The ornamental design for a playpenframe with triangle side braces, as shown and described.
FIG. 1 is a perspective view of a playpen frame with triangle side braces showing my new design;
FIG. 2 is a side view thereof.
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a bottom plan view thereof.
Only one side of the playpen frame with triangle side braces is showing in the subject drawings. All four sides of the subject invention are identical to the side view shown in FIG. 2. The broken lines shown in FIGS. 1 to 4 are for environmental purposes only and form no part of the claimed design.