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 (5) The rebound load test involves applying an increasing static
pressure over the entire face of the specific window that passed the proof
load test. The load shall be applied either as a suction pressure over the
exterior face of the window or as a positive pressure over the entire
interior face of the window. The window design shall be considered
acceptable if no glass pane breaks and the window frame does not break free
from its anchorage under a static pressure load less than the rebound proof
load, ru. An official of the contracting agency shall review the test
set-up and rebound analysis, and be present to observe the glass pane tests,
proof load tests, and rebound tests (if required). Any deviations from this
acceptance criteria must be approved by the Contracting Agency. All tests
shall be performed by a certified testing laboratory, and all rebound
analysis shall be prepared by a Professional Structural Engineer registered
in any jurisdiction.
4.
SPECIAL PROVISIONS FOR PRE-ENGINEERED BUILDING.
a. General. Standard pre-engineered buildings are usually designed for
conventional loads (live, snow, wind and seismic). Blast resistant
pre-engineered buildings are also designed in the same manner as standard
structures. However, the conventional loadings, which are used for the
latter designs, are quite large to compensate for effects of blast loads.
Further, as with standard buildings, pre-engineered structures, which are
designed for blast, are designed elastically for the conventional loadings
with the assumption that the structure will sustain plastic deformations due
to the blast. The design approach will require a multi-stage process,
including: preparation of general layouts and partial blast designs by the
design engineer; preparation of the specifications, by the engineer
including certain features as recommended herein; design of the building and
preparation of shop drawings by the pre-engineered building manufacturers;
and the final blast evaluation of the structure by design engineer utilizing
the layouts on the previously mentioned shop drawings. At the completion of
the analysis some slight modifications in building design may be necessary.
However, if the following procedures are used, then the required
modifications will be limited and in some cases eliminated for blast
overpressures upward to 2 psi.
b. General Layout. The general layout of pre-engineered buildings is
based on both operational and blast resistant requirements. Figure 67
illustrates a typical general layout of the pre-engineered building. The
general requirements for development of the layout should include:
(1) Structural Steel.
(a) The maximum spacing between main transverse rigid frames
(bay width) shall not exceed 20 feet.
(b) The maximum spacing between column supports for rigid
frames shall not exceed 20 feet while the overall height of frames shall
be 30 feet or less.
(c) Slope of the roof shall not exceed four horizontal to one
vertical.
However, the roof slope shall be as shallow as physically
possible.
(d) Spacing between girts shall not exceed 4 feet while the
space between purlins shall not be greater than 5 feet.
2.08-236
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