Application of nonlinear finite strip technique to concrete deep beams

The salient features of an alternative version of the nonlinear finite strip method for analysing reinforced concrete elements is presented. Unlike the conventional finite strip models which can only handle structures whose geometry does not change in one direction, the newly developed finite strip model can analyse certain structures whose geometry (although still fairly simple) can change along their length such as deep beams with local changes of crosssection along their span(s). Moreover, unlike the conventional finite strip models, the new alternative model has the desirable feature of being able to incorporate any desired boundary conditions and different number of harmonics in various strips with minimal effort. Although the proposed model may, in certain cases, suffer when compared with the conventional alternatives, from the potential drawback of an increased number of strips with associated increases in computer storage, the present model needs many less displacement parameters at each nodal line because of the often substantially shorter lengths of the finite strips (cf. conventional strips) and, hence, needs a much narrower half-bandwidth (HBW) in the stiffness matrix with obvious savings in the subsequent computer running time. Very encouraging correlations have been found between predictions based on the present model and some recently reported test data on deep beams: these include continuous RC deep beams with changes of cross-sections over the supports and also simply supported RC deep beams covering a wide range of design parameters. In addition, the present method has been used to analyse data from a series of tests on RC deep beams with fixed-fixed boundary conditions. The numerical results for deep beams with fixed-fixed boundary conditions based on the present model provide a desirable double check on the validity of a recently reported, largely hand-based, method and should be valuable in identifying the areas in which further work may be required.