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Among the most important conclusions of the joint committees which prepared reports on the fire resistance of concrete structures were those stating that:
(i) ‘Full appreciation of ultimate limit states of concrete structures at normal temperatures is the essential prerequisite for being able to predict reliably their behaviour in fire.’
(ii) ‘The concept of “nominal shear stress” is not appropriate for a cracked section.’
(iii) Enough information is available to recommend guidelines based on: ‘Analytical procedures, which may be necessary only in some cases, to determine the limit state of collapse when the performance of the structures is largely controlled by the behaviour of the steel reinforcement.’
The paper describes an approximate method of allowing for the second order effects produced by axial forces in the members of multistorey, plane frames, unbraced against side-sway. The displacements and axial forces, given by a standard linear elastic analysis, are used to calculate an equivalent system of loads which, when applied to the frame, produce approximately the same additional deformations us would be cuused by the out-of-balance axial forces. A second linear elastic solution is then performed with the equivalent set of loads applied to the frame, and the complete solution obtained by superposition of the two linear elastic solutions. A check on the validity of the method is the accuracy with which the results can be used to estimate the elastic critical load of the frame.
It may have seemed as though every member of the Institution has submitted a solution of Pythagoras in this column, but we have two late entries from areas of the world that were coloured red in our old school atlas.