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Aesthetic Concrete Barrier Design (2006)

Chapter: Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines

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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
×
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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
×
Page 62
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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
×
Page 63
Page 64
Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
×
Page 64
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Suggested Citation:"Chapter 6 - Crash Testing and Further Evaluation of Preliminary AestheticDesign Guidelines." National Academies of Sciences, Engineering, and Medicine. 2006. Aesthetic Concrete Barrier Design. Washington, DC: The National Academies Press. doi: 10.17226/13888.
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56 CHAPTER 6 CRASH TESTING AND FURTHER EVALUATION OF PRELIMINARY AESTHETIC DESIGN GUIDELINES Once the preliminary guidelines were developed using the finite element simulations, a full-scale crash-testing phase was conducted. The results of these crash tests were used to for- mulate the final design guidelines by assisting with refinement of the internal energy thresholds used to establish acceptable and unacceptable impact performance. A summary of details of the crash-testing phase are presented in this chapter. CRASH TEST CONDITIONS AND EVALUATION CRITERIA A brief description of NCHRP Report 350 test conditions and evaluation criteria is provided in the following sections. NCHRP Report 350 Test Designations According to NCHRP Report 350, two crash tests are required for Test Level 3 (TL-3) evaluation of length-of-need longitudinal barriers: • NCHRP Report 350 Test Designation 3-10: 820C vehicle impacting the length-of-need section at a speed of 100 km/h with the vehicle bumper at an impact angle of 20 degrees. • NCHRP Report 350 Test Designation 3-11: 2000P vehicle impacting the length-of-need section at a speed of 100 km/h with the vehicle bumper at an impact angle of 25 degrees. The small-car test is conducted for evaluating the overall performance characteristics of the length-of-need section of a longitudinal barrier in general and occupant risks in partic- ular. The pickup truck test is performed for the purpose of evaluating the strength of the section in containing and re- directing the larger and heavier vehicle. Occupant risks are of foremost concern in the evaluation of both tests. NCHRP Report 350 and Other Evaluation Criteria Crash tests were evaluated in accordance with the criteria presented in NCHRP Report 350. As stated in NCHRP Rep- ort 350, “Safety performance of a highway appurtenance cannot be measured directly but can be judged on the basis of three factors: structural adequacy, occupant risk, and vehi- cle trajectory after collision.” Accordingly, the following safety evaluation criteria from Table 5.1 of NCHRP Report 350 were used to evaluate the crash tests reported herein: • Structural Adequacy A. Test article should contain and redirect the vehicle; the vehicle should not penetrate, underride, or over- ride the installation, although controlled lateral de- flection of the test article is acceptable. • Occupant Risk D. Detached elements, fragments, or other debris from the test article should not penetrate or show potential for penetrating the occupant compartment or present an undue hazard to other traffic, pedestrians, or per- sonnel in a work zone. Deformation of, or intrusions into, the occupant compartment that could cause seri- ous injuries should not be permitted. F. The vehicle should remain upright during and after collision, although moderate roll, pitching, and yaw- ing are acceptable. H. Occupant impact velocities should satisfy the fol- lowing: Longitudinal and Lateral Occupant Impact Velocity—m/s Preferred Maximum 9 12 I. Occupant ridedown accelerations should satisfy the following: Longitudinal and Lateral Occupant Ridedown Accelerations—g Preferred Maximum 15 20 • Vehicle Trajectory K. After collision, it is preferable that the vehicle’s tra- jectory not intrude into adjacent traffic lanes. M. The exit angle from the test article preferably should be less than 60% of the test impact angle, measured at time of vehicle loss of contact with the test device.

