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 b. Solid Steel Plate Door. A solid steel plate door is first sized for
fragment penetration, if any, and then designed to resist the blast
pressures as a two-way element. The design charts, equations and procedures
are given in NAVFAC P-397. It was recommended in Healey's report to
consider the solid steel plate door as a two-way element simply supported on
all four sides. However, standard construction details (for the door)
indicate that the bottom edge of the door provides little or no lateral
support and as such, the door should be considered as a flat plate with
three edges simply supported and the fourth edge free.
(1) As stated in paragraph 1.b of Section 4 of this manual, the door
should be designed for a maximum (non-reusable) ductility ratio, Xm/XE =
10. A ductility ratio of 5 should be used for a reusable door. According
to Keenan, the door should be designed for a maximum deflection equal to
0.13L, where L is the clear horizontal span unless special requirements
dictate a lesser deflection.
(2) Figure 71 shows a typical solid steel blast door. The direct
load produced by the blast will be transmitted from the door to the supports
by bearing, while reversal action of the door and the effects of negative
pressure are transmitted to the door supports by several reversal bolts
along the vertical edges. The reversal bolts eliminate the need to design
the hinges for rebound. On wider doors, reversal bolts may be placed on the
top and bottom door also to take advantage of possible two-way action of
plate.
(3) A series of tests were performed on one-fifth scale models of
missile cell blast doors fabricated from ASTM A36 mild steel plates. The
results of the tests, which are published in the report by G. Warren titled
Experimental Evaluation of Blast-Resistant Steel Doors, indicate the
ductility ratios did not exceed 10 although measured deflections were well
into the plastic range. The reserve capacity (usable ductility)
underscores the significance of neglecting membrane action in the analysis.
(4) A problem solution is presented in paragraph 6.a of this section
to illustrate the use of the design charts and procedures.
c. Built-up Door. A typical built-up blast door usually consists of a
peripheral frame made from channels, with other horizontal channels serving
as intermediate supports for the steel plate. All of the channel sections
are connected by welding. The exterior cover plate, i.e., the plate facing
the blast loads, is usually thicker than the interior plate. The mechanism
for reversal loads is similar to that used for the solid steel door, except
the hinges usually are designed to serve as the reversal bolts on one side
of the door due to the lower magnitude of the blast pressures involved.
(1) Current design procedures, as stated in Healey's report,
recommend that the exterior plate be designed as a continuous member
supported by the transverse channels which, in turn, are designed as simply
supported members, the applied blast load being equal to the blast
pressures on the exterior plate. Certain conservative assumptions are made
by this design methodology (as stated by Warren in Formulation of an
Analysis Methodology for Blast-Resistant Steel Doors) which may result in
an unnecessarily heavy and costly door.
2.08-270
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