Columbia River Gorge National Scenic Area officials are asking hikers to honor the closure of the historic Benson Bridge across Multnomah Falls to pedestrian traffic.  Fencing closing off the bridge area was installed due to safety concerns following damage from a rock fall that occurred in early January.  But Scenic Area officials report the fencing has been repeatedly vandalized allowing illegal access into the closure area.   Signs informing visitors about the closure at Multnomah Falls and the Wahkeena Trailhead have been repeatedly removed and damaged.  The Forest Service asks people who see vandalism of the fencing or the signs to notify them at 541-308-1700.  Repairs to the bridge are expected to be completed by Memorial Day weekend.