Modelling of Constitutive Relationship of Steel Fiber-Concrete Interface

In this chapter, the modelling of constitutive relationship of steel-concrete interface is discussed. Studies of the interfacial zone between steel and bulk cementitious matrix demonstrated that the properties of this special region could be much different from the behavior of the bulk matrix and thus should be used as a physical background for the interface modelling. Various characterizations of steel-concrete interface are reviewed. In general, the constitutive relationship of steel-concrete interface can be divided into two categories according to the consideration of adhesion. If one assumes that adhesion exists on a part of the interface, then the constitutive relationship can be established by treating the interface as a bonded-debonded case. Otherwise, so called slip-based interface model, in which the constitutive equation is based on the bond stress-slip relationship, can be applied. For the bonded-debonded interface model, the constitutive equations are established by dividing the interface, corresponding to the bonded and the debonded regions. For the debonded case, three different methods of describing frictional force, i.e. constant frictional force distribution, Coulomb frictional force distribution and cohesive frictional force distribution, are examined. In this chapter, the constitutive relationship for bonded-debonded interface is emphasized and two criteria for interface debonding, stress based criterion and fracture parameter based criterion, are inspected. The various constitutive relationships are further evaluated by comparing them with the recently conducted Moire Interferometry test results. The comparison supports the bonded-debonded characterization for steel-concrete interface and shows the limitation of the modelling of frictional force in a debonded region.