The Grandstand at Cheltenham Racecourse is a great example of a cantilever roof. A cantilever is an overhang that is only anchored on one side. Early stadium roofs had pillars to support the open end of the roof. The problem with that is that sometimes your view of the action will be obscured if it happens to line up with a pillar. This is still a problem at Barrow AFC, the team I support. I decided to estimate the mass of the concrete section of the roof. I enlarged the photograph and counted 20 seats along in each of the blocks with coloured flags in. There are 6 of these blocks under the concrete roof. Say each person gets about 60cm to sit in, then you might get up to 15m per block including the stairway on the side. So let's say the roof is 90m long. It might by 1/4 of that length sticking out - so let's say the overhang is 15m. The concrete needs to be deep enough to cover the steel reinforcement and prevent rust. Let's say 50cm on average. That gives 675 cubic metres. Now concrete has a density of around 2.4 tonnes per cubic metre. That means the roof is at least 1500 tonnes. If you study Civil Engineering, you'll need to be able to make good estimations and will be taught how to keep the roof up!
