NONLINEAR FINITE STRIP TECHNIQUE APPLIED TO CONCRETE STRUCTURES

An alternative version of non-linear finite strip method for concrete structures is presented: unlike the conventional finite strip models w hich can handle only those structures whose geometry does not change i n one direction, the newly developed finite strip model can analyse ce rtain structures whose geometry (although, still fairly simple) can ch ange along their length, such as deep beams with local changes of cros s-section along their span. Moreover, unlike the conventional finite s trip models, the new alternative has the desirable feature of being su itable for incorporating any desired boundary conditions and different number of harmonics in various strips with minimal effort. Although t he proposed model may, in certain cases, suffer, when compared with th e conventional alternatives, from the potential drawback of increased number of strips with associated increases in computer storage, the pr esent model needs much fewer displacement parameters at each nodal lin e because of the often substantially shorter lengths of the finite str ips (cf. conventional strips) and, hence, needs much narrower half-ban d width (HBW) in the stiffness matrix, with obvious savings in subsequ ent computer running time. The proposed non-linear version of the pres ent model caters for concrete material non-linearities attributable to cracking and/or crushing, assuming perfect bond between reinforcing b ars and adjacent concrete. The stress-strain behaviour of plane concre te under biaxial state of stress is described by a new tangent stiffne ss (hypoelastic) constitutive law and saves considerable time (compare d with certain previously available secant modulus models). The propos ed model also incorporates a slightly modified version of a tangent st iffness model previously reported in the literature. Very encouraging correlations have been obtained between the predictions based on the p resent model and rather extensive experimental data on various structu ral elements. Owing to space limitations, the only numerical results p resented are those for a continuous deep beam with changes of cross-se ction at the points of support, where very encouraging correlations ha ve been found between the theory and experimental results up to failur e load.