Practical Method for Estimating Vehicular Impact Force on Reinforced Concrete Parapets for Bridge Infrastructure Design and Management

The AASHTO Manual for Assessing Safety Hardware (MASH) replaced the NCHRP Report 350 in 2009, becoming the new standard for evaluating safety hardware devices, including concrete bridge parapets; all new permanent installations of bridge rails on the National Highway System must be compliant with the 2016 MASH requirements after 31 December 2019, as agreed by the FHWA and AASHTO. However, due to the complexity of vehicular impact events, there are several different methods for estimating vehicular impact force on the parapets. They can be grouped into three main categories: theoretical, numerical and measurement methods. This paper presents a practical method based on analytical concepts for providing impact force estimates that can help bridge owners to evaluate the structural capacity of bridge parapets at a fraction of the cost of full-scale crash tests and finite element numerical simulations. This approach was developed based on fundamental dynamic principles and refined dynamic analysis of vehicle rigid-body motions during multi-phased impact events. Principles of impulse and momentum were first applied to determine both linear and angular velocities of a vehicle immediately after the initial impact; then coupled differential equations of motion were derived and solved to describe the vehicle’s plane-motion during the subsequent stage, which includes both translational and rotational movements. The proposed method was shown to be capable of providing reasonably accurate force estimates with significantly less demand for time and effort compared to other complex methods. These estimates can help infrastructure owners to make informed and sustainable decisions for bridge projects, which include selecting the most efficient bridge design alternatives, in a cost-effective and timely manner. Recommendations for future studies were also discussed.