A SIMPLE NONLINEAR CONSTITUTIVE MODEL FOR FINITE ELEMENT INVESTIGATION OF REINFORCED CONCRETE STRUCTURES.

摘要

This research develops a simple but reliable constitutive model for use in the finite element analysis of the ultimate capacity of reinforced-concrete members such as sea structures. These structures are typically quite massive and thus the availability of a simple model should greatly facilitate structural analyses to determine ultimate capacities.; The constitutive model assumes that loaded concrete behaves like a stress-induced orthotropic material. Many of the concepts used were consequently motivated by contemporary developments in fiber-reinforced composites. The model is suitable for essentially plane-stress states only. Principal strain axes in the concrete are assumed to coincide with the principal material directions of the orthotropic material. Stress-strain behavior is assumed to take the form of a parabola in both tension and compression. Both monotonic and cyclic loading models are developed. Structural degradation due to progressive damage is accounted for.; The performance of the constitutive model was validated by comparison with an existing plasticity theory, and with three different sets of experimental data. A diametrically loaded polygonal disk (tested by the author), cylindrical shell structures subjected to external hydrostatic pressure, and a deep beam cyclically loaded were all analyzed using the constitutive model in finite element programs. Also, a plate-like structure subjected to simulated extreme water-wave loading was modelled to further evaluate the performance of the constitutive model and to assess the feasibility of nondestructively monitoring progressive damage of offshore structures. This was done by studying the effect of material degradation on the shape and frequency of the fundamental mode of vibration.; Despite its simplicity, the constitutive model appears to be sufficiently accurate for engineering purposes. The model is a valuable analysis tool for the following reasons: It is relatively easy to use. The only input material parameters required are the uniaxial compressive strength of the concrete and the yield stress of the steel. Finally, the model's simplicity reduces computer time and therefore enhances cost effectiveness.