Bovian Junior Lwanga

TMT, TMX, TM-WHATEVER: THE BUILDING DID NOT FALL BECAUSE OF THREE LETTERS. Every taxi in the park has EXPRESS painted on its side. Yet the journey from Kampala to Mukono, about 22 km by road, can still take three hours. Labels are a promise, not a performance. Steel is the same. After the recent Eastleigh collapse in Nairobi, photographs began circulating from the pancaked pile of concrete slabs and steel. The exposed bars then triggered instant verdicts on X, and we all suddenly became metallurgists. “They used TMT bars,” said some, while others insisted that TMX is the superior, newer steel. It is a confident argument over three letters, but the letters are not where the engineering decision is made. I know what salesmen from Ugandan steel companies tell us at the conferences they sponsor: TMX is the new thing. As if every building we put up ten years ago is now a death trap. TMX is not a separate standardised class of reinforcing steel. It is usually a trade label for a TMT bar made through a particular quenching system, commonly Thermex. A short history helps. We began with plain round bars, smooth as a politician’s promise and not very good at gripping concrete. Then came cold-twisted bars, which raised strength but reduced ductility and introduced residual stresses. The industry moved on, for good reason, to hot-rolled ribbed bars strengthened through controlled cooling. That is TMT: thermo-mechanically treated steel. As the hot bar leaves the rolling mill, water rapidly cools its outside, then heat from the still-hot core tempers the surface. The result is a strong outer zone around a tougher, more ductile core. TMX is one branded route to make that kind of TMT bar. TMT is not an old steel that TMX replaced; it is the family of steel to which TMX belongs. So ignore the fashionable three letters and read the rest of the stamp. On a marking such as B500CWR, 500 is the strength promise: a 500 MPa characteristic yield strength. The ductility class, A, B, C or D, tells you how much the bar should stretch and deform before failure, while W means weldable and R means ribbed. These are the performance classes recognised under EAS 412. TMX is not one of them. A stamp is the CV; the laboratory is the interview. In the laboratory, the bar is pulled until it breaks to establish its actual yield strength, tensile strength and elongation. It is bent and rebent to see whether it cracks, weighed per metre, and checked for chemistry, including carbon, sulphur and phosphorus. These are standard tests under EAS 412, and UNBS or a properly equipped university or materials laboratory can run them. You do not need a laboratory for the first screening check. Take a one-metre offcut and put it on a scale. A nominal 12 mm bar weighs about 0.89 kg, while a 16 mm bar weighs about 1.58 kg. There are permitted tolerances, but if yours is noticeably lighter, do not argue with the stamp; send it to me and buy popcorn and watch a storm. For now, as a developer, just ask for a mill test certificate for every batch, send samples for independent testing, and weigh before you pay. A “16 mm” bar that weighs like a 14 mm bar has quietly stolen your steel before the concrete is even mixed. Buildings rarely fall because of the name printed on a bar. They fall because poor materials, weak concrete, undocumented alterations, bad workmanship and empty inspection hide behind confident labels. The bar can say whatever it likes; only the laboratory can say whether it is true. @ecoconcreteUG leads with knowledge, material testing and evidence. Inbox for a quick review/appraisal of your building project.

Did the ground floor bring down the building? My reading of the Eastleigh collapse video is that it did. The failure appears to begin at the ground-floor level, where the columns look relatively small and the floor is open, without the masonry walls that stiffen the upper levels. The upper building then comes down rapidly, almost as one mass. That is the signature of a possible soft-storey failure. A soft storey is a level that is substantially less stiff against sideways movement than the floors above or below it. In many buildings, masonry walls above help restrain movement. At ground floor, shops, parking or access spaces leave the frame open, so the columns alone must provide the required strength and stiffness. This is especially dangerous in high-rise buildings. During an earthquake, sideways movement concentrates at the open level while its columns are already carrying the accumulated weight of every floor above. If those columns cannot carry both the vertical loads and the lateral deformation, that one floor can fail and bring down the whole building. But there was no earthquake in Eastleigh. That makes the central question more serious: what caused the ground-floor supports to lose capacity? Were the columns underdesigned? Were they too slender? Was the reinforcement less than specified, smaller than specified, or of poor quality? Was the concrete below strength? Were construction loads, workmanship, or malice involved? The collapse looks disturbingly like a controlled demolition. The building comes down in a rapid, near-vertical and remarkably uniform manner. That resemblance will naturally make people ask: were explosives used? The video alone cannot answer that question. A rapid progressive collapse after the loss of several ground-floor columns can look much like a controlled demolition. The dust bursts from the base may simply be compressed air, pulverised masonry and debris escaping as floors collapse; they are not proof of explosives. But the possibility should be formally ruled out, not dismissed by social-media arguments. Investigators should preserve the site, inspect the surviving columns and debris for blast damage, test for residue where appropriate, examine available CCTV and phone footage, and reconstruct the failure of the ground-floor supports. If it was a structural failure, the evidence will show it. If foul play was involved, that too must be established by evidence. Of course, material quality cannot be treated as a side issue. Recently, I tested reinforcing bars from one of Uganda’s leading steel manufacturers. The bars split in a manner I had never seen before. I rejected them. Company representatives came to my site and threatened me. I insisted that steel from their factory would not be accepted until they explained the failure. They later told me the bars had come from a batch of poor-quality billets supplied to them, but that the billets had already been used up. I asked whether they would recall the bars made from that batch. I was told they could not. The bad billets may have been finished at the factory, but the bars were already in the market and inside projects. That experience does not prove what happened in Eastleigh. It shows why quality control is a cost only pennywise and pound-foolish builders avoid. The designer designs for a specified grade of steel and concrete. The standards bodies must protect the public by ensuring that what is sold in the market is tested, traceable and up to standard. Independent testing, batch tracking, factory surveillance and enforceable recalls are not luxuries. A building does not stand on an approved drawing. It stands on the actual bars, concrete and workmanship hidden inside its columns.