Flexural Limit Analysis of Concentrically Loaded Column Footings


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Title: Flexural Limit Analysis of Concentrically Loaded Column Footings

Author(s): Hans Gesund

Publication: Journal Proceedings

Volume: 80

Issue: 3

Appears on pages(s): 223-228

Keywords: columns(supports); flexural Strength; footings; limit design method; punching shear; reinforced concrete; reinforcing steels; structural analysis; structural design.

Date: 5/1/1983

A " flexural punching" mechanism has been derived for individual concentrically-loaded column footings. It has been shown that with use of this mechanism flexural strength of square individual column footings is less than that predicted by the cantilever design method specified in ACI318-77. The deficiency in strength is in the lopercent range for rectangular column cross sections and the I5 percent range for circular columns. When the footing is rectangular, the Code required concentration of reinforcement in the central band width will compensate for the defciency if the designer uses increased reinforcement over the entire lengih of the footing. Otherwise, because the mechanism spreads well beyond the presently spectfied central band width, strength gained from the additional reinforcement under and near the column will be dissipated by the reduced flexural strength outside the central band wrdth. Suggestions are made for revisions in the expression for the width of the central band and for the portion of the reinforcement to be placed within it, which should help to overcome the problem.