Try this, taking advantage of the dupliface function
Add a circle Curve, then in Edit Mode, edit it to create the profile of the whole bench

Go to Object Mode and press ALT+C -> Mesh from Curve (or click on Object -> Convert -> Mesh from Curve) to convert the curve object into a mesh object.
Then go to Edit Mode :

We want every vertices equally spaced, so be sure to have enabled the Loop Tool addon (File -> User Preferences - Addons -> enable Loop Tool in the Mesh category) that is perfect for this, and click on the “Space” button

Will lead into

Extrude the whole profile to obtain your bench shape

Go to Object Mode and click on the “Origin” button then select “Origin to Geometry” to put the origin of the mesh to its center.

Press SHIFT+S then “Cursor to Selected” (or click Object -> Snap -> Cursor to Selected) to put the 3D cursor to the selected object origin location

Now add a plane, it will be created at the cursor location then switch to Edit Mode to edit that plane and transform it into the plank base

Go back to Object Mode, then
-select the Plank
-hold SHIFT then select the bench shape
- Press CTRL+P -> Parent (or click on Object -> Parent -> Object) to parent the plank object to the bench object
Go to the Object Panel, scroll down to the Duplication tab and enable “Face” (the dupliface function)

As a result you will see the plank object duplicated on every faces of the bench object

(you can adjust those plank scale in the Duplication tab by enabling “scale” and tweaking the value)
To make those duplicated plank real (they’re only instances for now), you need (still in Object Mode) to press CTRL+A -> Make Duplicate Real (or click on Object -> Apply -> Make Duplicate Real)

You can then now delete the original plank object, and the bench object, if you wish you can select all the planks and CTRL+J to join them into a single object too