The document discusses the structural systems used in the Olympic Stadium built for the 2012 London Olympics. The stadium features several different structural systems, including a steel skeletal structure, rigid concrete frames with reinforcement, and prefabricated concrete. It also uses external steel bracing and bolted joints between elements. The steel structure supports the cable net roof and transfers loads through the various structural elements to the foundation of 5,000 piles. The document provides details on the different structural components and materials used to construct the lightweight and efficient stadium structure.