By Dennis Ayemba
Steel bars are used with concrete in civil engineering structures to create structures that are concrete reinforced like beams columns and slabs. Construction relied on twisted bars during the best part of the 20th century; but by early 1990s, numerous developed countries had adopted the use of deformed steel for concrete reinforcement due to the unreliable bonding nature of twisted steel.
Recently, Kenya has followed the likes of Uganda, in banning the use of twisted bars for concrete reinforcement in construction. This is attributed to new engineering findings that have triggered reservations over the structural properties of twisted bars that make them not the best candidates for concrete reinforcement. Instead, just like many other countries in the region; Kenya has resolved that only ribbed steel bars shall be manufactured and offered for sale in the country.
A ribbed steel bar is a type of deformed, high strength steel that is manufactured by controlled cold twisting of hot rolled bar. This bar has projections on its surface known as ribs hence the name Ribbed Steel Bar. They vary in sizes, ranging from 8 mm to 40 mm wide. These bars possess certain characteristics that make them preferable to twisted bars in reinforcement of concrete. These characteristics range from their flexibility to their cost saving nature.
High-yield ribbed bars have minimum guaranteed yield stress of 420n/mm2, tensile strength of 500n/mm2 and a percentage elongation of 10%. Accordingly, 420n/mm2 is generally used in design as the characteristic value for the yield strength of high-yield ribbed bars.
Apart from being able to bend through 180 degrees without a crack or fracture of any form, their structural properties makes it possible for them to be welded by electric flash such as arc welding and butt welding. These bars boast of excellent bonding properties than ordinary twisted bars hence the end hooks are unnecessary. Therefore, their use cuts the cost of reinforcement up to 30 to 40% hence they are very economical. Usually, ribbed bars are made of unfinished tempered steel, making it insusceptible to rusting. This is very important because, as rust occupies a greater volume than the steel from which it was formed, the surrounding concrete undergoes severe pressure, leading to cracking, flaking and eventually, structural failure.
Additionally, bending, fixing and handling of ribbed bars is very simple which reduces on labor; plus they can be used for all major types of reinforced concrete structures. Compared to twisted bars where the concrete may slip and cause cracks, the ribbed surface ensures a better bond with the concrete which improves the overall bearing capacity of the particular member where the bar has been used. Moreover, ribbed bars like almost all metallic products; can be recycled as scrap. They are normally combined with other steel products, melted down, and re-formed for re-use.
Mr. Kush Nathwani the Executive Director of Apex Steel Kush Nathwani insists that, there will be a radical shift within the construction sector to use deformed bars for reinforcement. This is due to the growing awareness and the need for builders to use quality steel for their projects; be it an infrastructure project, or a ‘home builder’ coupled with the recent ban by the Kenya Bureau of Standards (KEBS) in the manufacture and supply of twisted steel. “An increase in the sophistication of high rise buildings being developed in Kenya has also manifested itself with a need to use the right steel in reinforcement,” he said.
Apex Steel manufactures deformed bars that have raised the bar of quality within the East African market. APEX TMX the brand name as specified every one meter of the deformed bar; conforms to BS: 4449 – 2005 KENYAN ISO 6935 – 2 Grade 500+. Made under license from THERMEX Germany; its technological superiority ensures the product has superior elongation: 12% – 26%; thereby making it more conducive to sustain during seismic shocks.
As specified by KEBS; APEX TMX is consistent in its allowable tolerance in weight with yield strength of 500 N/MM2 – 600N/MM2. Apex Steel is LEED (Leadership in Energy and Environmental Design) certified making it the only steel in East Africa to be recognized as ‘Green Steel’.
As a result of its consistency in quality; Apex Steel was awarded the contract to supply steel to the Standard Gauge Railway (SGR). For that matter, 100% of the steel provided to the Thika Superhighway is APEX TMX. Now a Superbrand for the second consecutive time; Apex Steel is among East Africa’s elite.
According to Mr. Nathwani, cheap is expensive. Potential purchasers may get lured away to make the investment and purchase steel that is cheaper; however may get shortchanged as they would invariably purchase steel that is under weight and doesn’t conform to standard. “If a structure has to stand the test of time; be it deformed bars or hollow sections; buying material from a company of repute that has demonstrated its credibility will have offered the benefits of durability and strength. As per KEBS; Apex Steel Deformed Bars are sold only by weight (and not per piece) so one pays for what they get,” he asserted.
“High cost of energy; the manufacture and supply of deformed bars and other steel products that make a compromise on the desired weights and qualities are amongst the challenges faced within the industry. To add to this; an overall cash flow in circulation contributes to the constraints of a smooth functioning construction environment,” added Mr. Nathwani
Moreover, Mr. Nathwani is of the mind that the ban on twisted steel may pose some challenges in the short term as it is a ‘paradigm shift’. However in the long run; this will be a blessing as structures would be erected using steel manufactured to meet global standards thereby minimizing the chances of collapse due to steel.