Charles K. Kankam

Strength and ductility characteristics of reinforcing steel bars milled from scrap metals

The physical and chemical properties of reinforcing steel bars milled from scrap metal such as vehicle parts and obsolete machinery in some developing countries were investigated. At present there is inadequate information on the actual behaviour of these reinforcing steel bars which are already in use in structural concrete for the construction of all types of buildings, bridges, hydraulic structures, etc., yet they are classified as mild steel in design specifications. The current state of the art can mean that design of reinforced concrete in such countries may not be fully reliable. The primary observations made with the physical properties are that for the type of mild steel produced in Ghana from re-cycled steel, the characteristic tensile strength is too high with very little elongation leading to limited ductility compared with standard mild steel and high-yield steel. The bars did not exhibit any necking down and cup and cone failure, similar to those observed in the case of standard mild steel plain bars. Concrete beams, reinforced with such bars were fabricated on the basis of under-reinforced concrete design, and tested under monotonic or cyclic loading to study the flexural behaviour of the beams. Tested beams exhibited little deflection and very low ductility and deformation prior to collapse. This paper presents a description of the experimental investigation carried out on the steel bars and reinforced concrete beams. Observations made on the physical and chemical properties of the steel bars, and the ultimate strength, mid-span deflections and crack width under monotonic and cyclic loadings of the beams are included.

Flexural behaviour of babadua reinforced one-way slabs subjected to third-point loading

Abstract This paper presents the results of experiments carried out on 13 simply-supported one-way concrete slabs reinforced with babadua (botanical: thalia geniculata ) bars. The span-to-effective depth ratio of the slabs which were subjected to third-point line loads, ranged between 12.5 and 19.3. Experimental failure loads were found to average 175% of the theoretically predicted values. Cracking loads of the reinforced slabs were found to average 137% of the failure loads predicted for the unreinforced sections. Also the experimental failure loads averaged 67% of the design shear strength of the reinforced sections. The slabs exhibited high ductile behaviour and produced large deflections prior to failure which was remarkably gradual.

Structural behaviour of babadua reinforced concrete beams

Abstract The strength and deformation characteristics of concrete beams reinforced with babadua bars ranging from 2.87 to 12.13% were examined from tests performed on the beams. The beams were tested to failure mostly under third-point loading. Collapse of the beams occurred mostly through either flexural failure of concrete in compression or diagonal tension failure. The experimental failure loads averaged, respectively, 6.40 and 2.62 times the theoretical flexural strength and theoretical shear strength of the unreinforced concrete section. Also, the experimental failure loads were only approximately 1.18 times the theoretical flexural strength of the reinforced concrete and 1.05 times the theoretical shear strength of the concrete sections taking into consideration the resistance of the tension reinforcement.

Structural behaviour of bolted end-plated reinforced concrete beams

The paper reports a study on the flexural strength and deformation characteristics of concrete beams reinforced with threaded steel bars that were tensioned against steel plates bearing on the concrete ends by means of tightening nuts. Stressing of the beams was achieved when the nuts were turned until finger tight. Six beams were subjected to monotonic loading and 4–20 cycles of loading. Four control beams were also cast using normal non-tensioned bars. Cracking loads for the prestressed beams averaged 280% of the control beams. For the two series of beams, the ratio of cracking load Pcr to the failure load Pult was almost the same, averaging 0.25 and 0.22 for the prestressed and control beams, respectively. Cyclic loading of the prestressed beams was characterized by complete crack closure on the removal of the applied load, but for the unstressed beams, cracks remained open throughout the full load cycles. Failure loads for the stressed beams averaged 244% of the unstressed beams, even though the span-to-depth ratio was larger for the former. Failure loads for the stressed beams averaged 219% of the theoretical failure load (based on an assumed unstressed beam). At failure the maximum crack width in the beams ranged from 0.03 to 0.2 mm for the prestressed beams, and 2.9–3.5 mm for the unstressed control beams.