Investigation of Construction Collapse of Steel Structure of The Post Office Building in Chicago, Illinois

The post office building in Chicago, Illinois is a five-story tall steel-framed structure. The Architect/Engineer of the building designed the steel structure of the building including all connections and provided prescriptive structural steel and connection details on the contract drawings and specifications. After the construction contract was awarded, the steel erector changed the construction sequence of some of the beam-to-column connections to facilitate the construction of the connections. This change in connection construction sequence included the use of a temporary erection angle to temporarily support the beam while its permanent connection was being constructed. The design of the permanent connection of the beam was not changed by the change in the connection construction sequence. On November 3, 1993, while the structural steel frame of the building was being constructed, a 30 m (100 ft) by 32 m (106 ft) by five story tall section of the frame collapsed injuring several workers, some fatally. Our investigation of the collapse included: 1) Review of eyewitness descriptions and of the contractor's log on the collapse. 2) Review of structural design drawings, shop drawings, and specifications of the structural steel. 3) Inspection of steel members in the collapsed area, and inspection of erected steel members outside of the collapsed area.