Investigation of a concrete deck connection in reusable composite floor system

Abstract

In the construction industry, composite structures combining concrete and steel are commonly employed in floor systems due to their exceptional performance in compression and tension. With a growing emphasis on sustainability and Life Cycle Assessment (LCA), this thesis introduces a novel concept: a modularised floor system consisting of reusable concrete deck and composite beam. This research focuses on analysing the behaviour of an innovative demountable "concrete to concrete" by FEA. A connection between the composite beam and concrete deck connected by a shear connector (bolt). The goal is to understand the mechanical behaviour of such connections.
This design differs from cast-in-situ traditional composite floor systems by having a concrete deck divided into three separate parts that are connected by bolted shear connectors. The composite floor consists of composite girders and concrete decks. A key advantage of this system is the ability to extract the concrete deck from existing floor systems, offering economic benefits and reducing carbon emissions over its life cycle. The mechanical performance of the newly designed connection between two concrete segments (a composite beam and a concrete deck) is examined through a shear and bending model using Abaqus Software.
The shear model does not represent a real case loading, and it is introduced to gain confidence in the numerical analysis due to the absence of experimental data in this research. The specimen consists of two concrete blocks being pulled apart. These blocks are connected by a demountable shear connector (bolt) in the middle.
A three-point bending model presents the mechanical behaviour and realistic potential failure modes of the innovative demountable "concrete to concrete" connection. It consists of three connected concrete segments. This model reveals failure modes, including cracking at the “re-entrant corners” of the connection points, crushing of concrete at the mid-plane of the connection and under the bolt nut, and transverse concrete cracking originating from the bolt hole, refer to Figure 6.26.
To enhance the structural behavior of this modularised floor system, several methods are investigated. First, adding steel plates at the connections effectively mitigates concrete crushing at the mid-plane and prevents cracking at the re entrant corners. Second, relocating the connection to zero-bending moment positions results in a notable reduction in the three failure modes, improving loading capacity by about 10%. Furthermore, the environmental impact of this novel design is noteworthy. With the assumption given in this thesis, for an area of 5.67m*8m concrete deck, reusing the newly designed concrete deck can result in a savings of approximately 4.2 tonnes of CO2 emissions per subsequent life cycle. Similarly, reusing concrete decks from existing buildings can lead to a reduction of around 2.33 tonnes of CO2 emissions per life cycle with this size of the floor. Based on the assumptions made in this research, the results suggest that the newly designed concrete deck may have a lower loading capacity than traditional concrete slabs. However, its potential economic and environmental advantages make it a promising topic for future investigations.