On August 18, 1996, at 1850 hours Pacific daylight time, a Ryan ST3KR, N57011, veered off the runway and ground looped on landing at the Nuttree Airport, Vacaville, California. The aircraft was owned and operated by the pilot. Visual meteorological conditions prevailed at the time and no flight plan was filed for the cross-country personal flight. The aircraft sustained substantial damage. The certificated private pilot, the sole occupant, was not injured. The flight originated at Red Bluff, California, at 1745 hours as a flight to Vacaville. In his written report, the pilot stated that the touchdown and initial landing rollout were normal. As the aircraft slowed to 20 mph the aircraft started an arc to the right. The pilot stated that full left rudder and brake "made the arc tighten to the right...(and)...I released the left brake and applied a little right brake." The arc began to lessen, but not enough to prevent the aircraft from leaving the runway and heading for a drainage culvert. The pilot was concerned about the aircraft striking the culvert and nosing over onto its back so he intentionally "stepped hard on the right rudder and brake to purposely ground loop." During the ground loop, the aircraft wing struck a concrete barrier above the drainage culvert. The aircraft was examined by an FAA airworthiness inspector from the Sacramento, California, Flight Standards District Office. He reported that he did not observe any damage or defect of the landing gear or brakes not related to the impact sequence.