Ductility of Tie Connections in Precast Structures

Doktorsavhandling, 1992

Precast concrete structures are normally provided with tie connections that make it possible to transfer tensile forces across the joints. The tie connections are essential for the structural integrity and can contribute to the formation of alternative load-bearing systems in case of local damages of the structure. The aim of the present research was to develop a method for prediction of the load-displacement characteristics of tie connections in the plastic stage. Tie connections between concrete elements were studied experimentally. The load-displacement relationship and the strain distribution along the tie bar were evaluated from measurements. In most of the tests it was possible to obtain large plastic deformations and the ultimate displacement was determined by the rupture of the reinforcing steel. The anchorage capacity of tie bars anchored in grouted joints between hollow core elements was studied in separate test series. A numerical approach was developed for the analysis of tie connections in the plastic stage. The local bond-slip behaviour of the steel-to-concrete interface and the strain hardening of the steel were considered in the analysis. The bond-slip relationships that are recommended today could not be used in the calculations as the yield penetration along the embedded tie bar and, as a result, the displacement was considerably underestimated. Modified bond-slip relationships are proposed which take into account the yielding of the steel. It was found that the load-displacement relationship often had the same proportions as long as ductile types of tie bars were used even when the strength of steel and concrete varied substantially. The relative strain energy was defined and was found to be a valuable parameter describing the ductile behaviour of tie connections. An approach for the analysis of alternative load-bearing system is presented and exemplified. The approach is based on a condition of energy equilibrium. It is shown how the dynamic resistance of an alternative load-bearing system is affected by the ductility and the deformability of tie connections. The theoretical approach was confirmed by dynamic tests where a collapse situation was simulated.