Experimental and Finite Element Investigation on the Flexural Behaviour of LCA studied Steel-Concrete Composite Prefabricated Ultra-Shallow Slabs (PUSS)

This thesis investigates the environmental and flexural performance of the recently developed ultra-shallow flooring system known as Prefabricated Ultra-Shallow Slab (PUSS®). The prefabricated units consists of T-ribbed concrete slabs partially embedded within and connected to two side PFC channel steel beams via a novel horizontally-oriented shear connection system. This connection system incorporates either horizontally-oriented web-welded shear studs (WWSS), horizontal steel dowels welded to the webs, or a combination of both (WWSS with dowels). The unique configuration of the flooring system minimises its structural depth, yielding ultra-shallow floors with a high span-to-depth ratio, surpassing other shallow flooring systems in efficiency. Additionally, it reduces the material usage, and when combined with lightweight concrete, the flooring overall weight (load on beneath structure) and the associated environmental impacts are significantly reduced.
The environmental performance of the flooring system is evaluated through a comparative Life Cycle Assessment (LCA) study, focusing on the global warming potential (GWP) and embodied energy (EE) impacts of PUSS compared with the widely used hollow core precast slabs. The study examines 16 live load/ floor span scenarios and evaluates the benefits and drawbacks of utilising different concrete types in PUSS flooring, namely normal weight concrete (NWC), lightweight aggregates concrete (LWC) and geopolymer concrete (GPC). Results indicate that PUSS outperforms hollow core slabs in all scenarios, regardless of the concrete type used. PUSS with GPC offers the greatest GWP savings, achieving up to 50% reductions compared to hollow core slabs. However, PUSS with LWC demonstrates the best overall performance in terms of both GWP and EE, with up to 35% savings in EE and 46% in GWP, and its lighter weight reduces the load on supporting structural elements, further amplifying the overall environmental benefits.
Furthermore, the research explores the effect of a group of parameters on the flexural behaviour of PUSS and the performance of the implemented shear connectors under bending through a series of experimental and computational studies. The investigated parameters include concrete type, concrete strength, degree of shear connection, span and slab depth. Four full-scale specimens, each with a span of 4 m were constructed and tested under four-point bending tests at George Earle laboratory (GEL), University of Leeds. The results indicate that PUSS with LWC achieves similar flexural capacity to PUSS with NWC, though it exhibits lower initial stiffness and develops larger cracks. Additionally, the tests reveals that reducing the degree of shear connection lowers the slabs’ moment capacity and leads to failure of some shear connectors. Despite this, PUSS units demonstrates ductile behaviour in all cases.
A finite element model resembling the experimental tests was then developed, validated against the experimental results, and used in a comprehensive parametric Finite Element Analysis (FEA) study involving 324 models. The study shows that reducing the degree of shear connection leads to decrease in moment capacity, but the reduction is non-linear due to the parabolic relationship between moment capacity and the degree of shear connection. This highlights the complex interaction between shear connectors and overall slab performance. Larger discrepancies are noted between FE-derived moment capacities and hand calculations using existing shear capacity formulas, especially in lightweight concrete (LWC) models, underscoring the need for refinements in the shear resistance equation to achieve more accurate predictions.
The gathered data from both experimental and FEA studies were extensively studied, and analysed through regression analysis, leading to the development of an optimised empirical formula to predict the shear resistance of the shear connectors employed in PUSS and their corresponding degrees of shear connection. This formula provides a more accurate prediction of shear resistance and degree of shear connection compared to existing methods, aligning closely with the results of 328 experiments and FEA models. Additionally, a moment capacity design methodology for PUSS flooring system in accordance with the Eurocode 4 standards is presented. This methodology offers a solid framework for the practical implementation of PUSS in construction, with the potential to inform future revisions of design codes.