Experimental investigation of steel fiber RC hollow columns under eccentric loading

an investigation was conducted to identify the behavior of steel fiber reinforced concrete columns with an opening under eccentricity loading, focusing on square hollow columns section having different square hole sizes and various steel fiber dosages were cast and tested. The holes pass longitudinally at the center of the cross-section of the columns. The research includes a test of nine columns of dimensions (200 x 200 x 1600 mm). Test parameters were the steel fiber contents (0.5%, 1.0% and 1.5% volume fraction) and opening ratio (10% and 20% hollow ratio) with load eccentricity (eccentricity/column depth ratio is 0.75). The compressive strength cylinder tests are conducted for various steel fiber dosages in terms of volume fraction. First cracking load, lateral displacement and ultimate load for each column are calculated and compared with similar columns made of ordinary reinforced concrete with and without a hole. The experimental results show that for concrete columns with hollow ratios 10% and 20% (C2-I, C-II) and without steel fibers, the first cracking load reduction was 28.88% and 49.70% respectively compared with the solid column (C1-I, C1-II). The addition of steel fibers significantly improves the mechanical response of the tested specimens especially the cracking load. The cracking load for specimen C5-I (10% opening ratio with 1.5% steel fibers volume fraction) increased 2.346 times the cracking load for specimen C2-I (10% opening ratio without steel fibers) and for a specimen with a 20% opening ratio and 1.5% steel fibers volume fraction (C5-II), the cracking load increased 2.181 times the same specimen without adding steel fibers. The ultimate load-carrying capacity for specimen C5-I (10% opening ratio with 1.5% steel fibers volume fraction) increased 1.094 times the cracking load for specimen C2-I (10% opening ratio without steel fibers) and for a specimen with a 20% opening ratio and 1.5% steel fibers volume fraction (C5-II), the ultimate load-carrying capacity increased 1.23 times the same specimen without adding steel fibers. The test results indicate the addition of steel fiber enhanced the strength capacity, ductility and allowing these columns to absorb more energy compared with a similar column with ordinary reinforced concrete.