57 tee A2A04 Roadside Safety Features, Mr. Richard Powers of the FHWA issued “Draft Guidelines for Analysis of Passenger Compartment Intrusion.” These guidelines provided recom- mended procedures for evaluating occupant compartment intrusion to promote uniformity among testing agencies and the development of uniform acceptance criteria. Three levels of evaluation were established: acceptable if intrusion does not exceed 100 mm; marginal if intrusion is more than 100 mm, but less than 150 mm; and unacceptable if intrusion is signifi- cantly greater than 150 mm and at a location where serious injuries are deemed likely to result. Test Article Construction In November 2000, TTI performed a full-scale crash test on the Texas T501 longitudinal barrier (i.e., safety shape) with a soundwall.(24) The Texas T501 test installation re- mained intact at the time this project was initiated. It was modified and used as a structural support for the test instal- lations presented herein. The fascia construction methodol- ogy used for this study was previously developed in a Cal- trans research project.(19) The use of removable, relatively thin fascia panels attached to a support structure was used to minimize cost and construction time and to permit test instal- lations to be re-erected if additional testing on a particular rail face configuration was found necessary at a later date in the research project. The fascia panels were constructed to emu- late the geometric form of a standard concrete safety shape barrier (i.e., SBC05b & ROM01).(25) SELECTION CONSIDERATIONS FOR CRASH TEST CONFIGURATIONS Preliminary guidelines developed through simulation in- cluded three different curves for asperity angles of 45, 90, and 30 degrees. In these preliminary guidelines, thresholds for sur- rogate measures of OCD were used to identify regions of “un- acceptable” and “marginal/unknown” barrier performance for each of the asperity angles. The objective of the crash-testing phase was to reduce the region of “marginal/unknown” impact performance as much as possible. The asperity configurations subjected to crash testing were selected to bisect regions of un- known performance or to confirm points on the failure enve- lope. The results of the crash tests were used to adjust the pre- viously defined passing and failing thresholds for the surrogate OCD measure. Using the new thresholds, the “acceptable” and “unacceptable” regions of the guidelines for the surface treat- ment of safety shape barriers were adjusted. During the crash-testing phase, emphasis was placed on asperities with 45-degree angles of inclination. Of the seven crash tests performed, six were performed with 45-degree asperities and one was performed with 90-degree asperities. The 45-degree asperity is between the other angles investi- gated and was considered to be the most practical in terms of In addition, the following supplemental evaluation factors and terminology, as presented in the July 25, 1997, FHWA memo entitled, “Action: Identifying Acceptable Highway Safety Features,” are also used for visual assessment of test results: • Passenger Compartment Intrusion 1. Windshield Intrusion a. No windshield contact b. Windshield contact, no damage c. Windshield contact, no intrusion d. Device embedded in windshield, no significant intrusion e. Complete intrusion into passenger compartment f. Partial intrusion into passenger compartment 2. Body Panel Intrusion a. Yes b. No • Loss of Vehicle Control 1. Physical loss of control 2. Loss of windshield visibility 3. Perceived threat to other vehicles 4. Debris on pavement • Physical Threat to Workers or Other Vehicles 1. Harmful debris that could injure workers or others in the area 2. Harmful debris that could injure occupants in other vehicles • Vehicle and Device Condition 1. Vehicle Damage a. None b. Minor scrapes, scratches or dents c. Significant cosmetic dents d. Major dents to grill and body panels e. Major structural damage 2. Windshield Damage a. None b. Minor chip or crack c. Broken, no interference with visibility d. Broken and shattered, visibility restricted but remained intact e. Shattered, remained intact but partially dislodged f. Large portion removed g. Completely removed 3. Device Damage a. None b. Superficial c. Substantial, but can be straightened d. Substantial, replacement parts needed for repair e. Cannot be repaired One difficulty in evaluating OCD (e.g., floorpan/toepan damage) in tests is that the criteria are somewhat subjective and can be interpreted in different ways by different crash test agen- cies. In August 1999, at the summer meeting of TRB Commit-

