The Wisconsin Department of Transportation shut down the southbound on-ramp to Interstate 43 at the intersection of North 11th Street and Wisconsin Avenue Thursday night.

During a routine inspection held last Monday, cracks were found in the ramp’s concrete vertical support column. Further examination revealed the structure’s weight-carrying capacity is insufficient.

The structure, however, is not in imminent danger of collapsing.

The freeway ramp is part of the rebuilt Marquette Interchange and carries about 15,000 motorists daily. The DOT has set up a temporary detour to a different southbound on-ramp on Second Street.

The Marquette Interchange was undergoing its first set of reviews since its completion two years ago. No other cracks or problems were detected among the other inspected support columns.

HNTB Corp., an architecture and design firm based in Kansas City Mo., was the main designer for the Marquette Interchange. It has accepted responsibility for the design defect and has agreed to pay for the repair costs. The repairs are expected to keep the ramp closed for the next four to five months.

HNTB Corp. has released a repair plan stating that supports underneath the ramp will be reinforced in an effort to reopen one lane within the four to six weeks. The cracked support column will then be demolished and construction for a replacement is expected to take three months.