The single-engine retractable sustained substantial damage when it impacted the runway after a gear-up landing. The pilot reported that he had performed four practice instrument approaches. After the final approach, the pilot was cleared to circle to land on Runway 23. The pilot reported that he failed to lower the landing gear prior to landing, and the airplane touched down about 300 feet from the threshold in a gear-up configuration. The pilot reported that the landing gear warning horn did not sound prior to touchdown.