construction. As was discussed in the previous chapter, shal- lower asperity angles allowed for greater asperity depths, whereas steeper angles significantly reduced the acceptable asperity depths. The 90-degree asperity angle yielded “un- acceptable” results for almost all practical asperity depths. The test matrix was designed to be flexible in the sense that the outcome of one test determined the asperity configuration evaluated in a subsequent test. In other words, the test matrix was adjusted as crash tests were performed and results were analyzed in order to maximize the information available for adjusting and finalizing the preliminary relationships. The preliminary guidelines developed for the 45-degree asperities (see Figure 66) were used to select two initial asper- ity configurations for crash testing. The asperity geometry for these tests were: Test 1: d = 25 mm, W = 559 mm, Ws = 25 mm, θ = 45 degrees (pickup truck impact) Test 2: d = 13 mm, W = 178 mm, Ws = 25 mm, θ = 45 degrees (pickup truck impact) where (with reference to Figure 66): d = asperity depth, W = asperity width, and Ws = the spacing between adjacent asperities. 58 The asperity depth for the Test 1 configuration was in- tended to bisect the “unknown/marginal” region on the pre- liminary guidelines (see Figure 66). It was also selected on the basis of having the maximum asperity width included in the preliminary design guideline. This first test was to serve two purposes: (1) establish a data midpoint in an area that had “unknown/marginal” performance and (2) either confirm or deny the ability to use a criterion similar to one approved for use on the single-slope barrier in the FHWA acceptance letter B-110. The internal energy thresholds used for pass/ fail criteria were to be adjusted up or down as appropriate based on the outcome of this test, effectively reducing the “marginal/unknown” region of performance at that asperity width in half. If this asperity configuration passed the test, all configu- rations of lesser depth and greater width would become part of the newly defined “acceptable” region, and the “pass” threshold for the surrogate OCD measure would be increased accordingly. If the asperity configuration failed to meet crash test requirements, any asperity of greater depth and lesser width would also fail. In this case, some of the previously defined “marginal/unknown” region becomes part of the “unacceptable” region, and the “failure” threshold for the surrogate OCD measure would be appropriately decreased. Figure 66. Depth versus width guideline for 90-, 45-, and 30-degree asperity angles (reproduced from Chapter 5).

For the Test 2 configuration, the selected width corre- sponded to the first inflection point on the preliminary fail- ure curve established for the 45-degree asperity angle (see Figure 66). The depth for this test could have been selected to bisect the region of “marginal/unknown” performance. However, this would have involved testing asperities at a depth of approximately 6 mm, which was considered to be some- what meaningless for a realistic aesthetic surface treatment and would not yield any significant information for adjusting the surrogate OCD thresholds. Hence, the depth for this test was selected to verify the failure line established by the pre- liminary guidelines. CRASH TEST 1 (474630-1) The New Jersey concrete safety shape barrier evaluated in the first test had asperities that were 559 mm wide and 25 mm deep. The asperity inclination angle was 45 degrees, and the asperity spacing was 25 mm. A photograph of the barrier before the test is shown in Figure 67. The barrier was impacted by a 2,057-kg pickup truck at an angle of 26.5 degrees and an initial speed of 99.8 km/h. The barrier contained and redirected the pickup truck. The vehi- cle did not penetrate, underride, or override the installation. The vehicle remained upright during and after the collision period. The longitudinal occupant impact velocity and ride- down accelerations were within acceptable limits of the NCHRP Report 350 requirements. Maximum OCD was 139 mm laterally across the cab from kick panel to kick panel. In the immediate area of impact, three of the “ribs” between asperities were sheared off and the face of the barrier was gouged (see Figure 68). The crash test met the evaluation cri- teria presented in NCHRP Report 350. CRASH TEST 2 (474630-2) The New Jersey concrete safety shape barrier evaluated in the second test had asperities that were 178 mm wide and 59 13 mm deep. The asperity inclination angle was 45 degrees, and the asperity spacing was 25 mm. A photograph of the bar- rier before the test is shown in Figure 69. The barrier was impacted by a 2,112-kg pickup truck at an angle of 24.9 degrees and an initial speed of 99.3 km/h. The barrier contained and redirected the pickup truck. The vehi- cle did not penetrate, underride, or override the installation. The vehicle remained upright during and after the collision period. The longitudinal occupant impact velocity and ridedown accelerations were within acceptable limits of the NCHRP Report 350 requirements. Maximum OCD was 216 mm in the left firewall area, and the floor pan was sepa- rated at the seam between the firewall and the toe pan from the left side across the transmission tunnel. Some of the ribs between asperities were partially sheared off from the surface of the concrete barrier, while others re- mained attached and received scrapes and gouges (see Fig- ure 70). The crash test did not meet the evaluation criteria presented in NCHRP Report 350 due to excessive OCD. The FHWA guidelines define failure to be a value significantly greater than 150 mm. Figure 68. Barrier damage for Crash Test 1. Figure 69. Setup for Crash Test 2.Figure 67. Setup for Crash Test 1.

