A uniaxial model for concrete confined with fiber-reinforced polymers (FRP), but also with steel jackets or conventional transverse reinforcement, is presented. The model, which is suitable to be inserted into fiber-type beam-column models, explicitly accounts for the continuous interaction with the confining device due to the lateral strain of concrete, through an incremental-iterative approach. The relation between the axial and lateral strains is implicitly derived through equilibrium between the (dilating) confined concrete and the confining device. This relation allows one to trace the state of strain in the jacket and to detect its failure. The model is compared with a set of experimental tests and shows very good agreement in both the stress-strain and the stress-lateral strain response. Evidence of the main aspects of the behavior of FRP-confined concrete is given that points out differences in the response when using fiberglass or carbonfiber. Predictive equations to determine the ultimate strength and strain of concrete confined with FRP are derived and tested on a number of experimental data.

The effects of inelastic buckling on monotonic and cyclic behavior of reinforcing steel bars are studied. Experimental tests show that this phenomenon occurs when the ratio between length and diameter of the bar exceeds 5, and that it leads to a postyield softening branch in compression that strongly influences the cyclic behavior of the bar. An analytical model of rebars accounting for inelastic buckling is presented, suitable for inclusion in programs for the analysis of r/c sections using the fiber type of discretization. The model employs four hardening rules (kinematic, isotropic, memory, and saturation) as functions of four independent parameters (yield stress, elastic modulus, hardening ratio, and a weighing coefficient). An explicit stress‐strain relation in finite terms for loading branches is utilized. The model yields accurate results in predicting the cyclic behavior of rebars, both with and without inelastic buckling, for deformation paths of general nature.

This paper presents a new reinforced concrete beam finite element that explicitly accounts for the slip between the reinforcing bars and the surrounding concrete. The element formulation combines the fiber-section model with the finite-element model of a reinforcing bar with continuous slip. The section model retains the plane-section assumption, but the steel fiber strains are computed as the sum of two contributions, the rebar deformation and the anchorage slip. The model applies to any cross-sectional shape under biaxial bending and both monotonic and cyclic loads. The model theoretical framework is presented first. A sensitivity study on the monotonic and cyclic response of a reinforcing bar shows how the model traces the bar's reduced initial stiffness, bond degradation, and anchorage loss for insufficient anchorage length. Finally, comparison with an experimental test on a circular column shows that the prediction with the new model is in good agreement with the test, whereas the original fiber mode...

A modified real-coded genetic algorithm to identify the parameters of large structural systems subject to the dynamic loads is presented in this article. The proposed algorithm utilizes several subpopulations and a migration operator with a ring topology is periodically performed to allow the interaction between them. For each subpopulation, a specialized medley of recent genetic operators (crossover and mutation) has been adopted and is briefly discussed. The final algorithm includes a novel operator based on the auto-adaptive asexual reproduction of the best individual in the current subpopulation. This latter is introduced to avoid a long stagnation at the start of the evolutionary process due to insufficient exploration as well as to attempt an improved local exploration around the current best solution at the end of the search. Moreover, a search space reduction technique is performed to improve, both convergence speed and final accuracy, allowing a genetic-based search within a reduced region of the initial feasible domain. This numerical technique has been used to identify two shear-type mechanical systems with 10 and 30 degrees-of-freedom, assuming as unknown parameters the mass, the stiffness, and the damping coefficients. The identification will be conducted starting from some noisy acceleration signals to verify, both the computational effectiveness and the accuracy of the proposed optimizer in presence of high noise-to-signal ratio. A critical and detailed analysis of the results is presented to investigate the inner work of the optimizer. Finally, its performances are examined and compared to the most recent results documented in the current literature to demonstrate the numerical competitiveness of the proposed strategy