پایگاه تخصصی عمران ایران

Coupled damage and plasticity modelling in transient  dynamic analysis of concrete

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SUMMARY

In a concrete structure subjected to an explosion, for example a concrete slab, the material is subjected to various states of stress which lead to many modes of rupture. Closer to the explosive, a state of strong hydrostatic compression is observed. This state of stress produces an irreversible compaction of the material.Away from the zone of explosion, con"nement decreases and the material undergoes compression with a state of stress, which is slightly triaxial. Finally, the compression wave can be re#ected on a free surface and becomes a tensile wave, which by interaction with the compression wave, produces scabbing. We present, in this paper, a model aimed at describing these three failure modes. It is based on visco-plasticity and rate dependent damage in which a homogenization method is used in order to include the variation of the material porosity due to compaction. The model predictions are compared with several experiments performed on the same concrete. Computations of split Hopkinson tests on con"ned concrete, a tensile test with scabbing, and an explosion on a concrete slab are presented.

KEY WORDS:
concrete; dynamics; compaction; damage; plasticity

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NONLINEAR PROPERTIES OF REINFORCED CONCRETE STRUCTURES
Iftekhar Anam (1) & Zebun Nessa (2)

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Abstract:

The importance of various nonliearities involved in the static and dynamic analyses of Reinforced Concrete structures is investigated in this paper. The nonlinearities studied here are geometric (caused by large deformations and consequent effect on the elastic properties of the structure) as well as material (due to the nonlinear stress-strain relationship of concrete and steel). In the first part of the paper, the nonlinear moment-curvature relationship of arbitrary Reinforced Concrete cross-sections is developed numerically using nonlinear stress-strain relationships for concrete and steel. The relative importance of geometric and material nonlinearity is studied for a simple 2-storied frame under static vertical load. Although the effect of material nonlinearity is more important in most of the cases studied here, the geometric nonlinearity becomes significant at higher loads. The effect of axial load on the momentcurvature relationship is studied, and the effect of typical axial loads on the flexural behavior of column is found to be significant. The shear strength of the beams and columns (obtained from empirical equations suggested in the ACI Code) prove to be very important here. Using the nonlinear sectional properties thus obtained, the nonlinear structural dynamic analyses of the building are performed subjecting the structure to seismic vibrations using nonlinear structural dynamics. Recorded ground motion data from two major earthquakes of the past; e.g., the El Centro earthquake in USA (1940) and the Kobe earthquake in Japan (1995) are used in the dynamic analyses. The results show the difference between the linear and the nonlinear structural response.

1-Assistant Professor, Department of Civil and Environmental Engineering, The University of Asia Pacific.
2- Former Student, Department of Civil and Environmental Engineering, The University of Asia Pacific.

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