Axial Load Behaviour of Large Scale Concrete Columns

This research mainly intended to investigated the axial load behavior of large-scale rectangular columns, the test specimens were geometrically similar reinforced concrete columns of square cross-section with sides, D, of 50 mm, 100 mm and 200 mm., the effective lengths corresponding to the largest cross section were 580, 1080 and 2080 mm, the effective lengths corresponding to the middle section size were 290, 540 and 1040 mm and the effective lengths corresponding to the smallest cross section were 145, 270 and 520 mm. The above combinations resulted in three slenderness ratios, of 9.7, 18.0 and 34.7 (where l=L/r=L/0.3D). The columns in each group of the same slendernessratio were geometrically similar. The types of concretes used in this study were Grade 30 and the maximum aggregate (crushed limestone) size was 10 mm. 100 mm cubes (in sets of six) where manufactured for monitoring compressive strength at 28 day, together with cylinders (100x200 mm) to determine the tensile splitting strength and beams (100x100x500 mm) to determine the flexural strength were used in the study. The failure loads and axial displacement of the columns were measured. It was observed that for all slenderness ratios, the failure loads exhibited size effect. The nominal stress at maximum load (maximum load divided by nominal cross-sectional area) decreased as the size of the columns increased. This behaviour is not taken into account in current design codes, which make no allowance for such size effects, and indicates that failure is governed by the principles of fracture mechanics. In conclusion, the results are in good agreement with the size-effect law as proposed by Bazant

Keywords:

Concrete: Bearing strength , Size effect law