The ornamental design for a vertical supportstructure, as shown and described.
FIG. 1 is a front perspective view of a vertical support structure according to our design;
FIG. 2 is another front perspective view thereof;
FIG. 3 is a rear perspective view thereof;
FIG. 4 is another rear perspective view thereof;
FIG. 5 is a front elevational view thereof;
FIG. 6 is a rear elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof;
FIG. 9 is a left side elevational view thereof;
FIG. 10 is a right side elevational view thereof; and,
FIG. 11 is a front perspective view thereof in the context of a dump body.
The broken lines depict portions of the vertical support structure that form no part of the claimed design. Additional broken lines in FIG. 11 depict environmental subject matter that forms no part of the claimed design.