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.