Can't walk through

Hello My friends ! How Are you
Iam new in unrealengine 4
And i have a problem
When i download things from internet .3ds files and use them in maya and export them to .fbx files
when i go to add them i have 2 problem the first is to small but i fixed it by scale them when import them
the second i can’t walk through
like i add an arc from internet i can’t walk through it (Between the two columns)
But when i add an arc from Market place (Free) i can walk through the arc (Between the Two columns)