International Concrete Abstracts Portal

SP-237CD This CD-ROM is a collection of 19 papers presented at a workshop sponsored by Joint ACI-ASCE Committee 447, Finite Element Analysis of Reinforced Concrete Structures, and JCI Committee 016SP, in Maui, Hawaii, USA, in November 2003. A broad range of topics was addressed, including the creation of new experimental data sets for use in developing, calibrating, and validating models; the development and validation of plain, reinforced, and fiber-reinforced concrete constitutive models; new approaches to simulating the response of reinforced concrete continua; new element formations to enable improved simulation of component response; and new computational techniques.

Based on cyclic tests of RC beams that failed in flexural-shear without yielding of the transverse reinforcement, a mechanism controlling flexural shear failure is proposed. This mechanism, which is associated with ‘Error Catastrophe’ known as a theory of aging, was observed in the hinge region of the beams. The results of experimental testing indicate that a shear-resisting system forms in the flexural hinge region of a RC beam subjected to monotonic loading. Under reversed cyclic loading, the shear-resisting system temporarily disappears as cracks open and then is rebuilt as cracks close. A flexural shear failure occurs when the shear resisting mechanism is not rebuilt upon load reversal. What inhibits the rebuilding process and, ultimately, results in a failure to rebuild, is “errors” in the rebuilding process. These errors accumulate each time the shear-resisting system is rebuilt, and when the errors exceeded a certain tolerance, failure due to the malfunction of the rebuilding occurs.

Over the past years techniques for non-linear analysis have been enhanced significantly via improved solution procedures, extended finite element techniques and increased robustness of constitutive models. Nevertheless, problems remain, especially for real world structures of softening materials like concrete. The softening gives negative stiffness and risk of bifurcations due to multiple cracks that compete to survive. Incremental-iterative techniques have difficulties in selecting and handling the local peaks and snap-backs. In this contribution, an alternative method is proposed. The softening diagram of negative slope is replaced by a saw-tooth diagram of positive slopes. The incremental-iterative Newton method is replaced by a series of linear analyses using a special scaling technique with subsequent stiffness/strength reduction per critical element. It is shown that this event-by-event strategy is robust and reliable. First, the example of a large-scale dog-bone specimen in direct tension is analyzed using an isotropic version of the saw-tooth model. The model is capable of automatically providing the snap-back response. Next, the saw-tooth model is extended to include anisotropy for fixed crack directions to accommodate both tensile cracking and compression strut action for reinforced concrete. Three different reinforced concrete structures are analyzed, a tension-pull specimen, a slender beam and a slab. In all cases, the model naturally provides the local peaks and snap-backs associated with the subsequent development of primary cracks starting from the rebar. The secant saw-tooth stiffness is always positive and the analysis always ‘converges’. Bifurcations are prevented due to the scaling technique.

Over the past years techniques for non-linear analysis have been enhanced significantly via improved solution procedures, extended finite element techniques and increased robustness of constitutive models. Nevertheless, problems remain, especially for real world structures of softening materials like concrete. The softening gives negative stiffness and risk of bifurcations due to multiple cracks that compete to survive. Incremental-iterative techniques have difficulties in selecting and handling the local peaks and snap-backs. In this contribution, an alternative method is proposed. The softening diagram of negative slope is replaced by a saw-tooth diagram of positive slopes. The incremental-iterative Newton method is replaced by a series of linear analyses using a special scaling technique with subsequent stiffness/strength reduction per critical element. It is shown that this event-by-event strategy is robust and reliable. First, the example of a large-scale dog-bone specimen in direct tension is analyzed using an isotropic version of the saw-tooth model. The model is capable of automatically providing the snap-back response. Next, the saw-tooth model is extended to include anisotropy for fixed crack directions to accommodate both tensile cracking and compression strut action for reinforced concrete. Three different reinforced concrete structures are analyzed, a tension-pull specimen, a slender beam and a slab. In all cases, the model naturally provides the local peaks and snap-backs associated with the subsequent development of primary cracks starting from the rebar. The secant saw-tooth stiffness is always positive and the analysis always ‘converges’. Bifurcations are prevented due to the scaling technique.

Numerical analyses of reinforced concrete (RC) members using discrete approaches, called spring network models, are presented. RC members under certain conditions exhibit brittle failure with strain localization under shear failure. To distinguish this failure mode from ordinary shear failure, which is less brittle and results in a more distributed strain field, this failure mode is called a sliding shear failure. The mechanisms of sliding shear failure are not well defined. Since the spring network model is one of the discrete-type approaches that are well suited to problems where material discontinuities are dominant, the results of numerical analysis are used to improve understanding of sliding shear failure. The model is validated through comparison of simulated and observed response for RC beams that exhibit ordinary shear failure and RC panels subjected to pure shear forces that exhibit sliding shear failure. A parameter study is then performed using the proposed model.