CEMP-E
TI 809-02
1 September 1999
waived for small storage type buildings with areas less than 140 square meters (1500 square
feet).
10-4. STRENGTH AND SERVICEABILITY ISSUES.
a. General. Typically metal building systems have the minimum strength required, and
use high strength materials to keep strength to weight ratios at a maximum. This approach to
design under certain conditions can lead to serviceability problems.
b. Lateral Drift. Special attention should be paid to building drift under wind and
seismic loading conditions. The maximum allowable drift will depend on the type of exterior
cladding. For rigid claddings, such as precast concrete, brick, or block masonry, the maximum
drift should be limited to h / 600. This is much lower than the h / 60 limit commonly accepted
for buildings with flexible metal cladding.
c. Earthquake loadings. Metal building systems with heavyweight cladding must have
suitable lateral force resisting systems to resist the inertial forces generated by the cladding
during earthquake ground motions. The usual tension-only type bracing conventionally used in
metal building construction will not be adequate when heavyweight cladding is used. If rigid
cladding is used, the roof diaphragm must also have sufficient stiffness to limit out-of-plane
wall displacements so that the cladding will not fail when the building is subjected to
earthquake ground motions.
d. Mechanical Equipment Loads. The roof purlin system commonly provided with
metal building systems would not have the capacity to support hanging mechanical HVAC
units or rooftop units. Where the roof is required to support such units, special framing must
be provided.
e. Roof In-Plane Load Resistance. Metal building systems are commonly constructed
with a standing seam metal roof. Standing seam metal roof systems are incapable of resisting
in-plane loads due to wind and earthquake forces. Therefore, a separate horizontal bracing
system is required.
f. Serviceability Guidance. Metal building systems must meet the same serviceability
requirements specified for steel framed buildings in Chapter 7, "Steel Structure Design
Requirements". Additional guidance on serviceability can be found in the American Institute of
Steel Construction, Inc. (AISC) Steel Design Guide Series 3, "Serviceability Design
Considerations for Low Rise Buildings".
10-5. DESIGN RESPONSIBILITY. Performance specifications are generally used to obtain
metal building systems. A professional engineer representing the owner will specify the metal
building system including all framing elements, roofing system, exterior cladding, interior
partition walls, and architectural finishes. The same engineer will specify which design codes,
loads, and load combinations are to be considered in the design. Unusual loads such as
unbalanced snow loads, and concentrated roof loads must be clearly defined. If future
expansion is required, this must also be conveyed so end bays can be designed without
intermediate columns. Architectural requirements such as "R" factors for insulation should
also be included in the metal building specification. Metal building manufacturer's typically
10-2
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