1.- My apologies for the terminology - I took one overview class on the subject in Spanish, and haven't looked at it in the last 60 years. 2.- Agreed - that's why rebar on horizontal beams (and slabs) sometimes goes on the top edge and shifts to the bottom edge. 3.- By beams I do mean horizontal beams. This also applies to horizontal slabs. However, vertical columns also need rebar, especially in earthquake-prone areas. If the ground moves horizontally in an earthquake, the (vertical) columns have to transmit the motion to the upper parts of the structure. This create huge tension stresses on one side of the columns so they need vertical rebar rods on their perimeter.