Stone cantilevered staircases

摘要

Cantilevered stone staircases have been In use in England for over 350 years. For at least 200 of these years they were the standard answer for the principal flights in almost all decent town houses. Many thousands must have been built in this country and across Europe. Practically all of them are still in use today, so one can say with confidence that they have stood the test of time and are structurally sound. And yet there are still concerns about their real strength, as shown by recent correspondence in New Civil Engineer and on the ICE website. Problems like the dislodging of a tread at the bottom of a flight in Bedford Square raise worries, and engineers asked to check and approve existing stairs for crowd loading are uncertain how to proceed. The purpose of this paper is to throw some light on the structural mechanics of these stairs, and to propose a method for calculating the stresses. The paper concludes with some examples of new staircases designed by the authors, made of stone, of precast concrete and of wood.