"The 'brackets' around these sprinkler and standpipe risers are clamps used to transfer some of the pipes' vertical load (weight) to the building's structural support. Pipe clamps are required in multistory buildings. The clamps are intended to prevent pipe movement and should be secured and located so that the system piping remains in its original location and position."
Coffee Break Training - Fire Protection Series No. FP-2009-38
United States Fire Administration: http://www.usfa.fema.gov/