This informative video below shows the construction sequence of the building, showing a slipform core with skeletal steelwork following alongside. The benefits of slipform are the speed of construction and the structural strength of one solid piece of concrete as opposed to many different core sections stacked on top of each other.
Another good feature about the video is the time line at the bottom, that seems to be accurate judging from construction updates on this this website .
Construction update 24/10/10
What I like about the design is that it isn't a perfect pyramid - the curtain walls aren't flat from top to bottom, they taper slightly, creating interest all the way up the tower. They also cantilever, as the photo below shows:
I look forward to exploring this building when it's finished in 2012, and seeing London from a fresh angle. I enjoy looking at construction updates, as new buildings are so often viewed as only computer renderings or the final, finished product. I will check up on the website (linked above) every few weeks to see how the project is developing.
I think this concept sketch (parti) is beautiful, and surprisingly informative. It shows the different curtain walls, the cores, notes where the public observation galleries are, and shows the public realm beneath the skyscraper. All of this is evident in such a small sketch, something I hope to achieve with my own in future
The building's official website: