Verification of the P-delta effect for fiber reinforced UHPC short columns

The P-delta effect, i.e., second-order (nonlinear) effect, can lead to large lateral displacements hence resulting in premature failure of structural members under axial loading conditions. This study aims to verify the P-delta effect in ultra-high performance concrete (UHPC) short columns considering fiber contribution. Fourteen UHPC short columns with a slenderness ratio of 17.5 were tested under eccentric compressive loading. The results show that increasing the content of steel fibers in UHPC can improve the resistance of both the compression zone and the tension zone, which therefore delayed the crushing failure and effectively reduced the flexural cracks. For the columns under the eccentricity of 110 mm, the ultimate bearing capacity increased by 3.6 %-4.9 % when the fiber content increased from 1.0 vol% to 2.0 vol%, and the increase was at 17.1 % when the fiber content was up to 3.0 vol%. The moment magnifying coefficients for UHPC were calibrated through the theoretical analysis. The calibrated coefficients agreed well with the experimental results with a ratio of 0.97. The proposed analytical models for the ultimate bearing capacity also agreed well with the experimental results. The average ratios of the calculated axial load to the experimental result were 1.02 and 0.97 for the compression and tension-controlled models, respectively. By the first and second-order analysis, their average deviation of the analytical models was 6.2 %. The analytical model considering the second-order effect gave a more accurate prediction on the bearing capacity.