Correspondence on Plastic Instability Analysis of Space Frames by M. M. K. Khalifa

A programme of tests was carried out on 28 prestressed concrete beams with various combinations of prestressed web reinforcement and stirrups of mild steel or high strength deformed steel. The results are used to derive a formula to obtain the approximate width of inclined cracks and to discuss the calculation of the ultimate shear of beams with vertical prestress with particular reference to CP 110:1972. Prestressing part of the web reinforcement was found to increase both the inclined cracking shear and the ultimate shear. E.W. Bennett and G. Mlingwa

Numerical analyses of the strength of stiffened plates in compression have been carried out, covering a range of plate and stiffener slendernesses. Different ratios of flange/web and stiffener/plate cross-sectional area ratios are studied. C.A. Carlsen

This month's letters cover legislation for design checks, embodied carbon of modular construction approaches, and assessment of masonry buildings for earthquake resilience in New Zealand.