ASCE-7 and IBC 2003 use an "influence area" instead of a tributary area in their live load reduction calculations. The influence area is defined as the "floor area over which the influence surface for structural effects is significantly different from zero".

Influence areas are not calculated when BS 6399 or AS/NZ 1170.1 are used.

RAM Concept uses heuristic methods to calculate influence areas. These methods tend to define areas that are similar to those of that engineers would produce visually, but the methods do not calculate areas that are exactly the same as an engineer might calculate manually. RAM Concept 's influence areas can be shown on the plans so you can inspect the areas that Concept is using in its live load reduction calculations.

Per ASCE-7 and IBC 2003, RAM Concept limits the influence areas to be no larger than the following multiple of the tributary area: