Behaviour and Modelling of Bolted Connectors in Road Safety Barriers

Abstract

The purpose of this thesis is to study the behaviour of the connection between the guardrail and post in a steel road safety barrier subject to tensile, shear and combined loading conditions. This is accomplished by performing laboratory tests on a special-built test rig. Finite element models of the connection are created and validated in order to form a basis for large scale numerical simulations of road safety barriers.The laboratory tests all failed by thread stripping of the bolt in the connection. The ultimate failure load decreased by 15.9 and 17.3 percent when loading in 15\degree{} and 30\degree{} from pure tension respectively. A two-step finite element model was created to simulate the behaviour of the threaded bolt and nut assembly in question. The relative displacement between the bolt and the nut in an initial model of the guard rail and post with an unthreaded connection was enforced on a separate model of the bolt and nut with threads. A full model including the threaded connection was created and compared to the two-step model.The results indicate that the behaviour prior to failure is controlled by deformations in the guardrail, post and washers. Failure is controlled by the threaded bolt, and the ultimate load is highly dependent on the bolt material. It is possible to model the bolted connection, subject to combined tension and shear loading conditions, with an acceptable degree of accuracy. A consistent failure mode can be achieved with both the two-step model and the full model. The ultimate loads experienced in the two-step model were in close proximity to the experimental results in some load combinations. The full model was close to the laboratory results in most load combinations, where the deviation from the average failure load in pure tension was 1.1 - 2.7 percent.