Because Test 1 resulted in OCD within the limits defined in NCHRP Report 350, a pass point was established on the preliminary guidelines. Consequently, a passing line was established at asperity depth (d) of 25 mm and asperity widths (W) of 559 mm and higher. Test 2, on the other hand, failed due to excessive OCD, as expected. The failure line was verified for an asperity depth (d) of 13 mm and higher with a width (W) of 178 mm or less. For the next two tests, the following two asperity configu- rations were selected: Test 3: d = 38 mm, W = 559 mm, Ws = 25 mm, θ = 45 degrees (pickup truck impact) Test 4: d = 13 mm, W = 279 mm, Ws = 25 mm, θ = 45 degrees (pickup truck impact) The asperity configuration for Test 3 incorporated the same asperity width (W) as Test 1. Given the successful impact performance of Test 1 with an asperity depth (d ) of 25 mm, the region of unknown performance was once again bisected using an asperity depth of 38 mm (see Figure 66). If Test 3 were to be successful, the passing line would move up to an asperity depth of 38 mm for asperity widths of 559 mm or higher. If Test 3 were to fail, the failure line would move down to asperity depth of 38 mm at asperity widths of 559 mm or less. The passing line in this failure scenario would remain at an asperity depth of 25 mm for asperity widths of 559 mm or higher, as established by Test 1. Examining the asperity configuration selected for Test 4, it can be seen that the depth of the asperities was the same as Test 2 (i.e., 13 mm) while the asperity width was increased to 279 mm. The asperity depth for Test 4 could have been selected such that it bisected the remaining “marginal/ unknown” performance area (i.e., d = 7 mm). However, the usefulness of establishing a pass/fail point at a depth of 7 mm was debatable from the standpoint of realistic aesthetic sur- face treatment. Hence, the asperity width was increased slightly in order to provide a greater reduction of the “mar- 60 ginal/unknown” performance region. Summaries of Test 3 and Test 4 are presented below. CRASH TEST 3 (474630-3) The New Jersey concrete safety shape barrier evaluated in the third test had asperities that were 559 mm wide and 38 mm deep. The asperity inclination angle was 45 degrees, and the asperity spacing was 25 mm. A photograph of the barrier before the test is shown in Figure 71. The barrier was impacted by a 2,112-kg pickup truck at an angle of 25.1 degrees and a speed of 96.1 km/h. The barrier contained and redirected the pickup truck. The vehicle did not penetrate, underride, or override the installation. The vehi- cle remained upright during and after the collision period. The longitudinal occupant impact velocity and ridedown accelerations were within acceptable limits of NCHRP Report 350. Maximum OCD was 91 mm in the left firewall area. The second through fourth “ribs” between asperities downstream of the impact point were mostly sheared off, and the first and fifth “ribs” after impact were gouged (see Figure 72). The crash test met the evaluation criteria presented in NCHRP Report 350. CRASH TEST 4 (474630-4) The New Jersey concrete safety shape barrier evaluated in the fourth test had asperities that were 279 mm wide and 13 mm deep. The asperity inclination angle was 45 degrees, and the asperity spacing was 25 mm. A photograph of the barrier before the test is shown in Figure 73. The barrier was impacted by a 2,088-kg pickup truck at an angle of 24.6 degrees and a speed of 102.3 km/h. The barrier contained and redirected the pickup truck. The vehicle did not penetrate, underride, or override the installation. The ve- hicle remained upright during and after the collision period. The longitudinal occupant impact velocity and ridedown Figure 70. Barrier damage for Crash Test 2. Figure 71. Setup for Crash Test 3.

