Footbridges on the Kwinana Freeway, Western Australia

The paper describes detailed microscopic investigations of the extensibility and microcracking of the in-situ concrete in composite beams with precast prestressed concrete members and in-situ reinforced concrete members. The experimental work included the use of mirror extensometer gauges (sensitivity = 0.5 x 10 to the minus 6 strain approximately) to indicate the onset of cracking, and the location and examination of the cracks with a microscope of 100 magnification. R.H. Evans and F.K. Kong

Mr. I. M. Nitkin of the Engineering Laboratory, Cambridge, writes:- 'Professor Neal and Dr. Griffiths have demonstrated quantitatively that the capacity of a redundant truss is not necessarily exhausted upon first buckling. This is a fact not generally understood. It is interesting to note that, for the particular truss considered by the authors, the shape of the load-deformation curve for the strut BD makes very little difference to the ultimate load.'

Concepts of Structures, by William Zuk (New York: Reinhold Publishing Corp., 1963) 9 x 6 in., 79 pp., 48s.