The investigation at Walsall bus station was ordered after propping used during construction of the elliptical concrete roof was taken away.
“When we started to remove the scaffolding, we discovered some sagging in the roof,” said a spokesperson for client Centro, the West Midlands transport firm.
Removal of the temporary propping, which began two weeks ago, has been halted pending the outcome of the investigation, which is being carried out by project contractor Shepherd.
Centro ordered structural engineer Atelier One to take action because it was concerned that the roof was not behaving as the engineer had predicted. “It has sagged more than we were expecting,” said the Centro spokesperson, although she added that the movement, known as deflection, was less than 3 inches.
Atelier One director Aran Chadwick denied there was a problem. He said the deflection was in line with predictions.
However, the Centro spokesperson said: “There must be something going on or we would not be doing an investigation.”
Chadwick said the roof might be sagging because parts of it were still under construction. “In its temporary state, it [the roof] will deflect more than in its permanent state,” he said.
He added that the investigation was essentially a discussion about the order in which the props were to be removed.
The temporary propping is the responsibility of Shepherd. Shepherd site manager John Atkinson confirmed that there had been some deflection but emphasised that it was no more than the structural engineer had predicted.
A design team meeting was due to have taken place yesterday to discuss the extent of deflection and decide how to proceed with the removal of the props.
The roof is the main feature of the £3.7m Allford Hall Monaghan Morris-designed station. The concrete canopy is supported on steel, tree-like, columns. Its design features ventilation craters and glazed cowls. When complete the canopy will be carpeted with a layer of cactus-like plants.
Peter Morris, a partner in architect Allford Hall Monaghan Morris, said: “As far as I’m concerned there is no problem. It’s all to do with the removal of the propping.”