Structural performance of steel-concrete composite floor systems utilising reused concrete slabs

Abstract

In light of the growing impact of the production of construction materials, the imperative for sustainable design is considered a necessity. Newly developed design strategies and design for deconstruction offer great potential and perspective to achieve the sustainability goals that are set in the European Commission’s ”Green Deal” towards net zero greenhouse gas emissions by 2050. Demountable and reusable steel-concrete composite structures allow for the opportunity to contribute to these sustainability goals. Demountability in steel-concrete composites is generally offered through the application of demountable shear connectors. Multiple studies have investigated the performance of various shear bolt connectors. Shear connectors generally showed inferior structural performance compared to that of conventional welded shear studs. Throughout the years, there has been significant advancement in the practice of reusing structural steel elements in the construction industry. Conversely, the exploration of re-purposing concrete from existing structures for structural use has not been extensively investigated. In response to this growing emphasis, reusing concrete slabs appears to be a sophisticated and innovative strategy. To enable deconstruction and reuse practices in such steel-concrete composite structures, bolted connections are considered a key characteristic in establishing the incentive. To maintain the strength characteristics of conventional shear studs in composite beams, demountability of a steel-concrete floor system can be offered through a concrete deck-to-deck connection between the composite beam and concrete slab. However, there exists a scarcity of solutions for connecting concrete slabs through demountable shear connectors, limiting comprehension on the structural behaviour and performance on true floor level. This thesis presents two numerical finite element models, the first of which is a simplified deck-to-deck connection subjected to tensile loading conditions to determine basic characteristics and behaviour. The knowledge gained from the first model is implemented in the secondary finite element model, comprising a demountable floor system which is compared with a traditional conventional floor system. A subsequent parametric study focused on altering bolt spacing, edge distance and span width to allow for a broader perspective on the performance of the proposed demountable floor system. The numerical results showed that the demountable beam model is able to replicate the behaviour of the conventional beam system, where local plastic deformation of the connecting elements was hardly observed. The numerical results demonstrated that the serviceability loading capacity of the demountable floor system was 3% lower, and the discrepancy in ultimate loading resistance was magnified further. The parametric study indicated that modifications to the distance of the bolts from the edge of the slab and bolt spacing did not show a shift in the ultimate loading resistance and ductility. Increasing the span width of the demountable slab model indicated a gradual reduction of approximately 24% in load carrying capacity, where the ductility was not affected. While future research into the reliability and validity of the numerical results is considered necessary, the proposed solution for connecting concrete slabs has shown significant potential in terms of replicating the structural behaviour of conventional floor systems, without compromising the structural integrity. The solution demonstrated the ability to develop a demountable and reusable floor system, thus contributing to an enhanced sustainable and circular built environment.