A Berkeley engineering professor has a new way to retrofit buildings against terrorist attack. The professor says new research shows that hooking steel cables to the floors of existing buildings makes them stronger against some kinds of attack. Abolhassan Astaneh-Asl says the cables help buildings if their outer columns are hit by an explosion. The outer columns of a building are often the most vulnerable to attack because they are closest to streets and parking areas. But new research says that if the floors of a building are attached to the cables — they may sag but not fail completely when an explosion hits. Researchers say attaching the cables is relatively cheap.