Steel-concrete composite beams using precast hollow-core slabs and a demountable shear connection mechanism

Lead Research Organisation: Heriot-Watt University
Department Name: Sch of Energy, Geosci, Infrast & Society

Abstract

There is an urgent need for sustainable development in modern societies. As natural resources become more limited, and environmental pollution has reached alarming levels in many regions on the planet, man made activities need to switch to a more sustainable way of thinking and operation. Many governments worldwide have set ambitious sustainability targets for the near future. The UK government, specifically, has set as target the 80% reduction in carbon dioxide (CO2) emissions from all anthropogenic activities by 2050. The European Union has also included the drastic reduction of CO2 emissions, waste and energy consumption as first priorities in their agenda.
The construction sector can play an important role to achieving a sustainable environment, since: a) the production of new materials is an energy intensive process, which is responsible for about 15% of the global CO2 emissions; b) buildings are usually being demolished at the end of their useful life creating waste and pollution, e.g. demolition is responsible for one third of total waste in the UK, and more than half of this waste is still sent to landfill; and c) the material demands will be doubled globally by 2050 according to recent reports. In addition, recycling is not a sustainable solution, because the recycling process is still very energy intensive and requires only marginally less energy than creating materials from scratch.
A more sustainable solution is to find ways to avoid demolition of buildings at the end of their useful life. This can be done by developing innovative structural solutions that allow for the reuse of building components directly to new projects. In this way, the construction will produce less CO2 emissions (as there will be no need to manufacture new members or to recycle the old ones), much less waste will go to landfill, and the natural resources of the planet will be used more responsibly.
Steel-concrete composite buildings have a large market share (more than 70% in the UK for multi-storey offices and car parks) and more than half of them use steel-concrete composite floors, i.e. the concrete slab is mechanically connected to the steel sections, which results in more economic designs. The current practice of constructing a composite floor, however, uses a connection method between the concrete slab and the steel sections that makes their separation extremely difficult; thus, the disassembly of these buildings is highly problematic. This project proposes a novel way to connect precast concrete slabs with steel sections that offers the advantages of: a) off-site fabrication of all components; b) easy and fast installation on the construction site; c) disassembly of the composite floor; and d) direct reuse of all components in new projects.
The project will use experimental testing complemented by numerical analyses in order to develop the proposed novel structural system. Experiments will be conducted on both the slab-steel section connection system alone, in order to characterise its structural behaviour, and on large-scale composite beams replicating real beams in buildings. The experiments will provide evidence on the physical behaviour and the ultimate failure modes of the proposed system, whereas numerical simulations using advanced mathematical models will be used to study numerous geometrical configurations and generalise the results of the tests. Based on the results of the tests and the simulations, recommendations for the practical design of the proposed system will be proposed.
The project involves collaboration with leading academics and key industrial partners in order to deliver a reliable sustainable solution for composite floor systems.

Planned Impact

The successful completion of the proposed research will have the following economic and societal impact:
a) The project can contribute to the application of demountable and sustainable structural systems in practice. Credible research results will accelerate the revision of Structural Codes of Practice and the implementation of the 'design for deconstruction' concept in official regulatory documents. Thus, regulatory bodies will benefit from this research. This will be facilitated by the involvement of key people, such as Dr G. Couchman (Steel Construction Institute) and Profs. D. Lam and B. Uy, who are actively involved in the committees that are responsible for the future revisions of Codes of Practice for steel-concrete composite structures.
b) Codified design procedures are likely to accelerate the prioritisation of official policy recommendations and the provision of incentives to stakeholders in favour of the 'design for deconstruction' concept. In this regard, the UK economy will benefit from the reduction in CO2 emissions associated with the construction sector, as the energy and raw material demands will be less if demountable structural systems are applied in practice.
c) The proposed typology offers the additional advantages of adaptability and reconfiguration of buildings, i.e. change in geometry based on current needs, as well as the repair or retrofit of buildings. This means that private or public companies and investors can have significant economic benefits from avoiding demolition if a change in use of a building is needed.
d) The results will specifically benefit the three industrial partners of the project (as well as other construction companies and consulting firms) by increasing their know-how in innovative sustainable structural systems and giving them a competitive edge in the future.
e) The proposed system is highly modularised and facilitates the rapid dismantling, thus investors and construction companies can benefit from application in temporary buildings.
f) The project will contribute towards the achievement of the UK government sustainability targets in CO2 reduction. The people will benefit in the long term, by living in a healthier environment with less pollution and less waste.
g) The application of off-site construction methods with minimum on site operations, and the straightforward dismantling of a building will result in safer practices in construction for the workers.

Publications

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Description The experimental findings proved that the novel demountable shear connector proposed in this project can be successfully used in composite floors with precast slab units. The strength of the connector can be reliably predicted using equations derived from fundamental mechanics. Based on the failure modes observed in the experiments, local reinforcing details are proposed to ensure that the device works as intended. The capability for deconstruction and reuse of the components was verified experimentally.
Exploitation Route Professor Dennis Lam, academic partner of this project, will potentially bring the results to the attention of the committee responsible for drafting the next version of Eurocode 4 on composite structures, and explore the possibility of implementing the proposed technology in the future Standards. Laing O'Rourke, OCAM and Steel Construction Institute, industrial partners of the project, will disseminate the results to potential stakeholders and explore the possibility of using the proposed technology in real buildings.
Sectors Construction,Environment

URL https://sites.google.com/site/vasdravellis/