PLASTIC DESIGN IN ROOF

Press, Volume XCI, Issue 27593, 25 February 1955, Page 13

PLASTIC DESIGN IN ROOF

FIRST APPLICATION OF NEW PRINCIPLE

A taxi garage in Tuam street, rebuilt using new’ engineering principles, was the subject of a paper presented yesterday to the annual conference of the New Zealand Institute of Engineers by Mr I. L. Holmes. The garage has a clean looking roof structure of light steel joists spanning 67 feet. Mr Holmes explained that lighter members than usual were employed as the result of a new design theory and this was its first application in New Zealand. The theory originated at Cambridge University. Engineers in England were beginning to take a serious interest in the new method of design. Tests and research work had also been done in the United States. Further controlled tests on quartersize structures would be done this year at Canterbury University College. The new design method was based on a better understanding of the behaviour of steel structures under load, Mr Holmes said. Certain steel structures were stronger than was sometimes appreciated. As the result of recent research, engineers could now design structures using less weight of steel than formerly. Mr Holmes appealed to New Zealand engineers to use the new method which is known as plastic design.

The paper was introduced with coloured slides. These showed to advantage the clear span of the roof, as well as the bright colours used by the architects. The colours picked out the line of the structure and gave it full meaning. The roof frames are yellow, the heavy side beams deep blue, and a small secondary frame bright red. The architects were Messrs Pascoe, Hall and Mackenzie. The problems confronting the designer of members of a structure under combined bending and direct compression stresses were discussed by Mr A. I*. Andrews, of Wellington, and Mr E. G. S. Powell, of Christchurch, in another paper presented to the conference yesterday.