Prestressed Concrete Developments at the Field Test Unit Thatched Barn

MR. J. E. SWINDLEHURST, M.A., M.I.C.E., M.I.Struct.E., who takes office this month as President of the Institution of Structural Engineers for the Session 1950-1951, has spent the greater part of his professional life in the municipal service, and since 1924 has been Engineer and Surveyor to the Borough of Hampstead. He is the first President of the Institution to have specialised in this branch of engineering, and he will bring to the direction of its affairs the administrative qualities and executive ability which are such necessary characteristics of the Borough Engineer.

In a recent paper the author described a number of tests which he had carried out with the object of determining the stress distribution in various types of portal frame knees1 While these tests afforded a certain amount of information concerning the stress conditions in the connections within the elastic range, they gave no indication as to the maximum loads which could be carried, particularly when the joint is subjected to a "compressive” load. Under this loading condition, which is usual in portal frames, instability of the web or flanges at the knee is liable to develop and lead to a lower collapse load than would be expected from consideration of the elastic stress system only. It was therefore thought desirable to continue the investigation to study the strength of the various connections and to discover what stiffening would be necessary to prevent premature failure due to instability. The object of this paper is therefore to describe the results of a series of tests on portal frame knees under compressive loading; the extent to which the strength of complete portal frames is influenced by the knee design has been investigated by three tests on rectangular portals having different knee details. Arnold W. Hendry