Experimental investigation and modelling of the structural behaviour of confined grouted interfaces for a new steel–concrete connection

• The ultimate shear stress is a linear relationship of the applied normal stress.
• An increased interface roughness is favourable for increasing the shear resistance.
• The post-failure resistance follows an exponential decay towards the residual friction.
• Uplift at failure in the interface is independent of the normal stress.
• A safe fatigue failure criterion is proposed related to the accumulated slip.

Confined interfaces between cement grout and other materials such as embossed steel or rough concrete are formed in an innovative new steel-concrete connection for composite bridges. This article presents the experimental study of such interfaces and investigates the laws obtained from an analytical study, which describe the behaviour of those interfaces subjected to shear loading, static and cyclic, under different levels of constant normal stress. The laws describing the interface behaviour in monotonic shear loading are: (a) the relationship between the ultimate shear and the normal stress acting on the interface, i.e. the failure criterion, (b) the shear stress–slip relationship of the interface, called hereafter the constitutive law and (c) the relationship between the transverse separation (uplift) of the interface and the slip in the interface, called hereafter kinematic law. Concerning cycle shear loading, tests on interfaces enabled damage determination due to repeated loading. This damage is expressed by the development of an accumulated residual slip in the interface. Results indicate that as long as the applied shear stress in the interface, during cyclic loading, remains inferior to the elastic shear limit for static loading, the residual slip stabilizes with the number of cycles. A safe fatigue failure criterion is proposed relating the accumulated slip with the value of the slip at shear failure of the interface for static loading. The proposed laws together with the law describing the development of the confinement constitute the necessary input for a model to predict the behaviour of an innovative connection consisting of such confined grouted interfaces.