components of the structure with deflection basin measurements has not

yet been accomplished (63). The study presented herein is aimed at

developing an approach that would allow a layer-by-layer analysis of the

Dynaflect vibratory deflection basin.

 2.3.2.4 Dynamic Impact Load Response. Essentially, all impact

load testing methods deliver some type of transient force impulse to the

pavement surface and measure its transient response. The equipment uses

a weight that is lifted to a given height on a guide system and is then

dropped. Figure 2.4 illustrates this schematically. By varying the

mass of the falling weight or the drop height or both, the impulse force

can be varied.

 The width or duration of the loading pulse (loading time) is

controlled by the buffer characteristics, Figure 2.4, and it closely

approximates a half-sine wave (Figure 2.5). The duration of the force

is nominally 25-30 msec, Figure 2.5, which approximates the load

duration of a vehicle traveling 40 to 50 mph (123). The peak magnitude

of the force can be determined approximately by equating the initial

potential energy of the system to the stored strain energy of the

springs (buffer system) when the mass is momentarily brought to rest

(11,105). Thus


 F = (2Mghk)1/2 Eqn. 2.1


where

 M = mass of the falling weight,

 h = drop height,

 k = spring constant, and

 g = acceleration due to gravity.