The presentation and application of prestressed steel structure has come through about half a century, but the application of prestressed double layer space grids is merely twenty years.
预应力钢结构的提出和应用已经历了将近半个世纪，而预应力钢网架的应用，还只是近二十年的事。
2
The project was first one using prestressed anchors with double layer protect for construction in domestic hydraulic engineering.