The shear behaviour of non-prismatic reinforced concrete beams determined using digital image correlation

It can be seen that when subject to a uniformly distributed load, a prismatic, steel reinforced concrete beam with constant longitudinal and transverse reinforcement percentages is inefficient. Following simple optimisation routines can result in beams whose flexural and shear capacities reflect the requirements of their loading envelope, and such elements tend to be non-prismatic. Structural research into the use of flexible formwork has developed simple methods for the creation of such elements to offer material and carbon emission savings of up to 40%.

However, the shear behaviour of such variable section steel reinforced concrete beams has previously been an area of confusion for designers, who must often rely on empirical relationships derived from prismatic beam tests. This paper presents the results of new tests undertaken at the University of Bath on tapered concrete beams designed using BS EN 1992-1-1 [1], the compressive force path method and a strut and tie model, in which digital image correlation was used to analyse the specimens.

Using the 'MatchID' program, strain distributions in each of the specimens during loading were determined, with the results allowing important comparisons to be drawn between the various design methods. A digital image correlation (DIC) technique was subsequently used to verify new proposals for the shear design of non-prismatic concrete beams, which aim to provide improved guidance for designers of optimised concrete structures.