Effect of Load Eccentricity on the Strength of Concrete Columns

Abstract

This research presents a theoretical study to determine the effect of the load eccentricity on the reinforced concrete column strength taking into account the variables: amount of eccentricity ratio (e/h=0.1 and 1.0); amount of longitudinal reinforcement ρ%=1% to 8%; concrete compressive strength ( ' 21,28,35,42,63 84 ); c f = and MPa steel yielding strength ( 414 525 ); y f = and MPa the steel reinforcement distance ratiocondition of loading (Uniaxial and Biaxial bending); shape of the cross section (rectangular and circular) and finally the distribution of the reinforcement on two opposite sides and on four sides. Generally the strength of columns is reduced with existing the load eccentricity and amount of losses in strength increased with increasing the eccentricity amount. The average strength ratio in case of biaxial bending condition is about (82%) of the uniaxial condition in case of (e/h=0.1) and become (55%) in case of (e/h=0.1). For uniaxial bending condition, the average relative column strength is about (75%) in case of (e/h=0.1) and (14%) in case of (e/h=0.1); while for biaxial bending condition, the ratio is (60%) in case of (e/h=0.1) and (8%) in case of (e/ h=0.1). Increasing of concrete compressive strength ( ' ) c f , steel yielding strength ( ) s γ , steel distance ratio ( ) s γ and amount of longitudinal reinforcement (ρ%) cause increasing in column strength and reducing the losses in column strength. Also the results show great effect of the load eccentricity ratio (e/h) and bending condition (uniaxial and biaxial) on the reduction of column strength. The distribution of the reinforcement on two opposite sides gives upper limit results and maximum column strength, compared with the case of when the reinforcement distributed on four sides and rectangular section with circular distribution of the reinforcement, while circular columns gives lower limit results and minimum column strength compared with other cases mentioned above.