A rational approach towards modeling of post-peak shear deformation behavior of reinforced concrete frame elements within finite element context [electronic resource]

Inelastic response of reinforced concrete frame members to combined gravity and lateral loads involves the complex interaction of axial, moment and shear forces and deformations. Whereas there is a considerable body of experimental data and knowledge on the behavior of members that respond predominately in either inelastic shear or moment effects, the behavior of frame elements that are sensitive to combined shear-flexure interaction is less understood. At present, there is little agreement as to how to analyze the behavior of concrete frame elements that experience strength degradation under the combined nonlinear interaction of shear and moment. This study takes a closer look at existing analytical models that have been proposed for simulation of shear effects in frame elements. Experimental behavior of beam-columns as reported by other researchers is catalogued in order to develop an understanding of the actual physical behavior of concrete frame elements. Available experimental data of ductile and non-ductile columns is analyzed to identify key parameters which affect shear deformation behavior of beam-column elements. Bond slip penetration within the plastic hinge regions of the concrete frame elements is found to play a key role in causing shear failure and subsequent post-peak force deformation response of beam-columns. Existing concrete and steel material models are studied and an improved steel material model capable of simulating cyclic hardening, cyclic softening and mean stress relaxation is proposed. The proposed steel model is verified by comparing its simulated response with reported behavior of reinforcing bars. The suitability of the proposed steel material model to simulate random loading history is demonstrated. A numerical framework (i.e. kinematic description, solver routine and control algorithms), capable of simulating large rotation, large deformation, post-peak shear deformation behavior of frame elements is developed. A new analytical model for simulating shear deformation behavior of concrete frame elements subjected to axial, flexural and shear loading is proposed. While the modeling concepts are general, the implementation and verification of the proposed model is limited to two-dimensional response. The proposed element model is based on behavioral effects and parameters that are identified through careful analysis and interpretation of previously published tests of ductile and non-ductile beam-columns. This analytical model is then used along with the proposed numerical framework to simulate local and element level behavior of four non-ductile columns (tested by Sezen and Moehle at U.C. Berkeley), two ductile column stubs (tested by Ichinose, Imai, Okano and Ohashi at Nagoya Institute of Technology) and two beam specimens (tested by Popov, Bertero and Krawinkler at U.C. Berkeley). The proposed element formulation, along with the supporting computational framework (e.g., solution control algorithms), are shown to be capable and robust to simulate the post-peak response of beam-columns due to large flexural and shear deformations. The proposed formulation is shown to be capable of simulating the effect of cumulative flexural deformations, axial load and strength of longitudinal bars on shear strength of beam-columns. Complicated behavioral features, such as the opening of stirrups in non-ductile columns and degradation of aggregate interlock behavior with cycling, are captured in the analysis. The element model was shown to be capable of simulating the correct mode of failure observed in four tests of non-ductile columns. In addition, shear strain, stirrup strain and axial strain of beam-columns were simulated and compared with corresponding available experimental values. The values of the input parameters of the proposed element model were justified and the resulting response was compared with experimental behavior. Generally good agreement was observed between experimental and simulated values.

Advisor: Deierlein Gregory G. (Gregory Gerard)
Baker Jack W. advisor. Thesis advisor
Billington Sarah L. (Sarah Longstreth)