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 35
35 CHAPTER 8 Evaluation of Missing Blockout Damage The objective of this evaluation was to determine the effect bolt pulled through the w-beam rail at the non-splice location. of a missing blockout on barrier crash performance through The post-rail bolt at the non-splice location experienced large pendulum testing (Figure 29). The performance of the barrier bending deformation while the bolt at the splice location frac- section with a missing blockout was compared to the perfor- tured in the threaded region. Figure 30 shows the post dam- mance of a similar barrier section with a blockout in place. The age and the splice failure. No tear developed and none of the pendulum test setup is described in an earlier chapter on the splice bolts failed, but rather the bolt holes deformed enough research approach. to allow the two sections to separate. Figure 31 shows time For this damage mode, the blockout at the splice location sequential snapshots of the Test 03-7 obtained from the was not installed. The post-rail bolt remained connected to overhead high speed camera. simulate a wooden blockout that had split completely and was In the lower speed test (overhead sequence not shown), the no longer present. Two pendulum tests were conducted--one barrier was able to contain the pendulum mass impacting at at 19.0 mph and one at 18.2 mph. In both tests, there was 29.3 km/hr (18.2 mph) (Figure 32). Impact velocity was cal- approximately 178 mm (7 inches) of separation between culated based on the high-speed video footage. The deflection the near flange of the post and the back of the w-beam rail. of the rail was approximately 467 mm (26.7 inches) at 121 ms The splice location was thought to be the critical case as the after the initial impact. splice is the weakest link in the rail element. In Test 01-4, the barrier had a different impact performance. The barrier section contained the pendulum mass impacting at 30.9 km/hr (19.2 mph). Based on an analysis of the overhead 8.1 Results high speed video data, the maximum dynamic deflection of the For the missing blockout damage, a high-speed test and low- rail was 719 mm (28.3 inches) at 146 ms after the initial impact. speed test were performed. In the high-speed test (Test 03-7), The asymmetry caused by the missing blockout resulted in a the barrier was unable to contain the pendulum mass impact- significant twisting of the pendulum (approximately 6 degrees) ing at 30.6 km/hr (19.0 mph). Impact velocity was calculated in the horizontal plane. The vertical tear that developed at the based on the high-speed video footage. The barrier section splice location was 229 mm (9 inches) in length (approximately failed at the splice due to the splice bolts pulling through holes two-thirds of the total w-beam cross section) and along the line in the rail with none of the individual splice bolts fracturing. of the splice bolts. A close-up of the tear is shown in the center This failure was similar to that observed in Test 02-1 with the image in Figure 33. horizontal tear damaged section. Based on an analysis of the overhead high-speed video data, the deflection of the rail was 8.2 Recommendation approximately 678 mm (26.7 inches) at 106 ms after the ini- tial impact, which was just prior to penetration of the w-beam. A pendulum test conducted at 20 mph of a strong-post At 116 ms, the splice was completely separated. w-beam barrier section with a missing blockout at the splice The deformation of the posts was less than in the undam- location resulted in successful containment of the pendulum aged section test, as there was almost no torsion experienced mass (Test 01-4). There was strong evidence, however, that by the post at the splice location. There was no visible crack- this damage mode could result in tearing of the w-beam. Dur- ing of either post. As with most previous tests, the post-rail ing the test, the absence of the blockout allowed the rail to be
OCR for page 35
36 Field Example Pendulum Test Setup Figure 29. Missing blockout damage evaluated in pendulum tests. driven into the steel post resulting in a 9-inch tear in the rail. and into a barrier with a missing post are described later in It is possible that there may have been less of a propensity for this report. In the missing blockout simulations, the vehicle tearing for wood posts. Another pendulum test was conducted response was very similar to the missing post simulations at an impact speed of 17.5 mph to better represent the kinetic in the early phase of the collision. Early in the collision, the energy loading to a single section of barrier during a full-scale vehicle interacts with a rail with no blockout or post support. NCHRP Report 350 test. In this test, the barrier successfully However, once the vehicle has deflected the rail the width of contained the pendulum mass with no evidence of w-beam a blockout, the vehicle begins to interact with the post. The tearing. To be cautious, the research team has proposed a simulation from this point on greatly resembles an ordinary threshold of one or more missing blockouts. This damage has collision into an undamaged rail section. The missing block- been assigned a medium priority based on the potential for out case does however result in elevated vehicle instability, rail tearing that has been observed in the pendulum test. but not to the extent of the missing post case. The research With regards to potential vehicle instability resulting from team has set the repair priority of a missing post accordingly impact, the research team's rationale was that collisions into as "medium" which falls between the undamaged case and the barriers with a missing blockout would fall between a missing high-priority repair of a missing post damage mode. Note that post case and the undamaged case. Finite element simulations this repair priority is also consistent with the rail-post separa- of a 2000P pickup truck collision with the post missing the tion case which allows small amounts of separation (less than blockout were conducted to verify this. The results of finite 3 inches), but rates higher rail-post separation as a medium- element simulations of collisions into an undamaged barrier priority repair (Exhibit 5.0). Figure 30. Test 03-7: splice failure (left) and post damage at splice (center) and non-splice location (right).
OCR for page 35
37 Missing Blockout Damage, Test 03-7 (30.6 km/hr) 0.017 s 0.034 s 0.051 s 0.068 s 0.085 s 0.102 s 0.119 s 0.136 s Figure 31. Sequential overhead photographs for missing blockout damage. Figure 32. Test 07-5: overall damage (left), detail view of damage at splice (center), and post damage at non-splice location (right).
OCR for page 35
38 Figure 33. Test 01-4: overall damage (left), rail tear at splice (center), and post damage at splice location (right). Exhibit 5.0. Recommendation for missing blockout damage repair. Damage Mode Repair Threshold Relative Priority Missing Any blockouts that have the following issues: Medium Blockout Missing, Cracked across the grain, Cracked from top or bottom of blockout through post-bolt hole, and Rotted.