A subcontractor hired to construct and install the steel structure within the Concorde overpass in Laval said he had to improvise because the original design was flawed.

In his testimony at the Johnson overpass enquiry on Thursday, Claude Robert, an engineer who owns Acier d'Armature de Montréal, said his company was hired to make the steel reinforcement bars embedded inside the concrete structure.

The Johnson commission is investigating the Concorde overpass collapse, which killed five people on Sept. 30, 2006 when a section of concrete broke off the structure and crushed several cars below.

Robert said when the overpass was first built more than three decades ago the steel bar stirrups were about two inches too short.

Robert's company decided to add extra bars to compensate for the shortage, and hired an outside contractor to install the reinforcements, he told the commission.

But the engineer couldn't remember the company's name, and he couldn't say who authorized the extra bars.

The commission's head Pierre Marc Johnson honed in on this point. "What you're saying is once you contract out the job, that's it? You wash your hands of it?" he asked Robert.

Robert replied that the contractor knew what it was doing and that's why it was hired for the job.

His testimony follows troubling evidence heard earlier this week about Transport Quebec's structural inspection methods. 

The engineer in charge of Transport Quebec's structural department, Guy Richard, testified at the commission on Wednesday that his department has tried to improve inspection methods in light of the deadly overpass collapse.

Richard said two separate engineers inspected the structure two years before its collapse, and while noting deterioration there were no indications that it was threatening to fall apart.

One of the engineers in question, Christian Mercier, told the commission he did a visual inspection and the only tool he used to gauge the structure's soundness was a small geologist's hammer.