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Tributary area is the area surrounding the column that is bounded by a panel centerline. In order to calculate the forces and static loads transferred from floor slabs to the columns tributary area method is used.

Commonly, designers use tributary area in columns for transferring loads from slabs to columns or compute reactions of the beams framing into the columns. The application of the former method is more common.

Tributary Area in Column

The area surrounding the column bounded by the centerline of the panel is the tributary area on which loads are supported by the column at the center of the area, as shown in Fig. 1. The dead load supported by the column is equal to the dead load per unit area times the tributary area.

Tributary Area in Columns
Fig. 1: Tributary Area in Columns

In Fig. 2, tributary areas for column Z (corner column), Column Y (edge column), and Column X (center column) are shown. If the spans between columns are nearly equal, then loads on the corner column are quarter and half of the center column and edge column, respectively.

Tributary Area in Columns at the Corner, Edge, and Center of Floor Slab
Fig. 2: Tributary Area in Columns at the Corner, Edge, and Center of Floor Slab

When the tributary area is used, the position of floor beams is not taken into consideration, but an allowance for their weight is included.

Designers can use the tributary area to calculate live loads, given that the design codes specify the percentage of live loads transmitted to a column is an inverse function of the tributary areas; that is, as the tributary areas increase, the live load reduction increases. That is why this method of load transfer in columns is favored by designers. The live loads reduction details can be found in ASCE7 standard.

About Madeh Izat HamakareemVerified

Madeh is a Structural Engineer who works as Assistant Lecturer in Koya University. He is the author, editor and partner at theconstructor.org.