What is the preferred Pole/Tree Collision analysis method?

Topics related to collision & Trajectory analysis formerly on our 'Registrants only' area however which we get asked about frequently so believe shoud be in the open forum too
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MSI
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What is the preferred Pole/Tree Collision analysis method?

Post by MSI » Mon Nov 09, 2009 8:15 pm

Depending on the nature of the physical evidence in pole/tree collisions, two separate analytical approaches may be applicable to approximate vehicle speed and impact severity.
  • One approach is based on the vehicle motions preceding and following the collision.
    • In cases where motions subsequent to the impact are sufficiently defined, work-energy relationships can be applied to approximate the work done against motion resisting forces and,thereby, determine the linear and angular velocities at separation from the pole/tree. The principle of conservation of angular momentum can then be used to determine the corresponding components of vehicle velocity at the point of impact with the pole/tree.
    The second approach is based on the nature and extent of vehicle damage.
    • The nature and extent of vehicle crush can serve as a separate basis for approximating vehicle speed and impact severity. Empirical crush properties, combined with vehicle specifications, and the degree of collision offset, can be applied to approximate the extent of energy absorption by vehicle crush and the corresponding impact speed-change.
For additional information, see analytical presentations in the Pole/Tree Collisions section of McHenry Accident Reconstruction: We will also add some recent references with vehicle Pole/Tree collisions to this thread.
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Re: What is the preferred Pole/Tree Collision analysis metho

