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M o d e l N o . M E - 6 9 9 1
M e a s u r i n g B r i d g e D e f l e c t i o n U n d e r L o a d
11
Measuring Bridge Deflection Under Load
Because the members are made of plastic, it is easy to show bending in a bridge using
relatively small loads.
Using a Motion Sensor
In Figure 24, the bridge is loaded by hanging a weight (Large Slotted Mass Set, PASCO Model ME-7566) from
the center of the bridge. A Motion Sensor (PS-2103) is placed on the floor and pointed up toward the bottom of
the weight hanger. A PASPORT inteface (in this case, the Xplorer GLX, PS-2002) is used to record the amount
of mass and the distance to the bottom of the weight hanger. A graph of the deflection as a function of the load is
shown next to Figure 24.
Hint: For the GLX, set the Motion Sensor sample rate to 50 Hz. In the Sensor Setup window, change the
‘Reduce/Smooth Averaging’ from ‘Off’ to ‘5 points’.
Using Load Cells
Figure 25 shows two bridges of the same type but dfferernt scale. For a given load the deflection is different.
Also note that the forces in some of the members are being measured using load cells to discover the difference
caused by the size of the bridge.
NOTE: Do not attempt to
load the bridge to the
point of breaking.
Figure 24: (Left) Deflection of bridge under
load. (Above) Displacement vs. Mass plotted
using PASCO’s DataStudio software
Figure 25: (Above) Same load for different scale bridges.
(Right) Displacement vs. mass