accelerations were within acceptable limits of NCHRP Report 350. Maximum OCD was 120 mm in the left firewall area. The first through ninth “ribs” between asperities down- stream of the impact point were mostly sheared off, as was part of the tenth (see Figure 74). The crash test met the eval- uation criteria presented in NCHRP Report 350. Given the success of Test 3 and Test 4, the passing line on the preliminary guidelines for the 45-degree asperity angle was further adjusted upward to coincide with the asperity con- figurations that were evaluated. It was observed in Test 1 through Test 4 that several of the 25-mm-wide “ribs” between the concrete asperities were mostly sheared off in the immediate vicinity of the impact. What was not known was the force at which the concrete sheared and how close this force was to the maximum force that would be generated had the asperities been perfectly rigid. Some damage is expected to occur for any concrete protru- sion subjected to an impact event of this severity. However, a question arose regarding the influence of the asperity spacing on the degree of concrete damage and level of snagging force that may be generated. 61 If the narrow “ribs” created by the 25-mm asperity spacing sheared off at a much lower force than would have been gen- erated by a wider section of concrete that would be associated with a wider asperity spacing, then the severity of snagging would decrease. Consequently, the OCD would be reduced. Conversely, if the “ribs” created by the 25-mm asperity spacing sheared off at a force close to the maximum possible force that can be generated by rigid asperities, then little change in snagging severity or OCD would be expected as the asper- ity spacing increases. Recall that because of a lack of a robust concrete material model with damage capabilities, the barri- ers and their asperities were modeled as rigid materials in the simulations. Therefore, it was important to further investi- gate the effect of asperity spacing failure on the outcome of the results to help confirm the validity of using the crash test data to adjust the guidelines for aesthetic surface treatment of safety shape barriers. To help investigate the influence of asperity spacing on test outcome (primarily OCD), it was decided to conduct Test 5 using an asperity configuration with a wider asperity spacing. It was theorized that if the spacing of the asperities were increased, concrete failure would occur only at the outer edges of the asperities and the region between asperities would not be sheared off. This would enable an evaluation of the effect of concrete failure and would also help verify the preliminary guidelines developed through simulations with rigid barriers. The asperity configuration used for the fifth test was: Test 5: d = 38 mm, W = 559 mm, Ws = 203 mm, θ = 90 degrees (pickup truck impact) The asperity spacing (Ws) was increased from 25 mm (which was used in previous tests) to 203 mm. In order to maximize the information obtained from the crash test, the angle of as- perity inclination selected for Test 5 was 90 degrees. The depth of the asperities was selected such that it bisected the “marginal/unknown” performance region at the asperity width (W) of 559 mm (see Figure 66) for the 90-degree curve. This Figure 72. Barrier damage for Crash Test 3. Figure 73. Setup for Crash Test 4. Figure 74. Barrier damage for Crash Test 4.

