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79 Table 29. Methods of evaluating each damage mode. Damage Mode Pendulum Tests Full-Scale Finite Element Crash Tests Modeling Rail / Post Deflection x x x Vertical Tear x Horizontal Tear x Twisted Blockout x Missing Blockout x Splice Damage x Hole in Rail x Missing Posts x Post-Rail Separation x Rail Flattening x Generic End Terminal Damage the motorist. The objective was to evaluate the crash perfor- presence/absence of vaulting. The results of each evaluation mance of barriers with each of these minor damage modes, and were used to set the threshold for repair. to develop quantitative criteria for when repair of this minor barrier damage is warranted. To develop a strong technical 15.3 Recommended Criteria foundation for the guidelines, the research team's approach for Restoration of was to evaluate the more common damage types with a com- Longitudinal Barriers bination of controlled experiments and computational model- ing and adjust the preliminary proposed guidelines as neces- This section presents guidelines for repairs to damaged sary. The generic end terminal repair guidelines were based longitudinal barriers in order to restore them to operational upon a procedure developed by the Ohio Department of Trans- performance. Included are guidelines for repair of minor dam- portation. Table 29 presents the target damage modes and the age to w-beam, generic end-terminals, and guidance for repair method(s) used to evaluate each of these damage modes. of more severe barrier damage. The results of each damaged barrier impact experiment The following guidelines are based on the assumption that or simulation were evaluated using criteria based heavily on a damaged barrier will be subjected to a second collision with NCHRP Report 350. Pendulum tests were evaluated based on impact conditions similar to NCHRP Report 350 test level 3 the ability of the barrier to contain the pendulum, i.e., no (TL-3) conditions. The crash performance of barriers with pendulum penetration, underride, or override. For the full- different types of damage was assessed under the same impact scale crash tests and computational simulations of full scale conditions. Depending on individual conditions at a specific crash tests, the criteria shown in Table 30 were used to evalu- site, however, the probability of a second impact to a previ- ate crash performance. The full scale crash tests and simula- ously damaged longitudinal barrier will vary considerably. tions were also assessed for vehicle instability resulting from The determination of the risk of a second collision is beyond impact including roll, pitch and yaw, wheel snagging, and the the scope of this document but should be another factor that Table 30. Barrier crash performance requirements. Criterion Required Performance Structural 1. Barrier contains and redirects the vehicle Adequacy 2. No vehicle penetration, underride, or override Occupant 3. Vehicle should remain upright during and after the Risk collision; moderate pitch and roll are acceptable 4. Lateral and longitudinal occupant impact velocity < 12 m/s (as computed by the flail space model) 5. Lateral and longitudinal occupant ridedown acceleration < 20 G (as computed by the flail space model) Vehicle 6. Vehicle intrusion into adjacent traffic lanes is limited or Trajectory does not occur 7. Vehicle exit angle should preferably be less than 60 percent of the impact angle

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80 is considered when determining the repair priority of a dam- aged but should function adequately under the majority of aged barrier section. impacts, and (3) Damaged, but should not impair the guard- rail's ability to perform. The intent of this section is to provide improved guidance for 15.3.1 W-Beam Repair Guidelines classification of barriers into categories 1 or 2 based on the sim- The w-beam barrier repair guidelines are summarized in ulation and testing conducted under NCHRP Project 22-23. Table 31. These guidelines are intended to mark the level of bar- Table 33 summarizes the details of categories 1 and 2 from the rier damage that begins to significantly affect the crash perfor- original w-beam guardrail repair guide. mance of the barrier and are intended to be the base thresholds Table 34 summarizes the proposed changes to the criteria to which barrier repair is recommended. The rationale for each for categories 1 and 2 based on the findings of the research of the guidelines has been presented throughout the report. team to date. Barriers with damage less than the threshold values shown The full-scale crash test conducted at MGA Research con- in Table 31 have a crash performance that is indistinguishable sisted of a TL-3 impact of a 2000P test vehicle into a strong-post from new barriers. For damage extent above the threshold, w-beam barrier with approximately 14 inches of rail deflection. Table 31 provides a relative repair priority for each damage The vehicle impacted the barrier, climbed the deflected posts, mode using a three category scale: high, medium, and low. and subsequently vaulted the barrier. Marzougui et al. (2007) While the priority assignments are not intended to dictate an showed that if rail height declines by 2 inches, vehicles can exact time frame in which to repair a damaged barrier, they rollover or vault over the rail. A 2-inch decrease in rail height do provide maintenance personnel with general guidance on corresponds to a 10.5 inch deflection. Based on the results of how differing damage modes are expected to affect the crash the full-scale test and the findings of the Marzougui study, the performance of the barrier relative to one another. A brief de- research team recommends reducing the category 1 deflection scription of each priority level is provided below: from 18 inches to 10 inches. Finite element simulations have shown that a 2000P pickup High Priority: Indicates damage where the crash perfor- truck striking a section missing even a single post will become mance of the barrier has been compromised to such a degree unstable. Hence the guidelines have been revised to recom- that a second impact to the damaged barrier would result mend the repair of a rail with any missing posts. in unacceptable vehicle and/or barrier performance. This would include vehicle penetration of the barrier (via rail 15.3.4 Barrier Locations with More than rupture, vehicle override, or vehicle underride) and vehi- One Damage Mode cle rollover. Medium Priority: Indicates damage where the crash per- Note that the thresholds and corresponding repair prior- formance of the barrier has likely been compromised ities above have been based on the presence of a single dam- to some degree but the damage is less likely to result in age mode. Often, longitudinal barrier damage consists of unacceptable vehicle and/or barrier performance than more than one damage mode. For instance, rail flattening high-priority damage. almost always occurs in tandem with post and rail deflection. Low Priority: Indicates damage where the crash per- A majority of the current analysis has focused on individual formance of the barrier is indistinguishable from the un- damage modes in an effort to more fully understand the ef- damaged condition. fect of a single damage mode on the crash performance of the barrier. The research team, however, does recognize the need 15.3.2 Generic End Terminal Guidance for guidance regarding barriers with multiple damage modes. Until a more thorough analysis of barrier damage combi- The criteria for repair of generic end terminals are sum- nations can be conducted, the research team proposes that marized in Table 32. These guidelines have been based on an barrier repair be based on the highest priority level of the com- Ohio Department of Transportation Energy Absorbing End bined damage modes. For instance, if a barrier has both a Terminal Maintenance Checklist (Focke, 2007). twisted blockout along with rail flattening, the repair priority would be "medium" based on the rail flattening. 15.3.3 Guidance for Substantial Barrier Damage 15.3.5 Limitations National guidance regarding the repair of w-beam barriers This study had several limitations. The approach was to is provided by the Federal Highway Administration (FHWA) evaluate longitudinal barriers with damage under the worst in a 2008 report entitled "W-Beam Guardrail Repair" (FHWA, practical conditions. However, there are a number of other 2008). Based on this document, a damaged barrier is classified conditions, not examined in this study, to which these barriers into one of three categories: (1) Non-Functional, (2) Dam- may be subjected to potentially adverse consequences. The

