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13 Table 10. 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 3.1.3 Phase III: Recommendations for each damage mode. The following sections describe the fol- Improved Repair Guidelines lowing techniques: In the third and final phase of the project, the results of the Pendulum Testing Plan impact tests and simulations were used to develop a recom- Full Systems Crash Test Plan mended set of repair guidelines in a form suitable for mainte- Finite Element Modeling Plan nance personnel in the field. The end customer for these repair Validation of Finite Elements Models guidelines are highway maintenance personnel. In addition to being based upon a strong analytical foundation, the guide- lines must be easily understood and implemented. The repair 3.2 Pendulum Testing Plan threshold guidelines were presented in a graphical format that Pendulum tests were used in this research program for two clarified how damage to w-beam barriers should be measured purposes: (1) as tests of structural integrity and (2) to provide and repair priority assessed. test data for validation of computational models. Pendulum A workshop on the new guidelines was presented to an Iowa tests are a better method than finite element modeling to DOT maintenance group to obtain the feedback from actual check for structural integrity under impact conditions which maintenance practitioners in Mason City, IA, in May 2009. might result in tearing or fracture. Finite element modeling Comments from the workshop participants were invaluable using the LS-DYNA code is a less than ideal method of model- and were used to fine-tune the guidelines for improved read- ing this type of damage. Examples would include vertical tears, ability and practicality. horizontal tears, holes, and splice damage. The pendulum tests were conducted at the Federal Outdoor Impact Laboratory 3.1.4 Damage Evaluation Techniques (FOIL) in conjunction with the FHWA. The remainder of this chapter describes the methods used to evaluate the crash performance of longitudinal barrier with 3.2.1 Experimental Design Development and Test Methodology Pendulum Apparatus and Impactor Face. The pendulum Table 11. Preliminary proposed repair tests used the pendulum device currently located at the FHWA priority scheme. FOIL in McLean, VA. The FOIL pendulum consists of a sup- Priority Description port structure, a 2000-kg (4500 lb) pendulum mass (center Level image in Figure 3), and two rigid posts (left image in Figure 3) High A second impact results in unacceptable located on either side of the suspended pendulum mass. A safety performance including barrier penetration and/or vehicle rollover. rounded triangular pendulum impactor face was fabricated for Medium A second impact results in degraded but the tests (right image in Figure 3). The radius of chamfer at the not unacceptable safety performance. impactor face center was 152 mm (6 inches), which was based Low A second impact results in no discernible difference in performance from an on measurements of a 2006 Chevrolet 1500 pickup truck. The undamaged barrier. impactor face is 420 mm (16.5 inches) tall and is capable of

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14 Figure 3. Existing rigid posts (left), FOIL pendulum mass (center), and new impactor face (right). engaging the full w-beam cross section. The combined mass of oriented such that the impact was mid-span between the two pendulum and the impactor face was 2061.5 kg (4,545 lbs) to posts. Figure 4 is a schematic of the overall test setup. The represent the mass of the NCHRP Report 350 2000-kg pickup overall rail length is approximately 5 meters (198 inches) and truck (2000P) test vehicle. Note that the pendulum mass is the posts were W150 13.5 steel posts, 1830 mm (6 feet) in slightly higher than the 2045 kg recommended mass limit spec- total length. ified by NCHRP Report 350 for the 2000P test vehicle. Developing an appropriate method to anchor each end of the test section to the rigid posts proved to be the most chal- W-Beam Test Section, Anchorage, and Embedment. A lenging portion of the test setup. The goal was to replicate a two-post section of modified G4(1S) strong-post w-beam two post section as if it was within a full length barrier section, barrier with wood blockouts was selected for testing. The bar- which requires each end of the test section some freedom to rier test section length was constrained by the available span both translate and rotate. Due to the close proximity of the (approximately 5.5 meters) between the existing rigid posts rigid posts on either side of the pendulum, the primary focus on either side of the FOIL pendulum. Using standard 1905 mm was on designing the end fixture to allow rotation of each end (6.25 feet) post spacing and 3810 mm (12.5 feet) rail lengths, of the w-beam test section. Also, an effort was made to use as this allowed for one post to be located at a rail splice and the much standard guardrail hardware as possible in the end fix- other post a non-splice location. As this section represents the ture design. The original end fixture design selected consisted smallest repeating unit for the strong-post w-beam barrier, of 3 standard cable anchor brackets and a 910 mm (3 feet) ver- this configuration was thought to be most representative of a sion of the standard 1830 mm (6 feet) swaged cable typically typical full-length installation. Note that this two post section used to anchor w-beam terminals (left image of Figure 5). This is roughly one tenth the length of a barrier in a full-scale crash configuration was originally selected to ensure w-beam rail test, which typically has 29 posts. The w-beam section was rupture would occur before failure of the anchorage. Figure 4. Overall pendulum test setup for an undamaged section.

