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.

Two interior column (RC)-beam (PPC) specimens were tested. The specimens were first subjected to reversed, repeated cyclic loading to maximum rotational angles of 1/30 and 1/16, respectively. The specimens were then repaired using resin injection and mortar covering. Mechanical properties obtained following repair were almost the same as those obtained during the initial loading, probably, due to the confined concrete used in the beam ends. However, a reduction in initial stiffness of approximately 30% was observed.

In most structural members, strength tends to decrease as the member size increases. This phenomenon is known as scale effect. Many experiments investigating the impact of scale effects on RC structures have already been conducted. However, since few laboratories have the capacity to test large-scale specimens, few experimental investigations have tested near full-scale RC members. This paper investigates the scale effect in reinforced concrete members subjected to shear loading. Two different sized test specimens were prepared and tested. The results clearly indicate that the member strength decreases as its size increases. The Japanese building code, an empirically-based code with no scale effect parameter in the shear formulas, generates overly-conservative predictions for full-scale members. Using plane concrete monotonic compression strength data, a formula defining the shear strength of reinforced concrete members is proposed. Experimental results show that the proposed formula for computing ultimate strength agrees better with the experimental data than existing formulas.

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.