The ornamental design for a structuralmonitoringdevice, as shown and described.
FIG. 1 is a perspective view of a structural monitoring device embodying the new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a left side elevational view thereof; and,
FIG. 6 is a right side elevational view thereof.
The broken lines shown in the drawings are for the purpose of illustrating unclaimed portions of the structural monitoring device and form no part of the claimed design. The bottom side is not visible during normal use and forms no part of the claimed design.