Structural behaviour of thick concrete plates

Rizk, Emad Raouf (2010) Structural behaviour of thick concrete plates. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (14MB)

Abstract

Most concrete codes have empirical equations to estimate the minimum steel reinforcement requirements for flexural members. High-strength thick concrete plates are used as structural component in offshore and containment structures for nuclear power generation. An accurate estimate of the minimum steel flexural reinforcement ratio can result in saving millions of dollars for a single project. The recommended concept utilizes the fracture mechanics principles to modify the sandwich panel model and to account for slab thickness. In summary, the two new main contributions in this research includes consideration of the size effect through fracture mechanics and consideration of the torsional moment for thick plates in calculating the minimum reinforcement of thick plates. -- Different design codes have different formulae to calculate crack spacing and crack width developed in flexural members. Most of these formulae are based on the analysis of results on beams or one-way slabs. Crack control equations for beams underestimate the crack width developed in plates and two-way slabs due to loading and constraint effects. It seems that little attention has been paid in determining the crack spacing and width in reinforced concrete plates. The behavior of reinforced concrete plates is different from beams or one-way slabs; therefore, the methods developed for beams cannot be directly applied to plates and two-way slabs. In this research investigation, a two-way numerical model is proposed for calculating the crack spacing for plates. A special focus is given to thick concrete plates used for offshore and nuclear containment structures. The proposed equation takes into account the effect of steel reinforcement in the transverse direction through the splitting bond stress. The equation provides good estimates for crack spacing and crack width in plates and two-way slabs with different concrete covers. -- Concrete slabs without shear reinforcement usually exhibit brittle shear failure under a concentric force transferred between the column and the slab. Conventional design methods consider potential shear failures of a slab as a wide beam as well as punching failures in the vicinity of concentrated loads. Most of design codes try to avoid minimum shear reinforcement requirements for slabs by limiting nominal shear stresses at well-defined critical sections to guard against such failure modes. With the extensive use of thick plates of more than 250 mm thick, made of high strength concrete (HSC) for offshore structures, different guidelines must be used to provide minimum shear reinforcement requirements for thick concrete plates. The current research provides procedure for dimensioning of the plate shear core that is the main interest of this work. The proposed models to calculate minimum shear reinforcement for thick plates account for member size effect through fracture mechanics concepts. -- The experimental phase of this research work includes testing of two groups of specimens. The first group (Group A) is designed to investigate the effect of small reinforcement ratios and slab thickness on the behaviour of two-way slabs. The second group (Group B) is designed to investigate the effect of slab thickness, reinforcement ratio and shear reinforcement on the structural behavior of thick concrete plates. -- The strut-and-tie method is a rational approach to structural concrete design that results in a uniform and consistent design philosophy. A strut-and-tie model is developed to model the punching shear behaviour of thick concrete plates. This model provides a quick and simple approach to evaluate the punching shear capacity of concrete slabs.

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