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81 Table 31. Summary of W-Beam barrier repair threshold guidelines. Damage Mode Repair Threshold Priority for Damage above the Threshold Post and Rail One or more of the following thresholds: High Deflection More than 9 in. of lateral deflection anywhere over a 25-ft length of rail Top of rail height 2 or more in. lower than original top of rail height 6-9 in. lateral deflection anywhere over a 25-ft length Medium of rail Less than 6 in. of lateral deflection over a 25-ft length Low of rail Rail Deflection 6-9 in. of lateral deflection between any two adjacent Medium Only posts Note: For deflection over 9 in., use post/rail deflection guidelines. Less than 6 in. of lateral deflection between any two Low adjacent posts Rail Flattening One or more of the following thresholds: Medium Rail cross-section height more than 17 in. (such as may occur if rail is flattened) Rail cross-section height less than 9 in. (such as a dent to top edge) Rail cross-section height between 9 and 17 in. Low Posts Separated 2 or more posts with blockout attached with post- Medium from Rail rail separation less than 3 in. 1 or more posts with post-rail separation which exceeds 3 in. Note: If the blockout is not firmly attached to the post, use the missing blockout guidelines. Note: If separation over 3 in., use deflected post/rail guidelines. 1 post, with blockout attached, with post-rail Low separation less than 3 in. Missing/Broken 1 or more posts High Posts Missing Cracked across the grain Broken Rotted With metal tears Missing Blockout Any blockouts Medium Missing Cracked across the grain Cracked from top or bottom of blockout through post bolt hole Rotted Twisted Blockouts Any misaligned blockouts, top edge of block 6 in. or Low more from bottom edge Note: Repairs of twisted blockout are relatively quick and inexpensive. Damage at a rail More than 1 splice bolt: High splice Missing Damaged Visibly missing any underlying rail Torn through rail 1 splice bolt: Medium Missing Damaged Visibly missing any underlying rail Torn through rail (continued on next page)

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82 Table 31. (Continued). Damage Mode Repair Threshold Priority for Damage above the Threshold Non-Manufactured More than 2 holes less than 1 in. in height in a High holes 12.5' length of rail Any holes greater than 1 in. in height (such as crash- Any hole which intersects either the top or bottom induced holes, edge of the rail lug-nut damage, or holes rusted- 1-2 holes less than 1 in. in height in a 12.5-ft. length of Medium through the rail) rail Vertical Tear Any length vertical (transverse) tear High Horizontal Tear Horizontal (longitudinal) greater than 12 in. long and Medium greater than 0.5 in. wide Note: for horizontal tears less than 12 in. in length or less than 0.5 in. in height, use the non-manufactured holes guidelines. Table 32. Summary of proposed generic end terminal repair guidance. Damage Repair Threshold Relative Priority Damaged end post Not functional (sheared, rotted, High cracked across the grain) Anchor cable Missing High Loose--more than 1 in. of Medium movement when pushed down by hand Cable Anchor Bracket Loose or not firmly seated in Medium rail Stub height of steel tube or Height which exceeds 4 in. Medium hinged post Lag bolts on impact head Missing or failed lag bolts High (Energy Absorbing Terminals Only) Bearing Plate Loose or Misaligned Medium Missing High Table 33. FHWA W-beam damage classification details (FHWA, 2008). Damage Category Damage Attributes (1) Non-Functional A. Rail element is no longer continuous. B. 3 or more posts are broken off or no longer attached to the rail. C. Deflection of rail element is more than 18 in. D. Rail element is torn. E. Top of rail is less than 24 in. (2) Damaged but A. Rail element is continuous (can be bent or crushed should function significantly). adequately under B. 2 or fewer posts are broken or separated from the rail majority of impacts element. C. Deflection of the rail element is less than 12 in.