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 (3) Apply a 20 percent safety factor to the charge weights
and determine the average unit impulse loads on the foundation slab within
the cell. To determine the loads on the foundations of cantilever wall
barriers, utilize the procedures of NAVFAC P-397 or the computer program by
S. Levy in the report, An Improved Computer Program to Calculate the Average
Blast Impulse Loads Acting on a Wall of a Cubicle.
(4) Correlate the available test and descriptive data for the
soil at the construction site with the data of Tables 32 and 33, and
establish the range of critical soil properties to be utilized in the
analysis. The structure is analyzed for both the soft and compact
conditions (specified in the tables) of the actual soil. In the event that
more accurate data is available, only the actual soil condition need be
considered in the analysis.
(5) Prepare the input data for Computer Program OVER
according to the instructions of Section 5 of Stea's report.
(6) Run the analysis utilizing the overturning analysis
computer program.
(7) Inspect the results of both analyses and determine for
each:
a) If the structure reached its peak response. If not,
rerun the analysis utilizing more integration time
steps.
b) If the structure overturned. If so, it was probably
due to the soft condition of the soil. If overturning
occurs, the length of the foundation extension will
have to be increased and both analyses rerun.
c) If the structure experienced excessive horizontal
(sliding) displacements under the action of the blast.
Horizontal displacements become a factor when
explosives are stored nearby. In this situation,
there is danger of the structure sliding into the
explosives and detonating them, thereby propagating
the explosion. Generally, large sliding motions will
occur on the cohesive (clay) soils. This condition is
remedied by adding mass to the structure foundation in
order to increase the friction forces between the
structure and the soil. The added mass will also
lower the center of gravity of the structure which
causes the toe of the foundation to penetrate further
into the soil, thereby decreasing the sliding motions.
However, this will increase the rotations of the
structure and therefore the foundation extension may
have to be lengthened, depending on the results of the
previous analysis. The revised structure is always
reanalyzed for both conditions of the soil.
Further evaluation of the results is deferred until both analyses indicate
that the structure attained it peak response and will neither overturn nor
translate large distances under the action of the blast.
2.08-312
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