Performance Evaluation Of Cable Barriers On A 6:1 Sloped .
Final ReportPerformance Evaluation of Cable Barriers on a 6:1 SlopedMedian under MASH TL-3 ConditionsPrepared ByHowie Fang, Ph.D.Emre PaltaZheng LiOyeboade FatokiUniversity of North Carolina at CharlotteDepartment of Mechanical Engineering & Engineering ScienceDepartment of Civil & Environmental EngineeringCharlotte, NC 28223-0001March 31, 2019
Technical Report Documentation Page1.Report No.2.Government Accession No.3.Recipient’s Catalog No.5.Report DateMarch 31, 20196.Performing Organization CodePerforming Organization Report No.NCDOT 2017-134. Title and SubtitlePerformance Evaluation of Cable Barriers on a 6:1 SlopedMedian under MASH TL-3 Conditions7.Author(s)Howie Fang, Emre Palta, Zheng Li, Oyeboade Fatoki8.9.Performing Organization Name and Address10. Work Unit No. (TRAIS)The University of North Carolina at Charlotte9201 University City BoulevardCharlotte, NC 28223-000111. Contract or Grant No.12. Sponsoring Agency Name and Address13. Type of Report and Period CoveredNorth Carolina Department of TransportationResearch and Analysis Group1 South Wilmington StreetRaleigh, North Carolina 27601Final ReportAugust 1, 2016 – February 28,201914. Sponsoring Agency CodeNCDOT 2017-13Supplementary Notes:16. AbstractIn this study, non-linear finite element simulations were conducted to evaluate the performance of the current NCDOTcable median barrier (CMB) and two retrofit CMB designs (named “Sixth Design Retrofit” and “Four-cable DesignRetrofit”) placed on a 6H:1V sloped median. The aim of this research was to investigate possibility of replacing thecurrent CMB design with one of the two retrofit designs. All three CMB designs were evaluated under MASH TL-3conditions, i.e., under the impacts of a 1100C passenger car and a 2270P pick-up truck at 100 km/hr (62 mph) and a25-degree impact angle. The CMBs were impacted from both front-sides and backsides at two different impact locations:1) on a post in the CMB mid-span, and 2) at the midpoint between two adjacent posts in the mid-span. The CMBperformance was evaluated using vehicular responses specified in MASH, i.e., the exit-box criterion, MASH evaluationcriteria A, D and F, exit angle, yaw, pitch and roll angles, and transverse velocities.The simulation results demonstrated the effectiveness of each of the three CMB designs on a 6H:1V sloped median undervehicular impacts. The simulation results showed that cable heights and the number of cables played an important rolein the effectiveness of CMBs when placed on sloped medians. The finite element modeling and simulation works wereshown to be both effective and efficient and can be used to study crash scenarios that are difficult and/or extremelyexpensive to conduct with physical crash testing.17. Key WordsCable systems; Median barriers; Roadside structures;Highway safety; Retrofitting; Finite element method19. Security Classify. (of this report)UnclassifiedForm DOT F 1700.7 (8-72)18. Distribution Statement20. Security classify. (of thispage)Unclassified21. No. of Pages77Reproduction of completed page authorizedii22. Price
DisclaimerThe contents of this report reflect the views of the authors and not necessarily the views of theuniversity. The authors are responsible for the facts and the accuracy of the data presentedherein. The contents do not necessarily reflect the official views or policies of either the NorthCarolina Department of Transportation or the Federal Highway Administration. This reportdoes not constitute a standard, specification, or regulation.iii
AcknowledgmentsThis study was supported by the North Carolina Department of Transportation (NCDOT)under Project No. 2017-13. The authors would like to thank NCDOT personnel from theTraffic Engineering and Safety Systems, Roadway Design Unit, Highway Division 5 – District1, FHWA – NC Division, and the Research and Development Unit for their support andcooperation during the grant period.iv
