MODE OF COLLAPSE OF SQUARE SINGLE PANEL REINFORCED CONCRETE SPACE- FRAMED STRUCTURES WITH RIGID BEAM-COLUMN JOINTS

The behavior of the structural elements of a space-framed structure depends on their support conditions. These support conditions can be hinged or rigid for beam-column joints, while for slab these support conditions can be simply supported on walls that are not monolithically constructed together, simply supported on beams that are monolithically constructed together and, can be freely supported on one, two or three edges. This paper studies the mode of collapse of collapse of a single-paneled reinforced concrete space-framed structure with rigid beam-column joints. Five models were investigated for the interactive behavior of slabs, beams and columns. The models were loaded directly till collapse. The estimated and actual collapse loads of the five models were compared. The estimated collapse load for the slab was 35 kN/m2. Also, the numerical estimate of the collapse load for the beam was 10.2kN/m (with an equivalent slab load of 40.8kN/m2), while the shear capacity at the beam-column joints was estimated to be 19.14 kN. The mode of collapse for all the five models was by shear failure at the beam-column joints at an average shear force of 7.13 kN as against the estimated shear capacities of 19.14 kN,  showing that the existing formulae for predicting shear capacity of beam-column joints gave an overestimated value of joint shear capacity up to about 168%. It was found that the space framed models failed by shearing at the beam-column joints, and that the estimated shear capacity was greater than the shear force at collapse.  http://dx.doi.org/10.4314/njt.v35i1.

EFFECTS OF POLYTHENE FIBRES ON SELECTED PROPERTIES OF SANDCRETE BLOCKS

 The aim of this study is to explore the possibility of using polythene fibres to increase the strength of sandcrete blocks without increasing the weight and cost of production. It is a comparative study of the properties and performance of polythene reinforced and plain sandcrete blocks. The graded soil sample has a specific gravity of 2.64. Polythene fibres were got from shredded sachet water bags. The fibres were mixed at 0.25%, 0.50% and 0.75% by mass of the block with sand and cement to produce the reinforced sandcrete at water – cement ratio of 0.4. Compressive strength, water absorption, split tensile strength tests were carried out on the various samples. The results show that the addition of polythene fibre to sandcrete blocks has very little effect on the compressive strength, although at 0.5% fibre content, the tensile strength increased. Heating the blocks at 100oC for 24 hours, the compressive strength of the heated blocks are higher than the non - heated blocks. The results reveal that at an optimum fibre content of 0.5%, fibres are good in reinforcing sandcrete blocks if heated. Addition of polythene fibres to sandcrete blocks will increase the tensile strength and can limit the propagation of cracks.  http://dx.doi.org/10.4314/njt.v35i1.