Calculating an Influence Line from Direct Measurements

The response of a bridge to a pre-weighed truck can be
measured on site. This paper describes a mathematical
method for converting the measured response of a load
effect into an influence line for that effect. One influence
ordinate is calculated for each scan of the data acquisition
system. The vector of ordinates is found by solving a large
set of simultaneous equations expressed in matrix form.
The general form of the matrices is described, and the
particular matrices for a three-axle truck are given.
The technique is demonstrated using measured strain
on two bridges using pre-weighed trucks with different
numbers of axles.