R.N.F. Carmo

Available plastic rotation in continuous high-strength concrete beams

An experimental program was formulated to study moment redistribution in continuous high-strength concrete beams. The evaluation of ductility is important for this type of beam as, for high-strength concrete, the ductility decreases as the concrete strength increases. It is therefore necessary to determine whether the critical sections are able to develop appreciable plastic rotations to justify the application of a linear elastic analysis with moment redistribution. This work specifically examined the influence of the tensile reinforcement ratio and the transverse reinforcement ratio on the rotation capacity of plastic hinges. The moment redistribution obtained experimentally is compared with the guidelines recommended in Eurocode 2, CEB-FIP Model Code 1990, and ACI 318. The results show that ACI 318 recommendations for linear analysis with moment redistribution are too conservative and that the predictions, according to Eurocode 2 and CEB-FIP Model Code 1990, agree with experimental evidence.

Numerical modeling of concrete beams under serviceability conditions with a discrete crack approach and noniterative solution-finding algorithms

This paper describes the development and validation of a comprehensive numerical model enabling the simulation of reinforced concrete beams under serviceability conditions using a discrete crack approach. The highly nonlinear behavior introduced by the different material models and the many localized cracks propagating within the member pose a challenge to classic iterative solvers, which often fail to converge. This limitation is solved using a noniterative solution-finding algorithm to overcome critical bifurcation points. The finite element model was validated using experimental data on lightweight aggregate concrete beams under flexural loading. It was shown that the model properly simulates both the overall and localized features of the structural response, including curvature, crack openings, and crack patterns. The model was used to carry out a numerical study of the role of longitudinal reinforcement ratios and crack widths in reinforced concrete beams. It was observed that the total crack openings along a member seem to remain nearly independent of the tensile reinforcement for ratios >2.5% and the same level of strength.

VALIDATION OF A DISCRETE CRACK MODEL FOR LIGHTWEIGHT AGGREGATE CONCRETE BEAMS

The development of crack models capable of simulating the discrete nature of fracture is of interest to many different areas of research. For example, the structural analysis innovative designs now made possible by new ultra-high performance concrete mixtures would certainly benefit from such improved predictive capabilities. Currently, there are numerous numerical approaches available in the literature, for instance based on nodal or element enrichment techniques, or even on remeshing strategies. Typically, the validation of such approaches was achieved using benchmark tests that contained few cracks and where the overall displacements were compared until failure. Having this into account, this paper describes a detailed validation of a discrete crack model based on embedded discontinuities for predicting the behaviour of lightweight aggregate concrete. The model itself includes the rigid body movements associated with the opening of cracks and relies on a robust noniterative algorithm to overcome convergence difficulties typically found with numerous cracks and material non-linearities. Validation was achieved using experimental data from tests performed on lightweight concrete beams (LWAC) under flexural load, where displacements, curvatures and cracks width were properly monitored. This data include, not only overall displacements, but also the complex crack patterns produced during the tests. The model was shown to predict well the overall crack patterns and openings, and was used to perform extrapolations on crack widths for different reinforcement ratios. D. Dias-da-Costa, R. Graça-e-Costa and R.N.F. Carmo