Analysis of special performance vehicle-barrier crash and its impact on the foundation of an integral barrier-wall system

Abstract

Use of roadside safety barriers has greatly enhanced highway safety and reduced the severity of traffic accidents and injuries. Generally speaking, safety barriers should be sufficiently designed to contain and redirect the vehicle away from its errant travel without causing any severe injuries to vehicle occupants and road pedestrians. A significant body of literature already exists on designing roadside safety barriers to achieve high standards of safety to road users, but the literature, in general, does not provide clear insights on the effects of vehicular impact on the foundation of the barrier systems. Alhough the 2D plane-strain approach is commonly used for the stability design of the retaining structures including barrier systems, none of the design codes in Australia, USA and Europe provide adequate guidance to convert the vehicular impact loading to an equivalent plane-strain loading. The consequence of this is that there is a lot of guesswork without much rational basis currently being applied within the geotechnical community to analyse vehicular impact loading on foundations. This thesis is concerned with a finite element study of a vehicle crash against the safety barrier system and its impact loading on the system foundation. The possible combinations of vehicle-barrier system crash are extremely large, but this thesis is only focused on the combination of a 44t special performance vehicle crashing against the barrier crash of a 3m high reinforced concrete integral barrier-wall system. The integral barrier-wall is a type of system where the barrier is fully integrated with and located at the top of the retaining wall. Moreover, a 44t special performance vehicle is the largest class of vehicle by weight to which the safety barrier is to be designed against based on current design codes. This class of safety barrier is known as the "44t special performance level" barrier and it is the highest class specified in AS5100.2:2017. It has been chosen for this study because of the potential catastrophic effects of such a crash not just on the vehicle and its occupants, but also on the integrity of the foundation of the barrier-system. One of the main reasons numerical modelling is such an important tool in vehicle-barrier crash study is because full-scale physical crashes are very expensive to conduct, and the larger the crash the more costly will be the test. Very few full-scale tests have actually been conducted for the vehicle-barrier crash of the 44t special performance level. The lack of real test data is also compounded by the fact that vehicle-barrier crash tests were mainly concerned with the performance of the safety barriers, and paid little heed to the performance of the barrier system foundation. Therefore, the main goal of this thesis is to develop a 3D finite element model of the 44t special performance vehicle-barrier crash which impacts a 3m high integral barrier-wall system. The model was created and analysed using Abaqus/Standard and Abaqus/Explicit software. It was calibrated against the design impact loading for a 44t special performance vehicle specified in AS5100.2:2017, and the calibrated model was then used to perform further numerical simulations to investigate the foundation responses due to the impact loading. This study has defined foundation responses as: (1) mobilised normal reaction (2) mobilised moment reaction (3) mobilised shear resistance of the foundation at the foundation-soil interface. Based on these analyses, an effective length corresponding to the length to which the impact loading of the vehicle-barrier crash has dispersed along the foundation is established. The effective length is then used to calculate the equivalent 2D plane-strain loading to apply in the stability design of the 3 m integral barrier-wall system. In addition, a sensitivity study was carried out to assess the mobilised effects on the foundation by varying the impact angle and impact velocity. It is found that the effective length is only marginally sensitive to these variations. Hence it may be surmised that the recommended effective length and 2D-plane strain loadings are reasonably robust.

Date of Award	2018
Original language	English