Nonlinear Finite Element Analysis of Shrinking Reinforced Concrete Slabs-on-ground

Detta är en Master-uppsats från KTH/Betongbyggnad

Sammanfattning: Concrete slabs-on-ground are commonly used in many types of industrial floors, warehouses, highways, parking lots and buildings. Cracks and deflection of slabs are undesired events caused by differential shrinkage, which limits the service life of the slabs. Non-linear behavior of cracks and deflections, interaction of concrete and reinforcement increase the complexity in predicting the occurrence and positioning of cracks. The Eurocode 2 provides a reference for theoretical approximation for design of concrete structures. This thesis intent to investigate the crack behavior of slabs-on-ground subjected to gradient shrinkage using nonlinear finite element analysis, as implemented in the software package Atena 2D. The first part of the thesis is focused on suitable modeling techniques for predicting cracks in concrete slabs-on-ground due to gradient shrinkage. The second part is directed towards parametric studies, performed to explore the significance of varying thickness, length, concrete strength class, bond types, reinforcement content and friction coefficient. The results obtained with the Atena 2D was validated using the design software WIN-statik for calculating the maximum crack width in the context of obtaining realistic results. Finally, the WSP guide recommended parameters were tested as inputs to the model. A slab-on-ground was modeled in Atena 2D considering these as statically indeterminate structures, where both slab and grade were included and the convergence analysis performed under plane stress conditions enabling prediction of the maximum crack widths for increasing applied shrinkage loads. Parametric studies demonstrate the dependency of the slab length, showing that a smaller length reduces the crack width, since such a slab is less constrained by the sub-base. To avoid cracks in the slabs their relative thickness should not be increased above a certain thickness, instead the reinforcement content should be increased. The numerical simulation shows that different concrete strength classes give similar cracks widths. Sand as sub-base provides less crack widths for interface materials EPS, sand and gravel. Although, dry sand as interface material gives similar crack widths as EPS, it is the best to use EPS that is also used to retard the moisture diffusion from the sub-base. The numerical model developed was validated for the recommended values given by the WSP guide, which gives less crack widths and deflections. The numerical model gives less crack widths compared to the Eurocode 2, which considers only the statistically determinant problems overestimating the crack widths. The presented examples demonstrate that the developed model can accurately predict crack formation, crack behavior and vertical deflection in concrete slabs-on-ground subjected to gradient shrinkage loads.

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