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Reusable precast steel-concrete composite floors

Periodic Reporting for period 1 - REUSE (Reusable precast steel-concrete composite floors)

Reporting period: 2019-05-15 to 2021-05-14

The project addresses the urgent need to drastically reduce CO2 emissions and to manage our natural resources more responsibly. In construction, most of the buildings are usually demolished at the end of their service life, with severe negative consequences to the environment, including generation of waste going to landfill, need to produce new structural components from scratch each time a building needs to be built, therefore increased CO2 emissions, and over-consumption of planet's finite natural resources (e.g. coal).

This project proposes novel construction methods, specifically for steel-concrete composite structures, to design buildings that can be dismantled at the end of their service life and all structural components reused in other projects. By adopting this design approach, demolition is avoided, CO2 emissions are drastically reduced since there will be no need to produce new structural components, waste will be minimised, and we will consume our resources more efficiently. Thus, the project benefits society as a result of contributing to more environmentally friendly construction procedures.

The overall objectives of the project are
1. To assess the structural behaviour of the proposed novel sustainable construction methods through experimental testing.
2. To perform numerical simulations of the proposed structural details and to exhaustively study all the parameters affecting their design.
3. To study the behaviour of buildings using the proposed technologies.
4. To propose reliable design procedures for both the construction and deconstruction of the proposed composite structures.
Research activities:

1. Two novel typologies of demountable shear connector (DSC) for steel-concrete composite beams or girders have been proposed. Their geometries have been finalised using preliminary finite element method (FEM) analyses and fundamental principles. The first type (WDSC) uses a steel tube and a compatible stud that is welded on top of the steel flange. The second type (LBDSC) uses a steel tube and a compatible partially threaded bolt that is inserted though pre-drilled holes in the steel flange. Both types produce a shear connector that can be easily installed and uninstalled, thus facilitating the deconstruction of the slabs from the steel sections and the reuse of all components.
2. The structural performance of two DSC types has been evaluated through a series of push-out tests in the Laboratory. The proposed connectors have been subjected to static loading (relevant to buildings), fatigue loading (relevant to bridges) and cyclic inelastic loading (relevant to earthquake-prone regions). The results indicate that the structural properties of the connectors enable them to be used in steel-concrete composite structures.
3. To generalise the experimental results and to expand their validity to a range of different geometries, numerical models of the tests have been created and calibrated against the experimental results. The validated numerical models were then used to perform parametric studies and propose reliable design rules for the connectors.
4. The structural performance of beams and buildings using the proposed demountable shear connectors was assessed through nonlinear numerical analysis, using the design rules based on the experimental and numerical results, and it was found that both connector types can be used in beams or girders for both serviceability and ultimate state design.
The project goes beyond the state of the art in demountable steel-concrete composite floors by addressing some of the issues of previously proposed demountable shear connectors (DSCs). These include the issue of tolerance between the bolt and the pre-drilled hole in the steel flange, and the issue of limited slip capacity that was observed in most of the previous DSCs. The tolerance issue is addressed in both the WDSC and LBDSC types. In the first, the compatible stud is welded, so there is no pre-drilled hole in the steel flange, but the connector is still demountable. In the second type, the partially threaded bolt has a geometry that locks in the hole of the flange and eliminates the initial slip due to tolerance. In addition, the slip capacity of both connectors is sufficiently large so that they can be safely characterised as ductile (slip greater than 6 mm), and therefore can potentially be adopted by Eurocode 4.
Implementation of DSCs in the next revision of Eurocode 4 will unlock the practical application of demountable composite structures. This will enable the reuse of structures or components, and in the long term will result in significant socio-economic benefits, since the construction sector is responsible for the 15% of total anthropogenic CO2 emissions worldwide (due to the production of steel and cement alone) - and for a vaast amount of waste going to landfill.
The proposed demountable shear connectors