In February, 2008, a three pound pyramid-shaped piece of millwork fell from the ornate wood ceiling of Holy Name Cathedral (Holy Name) in Chicago, Illinois. The affected piece of millwork was originally located at the peak of the ceiling at the nave and transept intersection. Initial investigation of the fallen millwork indicated that movements (deflections) of the ceiling resulted in separations at the peak of the ceiling, which caused the millwork to become dislodged and fall. Further inspection of the ceiling revealed that the ceiling and roof were visibly deflected in the area where the nave and transept intersect. These observations led to a structural analysis of the roof trusses, which revealed that the calculated forces for the sloping tension bottom chord members of the scissors trusses were significantly greater than the published capacity of its 3/4 in. diameter, single bolt connections between the top chords and bottom chords. To address the observed roof deflections, and calculated overstresses, steel tension ties (rods) were recommended for the roof trusses.
展开▼
