Summary This paper describes the principle, design and use of a form of demountable mechanical strain gauge which has been found particularly useful for determining strains in concrete structures. The instrument which uses a lever and dial gauge is cheap to make and use, and is located on 8 in. gauge lengths which are formed by pairs of punched and drilled steel discs glued to the concrete surface. With practice, 200 strains per hour may be measured with an accuracy of about ±5 × 10−6 under most laboratory test conditions. Even greater accuracy has been obtained using the gauge in its ideal horizontal position and with the readings lying within a small range on the dial. In development tests of this kind 90 per cent of measured strains were within ±3 × 10−6 of the mean. Tests on various locating discs show that normal, drilled mild steel discs give the best results.

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Summary The practice has developed in recent years of constructing statically indeterminate prestressed concrete structures by applying connecting restraints to two or more statically determinate prestressed concrete members. The present paper discusses a joint that may be used to convert two or more simply supported prestressed concrete beams into a continuous beam by joining them together over the supports. This joint utilizes unprestressed continuity steel contained within the crosssection of the continuous beam. Alternative designs for such a joint are proposed and examined for suitability in fulfilling the necessary functions. Some remarks are added on the design of composite continuous beams. Tests are reported on five two-span composite beams each made from two post-tensioned, grouted beams. The ratio of the ultimate moments of resistance of the critical sections was varied. The tests demonstrated the essentially satisfactory nature of the proposed joint.

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Summary A theoretical analysis of the modes of failure and ultimate strength of slab bridges shows that the normal method of elastic analysis leads to a design in which the transverse flexural strength is considerably greater than that required to give a factor of safety in the structure as a whole equal to that of longitudinal elements considered alone. It is suggested, therefore, that in the design of slab bridges advantage can be taken of this by permitting moderate tensile stresses when calculating the degree of transverse prestressing required, and that in reinforced slab bridges the amount of transverse reinforcement can be appreciably reduced.