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The teaching of impact dynamics
Published in Peter J. Moss, Rajesh P. Dhakal, Progress in Mechanics of Structures and Materials, 2020
Our built environment is constantly exposed to the risks of extreme impact actions which are created either by nature, accidents or by human with criminal/terrorism intent. Yet, little is written on Standards and codes of practices to provide guidelines to civil engineers in accounting for such risks in the design of structures. Explicit provisions for collision on parapets and bridge piers can be found in highway codes of practices. A notional force is typically stipulated to represent the impact of a vehicle. For example, the Austroads Bridge Design Code (1992) stipulates an equivalent static load of 1000 kN to be applied to a bridge pier which is not protected by a traffic barrier. Little background of the 1000 kN load is given in the commentary except for the brief remarks that “the maximum force depends on the flexibility and its mass, and the crushing characteristics and velocity of the colliding vehicles”. Provisions in the same document for marine and river piers exposed to impact by ships were also vague: “The design engineer shall consider possible impact loads from shipping…Specialist literature shall be consulted”. Lhe brief commentary on this clause does not provide much additional information as to what is exactly required of the bridge pier in countering the risks of impact. Lhese very brief provisions were extracted from a 40 page long document addressing potential loading on bridges. In contrasts, much was written on gravity loading and temperature loading. Lhis reference to the bridge codes of practices is just a single snapshot showing how little attention is paid by civil engineers to address impact hazards. Even less information on designing structures to withstand impact can be found from building codes of practices.
Modeling the impact of various variables on severity of crashes involving traffic barriers
Published in Journal of Transportation Safety & Security, 2020
Amirarsalan Mehrara Molan, Mahdi Rezapour, Khaled Ksaibati
Table 1 shows the categories for the response and significant predictors. Vehicles were divided into six groups based on differences in dimension and dynamic characteristics in comparison to each other. Four traffic barrier types were included in this study: cable systems, rigid (mostly concrete), guardrail (face), and guardrail (end). The categories were consistently divided in accordance with the recommendation in RDG (AASHTO, 2011) and used by past studies (PennDOT, 2017; Russo & Savolainen, 2018; Zou et al., 2014). However, this research considered an exclusive category for the substantial number of crashes caused by hitting the end section (end treatment) of the guardrails. This approach provided new findings for the comparison with the past studies (pointed above) regarding the effect of guardrail ends on crash severity. Dry, wet, snow, and ice on road surfaces are the most typical conditions observed in Wyoming. The 55-mph limit was also the reference used in two recent studies in the United States (Russo & Savolainen, 2018; Zou et al., 2014). Driver’s age threshold of 35 years was chosen because it divided the data into two groups with almost the same number of observations. The rest of the variables were considered binary (mostly in yes/no categorizes) without needing to define each group or threshold.
A comprehensive sequential strategy for structural equation modeling of traffic barrier crashes
Published in Journal of Transportation Safety & Security, 2021
Mahdi Rezapour, Shaun S. Wulff, Khaled Ksaibati
Fixed object crashes account for a large portion of traffic fatalities in the US. Although traffic barriers are designed to mitigate the severity of collision with a fixed object, traffic barrier crashes still account for a significant proportion of fatalities. Traditional statistical analyses have been used to extensively model crash severity for these types of crashes. However, the number of deaths and injury crashes were excluded because of the correlations among these responses and the difficulty in simultaneously modeling multiple categorical responses. The traditional models can also be adversely affected by multicollinearity and the assumption that all indicators of crash severity have been observed and measured.