Effect of TMT Bar Lugging on Steel Reinforcement Failure Mode under Monotonic Loading

Abstract

Thermo-mechanically treated (TMT) ribbed bars modify the overall progress of failure in reinforced concrete. The ribs maintain anchorage after friction on the rest of the bar is eliminated during deformation, taking up the ultimate compressive load. This however, is inadvertently jeopardized by the stress concentration effect of the rib geometry. This paper analyses the extent to which some of the geometric forms of bar lugging affect the prevalence of ductile failure in the steel-concrete composite under monotonic loading otherwise imparted by their preconceived chemical and metallurgical constitution. Thirty pieces of two different types of rib pattern designs of Φ20 mm thermo-mechanically treated ribbed steel bars were subjected to uniaxial tensile testing. Portions of these were stripped of their lugging and subjected to the same test. The tests were repeated after corresponding parts of the same bars were annealed. The fractured surfaces were then examined with a lens for macroscopic features and using an optical microscope at X50. Fracture traits varied from microvoid coalescence ductile features to external transgranular cleavage or intergranular separation. In 28% of the samples, the origin of the fracture was traceable to the rib joints. This reduced to 20% when the samples were annealed with a corresponding average increase in strain after yield evaluated by u/ b of 14 and 8% for ribbed and machined bars, respectively. In 82% of the samples stripped of their lugging, the fracture originated from the center of the bars. This shows that under monotonic loading the presence of ribs originates a stress concentration effect that directs the fracture source to the rib nodes and corners and also reduces of the deformation available after the yield point, curtailing the reinforcing effectiveness of the bar in the steel-concrete composite even in the absence of the surface hardening due to thermo-mechanical treatment.

Cite this Article

Christopher Senfuka, John B. Kirabira, Joseph. K. Byaruhanga. Effect of TMT Bar Lugging on Steel Reinforcement Failure Mode under Monotonic Loading. Trends in Mechanical Engineering & Technology. 2015; 5(3): 8–14p.