Design of concrete structures to EN1992 - common rules and design requirements for fire

Providing access for the cleaning of the internal surfaces of the dome and cone at St Paul’s Cathedral whilst maintaining business as usual was a challenge. Constructing an access system to a height of 45m suspended 33m above the church floor without contact or anchoring into the surrounding structure, and then to rotate it through sectors of 90°, was an even greater challenge. Raymond Gold, BSc(Eng), CEng Managing Director, RDG Engineering Consultants Ulrike Knox, BA(Hon) Dip.Arch. RIBA Associate, Purcell Miller Tritton

The response of reinforced concrete to shear forces depends on the transfer of shear across cracks. If aggregates fracture when cracks are formed, shear resistance is likely to be reduced and the loss of strength is likely to be a function of crack width and thence, in some cases, member depth. The analysis of new test results reported here, and others available from the literature, shows that, with limestone aggregate, the shear strengths of members without shear reinforcement are often below characteristic resistances calculated according to EC 2 and other recent recommendations. A considerable proportion of the experimental strengths can be below design resistances. The deficits of resistance are greatest where high concrete strengths are combined with relatively large effective depths. The same phenomenon appears to occur with other aggregates, but to a lesser extent. Members with shear reinforcement are similarly likely to be affected but to an extent less than that in members without shear reinforcement P. E. Regan, BSc, DIC, PhD, CEng, FIStructE Consultant I. L. Kennedy-Reid, BSc, MEng, CEng, MICE, MIHT Atkins – Highways and Transportation A. D. Pullen, BSc(Eng), ACGI Dept. of Civil and Environmental Engineering, Imperial College London D. A. Smith, BEng, CEng, MICE Atkins – Highways and Transportation