Kenya has banned the manufacture, importation and use of twisted steel bars in construction starting April 2017 over safety concerns. Kenya has been the only country in the region that still allows the manufacture and use of twisted steel bars for reinforcement of concrete.
Internationally, twisted bars have been phased out for use in structural reinforcement of concrete due to their poor bonding and structural properties. The mover by Kenya Bureau of Standard (KEBS) is seen as a measure to curb the continued collapse of buildings in Kenya. The use of twisted bars started around the middle of the 20th century but by the 1980s and early 1990s most of the developed nations had already ceased their use due to these inadequacies preferring the ribbed bars
Two identical bars may be of the same tensile strength but a ribbed bar is more preferable as its skin friction gives it a superior bonding characteristic over the twisted bar. The difference is that ribbed bars offer better bonding with concrete when used as reinforcement and this increases the overall bearing capacity of the respective member where the bar has been used. Ribbed bars have ridges, projections or ribs on their surface to provide better anchoring for concrete.
A ribbed bar is a rod for reinforcing concrete, having surface irregularities, as transverse ridges, to improve the bond. They are commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression. The bar is usually formed from carbon steel, and is given ridges for better mechanical anchoring reinforced concrete.
Twisted Bars on the other hand are made by twisting the bars after hot rolling. The Twisted Bars are put in a cooling bed then twisted at room temperature. The bars are stretched to some extent during twisting thus the inside grains are crushed increasing the strength of the bar. They have been judged of a poor quality than ribbed bars in concrete reinforcement.