This paper summarizes the results of an investigation on objective modeling and prediction of deformation localization in nonlinear force-based frame elements. Emphasis is placed on the behavior of reinforced concrete structures where localization is most likely to occur. The discussion begins with a brief review of the force-based element formulation. Next, plastic hinge behavior is classified into three categories: hardening plastic hinges, perfectly plastic hinges, and softening plastic hinges. The three types of inelastic behavior pose an increasing challenge to objective postpeak modeling. The physical and numerical characteristics of localized failure are outlined. Two regularization techniques for maintaining postpeak objectivity are proposed: (1) a constant fracture energy criterion, which provides objective response on the element force-displacement level; and (2) geometric scaling, which provides objective response on the local moment-curvature level in plastic hinge regions. The discussion concludes with three applications to different reinforced concrete structures: a frame, a bridge pier, and an overreinforced concrete beam. In all three cases, the proposed regularization technique successfully yields objective model predictions.

This paper presents the current state of the art of nonlinear analysis of steel-concrete composite structures. The focus is on frame elements, which are computationally faster than continuum finite element models. First, section models are presented, with a review of resultant and fiber models and a discussion of possible practical applications. The presentation of frame elements follows. Models with lumped and distributed inelasticity, as well as models with perfect and partial connections are covered. Rigid and partially restrained joints are then reviewed and discussed at length. A discussion of the analysis of structural walls completes the presentation of the models. Modeling applications to the analysis of composite frames are also presented. This state-of-the-art review focuses on developments that have stemmed from the recently completed National Science Foundation sponsored U.S.-Japan program on composite and hybrid structures.

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...

Composite floor systems, consisting of reinforced concrete slabs and steel girders, are common in buildings and bridges. Partial restraints at the interface of the concrete slab and the steel girder have significant effects on the response of the composite beam. A few analytical models capable of accounting for these effects are available; however, none can be efficiently used for the nonlinear analysis of composite beams. In this paper, the basic governing equations are presented for a composite beam with deformable shear connectors under small displacements. Based on these equations, a new composite beam element is developed using the force method of analysis. The performance of this new element is compared with that of a previously developed displacement-based composite beam element. Both elements consist of two beam components connected through a deformable interface. A distributed spring model is used to account for the shear deformation at the interface. Two numerical examples on the nonlinear behav...