No abstract

Test results obtained as part of a size-effect study on axially loaded plain concrete columns are presented. The test specimens were geometrically similar concrete columns (with dimensions in the ratio 1:2:4) having slenderness ratios of 9·7, 18·0 and 34·7. The columns were of square cross-section with sides of 50, 100 and 200 mm and varied in length from 145 mm to 2080 mm. Although such columns are at the bottom end of practical column sizes, the test results extend existing research information on size effects in columns. It was observed that for all slenderness ratios, the failure loads exhibited a 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 and needs further investigation to include practical column sizes. The results are not inconsistent with the 'size-effect law' proposed by Bazant.

The size effect has been investigated and fracture energy, G F, determined for a range of different strength concretes. The test specimen geometry used in the study was a compact compression prism. Five sizes of geometrically similar specimens with increasing square crosssectional area (length = depth) and constant thickness (100 ram) were used in the experimental work; the length/depth dimensions of the test specimens were 100, 150, 200, 300, and 400 ram, giving an overall size range ratio of 1:4. The grades of concrete used in this study were C50, C70, C80 and C90, and the maximum coarse aggregate (crushed limestone) size was 10 ram. A strong size effect was observed in the results and it is concluded that the test geometry is good for size effect studies in concrete. Furthermore, it was observed that with increasing strength the size effect becomes more pronounced as the brittleness is increased. RI~SU MI~