Numerical simulation of failure in steel posttensioned connections under cyclic loading

Posttensioned energy dissipation (PTED) connections are systems employed in structures to prevent the earthquake imposed failure and minimize the post-earthquake damage by eliminating residual deformation and dissipating seismic energy. Ever increasing trend in research regarding posttensioned frames has raised the necessity toward studying failure modes in these systems to identify and avoid the probable damages. This paper investigates the possibility of modeling the various failure modes in a relatively complex steel frame. Three PTED connections with bolted top-and-seat angles as energy dissipater devices with different failure modes including beam local buckling, strand yielding and angle fracture are simulated under cyclic loading. To remove the convergence difficulty in the analysis, explicit method has been used which is capable of modeling fracture and failure without convergence checking. Comparing the analytical results with experimental data indicates finite element models are able to predict the behavior of PTED connections. This research demonstrates that with existing methods for modeling failure of steel and cable which are mostly used in small scale, the failures modes of full scale complicated steel frames can be captured with sufficient precision. Furthermore, an investigation has been done to evaluate one of the applications of modeling failure which is finding a solution to enhance the behavior of a member which is subjected to damage. In this study a method has been presented to resolve fracture in energy dissipater devices. Low yield point (LYP) steel has been used in the angles which significantly improve the behavior of PTED connection by postponing the fracture point from 4% to 7% drift. It also results in up to 222% increase in total energy dissipation capacity of the connection.