Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 60
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- Figure 70. Barrier damage for Crash Test 2. cle remained upright during and after the collision period. The longitudinal occupant impact velocity and ridedown accelerations were within acceptable limits of NCHRP Report Because Test 1 resulted in OCD within the limits defined 350. Maximum OCD was 91 mm in the left firewall area. The in NCHRP Report 350, a pass point was established on the second through fourth "ribs" between asperities downstream preliminary guidelines. Consequently, a passing line was of the impact point were mostly sheared off, and the first and established at asperity depth (d) of 25 mm and asperity fifth "ribs" after impact were gouged (see Figure 72). The widths (W) of 559 mm and higher. Test 2, on the other hand, crash test met the evaluation criteria presented in NCHRP failed due to excessive OCD, as expected. The failure line Report 350. 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- CRASH TEST 4 (474630-4) rations were selected: The New Jersey concrete safety shape barrier evaluated in the fourth test had asperities that were 279 mm wide and Test 3: d = 38 mm, W = 559 mm, Ws = 25 mm, = 45 degrees 13 mm deep. The asperity inclination angle was 45 degrees, (pickup truck impact) and the asperity spacing was 25 mm. A photograph of the Test 4: d = 13 mm, W = 279 mm, Ws = 25 mm, = 45 degrees barrier before the test is shown in Figure 73. (pickup truck impact) 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 The asperity configuration for Test 3 incorporated the same contained and redirected the pickup truck. The vehicle did asperity width (W) as Test 1. Given the successful impact not penetrate, underride, or override the installation. The ve- performance of Test 1 with an asperity depth (d ) of 25 mm, hicle remained upright during and after the collision period. the region of unknown performance was once again bisected The longitudinal occupant impact velocity and ridedown 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- Figure 71. Setup for Crash Test 3.
OCR for page 60
61 Figure 72. Barrier damage for Crash Test 3. Figure 74. Barrier damage for Crash Test 4. accelerations were within acceptable limits of NCHRP If the narrow "ribs" created by the 25-mm asperity spacing Report 350. Maximum OCD was 120 mm in the left firewall sheared off at a much lower force than would have been gen- area. The first through ninth "ribs" between asperities down- erated by a wider section of concrete that would be associated stream of the impact point were mostly sheared off, as was with a wider asperity spacing, then the severity of snagging part of the tenth (see Figure 74). The crash test met the eval- would decrease. Consequently, the OCD would be reduced. uation criteria presented in NCHRP Report 350. Conversely, if the "ribs" created by the 25-mm asperity Given the success of Test 3 and Test 4, the passing line on spacing sheared off at a force close to the maximum possible the preliminary guidelines for the 45-degree asperity angle force that can be generated by rigid asperities, then little change was further adjusted upward to coincide with the asperity con- in snagging severity or OCD would be expected as the asper- figurations that were evaluated. ity spacing increases. Recall that because of a lack of a robust It was observed in Test 1 through Test 4 that several of the concrete material model with damage capabilities, the barri- 25-mm-wide "ribs" between the concrete asperities were ers and their asperities were modeled as rigid materials in the mostly sheared off in the immediate vicinity of the impact. simulations. Therefore, it was important to further investi- What was not known was the force at which the concrete gate the effect of asperity spacing failure on the outcome of sheared and how close this force was to the maximum force the results to help confirm the validity of using the crash test that would be generated had the asperities been perfectly rigid. data to adjust the guidelines for aesthetic surface treatment of Some damage is expected to occur for any concrete protru- safety shape barriers. sion subjected to an impact event of this severity. However, a To help investigate the influence of asperity spacing on test question arose regarding the influence of the asperity spacing outcome (primarily OCD), it was decided to conduct Test 5 on the degree of concrete damage and level of snagging force using an asperity configuration with a wider asperity spacing. that may be generated. 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, = 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 Figure 73. Setup for Crash Test 4. (W ) of 559 mm (see Figure 66) for the 90-degree curve. This