Methods of transmitting stresses from RCC columns to footings

To make the design of the footings, it is necessary to have sound understanding about the transmission of stresses (caused by applied loads) from columns to the footings or piles. Factored forces and moments at the base of columns are delivered to the supporting foundations by providing support on concrete as well as by the extension of longitudinal reinforcement into the footing or arrangement of dowels.

Any of the above method can be employed on the basis of the specifications of the relevant design codes like ACI 318-14. The detailing of reinforcement should be done sufficiently for dispersing the stresses to footings perfectly and then further above the basic soil layer.

Methods of transmitting the stressed from Columns to Footings:

1. Expansion of the Longitudinal Steel into the Footing

Expanded reinforcement should be prepared to transmit the compressive forces that surpassed the lesser of the concrete bearing capacities of either the supported member or the foundation, and any computed tensile force across the column-footing interface.

Minimum four bars should be expanded.

The stress-transfer bars should extend into the base with adequate compression-embedment distance to transmit the stress in the column bars to the base concrete.

Whatever the case may be, a minimum steel area of 0.5% of the column-area should be arranged for transmitting the load.

2. Dowel

a. Dowels should be prepared to transmit the compressive forces which go beyond the lesser of the concrete bearing capacities of either the supported member or the foundation, and any computed tensile force across the column-footing interface.

b. There should be minimum four dowels.

c. The diameter of the dowel should not go over the column-bar diameter in excess of 0.15 in.

d. If the desired dowel length remains greater than the footing depth less 3 in, any smaller-diameter bars containing the same area should be applied or a monolithic concrete cap should be included for raising the concrete depth.

e. The dowels should deliver minimum one-quarter of the tension strength of the column bars on each column face.

f. The dowels should be expanded into the column with a distance equivalent to that necessary for compression lapping of column bars.