Why are the big stadiums in the open?

Stadiums are mainly for football or track games, because the stadium area is large, it is difficult to build top roof, and football often has a very high ball, will hit the ceiling. And if too big stadium completely enclosed, ventilation is a big problem. So most of the big stadiums will be built in the open. In the stadium to watch the game, the design of top view is particularly important, need to pay attention to the following points:

1. The roof of the stadium should be shockproof to protect the audience from the influence of rain, strong wind, earthquake and other weather.
2. The roof of the stadium should be beautiful and light, which can be achieved by the steel spaceframe structure, especially suitable for the large-span stadium.