15 September 1999
EXAMPLE PROBLEM C4
STEEL FRAME BUILDING
C4-1. Building Description
Building 745 consists of three 1-story structures located at McChord Air Force Base (AFB),
Washington. The buildings are used as shops for aircraft engine inspection and repair. One is
of timber construction (built in the 1950s), and the other two are steel construction (built in 1961
and 1965), and all are structurally independent of each other. One of the steel structures is
used here to demonstrate the structural review procedures.
The example building was constructed in 1965 and consists of a pre-engineered and pre-
fabricated gable-framed structure (Figure C4-1). The plan dimensions of the building are
approximately 131 feet by 155 feet. The roof framing consists of insulated metal roofing over
purlins that are spaced at 5-foot intervals. Steel-gable frames with tapered steel beam-columns
at each end span the transverse direction. The beam-columns are 10-inch by 12-inch built-up
steel sections at the base and 10 inches by about 30 inches at the top, and are spaced at 20-
foot intervals. The steel beams are approximately 30 inches deep, and are supported at the
midpoint by 12-inch by 12-inch wide-flange steel columns. Two sets of crane rails are
suspended from the beams. Each crane has a maximum lift capacity of 8 tons.
The east end wall and both side walls consist of 6-inch-thick by 4-foot-high precast concrete
wainscot and insulated metal siding over steel girders spaced at approximately 4-foot intervals
above (except for door and window openings). The west wall is an 8-inch-thick CMU firewall,
and is connected to the steel columns with metal clips.
a. Vertical-Load-Resisting System
. Steel framing and concrete columns carry the vertical
loads. The footings of the steel frames consist of 3-foot, 6-inch-square spread footings for each
column, with strip footings between the columns. The interior columns are 12-inch-square, with
reinforcing of four #6 bars and #3 ties at 12 inches. The footings below the center columns are
2-foot, 6-inch-square spread footings.
b. Lateral-Load-Resisting System. The lateral forces in the transverse direction are
transmitted through the gable-frame system to the foundation. The lateral forces in the
longitudinal direction are transmitted to the foundation by three sets of -inch rod X-bracing
in the roof and two sets of 3-inch by 3-inch angle X-bracing in the side walls (one leg of the
angle is notched at the intersection).
C4-2. Building Review Report
a. Seismic Review of Structural Systems. The review procedure described in Chapter 2 is
performed using the Lateral Load System Data Sheet and Structural Review Score Sheet. The
information is extracted from the building drawings (made available by the Base Master
Planning office), and by visual inspection of the building. For this building, there were no
fabrication drawings showing the frame sizes and bracing locations. It was necessary to obtain
this information by field measurement where they were accessible, and by estimation where
they were not. The completed forms are shown in Figures C4-2 and C4-3.