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This paper describes the early developments on prestressed concrete carried out under field conditions at Thatched Barn for the Ministry of Works. The work covers the development of special equipment and the casting and testing of structural components prestressed by both the bonded and end-anchored systems.
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