H-4 FIRE STATION
This design example illustrates the seismic design of a two-story fire station. The step by step procedure as
shown in Tables 4-5 and 4-6 was followed almost verbatim for the design of the buildings basic structural
elements. This rigid adherence to the outlined procedures was done in order to provide a clear
demonstration of the use of this manual.
(1) Purpose. The objective of this problem is to demonstrate the procedure to be used for
designing a building with an enhanced performance objective.
(2) Scope. The scope of this example problem includes; the design of all major structural
steel members such as beams, columns, and braces, as well as the design of several example structural steel
connections. The design of the foundations, nonstructural elements and their connections, and detail design
of some structural elements such as concrete floor slabs were not considered part of the scope of this
problem and are therefore not included. Additionally, this problem considers only seismic and gravity
(1) Function. This building functions as a fire station, and provides living quarters to station
personnel as well as garage space for equipment such as fire engines.
(2) Seismic Use Group. As a fire station, this building will be required for post-earthquake
recovery and as such performs a mission essential function. Therefore, this building is categorized with a
seismic use group of IIIE, Essential Facilities. With the Seismic Use Group known, the structural system
performance objectives are obtained from Table 4-4. Structures in seismic use group IIIE are to be
designed for performance level 3; Immediate Occupancy. Ground motion B (3/4 MCE) is to be used for
performance objective 3B. The minimum analysis procedure to be used is the liner elastic with R factors
and linear elastic with m factors. The structure is designed first for performance objective 1A following the
steps laid out in Table 4-5. After completion of the preliminary design, the enhanced performance
objectives outlined in Table 4-6 for performance objective 3B are checked and the building design is
updated accordingly to meet those objectives.
(3) Configuration. As shown in Figure 1, the building is rectangular in plan measuring 70
feet (21.35m) by 30 feet (9.15m). It contains a one-story low roof garage area that is connected to an
adjacent two-story high roof office area and dormitory. Story height of the low roof area is 15 feet
(4.58m), and of the high roof area is 11 feet (3.36m).
(4) Structural Systems. The building consists primarily of steel frame construction composed
of wide flange shapes, hollow structural sections, and metal decking. However, the second floor
incorporates a reinforced concrete slab. Structural systems are shown in Figure 1.
The gravity load resisting system consists of untopped metal decking that spans to open web steel joists,
which span to wide flange steel beams and columns. The second floor consists of a reinforced concrete
slab that spans between wide flange beams, which are supported by the same columns that support the roof
The lateral load resisting system consists of both flexible and rigid diaphragms that span between steel
moment frames in the transverse direction, and steel braced frames in the longitudinal direction. Roof
diaphragms consisting of flexible untopped metal decking that place tributary load on the lateral load
resisting system. The second floor diaphragm, however, consists of a rigid concrete slab for which torsion
must be considered.