Executive SummaryIn this study, non-linear finite element simulations were conducted to evaluate the performanceof the current NCDOT cable median barrier (CMB) and two retrofit CMB designs (named“Sixth Design Retrofit” and “Four-cable Design Retrofit”) placed on a 6H:1V sloped median.The aim of this research was to investigate possibility of replacing the current CMB designwith one of the two retrofit designs. All three CMB designs were evaluated under MASH TL3 conditions, i.e., under the impacts of a 1100C passenger car and a 2270P pick-up truck at100 km/hr (62 mph) and a 25-degree impact angle. The CMBs were impacted from both frontsides and backsides at two different impact locations: 1) on a post in the CMB mid-span, and2) at the midpoint between two adjacent posts in the mid-span. The CMB performance wasevaluated using vehicular responses specified in MASH, i.e., the exit-box criterion, MASHevaluation criteria A, D and F, exit angle, yaw, pitch and roll angles, and transverse velocities.The simulation results demonstrated the effectiveness of each of the three CMB designs on a6H:1V sloped median under vehicular impacts. The simulation results showed that cableheights and the number of cables played an important role in the effectiveness of CMBs whenplaced on sloped medians. The finite element modeling and simulation works were shown tobe both effective and efficient and can be used to study crash scenarios that are difficult and/orextremely expensive to conduct with physical crash testing.v
Table of ContentsTechnical Report Documentation Page . iiDisclaimer . iiiAcknowledgments. ivExecutive Summary . vTable of Contents . viList of Tables . viiiList of Figures. .ix1. Introduction . 11.1 Background . 11.2 Research Objectives and Tasks . 22. Literature Review. 52.1 Performance Evaluation of Cable Barriers . 52.2 Finite Element Modeling and Simulations of Vehicular Crashes . 103. Finite Element Modeling of Vehicles and Cable Median Barriers . 163.1 FE Models of a Passenger Car and Pickup Truck . 163.2 FE Models of the Cable Median Barriers . 173.3 Simulation Setup . 234. Simulation Results and Analysis . 254.1 Case 1: Evaluation of the Current CMB Design. 264.1.1 Dodge Neon Impacts from the Front-side . 264.1.2 Dodge Neon Impacts from the Backside . 294.1.3 Ford F250 Impacts from the Front-side . 314.1.4 Ford F250 Impacts from the Backside . 334.2 Case 2: Evaluation of the “Sixth Design Retrofit” . 354.2.1 Dodge Neon Impacts from the Front-side . 354.2.2 Dodge Neon Impacts from the Backside . 384.2.3 Ford F250 Impacts from the Front-side . 414.2.4 Ford F250 Impacts from the Backside . 424.3 Case 3: Evaluation of the “Four-cable Design Retrofit” . 454.3.1 Dodge Neon Impacts from the Front-side . 464.3.2 Dodge Neon Impacts from the Backside . 48vi
4.3.3 Ford F250 Impacts from the Front-side . 504.3.4 Ford F250 Impacts from the Backside . 524.4 Comparison of All Three CMB Designs Placed on a 6H:1V Sloped Median . 545. Findings and Conclusions . 576. Recommendations . 597. Implementation and Technology Transfer Plan . 60References . 61APPENDIX A. Performance Evaluation of Three CMB Designs on a Flat Terrain underMASH TL-3 Conditions . 68APPENDIX B. Performance Evaluation of Two CMB Designs on a Flat Terrain underImpacts by a MASH 1500A Vehicle . 76vii
List of TablesTable 3.1: Specifications of the two test vehicles used in crash simulations . 16Table 3.2: Simulation conditions for all cases . 24Table 4.1: The exit box criterion defined in MASH . 25Table 4.2: Exit box dimensions for the test vehicles of this project . 26Table 4.3: Summary of simulation results for Case 1 . 26Table 4.4: Summary of simulation results for Case 2 . 36Table 4.5: Summary of simulation results for Case 3 . 45Table 4.6: Summary of simulation results for Dodge Neon. 55Table 4.7: Summary of simulation results for Ford F250 . 56viii
List of FiguresFigure 1.1: In-service three-strand, low-tension cable barriers in North Carolina . 1Figure 1.2: Current and the two retrofit CMB designs. . 2Figure 1.3: Illustration of the CMB placed on a 6H:1V sloped median and impacted by apassenger car from both front- and back- sides. . 3Figure 1.4: Definition of vehicle responses. . 3Figure 3.1: Finite element models of two MASH compliant vehicles used in this study. 16Figure 3.2: Sketch of the three CMB designs for this project. . 18Figure 3.3: Components of the FE model of CMB. 19Figure 3.4: The FE model of the four-cable CMB anchor block. . 20Figure 3.5: FE models of the three CMB designs. . 21Figure 3.6: FE model of entire section of the current CMB design. . 