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 1. The minimum length of the foundation extension
required for anchorage of the reinforcement in the concrete; or
2. The minimum required plan size to transfer the
conventional (dead and live) working loads to the supporting soil without
exceeding the allowable bearing pressure for the soil.
In the event that piles are utilized, Item 2. above can be ignored.
(4) The criteria presented in this section and the data prepared
in Tables 32 and 33 are intended to be used where more reliable soil data is
not available. If more reliable data is available, the structure should be
analyzed for the specific properties derived from the data. In this
situation, the structure can be permitted to rotate to the point of
incipient overturning under the action of the blast.
4.
EXAMPLE PROBLEM - Design of Simple Type Foundation Extension.
Problem:
Design a foundation extension for a cantilever wall barrier.
Determine the length, thickness, and amount of reinforcing
steel required for the foundation extension.
Given:
(1) Configuration of the structure and details of the wall
which is designed to the incipient failure condition.
(2) Quantity of explosive and location relative to structure.
(3) Soil data.
(4) Design strength for building materials.
Solution:
(1) Based on the configuration of the structure and the
guidelines of Section C.2.2 of Stea's report, estimate the dimensions of the
foundation extension to be utilized in the overturning analysis. For single
cell barrier(s) supported by buttress walls, determine the area of
reinforcement required for the foundation to develop the strength of the
backwall and sidewall of the structure.
(2) Determine the soil bearing pressures beneath the
foundation (using the foundation dimensions estimated in Step 1) for the
working (dead and live) load condition.
The foundation must have sufficient plan size to transfer the dead and live
loads to the supporting soil without exceeding the allowable bearing
pressure for the soil. If the allowable bearing pressure is exceeded, the
length and, where feasible, the width of the foundation should be increased
in order to provide the plan size required. If an excessively large plan
size is required, piles should be used. In any event, the plan size should
not be decreased unless the results of the subsequent overturning analysis
indicate otherwise.
2.08-311
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