asperity width is the same as that used in Test 1 and Test 3. A summary of Test 5 follows. CRASH TEST 5 (474630-5) The New Jersey concrete safety shape barrier evaluated in the fifth test had asperities that were 559 mm wide and 38 mm deep. The asperity inclination angle was 90 degrees, and the asperity spacing was 203 mm. A photograph of the barrier before the test is shown in Figure 75. The barrier was impacted by a 2105-kg pickup truck at an angle of 24.5 degrees and a speed of 97.8 km/h. The barrier contained and redirected the pickup truck. The vehicle did not penetrate, underride, or override the installation. The vehi- cle remained upright during and after the collision period. The longitudinal occupant impact velocity and ridedown accelera- tions were within acceptable limits of NCHRP Report 350. Maximum OCD was 77 mm in the left firewall area. The first through fifth “ribs” between asperities downstream of the im- pact point showed some scraping close to the edges but were intact after the test (see Figure 76). The crash test met the eval- uation criteria presented in NCHRP Report 350. The asperity configuration in Test 5 was similar to that in Test 3, except that the asperity angle was changed from 45 de- grees to 90 degrees and the asperity spacing was increased from 25 mm to 203 mm. The OCD values from both tests were very close (74 mm in Test 3 versus 77 mm in Test 5). Other occupant risk values were also similar between the two tests. Simulation results, which were based on rigid asperities with a 25-mm asperity spacing, indicated that the internal energy of the floorboard was 8.4 kJ and 8 kJ for the asperity configurations evaluated in Test 3 and Test 5, respectively. Comparison of the results from the two tests indicates that although shearing off of the concrete between asperities may reduce the severity of the impact, the overall effect on test out- come is not very significant. Although the pickup truck is generally understood to be more critical than the small car in regard to evaluating sta- 62 bility and OCD, the research team decided to verify applica- bility of the guidelines for small passenger cars. The most severe asperity configuration evaluated in the first five tests was selected to evaluate small-car response. Recall that the asperity configuration evaluated in Test 2 generated unac- ceptable OCD in the pickup. This same configuration was used in Test 6 with the 820C vehicle. Values for the pertinent asperity variables are given below. Test 6: d = 13 mm, W = 178 mm, Ws = 25 mm, θ = 45 degrees (small-car impact) CRASH TEST 6 (474630-6) The New Jersey concrete safety shape barrier evaluated in the sixth test had asperities that were 178 mm wide and 13 mm deep. The asperity inclination angle was 45 degrees, and the asperity spacing was 25 mm. A photograph of the barrier before the test is shown in Figure 77. The barrier was impacted by an 854-kg Geo Metro at an angle of 19.4 degrees and a speed of 98.8 km/h. The barrier Figure 75. Setup for Crash Test 5. Figure 76. Barrier damage for Crash Test 5. Figure 77. Setup for Crash Test 6.

contained and redirected the small passenger car. The vehi- cle did not penetrate, underride, or override the installation. The vehicle remained upright during and after the collision period. The longitudinal occupant impact velocity and ride- down accelerations were within acceptable limits of NCHRP Report 350. There was no OCD, and the vehicle showed good stability. The third through tenth “ribs” between asperities downstream from the point of impact showed some scraping and gouging but were intact after the test (see Figure 78). The crash test met the evaluation criteria presented in NCHRP Report 350. There were no concerns related to stability or OCD with the 820C small car for an asperity configuration that was unacceptable for the pickup truck. Therefore, this test veri- fied that the pickup truck was a more critical vehicle than the small car in regard to establishing guidelines for aesthetic surface treatments for safety shape barriers. Simulation Study for Wider Asperity Spacing To investigate the effect of asperity spacing on severity of snagging, the asperity spacing (Ws) was increased in Test 5 63 from 25 mm to 203 mm. While this prevented the concrete between asperities from shearing off in the test, the effect of asperity spacing on the preliminary guidelines established using finite element simulations with rigid barriers was not completely known. To further investigate the effect of this variable on snagging severity and OCD, additional simula- tion runs were conducted to establish the relationship between asperity depth and asperity width for an asperity spacing (Ws) of 203 mm and an asperity angle of 45 degrees. The simu- lated configurations and their corresponding results for the surrogate OCD measure are presented in Table 7. Using the previously established thresholds for the surrogate OCD, a failure line similar to the previous preliminary guidelines was established. Figure 79 shows this failure line (for Ws = 203 mm) with the previously established failure line (for Ws = 25 mm) for the 45-degree asperities. During the course of this simulation study on asperity spacing, it was discovered that identical finite element mod- els (both barrier and truck) produced different results for the truck floorboard internal energy when different binary files of LS-DYNA were used. Consequently all new simulations were performed using the exact same binary files (LS-DYNA Version 970 Release 3858) that were used in the initial simulation effort on which the preliminary guidelines were established. The reason for this variance could not be identi- fied. However, using the same binaries that were originally used to establish the surrogate OCD thresholds eliminates variance when comparing the simulation results associated with the two different asperity spacings. It can be seen from Figure 79 that increasing the asperity spacing results in an offset (i.e., upward shift) of the failure line. That is, for a given asperity width, the acceptable asper- ity depth increases as the asperity spacing increases. Note that as the asperity width (W) decreases to a value of 200 mm or less, a significant increase in the asperity depth (d) can be achieved. This is because even though d is large, the larger asperity spacing (Ws) at an asperity width of 200 mm reduces the potential for vehicle parts to intrude into the asperity. Thus, the opportunity for vehicle snagging and cumulative vehicle Figure 78. Barrier damage for Crash Test 6. TABLE 7 Parametric study results for a 45-degree angle of asperity with 203-mm asperity spacing Asperity Width (W) [mm] Truck Floorboard Internal Energy [J] Asperity Depth (d) [mm]Run Vehicle Pass/Fail 1 2 3 4 5 6 7 8 9 Truck Truck Truck Truck Truck Truck Truck Truck Truck 559 559 559 280 280 180 180 180 180 51 76 0 51 0 1,108 10,300 10,620 1,108 9,600 1,108 3,730 3,250 3,050 19 0 38 63.5 Pass Fail Marginal Pass Marginal Marginal Marginal Pass Pass Passing Limit = 2,200 J Failure Limit = 10,700 J

