Grouted sleeve connectors in precast RC construction: methods of analysis and structural effects

Abstract

With the increasing adoption of prefabricated (precast) concrete construction for environmental and efficiency benefits, many connection methods for assembling prefabricated structural components have been developed over the past decades. Among these connection methods, the grouted sleeve connector (GSC) has been widely used in practice. In a typical GSC, two reinforcing bars are inserted into the opposite sides of the sleeve, which is then filled with high-strength, non-shrink grouting concrete. The GSC is designed to transfer force between precast members, mainly through the rebar-grouting concrete interaction (bond) mechanism. To ensure force transfer, connectors tend to be overdesigned, particularly in terms of length. Such overdesign can cause a reduction in the plastic deformation capacity within the connection region, thus negatively impacting the overall displacement capacity and ductility of the precast structure. This adverse phenomenon hampers the application of precast concrete structures in seismic regions.

To enable improvements in the design of precast RC connections involving GSCs, an accurate analysis of the strength and deformation capacities of GSCs is key. In this thesis, a comprehensive analytical model for predicting the bond behaviour in GSCs is developed. The analytical model encompasses two inter-connected aspects, i) analysis of local bond-slip behaviour and the bond strength under a sleeve confinement condition; and ii) analysis of whole connector behaviour (i.e., the longitudinal analysis), which couples with the local bond stress-slip analysis, with the consideration of other important features such as conical bond deterioration, yield penetration, and corresponding bond redistribution. The model enables accurate prediction of slip, confinement, and bond stress distribution along the embedded rebar. The overall force-deformation behaviour of the connector and associated failure mode can also be obtained from the proposed analytical model.

Following the analytical model, a parametric study is carried out to investigate the effect of key parameters on the performance of connectors and potential optimisation methods (e.g., reducing the length of connectors). A semi-empirical calculation scheme is established, allowing for the calculation of the overall strength and deformation capacities and potential failure modes of the connectors in design applications.

On the other hand, this thesis also proposes an equivalent transitional layer scheme to cater to the need for modelling the concrete-rebar bond behaviour in finite element (FE) simulations. The transition layer scheme assumes a perfect connection at the grout-rebar interface but preserves the equivalence of the macroscopic bond stress-slip behaviour through the shear stress and shear deformation of the transition layer concrete elements. Furthermore, the transitional layer introduces a meshobjective material property such that a consistent bond strength and slip are achieved, independent of the mesh grid size. The proposed transitional layer bond scheme is verified by FE simulation in ABAQUS for various scenarios, including general bond regions, grouted sleeve connectors, and both generic and precast RC members.

Finally, a FE model, which employs the proposed transition layer bond scheme, is established to investigate the performance of representative GSC-connected precast concrete columns. The FE simulation focuses on the influence of connector length and axial compression variations on the overall performance of the columns under lateral loading. The results highlight the deformability, ductility, curvature development, and longitudinal strain distribution with varied connector lengths and axial compressions. It is found that a decrease in the connector length can effectively reduce the disruption of deformation in the connection region, resulting in an improvement in the displacement capacity and ductility of the columns under lower compressive ratios.