Semi-static deflection measuring devices

Many semi-static devices have been developed ever since the first semi-static deflection measuring device, the California Travelling deflectograph in the early 1950s, was presented in Hveem s paper (1955). A good historical review of the evolution of semi-static deflection measuring devices can be found in the Andren report (Andren 2006). 

This paragraph covers most of the semi-static deflection measuring devices currently in use. 

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A general description of the various types of static and semi-static deflection testing devices and procedures for deflection measurement is provided by ASTM D 4695 (2008) or AASHTO T256 (2011). 

The non-destructive structural evaluation of a pavement may be carried out by a wide variety of deflection measuring devices. The devices may be classified into three categories (a) static devices, (b) semi-static devices and (c) moving or rolling devices. 

Dynaflect and Road Rater are vibrating load devices developed in the United States in the 1970s. They measure dynamic deflection while they are stationary, using a sinusoidal force. Unlike the Benkelman beam and semi-static devices, they are also capable of measuring the deflection basin since deflection is recorded by velocity transducers (usually five). Both devices comply with ASTM D 4695 (2008) and ASTM D 4602 (2008). 

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