Boost Your BIM comes the free Select Intersecting Elements add-in...
Run the command and select an element to select all elements that physically intersect with the element you selected.
Some categories (such as Structural Connections) cannot be selected based on physical intersection. If any such elements have a bounding box intersection with the element you select, the tool will provide the option of selecting all elements that have a bounding box intersection.
This tool finds elements whose 3D geometry intersect. Therefore, in cases such as when an architectural column and wall are joined and there is no geometric intersection, the wall or column will not be selected.
This free add-in may be downloaded from the Autodesk Exchange Apps website.