Nine spikes on Manchester's distinctive B of the Bang sculpture are being removed for testing.
The sculpture was unveiled by Linford Christie
Engineers are trying to discover why one of the parts fell from the 184ft (56m) artwork, outside the city of Manchester stadium, late last year.
Nine of its 180 steel spikes were being taken off on Monday, to be examined by experts.
A slip-road near the "Bang" is closed while work is under way but is expected to reopen by the end of the month.
New East Manchester, the regeneration company which oversees development work in the area, said the tests were part of "on-going" work.
Tom Russell, chief executive of New East Manchester, said: "B of the Bang is now an established Manchester landmark and we want to see it finished as soon as possible.
"We believe that it's a powerful piece of public art and like everyone we're disappointed that it's still not completed.
"From an engineering point of view it's a complicated structure so we need to be completely confident that the solution is the right one and any defects are identified."
B of the Bang was designed to commemorate the 2002 Commonwealth Games in Manchester.
It was officially unveiled by Linford Christie in January 2005.