Nonlinear analysis of high-strength concrete slabs

Chen, Zhiwei (1993) Nonlinear analysis of high-strength concrete slabs. Masters thesis, Memorial University of Newfoundland.

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Abstract

High-strength concrete slabs are frequently used in various structural engineering systems and a wide variety of civil engineering applications. A research program on the structural behaviour of such slabs is being carried out both experimentally and numerically at Memorial University of Newfoundland (M.U.N.). The work reported herein includes the experimental investigation on the tensile behaviour of high-strength concrete and finite element (F.E.) analysis of its slabs. The emphasis is placed upon the importance of the realistic material properties and the need of a valid concrete model in the F.E. analysis. Particular attention has been focused on the post-cracking tensile behaviour of high-strength concrete. -- The complete load-deformation behaviour of high-strength concrete in direct tension, including post-cracking softening response, was obtained by developing direct tension test technique. The test measurements were then characterized into a rational tension softening model. The understanding of the unique tension softening nature of high-strength concrete was enhanced by comparison to that of normal strength concrete in terms of fracture energy, mechanical properties and entire load deformation response. In addition the effect of the cold ocean water on the tensile properties of high-strength concrete was examined. The variability and relations of tensile strengths and compressive strength were also studied. -- Appropriate representation of post-cracking behaviour of reinforced high-strength concrete was developed for the F.E. analysis of its slabs. The developed models and measured stress-strain characteristics of high-strength concrete and reinforcing bars were then incorporated into a proposed plasticity- based concrete model implemented in the context of the 8-node quadrilateral shear-flexible thick shell element. The material model allows realistic concrete strain softening after both cracking and crushing. The validity of the model was established by comparison of F.E. numerical predictions to experimental results of sixteen slabs tested at M. U.N. The model performed satisfactorily in all the cases, with respect to the entire load-deflection response, ultimate load carrying capacity, ductility, and failure mode. -- The F.E. model was then used to carry out a parametric study to examine the structural behaviour of reinforced high-strength concrete slabs. The parameters under investigation include various material properties, slab boundary conditions, loading stub-column, and loading type and sequence. In addition, a tension stiffening model was approximately formulated, based on the fracture energy concept and comparison of F.E. predictions to experimental results of the tested slabs. The importance of the concrete tension stiffening behaviour was highlighted in the F.E. analysis of the slab selected.

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