ABSTRACT
The distinguishing feature of all underride/override crashes is that the primary load paths of at least one of the vehicles are engaged only slightly, if at all, because of height mismatches. In such crashes, the crush at one water level of a vehicle differs significantly from the crush at another. Of course, it is still desirable, for reconstruction purposes, to calculate the crush energy. Flat barrier test data are widely used for this purpose in other kinds of crashes. Since there is no reason to expect underride/override crash tests to be performed on a routine basis any time soon, the objective here is to tap into the wealth of data for frontal flat barrier crashes, and find a way to apply the information to frontal underride/override crashes.
Chapter 24 presents test results and analysis from frontal underride crashes into rigidized semitrailer underride guards by the National Highway Traffic Safety Administration (NHTSA) or into overhanging barriers by Exponent, Inc.
This chapter also summarizes a 2009 paper by Struble et al. that proposed a reconstruction method whereby the weighting factors for crush force between upper and lower structures could be ascertained by examining force data from a load cell barrier (LCB) test. For an accident vehicle, the crush forces and energies in the upper and lower structures are calculated by applying the overall structural characterization (A and B) to the two profiles, and then multiplying by the weighting factors obtained from the LCB test(s). The shear force is estimated at 0.35 times the average of the upper and lower structure forces. The shear deformation is equal to the absolute value of the difference between the average crush in the upper and lower structures. The shear energy is then the product of the shear force and the shear deformation. The total energy of deformation is the sum of the upper and lower structure crush energies, plus the shear energy.
This methodology was applied to the underride crash tests of Ford Tauruses and a Honda Civic. Predicted and actual Energy Equivalent Speeds are compared.
