A zinc panel from U.S. Bank Stadium’s problematic western prow fell to the ground early Monday while others have come loose again.

A missing horizontal strip of black panel stretches from the glass facade to underneath the U.S. Bank Stadium logo that appears on the 270-foot high prow.

“Extreme weather and high winds” caused panels to “partially disengage,” according to a statement from the Minnesota Sports Facilities Authority (MSFA). But one panel fell to the ground in the hours after midnight Monday.

Jenn Hathaway, MSFA spokeswoman, said in a statement that no one was injured. “We are awaiting a recommendation regarding next steps to permanently resolve this issue,” she said.

Representatives from contractor M.A. Mortenson and subcontractor McGrath, who installed the panels, arrived at the stadium Monday morning to investigate the damage and a portion of plaza was cordoned off. By late Tuesday afternoon, workers used a crane to get to the damage and assess it up close.

While the stadium was under construction, the Star Tribune installed a camera facing the western wall of the building that takes photographs every half hour. Photographs from the camera, which remains in place, showed the panels intact at 2:30 a.m. and gone or loose by 3:30 a.m. Monday, the day after an extremely wet and windy Christmas Day.

Both moisture and wind have previously caused trouble for the $1.1 billion building that opened in August. The zinc panels on the exterior have been the focus of a couple of concerns on the building.

Thousands of zinc panels line the exterior of the building. They are 12 inches high and 6 to 12 feet long.

Initially, the panels were bolted down only along the bottom edge. After heavy storms last summer, some panels came loose and flapped in the wind. Mortenson workers then reinforced the panels along the top edge.

Minnesota native Megan Goodwin, 27, was at the stadium for a paid tour with her family. She praised the design, but wondered how the building would stand up to rough weather. “What’s going to happen in the years to come? Will it hold up 20 years or more?”

Steve Ramgren, of Minneapolis, called the panel problems “ridiculous,” adding that “It’s common sense that if the wind blows [panels] down then it will happen again.”

Last summer, unexpectedly strong wind pressure on certain angles of the building were blamed for the flapping tiles.

In an unrelated problem, Mortenson also had to remove and reinstall some of the rectangular zinc panels to access and replace a faulty moisture barrier on the building. More than a year ago, workers noticed dampness on a parapet wall and pooling of water in a gutter.

Mortenson executive John Wood said the replacement of the barrier was expected to cost the company up to $4 million.

The building, $489 million of which was covered by the taxpayers, is under warranty by Mortenson for two years.

It is common for new buildings to exhibit unexpected stress in the first full cycles of seasons, particularly a massive and custom structure like the stadium.

Gordon Folke, of St. Paul, was showing guests from Arizona the building and the panel damage and worried about the potential harm from falling pieces on a game day.

“I just wonder what they spent that $1.1 billion on; it’s only [a few months] old and it’s already falling apart,” Folke said. “But I bet those luxury suites are holding up just fine.”

The Vikings, the building’s primary tenant, will play the final game of their season in the stadium at noon Sunday against the Chicago Bears.


Twitter: @rochelleolson