In 1993, with the roof of the Gottlieb-Daimler-Stadion (since 2008 Mercedes-Benz-Arena) in Stuttgart, he introduced the "speichenrad" principle to structural engineering. Indeed, this principle was employed for the first time in the history of Structural Engineering by the Italian engineer Massimo Majowiecki, the designer of the roof of the Olympic Stadium, Rome (built in 1990, three years before the Gottlieb-Daimler-Stadion). Since then, his company has successfully employed it in stadium projects across the globe. Other structures include the observation tower at the Killesbergpark in Stuttgart. Most of his work as well of that of his company is documented on their website. He was also the developer of the solar tower (or solar chimney) and is largely credited with inventing the strut and tie model for reinforced concrete.