Taisuke Ibaraki

Time-dependent deformation and stress transfer characteristics of steel concrete joints

Takumi Shimomura

In order to calculate the response of steel-concrete composite structures, the mechanical properties of the joints that unify the members are important. There are few examples of studies on the behavior of joints under service loads. The most common method is to calculate the response value by assuming the integration of steel and concrete and applying the constitutive law of the individual materials. 
However, it has been reported that deformations and stresses calculated based on such assumptions sometimes deviate from the measured results of actual structures. This implies that the computational assumptions may not adequately represent the real phenomena. It is assumed that local deformation and fracture of the concrete at the joints may occur due to shrinkage and sustained loading of the concrete under service conditions. This may have a non-negligible effect on joint deformation and stress transmission. The purpose of this study is to understand the basic properties of the time-dependent shear force-displacement relationship and the effects of sustained loading on the joints.
Time dependent behavior of the joints was obtained by performing push-pull tests on the headed stud joints under sustained load. Creep displacement increases rapidly immediately after start of sustained loading and then settles over time. The greater the sustained load level, the greater the creep displacement.
Creep displacement is linearly related to sustained shear force up to stud yield if the specimen properties are the same. The behavior of joints when shear forces vary with time cannot be reproduced by the superposition rule. Residual displacement increased and unloading misalignment stiffness decreased due to sustained shear force acting on the joint.