KARACHI, Sept 2: Experts and professionals have varied views about the collapse of a bridge on the Northern Bypass on Saturday as they could not comprehend how part of a box girder-bridge could collapse in such a fashion as such bridges are considered among the strongest of their sort.
“Such bridges are inherently strong with their pre-stressed construction. So how a significant portion of a new bridge could fall in such a manner is in fact a mystery for all of us,” Siddiq Essa, a consulting structural engineer, told Dawn.
He said the incident was the first of its kind in Karachi, which had shocked every professional in the field of structural engineering.
“It is very difficult to say anything decisive. It could be anything … it could be a fault in the construction or the design etc,” he said.
Mr Essa said he had visited the site of the incident out of professional anxiety on Sunday and looked for refurbishment on the other lane of the bridge, which is still intact.
“But, I could not find any refurbishment on the damaged portion,” he said.
He was referring to the statement of Communications Minister Shamim Siddiqui citing such refurbishment months ago.
Asked whether the use of Tor steel could be a reason behind the fall of the bridge, as is being thought by some experts, Mr Essa said in a bridge like this, steel became secondary because it was constructed using the pre-stressed method and not the reinforcement technique.
He said most of Karachi’s buildings and structures were built with Tor steel instead of TMT (thermo mechanically treated) steel and yet none of them collapsed.
“Tor steel could be dangerous during earthquakes but not in the situation which we have witnessed at the Northern Bypass,” he said.
Enhancing steel standards
Another structural engineer suggested to the Pakistan Standards and Quality Control Authority (PSQCA) to enhance its standard set for steel in the country, which could at least give the authorities advance warning of collapse of any structure and help save precious lives even if the building/structure had inherent flaws.
“By enhancing the set standard of steel bars no structure would collapse immediately and without giving any warning as the portion of the Northern Bypass did,” Jawed Akhtar, a structural engineer belonging to a private consultancy firm, said.
According to him, it had been suggested to the PSQCA to standardise TMT steel instead of Tor steel, which is in vogue in the country at present.
“Any building built with TMT could give ample time before its collapse if its fault becomes grave and causes ultimate damage, which is not the case with Tor steel,” he said. According to him, most of Karachi’s 50-plus bridges could not bear heavy loads for the same reason.
“Karachi falls in a seismic zone, which requires the capability of at least 16 per cent elongation (elasticity) to brave tremors of average intensity while Tor steel offers only 9 per cent,” he said.
Zarak Khan Khattak, another structural engineer, said TMT was introduced in India in 2001 and had now captured two-thirds of the steel market in the country.
