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54 CHAPTER 11 Evaluation of Missing or Broken Posts This section aims to quantitatively assess the effects of miss- 11.2 Validation of Finite ing posts in an otherwise undamaged section of strong-post Element Model w-beam guardrail. The ultimate goal was to develop recom- mendations to be used by maintenance personnel for the Ideally, the validation of strong-post w-beam systems with repair priority of missing posts. Posts can be missing from missing posts could be determined from crash tests, but there a guardrail for a variety of reasons. The posts in steel guardrail were no crash tests to the research team's knowledge with miss- may be missing, severely twisted, or completely flattened from ing posts in unmodified strong-post w-beam guardrail. As an a prior crash. The posts from a wooden post guardrail might alternative, the finite element model was validated against a be missing due to rot, insect damage, or shattering due to a crash test of a specialized variation of guardrail called a long- crash. Note that for this study, the research team also catego- span system (Polivka et al., 1999a; Polivka et al., 1999b). rizes posts as missing if they are present but so weakened due Long-span systems have posts that are missing by design. to damage or deterioration that they present little to no effec- They are used wherever posts cannot be driven into the ground, tive support of the rail. most commonly due to the presence of medium to large cul- verts under the roadway. Long-span systems are typically modified in order to compensate for the loss of one or more 11.1 Approach posts. Typically, the rails are nested (doubled up) over the A series of finite element simulations were run to deter- unsupported portion of the guardrail and the adjacent sec- mine the number of posts which could be removed from the tions of the rail that would be involved in the impact. Other strong-post w-beam guardrail while still maintaining accept- long-span systems may also incorporate changes to the post able crash performance. Simulations were conducted using spacing, the number of blockouts, or the substitution of the LS-DYNA software (LSTC, 2003) for strong-post w-beam wooden posts near the unsupported area to reduce the chance guardrail with 1, 2, and 3 missing posts. For each missing of snagging. post simulation, two different impact points were used to The crash test selected for validation was the crash test of a examine the effect that the impact point had on the crash long-span guardrail system missing three posts, performed by performance. These impact points were (1) at the post begin- the University of Nebraska-Lincoln (UNL) as part of a study ning at the unsupported span and (2) the mid-point of the of long-span systems (Polivka et al., 1999a). In this report, this unsupported span. test will be referred to as OLS2. This guardrail system included The missing post damage mode was a straightforward a 25-foot (7.62 meters) unsupported span with nested guard- damage condition to simulate. To reproduce the damage, rail used as compensation for the reduced strength in the un- the entire post, along with all the supporting elements, was supported region. A TL 3-11 impact of a Chevrolet C-2500 deleted from the model. The supporting elements consisted pickup truck into the long-span section test resulted in the of the soil, post bolt, post nut, and blockout. No compen- pickup truck overturning as it exited the guardrail. satory options such as nesting were added to the model to im- This crash test differed from the missing/broken model in prove the strength of the resulting section of unsupported several respects: (1) OLS2 used wood rather than steel posts, rail. An example of a completed full-scale model with a miss- (2) OLS2 used nested guardrail rather than the standard single ing post is shown in Figure 46. guardrail simulated in this study, and (3) the test used a 25-foot