Can't figure out how to generate normals for .obj with concave curvature

Can somebody explain to me how to generate normals for a wavefront object? The normal generation in the importer only seems to work for convex shapes, these arches still looks flat shaded. I also tried enabling smooth shading for the entire model in blender and exporting that, but that had no effect.

 

In Unity, a vertex can only have one normal. This means that, by default, a model can only be smooth shaded. To produce sharp corners, a model must use duplicate vertices, effectively disconnecting edges. It looks like your obj file has duplicate vertices, perhaps after using the edge split modifier? Does the model look smooth in blender?