The ornamental design for a bent wood arbor, as shown and described.
FIG. 1 is a front elevation view of a bent wood arbor of my design.
FIG. 2 is a perspective view of a bent wood arbor of my design; and,
FIG. 3 is a second embodiment front elevation view of a bent wood arbor of my design the difference from the arbor in FIGS. 1 and 2 being in the side rails.