damage is reduced. This effect is illustrated by the vertical fail- ure line in Figure 79 and is similar to the one observed for 90-degree asperities where greater asperity depths can be achieved for asperity widths of 30 mm and less (see Figure 66). CRASH TEST 7 (474630-7) Even though only six tests were budgeted for the project, the method of construction used to fabricate the barriers resulted in a cost savings. With the approval of the project panel, an additional crash test was conducted. This test was used to help verify the failure threshold of asperities with larger asperity spacing. The asperity configuration evaluated in Test 7 is given below. Test 7: d = 51 mm, W = 559 mm, Ws = 203 mm, θ = 45 degrees (pickup truck impact) The New Jersey concrete safety shape barrier evaluated in the seventh test had asperities that were 559 mm wide and 51 mm deep. The asperity inclination angle was 45 degrees, and the asperity spacing was 203 mm. A photograph of the barrier before the test is shown in Figure 80. The barrier was impacted by a 2,099-kg pickup truck at an angle of 25 degrees and a speed of 100.3 km/h. The barrier contained and redirected the pickup truck. The vehicle did not penetrate, underride, or override the installation. The 64 vehicle remained upright during and after the collision period. The longitudinal occupant impact velocity and ridedown accelerations were within acceptable limits of NCHRP Re- port 350. Maximum OCD was 260 mm in the left firewall area. The first and second asperity spacings after impact point showed some scraping near edges but were intact after the test. The third through fifth asperity spacings were gouged but intact after the test (see Figure 81). The crash test did not meet the evaluation criteria presented in NCHRP Report 350 due to excessive OCD. Figure 79. Simulation results with asperity spacing of 203 mm for a 45-degree asperity angle. Figure 80. Setup for Crash Test 7.

As can be seen from Figure 79, the asperity configuration tested in Test 7 was at the failure line established through simulation. The fact that the crash test failed due to excessive 65 OCD confirms that the originally developed energy thresholds are valid for wider asperity spacings (Ws). In conclusion, it was noted that snagging severity may be reduced below levels expected for rigid asperities when an asperity spacing of 25 mm is used. This is because the narrow concrete regions between asperities tend to shear off during impact. As the asperity spacing increases, the width of the concrete region between asperities increases. When this con- crete region between asperities becomes sufficiently wide, the concrete is not completely sheared off. However, even though these concrete regions remain intact, the increased asperity spacing offsets (and in fact reduces) any increase in the over- all snagging severity. In fact, the severity associated with the larger asperity spacing is actually reduced, even though the concrete spalling is significantly reduced. As a last step in formulating the final design guidelines, all of the available crash test data were evaluated and used to make adjustments to the preliminary guidelines developed through simulation. The details of these adjustments are presented in the next chapter along with the final design guidelines. Figure 81. Barrier damage for Crash Test 7.

Next: Chapter 7 - Final Design Guidelines »
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TRB’s National Cooperative Highway Research Program (NCHRP) Report 554: Aesthetic Concrete Barrier Design provides guidance for the aesthetic treatment of concrete safety shape barriers.

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