The Manhattan parking garage that collapsed this week, killing one and injuring five, had a lengthy history of structural issues that required substantial repairs — including huge, 11-foot-long cracks in the walls and roof, engineering docs obtained by The Post show.

The extensive work required to make the Financial District parking deck safe was laid bare in a 2010 engineering report after the owners of the Ann Street building were slapped with a violation summons by the city.

The punch list of repairs included multiple 11-foot long wall cracks on the second floor and cracks in the roof measuring 10-feet and 4-feet. Fractures were also discovered in at least one spot where the building’s ground floor columns connected to a ceiling support beam, according to the report.

It’s not clear if any of the dangerous issues were ever repaired.

“These are major items. Beams are a big deal,” an engineering expert, who reviewed the documents, told The Post.

“The repairs were severe enough that they were told to inspect them in front of an engineer. That tells you everything you need to know.”

The dangerous conditions were first flagged in a 2009 violation summons issued by the city’s Department of Building against the property’s owners. As part of the summons, the owners were ordered to hire an outside engineer to assess the damage and flag required repairs.

In addition to the massive cracks, the engineer identified more than a dozen bolts that needed to be removed from the roof and the holes left behind patched up. The report didn’t elaborate on the reason the bolts needed to come out.

The schematics also called for temporary jacks to be installed to shore up the walls on the ground and second floors.

“One thing like this, one structural member goes and it hits with extreme force. All the pressure from the top driving down on this weakness, the whole thing just goes. It’s all structural,” the engineering expert told The Post of the issues flagged in the report.

He added that the calls for temporary jacks showed it had “potential structural issues all throughout.”

“It’s likely the beams, not the slabs. But the slabs are in pretty bad shape,” the expert said.

“The third floor there’s steel beams that were required to be probed – meaning inspected – within the presence of an engineer. That’s serious. They’re not just trusting any contractor to take their word for it.”

The repair permits were lodged with the DOB in 2010 but it’s unclear — based on online records — if the repair work was ever finished.

A DOB spokesperson said inspectors had visited the site in November 2011 and found the work was “ongoing and interior maintenance of the building was in good condition.”

Two years later, an inspector returned but “did not issue any violations for structural concrete issues, as was done in 2009,” the spokesperson added.

The DOB wouldn’t comment when asked if the inspector had checked off the specific list of repairs flagged in the 2010 engineering report.

The owners of the building never ended up filing the required paperwork showing that they had corrected the violations — and were fined $200 by the DOB as a result, records show.

It is unclear if the failure to file the documents meant the work had not been finished — or if it was just a paperwork snafu. Regardless, the lack of paperwork meant the department was unable to close the case.

The building’s owners — Ann Street Realty Associates, which is controlled by brothers Jeffery and Alan Henick — did not respond to The Post’s request for comment.

Overall, the building has been hit with more than 40 violations by DOB inspectors since 1976, records show. It remains unclear if any of the defects or failures found by inspectors could have contributed to the structure’s eventual collapse.

Officials are still probing the cause of Tuesday’s collapse, which killed garage manager Willis Moore and left several others briefly trapped beneath the concrete-and-steel wreckage.  

An FDNY internal memo said the working theory behind the cause was that the three-story garage likely crumbled under the weight of the many vehicles on the roof. The structure’s advanced age — it was originally built during the Coolidge administration in 1925 — also likely contributed, the memo said.

Separately, the Manhattan District Attorney’s Office has opened an official investigation into why the structure fell.