Papers by Giuseppe Tizzani
A database of 239 tests on reinforced concrete (RC) specimens of beams, columns with rectangular ... more A database of 239 tests on reinforced concrete (RC) specimens of beams, columns with rectangular or circular sections, rectangular or barbelled walls, and hollow rectangular piers that failed in shear after initially yielding in flexure are used to fit two alternative models for the degradation of shear resistance, as controlled by transverse reinforcement with cyclic displacement ductility demand. Both models include a distinct, physically-based mechanism for the effect of axial compression on shear resistance and base the contribution of web reinforcement to shear strength V s on the classical 45-degree truss analogy. Between the two models, the one that provides for degradation with cycling of both the web steel and concrete contributions-V s and V c , respectively-gives a slightly superior fit to the data. Although the data for large ductility demands are limited, they suggest that shear resistance does not degrade further beyond a displacement ductility limit demand of approximately 6. The fit to the data achieved by the two models is better than that of previous ones, which were fitted to much smaller sets of data of columns with either rectangular or circular sections. On the basis of the present, much larger, dataset, earlier models are found to give very good average fit for the type of cross section for which they were developed-albeit with larger scatter than that of the two models proposed herein-but significant bias for the other type of section.
Parameters affecting the shear strength of reinforced concrete columns having a rectangular cross... more Parameters affecting the shear strength of reinforced concrete columns having a rectangular cross section and light transverse reinforcement are investigated using data from numerous column tests. A new model is proposed to predict the column shear strength based on theoretical formulations and experimental evidence. The proposed shear strength equation includes contributions from the concrete and transverse reinforcement. Primary parameters in the shear strength model are the column cross-sectional dimensions, concrete compressive strength, column aspect ratio, axial load, and displacement ductility demand. The proposed model is compared with other shear strength models using the available column test data and is shown to result in improved accuracy. A conservative shear strength model for use in design and assessment is proposed based on statistical evaluation of computed and actual shear strengths.
The need for a consistent seismic design philosophy to establish design shear forces for reinforc... more The need for a consistent seismic design philosophy to establish design shear forces for reinforced concrete columns of bridges and buildings under seismic attack is discussed. It is shown that because of a combination of the effects of conservatism in flexural strength design equations and approximations in representation of seismic loads for analysis purposes, real shear forces generated during earthquakes may exceed three times the shear corresponding to code levels of seismic latera/loads. Existing U.S. and New Zealand design expressions for shear strength of circular columns are discussed and compared with results from a comprehensive test program involving 25 circular columns tested under axial load and cyclic lateral inelastic displacements. It is shown that existing design equations are inconsistent and very conservative for initial shear strength. The experimental results indicate, however, that the shear strength reduced with increasing flexural ductility for displacement ductility factors in excess of 2. A model for the influence of flexural ductility on shear strength is advanced, with design equations for initial shear strength applicable for low flexural ductilities, and for final shear strength applicable for fully ductile flexural designs.
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Papers by Giuseppe Tizzani