22Figure 3.7: FE model of entire section the sixth CMB design retrofit. . 22Figure 3.8: FE model of entire section of the “Four-cable Design Retrofit”. . 23Figure 3.9: A Dodge Neon impacting the CMB at a post (left) and the mid-span (right). . 24Figure 4.1: The exit-box criterion in MASH. . 25Figure 4.2: A Dodge Neon impacting the current CMB design at a post from front-side. 27Figure 4.3: A Dodge Neon impacting the current CMB design at mid-span from front-side. . 27Figure 4.4: Yaw, pitch, and roll angles of a Dodge Neon impacting the current CMB design fromfront-side. . 27Figure 4.5: Vehicle-barrier interactions for Dodge Neon impacting the current CMB design fromfront-side. . 28Figure 4.6: Transverse velocity of a Dodge Neon impacting the current CMB design from frontside. 28Figure 4.7: A Dodge Neon impacting the CMB (current design) at the post from backside. . 29Figure 4.8: A Dodge Neon impacting the CMB (current design) at mid-span from backside. . 29Figure 4.9: A Dodge Neon impacting the current CMB design at a post from backside. . 29Figure 4.10: A Dodge Neon impacting the current CMB design at mid-span from backside. . 30Figure 4.11: Yaw, pitch, and roll angles of a Dodge Neon impacting the current CMB designfrom front-side. . 31ix
Figure 4.12: A Ford F250 impacting the current CMB design at a post from front-side. . 31Figure 4.13: A Ford F250 impacting the current CMB design at mid-span from front-side. . 31Figure 4.14: The yaw, pitch, and roll angles of the Ford F250 impacting the current CMB designfrom front-side. . 32Figure 4.15: Vehicle-barrier interactions for Ford F250 impacting the current CMB design fromfront-side. . 32Figure 4.16: Transverse velocities of the Ford F250 impacting the current CMB design fromfront-side. . 33Figure 4.17: A Ford F250 impacting the current CMB design at a post from backside. . 33Figure 4.18: A Ford F250 impacting the current CMB design at mid-span from backside . 33Figure 4.19: Yaw, pitch, and roll angles of the Ford F250 impacting the current CMB designfrom backside . 34Figure 4.20: Vehicle-barrier interactions for Ford F250 impacting the current CMB design frombackside. 34Figure 4.21: Transverse velocities of the Ford F250 impacting the current CMB design frombackside. 35Figure 4.22: A Dodge Neon impacting the “Sixth Design Retrofit” at a post from front-side. . 36Figure 4.23: A Dodge Neon impacting the “Sixth Design Retrofit” at mid-span from front-side . 36Figure 4.24: Yaw, pitch, and roll angles of a Dodge Neon impacting the “Sixth Design Retrofit”from front-side. . 37Figure 4.25: Vehicle-barrier interactions for Dodge Neon impacting the “Sixth Design Retrofit”from front-side. . 38Figure 4.26: Transverse velocities of a Dodge Neon impacting the “Sixth Design Retrofit” fromfront-side. . 38Figure 4.27: A Dodge Neon impacting the “Sixth Design Retrofit” at a post from backside. . 39Figure 4.28: A Dodge Neon impacting the “Sixth Design Retrofit” at mid-span from backside. 39Figure 4.29: Yaw, pitch, and roll angles of a Dodge Neon impacting the “Sixth Design Retrofit”from backside. . 39Figure 4.30: Vehicle-barrier interactions for Dodge Neon impacting the “Sixth Design Retrofit”from backside. . 40x
Figure 4.31: Transverse velocities of a Dodge Neon impacting the “Sixth Design Retrofit” frombackside. 40Figure 4.32: A Ford F250 impacting the “Sixth Design Retrofit” at a post from front-side. . 41Figure 4.33: A Ford F250 impacting the “Sixth Design Retrofit” at mid-span from front-side. . 41Figure 4.34: Time sequences of the Ford F250 impacting the “Sixth Design Retrofit” at a postfrom front-side. . 41Figure 4.35: Yaw, pitch, and roll angles of the Ford F250 impacting the “Sixth Design Retrofit”from front-side. . 42Figure 4.36: Transverse velocities of the Ford F250 impacting the “Sixth Design Retrofit” fromfront-side. . 42Figure 4.37: A Ford F250 impacting the “Sixth Design Retrofit” at a post from backside. 43Figure 4.38: A Ford F250 impacting the “Sixth Design Retrofit” at mid-span from backside. . 43Figure 4.39: Vehicle-CMB interactions during impacts by a Ford F250 on the “Sixth DesignRetrofit” at a post. . 43Figure 4.40: Yaw, pitch, and roll angles of the Ford F250 impacting the “Sixth Design Retrofit”from backside. . 44Figure 4.41: Vehicle-barrier interactions for Ford F250 impacting the “Sixth Design Retrofit”from backside. . 