An Investigation of the Strength of Certain Welded Portal Frames in Relation to the Plastic Method o

In 1938 Baker and Roderick published a paper containing the results of tests on a number of model portal frames which showed in a convincing manner that the "collapse loads" of these structures could be calculated with considerable accuracy. Subsequent
investigations by Professor Baker and his co-workers have demonstrated that the method employed in estimating the collapse loads of the portal frames tested in their first experiments could be developed into a powerful design procedure possessing certain advantages over the present methods based partly on long experience and partly on the theory of elasticity. The "plastic" design method, as it has come to be called, is of particular application to welded structures, such as portal frames, where its use in place of the "elastic" method is likely to lead to more economical designs, simplification of design calculations and, of the greatest importance, it places these calculations on a more rational foundation. Before the plastic method can be applied with confidence in the design office, it is obvious that a good deal of fundamental knowledge must be accamulated regarding the carrying capacity of mild steel members
and structures under various loading conditions and, further, that this information should be systematised in a form suitable for design purposes. This will necessarily take some time to achieve for structures in general but as the advantages to be gained from the use of the plastic method are likely to be very considerable it would be desirable if it could be applied to particular structures in the meantime. The author has, therefore, investigated the strength of a number of two-pinned rectangular portals carrymg vertical loads on the beam, with the object of determining the limits of application of the simple plastic theory to bridge type portal frame girders which are subject to this loading condition.

Arnold W. Hendry