Karnak: a forest of colums

dimensions of joists

The tension in a joist isn't proportional to the span, but to the square of it. So it becomes huge very quickly. As a practical rule one can take 1/10th of the span as the height of the joist and 1/20th as the width of it. Next applet calculates the weight of a marble joist according to a given span.

The great hall of Karnak

By increasing the span, joists become increadibly heavy very quickly. That's the reason that while using architraves, the span is always kept very moderate. It's not a problem to cross the width of a door, but for creating large halls one has to wait until the invention of armed concrete, around 1900. The great hall in the temple of Karnak measures 5000 m². 134 columns are aligned on 16 rows. The middle ones are 24m high with a perimeter of 10 m. But as a visitor you still got the feeling just to walk in a forest of colums, rather than in a huge hal.