44Figure 4.42: Transverse velocities of the Ford F250 impacting the “Sixth Design Retrofit” frombackside. 45Figure 4.43: A Dodge Neon impacting the “Four-cable Design Retrofit” at a post from front-side. 46Figure 4.44: A Dodge Neon impacting the “Four-cable Design Retrofit” at mid-span from frontside. . 46Figure 4.45: Vehicle-barrier interactions at the maximum dynamic displacements for DodgeNeon impacting the “Four-cable Design Retrofit” from front-side. . 46Figure 4.46: Yaw, pitch, and roll angles of Dodge Neon impacting the “Four-cable DesignRetrofit” from front-side. . 47Figure 4.47: Transverse velocities of the Dodge Neon impacting the “Four-cable DesignRetrofit” from front-side. . 47Figure 4.48: A Dodge Neon impacting the “Four-cable Design Retrofit” at a post from backside.xi
. 48Figure 4.49: A Dodge Neon impacting the “Four-cable Design Retrofit” at mid-span frombackside. 48Figure 4.50: Vehicle-barrier interactions at the maximum dynamic displacements for DodgeNeon impacting the “Four-cable Design Retrofit” from backside. 48Figure 4.51: Yaw, pitch, and roll angles of the Dodge Neon impacting the “Four-cable DesignRetrofit” from backside. 49Figure 4.52: Transverse velocities of the Dodge Neon impacting the “Four-cable DesignRetrofit” from backside. 49Figure 4.53: A Ford F250 impacting the “Four-cable Design Retrofit” at a post from front-side. 50Figure 4.54: A Ford F250 impacting the “Four-cable Design Retrofit” at mid-span from frontside. . 50Figure 4.55: Vehicle-barrier interactions at the maximum dynamic displacements for Ford F250impacting the “Four-cable Design Retrofit” from front-side. . 50Figure 4.56: Yaw, pitch, and roll angles of the Ford F250 impacting the “Four-cable DesignRetrofit” from front-side. . 51Figure 4.57: Transverse velocities of the Ford F250 impacting the “Four-cable Design Retrofit”from front-side. . 51Figure 4.58: A Ford F250 impacting the “Four-cable Design Retrofit” at a post from backside. 52Figure 4.59: A Ford F250 impacting the “Four-cable Design Retrofit” at mid-span frombackside. 52Figure 4.60: Vehicle-barrier interactions at the maximum dynamic displacements for Ford F250impacting the “Four-cable Design Retrofit” from backside. . 52Figure 4.61: Yaw, pitch, and roll angles of the Ford F250 impacting the “Four-cable DesignRetrofit” from backside. 53Figure 4.62: Transverse velocities of the Ford F250 impacting the “Four-cable Design Retrofit”from backside. . 53xii
1. IntroductionRoadside safety barriers are important devices to enhance transportation safety. Over the years,different types of barriers have been developed and can be categorized into rigid, semi-rigid, andflexible systems. Roadside barriers serve the purpose of safely redirecting run-out-of-way vehiclesand preventing vehicles from intruding into oncoming traffic. All barriers used on U.S. highwaysare designed following the guidelines of the American Association of State Highway andTransportation Officials (AASHTO) (AASHTO 2002, 2005) and must be tested to satisfy thesafety requirements specified by Manual for Assessing Safety Hardware (MASH).1.1 BackgroundCommonly used barrier systems include concrete barriers, W-beam and thrice-beam guardrails,and cable barriers. Concrete barriers belong to the rigid category; they have relatively higher initialcosts, require less maintenance, and are less forgiving in severe crashes than other barrier systems.The W-beam or thrive-beam guardrails consist of steel rails mounted on wood or steel posts withend treatments and transitions. W-beam and thrie-beam guardrails are intended to be sacrificial;therefore, substantial replacements and/or repairs are required after major vehicular crashes. Evenlow-energy impacts can bend and damage the rails and displace the posts enough for the barriernot to perform properly in a subsequent crash event. The cost of maintaining these systems isgenerally high.NCDOT currently has approximately 750 milesof low-tension cable median barriers (CMBs)installed across the state’s highways as shownin Fig. 1.1. The CMB system has been shownto be generally effective with a high rate ofsuccess in reducing cross-median crashes andfatalities since the first installations in the mid1990’s. Although these low tension