DiscussionThe chairman, said that with this work, as with all research, what was important was the application of the results in everyday practice. If he had read the Paper aright, it seemed to him that the Author was really advocating that in design one should, calculate on a composite structure, so arranged as to eliminate sway, which meant taking into consideration the infilling or any other factor which contributed towards the stability and strength of a tall frame. In practice, of course, that was extremely diflicult. Many frames were designed without any very clear idea of the details of the infilling. He did not know if that was the fault of architects or of engineers, but it certainly happened in practice, and he was very well aware of it, because as the Engineer to a local authority he was responsible for c h e c k h literally hundreds of structures of the nature in question which were submitted by structural engineers; at the time that they were submitted and had to be approved within a statutory period there were no details of m n g , or at least not s a c i e n t details to make it possible to make proper calculations of the rigidity.65. If the design were so accurate and economic as to have taken note of all the strengthening effects, which in most buildings would be due to infilling rather than bracing, what happened when, as was usual, somebody decided to cut openings in the infilling? Presumably the factor of safety would have to take care of it.66. Crude though the observation might be, therefore, it was important to remember the practical conditions of application, while at the same time acknowledging and being grateful for the very meticulous and careful analysis of the factors themselves in formulating improved methods of design. Dr M. R. Home (Lecturer, Department of Engineering, University of Cambridge) said that there was one point of great practical importance on which he would place much greater emphasis than did the Author, namely, in relation to strain-hardening. In the Author's second example of frame instability, a four-storey frame bent " strong ways", the Author had stated in 8 54: "it is unlikely that strain-hardening occurred except at the centre of the third-storey beam." It was important to remember that the conception of a plastic hinge was an idealization. Unless a hinge formed in a region of uniform bending moment, it never behaved as an ideal hinge and consequently its stiffness did not vanish. This was a direct result of strain-hardening and should be taken into account when dealing with the effect of plastic hinges on stabiIity.68. Fig. 24 showed experimental loadideflexion curves for 8-in. X 4-in. joists submitted to single-and two-point loads. For a two-point load (joist J.3), where between the loads the beam was under a uniform moment, the plastic hinge conception of zero rigidity at the plastic collapse load was almost attained, but under a singlepoint load (joist J.2) the beam retained a rigidity which, although much less than the elastic value, was far from negligib...