Post by MSI » Thu Nov 19, 2009 10:03 pm

The following are some Pole impact tests and papers. There seems to be a battle of companies. SEA out of Ohio and Collision Safety out of Utah. The following is a list of some papers, in no particular order, from those organizations about pole impacts which include full-scale crash test data, etc.
SAE paper 980214, Wooden Pole Fracture Energy in Vehicle Impacts By Kent and Strother
SAE 2008-01-0170 Pole and Vehicle Energy Absorption in Lateral Oblique Impacts with Rigid and Frangible Poles, Tanner, Chen, Cheng
SAE 2006-01-0062 Development of Pole Impact Testing at Multiple Vehicle Side Locations As Applied to the Ford Taurus Structural Platform", Warner and Nordhagen
SAE 2006-01-0899 "Accident Reconstruction for Rear Pole Impacts of Passenger Cars" Nordhagen, Warner, Perl, Kent
SAE 2004-01-1615 "Pole Impact Speeds Derived from Bilinear Estimations of Maximum Crush for Body-On-Frame Constructed Vehicles, Chen ,Tanner, Durisek, Guenther
SAE 2006-01-0062 "Development of Pole Impact Testing at Multiple Vehicle Side Locations As Applied to the Ford Taurus Structural Platform"Warner Nordhagen
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SAE paper 980214, Wooden Pole Fracture Energy in Vehicle Impacts By Kent and Strother
  • ABSTRACT Impacts with trees and wooden utility poles represent a significant subset of vehicular collisions. For example, while fixed object collisions account for less than 8% of all crashes, they represent nearly 30% of all fatal crashes. Also, nearly half (over 43%) of all fixed-object impacts are into a tree, pole, or post. This paper is viewed as a first attempt to understand the energy absorbing processes operating when vehicles strike trees and wooden poles in order to make reasonable estimates of the magnitude of the tree/pole energy dissipated in the crash. This initial study is comprised of a literature review, a series of scale model pole/pendulum impacts, and an analytical study which is comprised of both a static analysis and a dynamic finite element model (FEM) analysis of a vehicle/pole impact. As a result of this work, a methodology has been evolved for making estimates of tree/pole energy. This methodology considers whether or not the struck object was displaced in its moorings and/or partially or completely fractured by the impact.
    From Conclusions: The implementation of the methodology outline herein requires the accident reconstructionist to acquire certain additional data during his investigation. Namely:
    1. The geometry of the struck pole/tree (i.e. the diameter and height)
    2. The species of wood making up the pole or tree in question (however conservatively, the accident reconstructionist can assume the pole or tree was constructed of a material which will produce a minimum amount of energy).
    3. The likely moisture content of the pole or tree in question (poles can generally be assumed to be of low moisture content, i.e. less than 6 percent, trees generally have moisture contents greater than 20 percent). In addition, many books give properties for
    both dry and green wood specimens [FPL 90].
    4. The nature of the damage to the pole or tree. That is, the location of the fracture (to make sure that this method is applicable) and whether the fracture was just initiated, total, or at some intermediate level.
SAE 2008-01-0170 Pole and Vehicle Energy Absorption in Lateral Oblique Impacts with Rigid and Frangible Poles, Tanner, Chen, Cheng
  • ABSTRACT Many vehicle-to-pole impacts occur when a vehicle leaves the roadway due to oversteer and loss of control in a lateral steering maneuver. Such a loss of control typically results in the vehicle having a significant component of lateral sliding motion as it crosses the road edge, so that impacts with objects off of the roadway often occur to the side of the vehicle. The response of the vehicle to this impact depends on the characteristics of the impacted object, the characteristics of the vehicle in the impacted zone, and the speed and orientation of the vehicle. In situations where the suspension or other stiff portions of a vehicle contacts a wooden pole, it is not uncommon for the pole to fracture. When this occurs, reconstruction of the accident is complicated by the need to evaluate both the energy absorbed by the vehicle as well as the energy absorbed by the pole. In addition,
    stiffness characteristics for the vehicle suspension and its mounts are not typically available since most side impact testing involves staged impacts between the vehicle wheels.
    CONCLUSIONThis paper has discussed the results of a pair of matched oblique pole side impact tests in which the only significant variation between tests was the use of a rigid pole barrier in one test, and the use of a frangible wooden pole in the second test. Because the area of the vehicle that was impacted was the front suspension and wheel arch, data was available to determine the stiffness of that portion of the side vehicle structure.
    From this analysis, it was found that the vehicle suspension is far stiffer than typical side impact parameters as determined from impact tests in which the struck vehicle is impacted between the front and rear wheels of the vehicle. In fact the stiffness is as much as three times greater. While this result was only determined for the vehicle tested, a similar stiffness ratio might be expected for other mid-sized front wheel drive passenger cars. However, since only one vehicle was tested in this configuration, extending these results to other vehicles must be done with caution.
    From the data described in this paper, an analysis was performed to determine the energy required to fracture an 11inch diameter wooden pole in a motor vehicle impact. While some references have described means for estimating this value, there are few, if any, controlled vehicle impact tests from which such information can be derived. As a result of the analysis, it was determined that the fracture energy of a well supported pole was
    between about 19,000 and 28,000 ft-lbs. This is in good agreement with the data available for estimating pole fracture stiffness, and for a typical passenger car corresponds to a barrier equivalent velocity (BEV) or energy of between about 13.5 and 17 miles per hour. While this result is in reasonable agreement with the other limited information available in the literature, because of the number of variables involved when
    dealing with poles, including the type of wood, condition of the wood, type of soil, and condition of the soil, extension of these results to other impacts must be done carefully.
SAE 2006-01-0062 Development of Pole Impact Testing at Multiple Vehicle Side Locations As Applied to the Ford Taurus Structural Platform", Warner and Nordhagen
  • ABSTRACT:A test method was developed whereby repeated pole impacts could be performed at multiple locations per test vehicle, allowing a comparison of energy and crush relationships. Testing was performed on vehicles moving laterally into a 12.75 inch diameter rigid pole barrier. Crush energy absorption characteristics at the different locations were analyzed, and the results compared to test data from broad moving barrier crashes and available crash tests with similar pole impacts.
    Crush stiffness characteristics for narrow impacts at various points on the side of the Taurus vehicle platform were documented. Factors encountered during the research include the importance of rotational energy accounting and uncertainties related to crush energy related to induced deformation. The findings show that the front axle and A-pillar regions are much stiffer than the CG and B-pillar areas to narrow rigid pole impact.
    The CG region produced stiffness relations that correspond well with published broad-impact data when the effective crush width was assumed to be roughly three times the pole diameter.
    Results of this research demonstrate that stiffness properties vary significantly along the side of a vehicle. Though not practical as a tool in every circumstance, the multiple impact location technique should be considered when side impact crush energy absorption characteristics are key to the outcome of a crash analysis.
SAE 2006-01-0899 "Accident Reconstruction for Rear Pole Impacts of Passenger Cars" Nordhagen, Warner, Perl, Kent
  • ABSTRACT: While vehicular rear pole impacts are rare, they do occur, and can be very serious. General accident reconstruction methods, which derive vehicle stiffness values from rear barrier crash tests, over-predict the impact speed for these types of pole impacts. Thirteen pole crash tests were run into the rear-ends of four 4-door, front-wheel drive sedans. Repeated crash testing was used on three of the vehicles. Two 1988 Acura Legends, which have one of the highest stiffness values from FMVSS 301 Rear Compliance crash testing, a 1988 Honda Civic, which has one of the softest rearend stiffnesses, and a 1986 Ford Taurus were tested. The repeated crash testing methodology was validated using one of the 1988 Acura Legends and a previously published Ford Taurus test. Residual crush was measured using maximum crush, point-to-point, longitudinal full-width, and longitudinal reduced-width methodologies. Crush was found to be linearly related to impact speed. The crash pulse when compared to barrier testing was longer and exhibited a later peak. Models were developed using linear regression to calculate crush energy or impact speed from the residual crush measurements. Methods were developed to transform rear-end B-values from barrier tests into B-values for use in rear pole impacts. The various models developed were compared using their coefficients of determination, standard deviations, and 95% confidence intervals to determine which models most closely predicted the impact speed. This analysis showed that models which used maximum crush had
SAE 2006-01-0062 "Development of Pole Impact Testing at Multiple Vehicle Side Locations As Applied to the Ford Taurus Structural Platform"Warner Nordhagen
  • ABSTRACTA test method was developed whereby repeated pole impacts could be performed at multiple locations per test vehicle, allowing a comparison of energy and crush relationships. Testing was performed on vehicles moving laterally into a 12.75 inch diameter rigid pole barrier. Crush energy absorption characteristics at the different locations were analyzed, and the results compared to test data from broad moving barrier crashes and available crash tests with similar pole impacts.
    Crush stiffness characteristics for narrow impacts at various points on the side of the Taurus vehicle platform were documented. Factors encountered during the research include the importance of rotational energy accounting and uncertainties related to crush energy related to induced deformation. The findings show that the front axle and A-pillar regions are much stiffer than the CG and B-pillar areas to narrow rigid pole impact.
    The CG region produced stiffness relations that correspond well with published broad-impact data when the effective crush width was assumed to be roughly three times the pole diameter. Results of this research demonstrate that stiffness properties vary significantly along the side of a vehicle. Though not practical as a tool in every circumstance, the multiple impact location technique should be considered when side impact crush energy absorption characteristics are key to the outcome of a crash analysis.
SAE 2004-01-1615 "Pole Impact Speeds Derived from Bilinear Estimations of Maximum Crush for Body-On-Frame Constructed Vehicles, Chen ,Tanner, Durisek, Guenther
  • ABSTRACT Accident reconstructionists use several different approaches to determine vehicle equivalent impact speed from damage due to narrow object impacts. One method that is used relates maximum crush to equivalent impact speed with a bilinear curve. In the past, this model has been applied to several passenger cars with unibody construction. In this paper, the approach is applied to a body-on-frame vehicle. Several vehicle-to-rigid pole impact tests have been conducted on a full-size pickup at different speeds and impact locations: centrally located across the vehicle’s front and outside the frame rail. A bilinear model relating vehicle equivalent impact speed to maximum crush is developed
    for the impact locations. These results are then compared to results obtained from other body-on-frame vehicles as well as unibody vehicles. Other tests such as impacts on the frame rail and barrier impacts are also presented. Limitations to this bilinear approach are discussed.
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Re: What is the preferred Pole/Tree Collision analysis metho

