PREDICTION OF SHEAR RESISTANCE FACTOR IN FLAT SLABS DESIGN USING CRITICAL PERIMETER OF SUPPORTING COLUMNS

The distribution of shear stresses at the slab–column connection of flat slabs become non–uniform in the presence of unbalanced moment. The shear resistance (β) factor is used to account for this distribution of shear stresses due to the transfer of unbalanced moment at the slab–column connections. The provisions of the American, Canadian, European and Model codes, regarding the transfer of unbalanced moment at slab–column connections of flat slabs are compared. The relationship of β-factor to the ratio of critical perimeter to the control perimeter of an internal column have been plotted as a simplified approach and additional approximate factors have been found for an internal corner column and various locations of cantilevered edge, corner and internal corner columns encountered in practice by engineers. These additional approximate factors have been proposed for inclusion in European code for situations where adjacent spans do not differ by more than 25%.http://dx.doi.org/10.4314/njt.v36i1.

SUITABILITY OF BURNT AND CRUSHED COW BONES AS PARTIAL REPLACEMENT FOR FINE AGGREGATE IN CONCRETE

The suitability of burnt and crushed cow bones (BCCB) as partial replacement for fine aggregate in concrete was studied. The percentages of replacements of fine aggregates of 0, 10, 20, 30, 40 and 50%, respectively of BCCB were tested considering 1: 2: 4 and 1: 11/2 :3 concrete mix ratios. The cow bones were burnt for 50 minutes up to 92oC before being crushed. Ninety-six (96) concrete cubes of 1: 2: 4 mix ratio and ninety-six (96) concrete cubes of 1 : : 3 mix ratio measuring 150x150x150mm were tested for the compressive strength at 7, 14, 21 and 28 days respectively. The research revealed that the BCCB acted as a retarder in the concrete. Water-cement ratio increased with the increase in the percentage of the BCCB. The mixes of 1:2:4 and 1::3 at 28 days curing yielded average compressive strengths in N/mm2 ranging from 16.49 - 24.29 and 18.71 - 29.73, respectively. For the mix ratios of 1:2:4 and 1:: 3 at 28 days curing age,  it was observed that increase in the BCCB content beyond 40 and 50%, respectively resulted to the reduction of the average compressive strength below recommended minimum strength for use of concrete in structural works.http://dx.doi.org/10.4314/njt.v36i3.