The pilot, who recently acquired the Cessna 180K airplane, was receiving instruction for insurance purposes. After some airwork was performed, the flight returned to the traffic pattern for landing practice. The pilot entered the traffic pattern and joined a left downwind leg for runway 23. On short final, flaps were lowered to 40 degrees and the airplane was slowed to 60 knots. At 15 feet above ground level, the airplane "came down hard" on the runway numbers. The left and right main landing gear failed and the airplane came to a stop on the right edge of the runway. Structural damage to the lower fuselage resulted. The pilot reported that the winds at the time of the accident were from 235 degrees at 10 knots, with gusts to 15 knots. He also reported that windshear occurred and they were unable to react quickly enough to prevent the hard landing. The reported wind at a nearby airport, about the time of the accident, was from 280 degrees at 15 knots. The pilot reported a total flight experience of 1,354 hours; of which, 3 hours were in the same make and model as the accident airplane and 3 hours were flown during the 90-day period preceding the accident.