Post by MSI » Sun Jul 22, 2012 2:25 pm

July 2012: Q: Can anyone direct me to staged collision data with the following features:
  • - Shallow-angle pole/tree impact to the side of the vehicle.
    - PDOF 15 to 30 degrees if the impact is to the right side or -15 to -30 degrees if the impact is to the left side.
A: Please see the top of this thread, in particular the summary of pole impacts contained in our analytical presentations in the Pole/Tree Collisions section of McHenry Accident Reconstruction:
    Work Energy Relationships, Conservation Of Angular Momentum and Damage Analysis[/list]
    For convenience we post the graphics summary of some tests below:
    pole_tests.jpg
    pole_tests.jpg (110.91 KiB) Viewed 4362 times
    VW Pole tests.jpg
    VW Pole tests.jpg (112.24 KiB) Viewed 4362 times
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    Re: What is the preferred Pole/Tree Collision analysis metho

    Post by MSI » Tue Jun 18, 2013 10:31 pm

    June 18. 2013: Q: I am looking for any crash testing video of a vehicle vs. fixed pole, preferably a metal one mounted in concrete. Any suggestion?

    A: From the first link of this thread above Preferred analysis method there is a link to Work Energy Relationships, Conservation Of Angular Momentum and Damage Analysis which is a section from our McHenry book (it's out of print until I update it!)
    At the end of that article are all the pole tests listed with the test number included
    Using the tests numbers go to NHTSA Crash Test database and enter the test number.
    Then you will find the reports and many of the tests also include videos
    (I would start with the most recent tests and work back)
    (I have many of the pole tests videos and i expect i got them from the NHTSA site)
    also FYI that list of pole crash tests from my book is 8 or more years old so there are many more tests.
    it should give you clues as to what search terms to use to find more recent pole tests.
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