Strengthening Old Floors

by David J. Galey, (M.ASCE), Assoc. Vice Pres.; Hammel Green & Abrahamson, Minneapolis, MN,

Serial Information: Civil Engineering—ASCE, 1987, Vol. 57, Issue 4, Pg. 72-74

Document Type: Feature article


The floors of the historic City Hall and Courthouse in Minneapolis had withstood 80 years of hard use before they have to be analyzed and brought up to code. The building is about 300 ft square in plan, occupies an entire city block and has seven major levels plus two towers. Primary floor framing is steel beams with hollow clay tile segmental arches spanning between them. The massive stone walls provide lateral stability for the building. After extensive testing, designs were made for reinforcing or having loads removed from about 60 beams, many of them in occupied jail spaces. Solutions included: 1) welding a plate to the bottom flange of an existing beam; 2) king post assembly with 1 inch diameter rods; 3) shear connectors welded to the top flange and non-shrink grout fill; 4) adding a new beam below the old one with shims at quarter points. Non-structural solutins included removing heavy partitions that had been added over the years. Cost of the project was $637,000.

Subject Headings: Floors

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