They were not planning any such thing. Their original raw plans were to set off some smoke and take down some signs, until the FBI plant got involved. This is the Associated Press (http://news.yahoo.com/fbi-5-men-arrested-wanted-blow-ohio-bridge-143112191.html):
"Baxter, Wright and Hayne considered different plots over time, including distracting law enforcement with smoke grenades while trying to bring down financial institution signs in downtown Cleveland."
Huffington Post (http://www.huffingtonpost.com/2013/01/08/fbi-occupy-wall-street-occupy-cleveland_n_2435224.html):
"Shaquille Azir, ex-con, bank robber, forger, passer of bad checks, and FBI informant, first visited Occupy Cleveland the night the activists were evicted from their camp. The young men were homeless, looking for a cause and a paycheck. At best they were failed gutter punks. It took months of convincing by Azir to get the plot in motion. After the camp folded, Azir gave the penniless Occupy activists construction jobs, and plied them with beer while they worked. He sent them home, according to a Rolling Stone magazine account, with more beer, weed and prescription drugs. At first, the activists rebuffed Azir's arms-dealer friend, who was an FBI agent. Azir continued to press them."
In-depth article at Rolling Stone on this and other recent FBI procedures -- http://www.rollingstone.com/politics/blogs/national-affairs/how-fbi-entrapment-is-inventing-terrorists-and-letting-bad-guys-off-the-hook-20120515