Norwegian design standard for slender reinforced concrete design

Abstract

The purpose of this project is to study and evaluate design method of slender reinforced concrete column recommended by Norwegian Design Standard, NS 3473E:2003, using experimental results investigated by other researchers. The comparison are based on 139 slender reinforced concrete test columns, which are pin-ended and subjected to short-term eccentric axial load about the minor axis with load eccentricity to depth ratio of 0 to 0.75. The slenderness ratios are ranged from 14.7 to 40, compressive strength of concrete ranged from 16.7 to 106.7 MPa and steel ratio varying from 0.77 to 5.24%. In NS 3473E:2003, Additional Moment Method was employed as the design philosophy to account for second order effect where the displacements of the slender columns are taken into consideration in the equilibrium conditions. In addition, force dependent slenderness that takes into account of geometrical slenderness as well as the function of axial force and reinforcement is used for the classification of column. The procedures of the design method and numerical example are presented in this report. On average, the experimental failure loads are 1.78 times of NS 3473. The failure loads predicted by NS 3473 gives conservative values when compared with 2 numerical predictions, P-Delta method and Transformation method, and 4 codes predictions of EC2, BS 8110, ACI 360 and AS 3600. NS 3473 generally provides a higher safety of margin from the experimental results. However, NS 3473 shows a good agreement between the predicted failure loads of ACI and AS 3600. In general, the major variables that influence the behaviour of column are the slenderness ratio and eccentricity of load. NS 3473 tend to underestimate the capacity of the column as the slenderness ratio increases. In addition, for columns with eccentricity of load, e/h=0.25, NS 3473 tends to underestimate the capacity by around 45%. However, for columns with eccentricity of load, e/h=0.5, the failure load will be nearer to the experimental failure load but still on the safer side. Therefore, NS 3473 is a safe design document for slender reinforced concrete column, considering the material factor of safety has yet to be included for this analysis.