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3.2.5 Advantages
The primary advantages of the Dynatest FWD, like many other impulse
deflection equipment, are that the created deflection basins closely
match those created by a moving wheel load of similar magnitude (11,45,
110,123), and the ability to apply variable and heavier dynamic loads to
assess stress sensitivity of pavement materials. The Dynatest FWD test
system has the added advantage that the resulting deflection basin is
constructed from seven deflection measurements compared to five and
three deflections in the KUAB and Phoenix Falling Weight Deflectometers,
respectively.
3.3 BISAR Computer Program
The analyses and evaluation of NDT deflection data in this study
involved the use of BISAR, an elastic multilayered computer program.
BISAR is an acronym for _Bitumen structures Analysis in _Roads. The
program, developed by Koninklijke/Shell Laboratorium, Amsterdam,
Holland, is a general purpose program for computing stresses, strains
and displacements in elastic multilayered systems subjected to one or
more uniform loads, acting uniformly over circular surface areas (32).
The surface loads can be combinations of a vertical normal stress and
unidirectional tangential stress.
The use of BISAR to compute the state of stress or strain in a
pavement requires the following assumptions (32):
1. Each layer of pavement acts as a horizontally continuous, isotropic,
homogeneous, linearly elastic medium.
2. Each layer has finite thickness except for the lower layer, and all
are infinite in the horizontal direction.