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11 CHAPTER 3 Research Approach 3.1 Research Plan ther be based upon straightforward metrics which are practi- cal for maintenance crews to use for quantifying minor barrier The goal of this research program is to develop guide- damage. The candidate set of guidelines and quantitative crite- lines to assist highway personnel in identifying levels of minor ria to gauge minor barrier damage were based on current met- barrier damage and deterioration that require repairs to restore rics employed by transportation agencies and supplemented operational performance. The guidelines are to be based upon as needed to address specific damage modes. The final set of objective and quantitative threshold values for which barrier candidate repair guidelines to be evaluated was presented to repair is recommended. This chapter describes the research and approved by the project Panel prior to commencement of approach used to develop these quantitative underpinnings. Phase II: Evaluation of Candidate Repair Guidelines. The research team's approach was to evaluate the more com- Table 8 presents the candidate list of damage modes for non- mon damage types with a combination of controlled experi- proprietary w-beam barriers, including strong and weak post ments and computational modeling to develop the repair w-beam barriers which were to be evaluated in this program. guidelines. The experiments were used both to directly eval- Table 8 also presents the objective repair criteria which were uate barrier performance and to validate the computational sought for each damage mode. The objective of Phase II was models. to analytically determine these repair criteria. The research program was conducted in the following three The Project Panel also requested that the final report spec- phases: ify repair criteria for generic end terminals. The intent was to specify guidance which was applicable to all end terminal Phase I: Candidate Repair Guidelines types (except as noted). Manufacturers of proprietary end ter- Phase II: Evaluation of Candidate Repair Guidelines minal systems may recommend additional repair thresholds Phase III: Recommendations for Improved Repair Guide- specific to an individual terminal. Note that this guidance was lines. based solely on engineering judgment; no finite element simulations or pendulum tests evaluating these end terminal 3.1.1 Phase I: Candidate Repair Guidelines damage modes were conducted. These guidelines, shown in Table 9, were based primarily on an End Terminal Routine The first phase of the research program was to develop a Maintenance Checklist developed for use by the Ohio DOT. candidate set of repair guidelines needed to address commonly observed modes of minor damage. Selection of the damage 3.1.2 Phase II: Evaluation of Candidate modes for which guidelines were needed was conducted based Repair Guidelines upon a survey of U.S. and Canadian transportation agencies presented in Chapter 2. Additional damage modes were added The candidate guidelines were evaluated through a combi- as needed based upon analysis of a photographic catalog of nation of controlled experiments and computational modeling. minor barrier damage categories developed through field Both pendulum tests and full scale barrier crash tests were inspection of damaged barrier sites, and consultation with conducted on longitudinal barrier into which a flaw, e.g., a the project panel. vertical tear, had been purposely introduced. The tests were The next step was to propose objective and quantifiable supplemented by a suite of computational simulations to fur- repair criteria for each damage mode. The guidelines must fur- ther evaluate the crash performance of longitudinal barrier

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12 Table 8. Repair thresholds to be determined for w-beam barriers. Component Damage Type Damage Description Quantitative Repair Criterion (to be determined) Rail Deflection Rail Deflection Deflection from as-built Element Rail Flattening (thickness) Percent Flattened Rail Flattening (height) Percent Flattened Tearing/Breaks / Non-Manufacturer hole in Diameter of hole Punctures Rail Non-Manufacturer holes Number of holes in in Rail single section Vertical Tear Length of tear Horizontal Tearing Length of tear Deterioration Any structural corrosion Amount of Section Loss Posts Deflection Post/Rail Deflection Deflection from as-built Steel Post torsion Number of damaged posts Tearing/Breaks Broken Posts Number of broken posts Deterioration Rotten Wood Posts (any Number of rotted posts visible rotting) Any Structural Corrosion Amount of section loss (hole or section loss) Blockouts Deflection Twisted/Misaligned Number of affected Blockouts blockouts Missing Missing Blockouts Number of missing blockouts Deterioration Rotten Wood Blockouts Number of rotted (any visible rotting) blockouts Connections Integrity Loss Splice Damage Amount of rail material left between splice and bolt hole Missing, Loose, or Number of affected Damaged Splice Bolts bolts Post Separated from Rail Number of posts (any) separated from rail with minor damage. The physical experiments were used cluding roll, pitch and yaw, wheel snagging, and the presence/ both to directly evaluate barrier performance and to validate absence of vaulting. In these cases, the baseline case (for the the computational models. qualitative comparison) was the respective vehicle impacting The results of each damaged barrier impact experiment an undamaged barrier. The results of each evaluation were or simulation were evaluated using criteria based heavily on used to set the threshold for repair. NCHRP Report 350. Pendulum tests were evaluated based on Repair priorities were assigned to the barrier damage evalu- the ability of the barrier to contain the pendulum, i.e., no pen- ated to provide maintenance personnel with guidance regard- dulum penetration, underride, or override. For the full-scale ing the relative importance of barrier damage types. This was crash tests and computational simulations of full-scale crash accomplished by qualitatively ranking each damage type based tests, the criteria shown in Table 10 were used to evaluate crash on the scheme presented in Table 11. The priority rankings performance. The full-scale crash tests and simulations were were based on the results of the finite element simulations and also assessed for vehicle instability resulting from impact in- pendulum tests. Table 9. Preliminary proposed repair thresholds for generic end terminals. Component Damage Description Rail Element Rail Element not Aligned Properly in Impactor Head* Posts Post Number 1 is Broken or Missing Blockouts Any Twisted / Misaligned Blockouts Connections > 1 in. of Slack in Anchor Cable or Missing Anchor Cable Bearing Plate Rotated or Missing Any Failed Lag Screws Securing Impactor Head * * Applies only to Energy Absorbing End Terminals