristic
strength and loads
Limit state method is
based on statistical concepts. Strength of materials and loads are highly
variable in a range of values. The test in laboratory on compressive strength
of concrete has indicated coefficient of variation of �10%. Hence in reinforced
concrete construction, If is not practicable to specify a precise cube
strength. Hence in limit state design uses the concept of 'characteristic
strength' fck indicates characteristics strength of concrete & by
characteristic strength of steel. In general fk indicates the characteristic
strength of material.
? f_{k} =
f_{m} -1.646 (2.6) here f_{m}
= mean strength.
Similarly
'characteristic load' is that value of load which has an accepted probability
of not being exceeded during the life span of structure. In practice the load
specified by IS875 - 1987 is considered as characteristic load. Equation for
characteristic load is
L_{k}
= L_{m} + 1.64_.