Finite Element Analysis and Design of Suspended Steel-Fibre Reinforced Concrete Slabs

Over the last 20 years, there has been a rapid expansion in the construction of pile-supported and elevated steel-fibre-reinforced [SFRC] concrete slabs. The use of fibres to replace some or all of the conventional steel reinforcement leads to a significant reduction in construction time. However, current guidance is limited and is dominated by approximate elastic and plastic classical solutions. The design guidelines and construction of the majority of constructed SFRC slabs is almost entirely proprietary (provided by fibre manufacturers and suppliers) and different guidelines from nations (embedded with safety concerns). As a result, designers are unwilling to underwrite current designs in the absence of adequate independent guidance.
In this research work, the behaviour of suspended SFRC slabs was studied under concentrated loadings. Available experimental data were used to study the effect of steel fibres on the post-cracking response of concrete. Subsequently, the SFRC constitutive model proposed by Lok and Xiao (1999) was adopted alongside the concrete damaged plasticity model of ABAQUS based on the validation work done. The reliability of the FE numerical model predictions was ensured by calibrating it against existing experimental data. Consequently, additional analyses were carried out examining three main case studies of SFRC slabs namely, single simply supported slabs, 4-panel pile-supported slab (i.e. statically-indeterminate) and 9-panel elevated slab. Parametric studies were carried out covering the full practical range of steel fibre dosages. The results testify that numerically steel fibres can replace rebar in slabs as obtained in the experiment and additional fibres increase the load-carrying capacity, strength and stiffness (thus enhancing response at both the serviceability and ultimate limit states). Ductility was improved by the additional Fibres, and the mode of failure was altered from brittle to ductile.

Thus three main parameters were considered in the parametric study, namely increasing the amount of fibres and characteristic strength and at the same time increasing the slab depth. The total removal of conventional reinforcement was achieved mainly by replacing them with steel-fibres. An FE numerical analysis is used to investigate the slab's structural behaviour under different loading conditions leading to transparent and well-defined design guidelines which are urgently needed by industry. Simple design equations were derived using regression analysis to estimate the yield load and the maximum load carrying capacity of the slabs with their corresponding central displacements. These equations were compared with existing design guidelines, and the equations perform better in their estimation.