CMBs havesatisfied the safety requirements of NCHRPReport 350, they should be evaluated underconditions of MASH which specifies moresevere impact conditions than those in the Figure 1.1: In-service three-strand, low-tension cablebarriers in North CarolinaNCHRP Report 350. In a current data analysisof the low-tension CMB hits from January 2011through December 2013, the CMBs received 4731 hits in which 151 crashes resulted in systempenetration (3.2 percent of the total hits). NCDOT would like to explore a solution to minimizethe percentage of crashes that may result in penetrations on the CMBs.In 2009, UNC Charlotte completed a research project, Finite Element Evaluation of Two RetrofitOptions to Enhance the Performance of Cable Median Barriers, for NCDOT. In this project, tworetrofit designs to the current NCDOT CMB were evaluated using finite element (FE) modelingand simulations and were found to have a potential to reduce the penetration occurrences comparedto the current CMB design. The two retrofit designs, named “Sixth Design Retrofit” and “Fourcable Design Retrofit” as illustrated in Fig. 1.2, have not been evaluated using the crash testing1
criteria specified by MASH. NCDOT would like to gain knowledge of the performance of thethree CMB systems under MASH testing criteria. If the “Four-cable Design Retrofit” performsbetter than the “Sixth Design Retrofit”, NCDOT would like to know how the fourth cable wouldbe added to the current design in terms of cable height and anchor block fixtures. Finally, NCDOTwould envision a follow-up project to complete a real-life crash test of the selected CMB retrofitdesign under MASH testing conditions in order to apply for federal approval to install the lowtension CMB retrofit.Figure 1.2: Current and the two retrofit CMB designs.1.2 Research Objectives and TasksIn this study, full-scale FE simulations were employed to evaluate the performance of the currentCMB design and two retrofit designs under MASH testing criteria. The evaluations were based onMASH TL-3 conditions, i.e., under the impact of a 1100C small passenger car and a 2270P pickuptruck. All three CMB designs were placed on a 6H:1V sloped median and impacted by these twovehicles at 100 km/hr and a 25-degree impact angle. The simulation results were analyzed todetermine the effectiveness of the two retrofit designs compared to the current design. The researchproject had six major tasks as stated below.Task 1: Literature Review and Data CollectionA comprehensive literature review was conducted on crash testing, modeling and simulations thatare related, in particular, to CMBs to assist with model validation and crash simulations. Literatureon performance evaluation of other roadside barrier systems as well as FE modeling work onroadside safety was also collected to assist the research of this study.Task 2: FE Model Development and ValidationIn this task, FE models for the three CMB designs were created and integrated with the medianand vehicle models according to NCDOT specifications and the crash scenarios of this study. Thetwo vehicles used in the modeling and simulation work for this study were a 1996 Dodge Neonwith a mass of 1,090 kg (2,400 lbs) and a 2006 Ford F250 pickup truck with a mass of 2,270 kg(5,504lbs). Finite element models of the two vehicles and the three CMBs, including the soil andanchor blocks, were discussed in details in Section 3.1.Task 3: Evaluation of the “Sixth Design Retrofit”In this task, the “Sixth Design Retrofit” CMB was evaluated at MASH TL-3 conditions (i.e., at animpact speed of 100 km/hr and a 25-degree impact angle). The differences between the “SixthDesign Retrofit” and the current design lie in the cable heights and cable placement on the sides2
of the post (see Fig. 1.2.). In the “Sixth Design Retrofit,” the top cable was placed on the oppositeside of the post but at the same height as that in the current design. The middle cable in the “SixthDesign Retrofit” is on the same side of the post and at the same hei
Figure 4.2: A Dodge Neon impacting the current CMB design at a post from front-side. 27 Figure 4.3: A Dodge Neon impacting the current CMB design at mid-span from front-side. . 27 Figure 4.4: Yaw, pitch, and roll angles of a
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