Lightweight Fire Protection and the Structural Engineer. Discussion on the Paper by A. R. Mackay, A.

Aerated concrete is one of a group of materials described collectively as 'lightweight concrete.' The term 'lightweight concrete' is somewhat arbitrary; in the past it has been customary to consider as 'lightweight, any concrete of dry density not exceeding 100 Ib/cu. ft., but the use of reinforced units has led to concretes with a density of 110-115 or even to 120 Ib/cu. ft. A. Short and W. Kinniburgh

The subject of this paper is the design and construction of hangars and workshops together with maintenance aprons which form part of the extension to British European Airways Corporation Engineering Base at London Airport. P. B. Edwards and R.B. Rigg

This month's letters discuss foundations in shrinkable ground and highlight a survey on structural optimisation in practice.