Strength of the steel used in the buildup of the skeletons of the National Stadium is twice that of the usual materials, said Hou Zhaoxin, an expert with the 2008 Project Construction Headquarters Office, Sunday morning.

Hou said the steel, defined Q460EZ235, is the top grade for construction and is produced independently by China.

The figure 460 stands for the strength of the steel, E is the parameter of tenacity and impact under negative 40 degrees, and Z235 means the highest performance of the material.

The use of the product will ensure that the Bird's Nest can bear the shock brought by such a deadly earthquake as the one that demolished the city of Tangshan on July 28, 1976, Hou said.