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15 Cable Anchor Bracket Soil Box Figure 5. Three cable (left) and two cable (center) w-beam end fixture and soil box (right). Later, an alternative 2-cable end fixture design was developed impact. Four high speed cameras were used in all tests to cap- (center image in Figure 5). A comparison of two undamaged ture the behavior of the w-beam section during the impact. section pendulum tests showed no discernable difference in Each test had a minimum of two common camera views: (1) a deflection. The 2-cable end fixture proved to be robust and top view of the middle of the w-beam section and (2) a perpen- was used in the remainder of the tests to simplify the test setup dicular rear view of the entire w-beam section. The other two and reduce costs. As experience was gained in conducting these high speed camera views varied between tests depending on the tests, several minor modifications were made to the 2-cable location of the minor damage. In addition to the high speed end fixture, primarily to prevent tearing and bending failures cameras, one real time camera was used to capture a perspec- within the fixture. Larger 82.6 mm (3.25 inches) outside diam- tive view of the test in real time. eter washers were used inside the rigid posts to prevent pullout of the cables from the rigid posts. The length of swaged cables Impact Conditions and Relevance to Full-Scale Crash was increased by 102 mm (4 inches) so the cable would bend Testing. As the FOIL pendulum is not capable of reproduc- instead of the swage. To prevent tearing in the fixture, the typ- ing an oblique impact characteristic of NCHRP Report 350 ical washers used in conjunction with the anchor brackets were longitudinal barrier test procedures, the tests were designed to replaced by an anchor plate. Results from pendulum tests con- mimic the lateral forces experienced in a NCHRP Report 350 ducted using both the 2-cable and 3-cable end fixture schemes redirectional test (Figure 6). will be presented later in this report. Pendulum tests were conducted at two impact speeds: As the anchor points on the existing rigid posts were higher 32.2 km/hr (20 mph) and 28.2 km/hr (17.5 mph). A 32.2 km/hr than the standard w-beam rail height, a soil box was used to (20 mph) impact speed was originally selected to approxi- raise the ground level around the posts by 7 inches (178 mm) mate the lateral forces that would result from a 2000 kg test as shown in the right image in Figure 5. The soil box was con- vehicle impacting at 100 km/hr (62 mph) and 20 degrees. As- structed of four 38 mm 235 mm 2.44 m (2 in. 10 in. suming that all the impact energy is absorbed in a two post sec- 8 in. long) pine boards and supported on each side by steel tion of a full-scale test barrier, these conditions represent a lat- rebar to provide the soil restraining force such that proper com- eral impact speed approximately 75 percent that of an NCHRP paction could be attained. As specified by NCHRP Report 350, the soil used in the test conformed to AASHTO M-147-65. A mechanical tamper was used to compact the soil surrounding each W150 13.5 steel post in 6-inch lifts. A nuclear density gauge (Troxler Model 3440) was used to determine the com- paction and soil properties of each soil lift for each post. For each lift, the preferred compaction level was 95 percent. Instrumentation. Instrumentation for all tests included two accelerometers located at the rear of the pendulum mass. Both accelerometers were in-line with the pendulum center of gravity and were aligned in the pendulum direction of travel. Tri-axial accelerometers were placed on each rigid post to Figure 6. Analogous NCHRP Report 350 and pendulum quantify the motion of the rigid posts during the pendulum impact scenarios.