Construction of the new central library in downtown Calgary is behind schedule due to the discovery of "micro cracks" in some of the steel truss beams created for the $245-million structure.

The discovery was made before the trusses were delivered to the site, but one of the pieces could not be fixed and had to be re-fabricated.

Construction did not stop as steps were taken to work around the delay, but the time it took to assess the problem, develop a temporary work-around and wait for new steel beams means the overall project is now running six weeks behind schedule.

A report to the city's audit committee says the project management team will have a better idea in April of the impact the delay will have to the overall timeline.

A new report on the construction status is expected the middle of next month.

The Calgary Municipal Land Corporation, which is overseeing the project, says it hopes to make up the lost time and that the new central library will open on time, late in 2018.