Guidelines for Evaluating Crashworthiness of Sign Supports and Breakaway Luminaire Poles (2024)

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PRE-PUBLICATION DRAFT—Unedited Text and Graphics Summary Guidelines for Evaluating Crashworthiness of Sign Supports and Breakaway Luminaire Poles The objective of this project was to evaluate selected systems and propose modifications to MASH to provide additional guidelines on selecting a critical test matrix for testing families of systems. Given the time and budget constraints, the two most common categories were selected for evaluation: (1) a breakaway steel luminaire pole with aluminum TB1-17 frangible transformer base and (2) a single 2¼-in. 12-gauge PSST steel sign support. LS-DYNA models for the pole and PSST systems were developed and partially validated using the available crash tests. Nine and seven full-scale crash tests were recommended for the pole and PSST families of devices. Because additional budget was needed to run all necessary crash tests, it was decided to provide guidelines regarding the crashworthiness of both families as best as possible. Note that the current project will proceed with distinct yet aligned objectives (i.e., NCHRP Project 17-105). The objectives of the continued research are to determine the maximum height and weight of breakaway poles and hardware that will meet MASH requirements. The research efforts will include (a) physical tests to correlate roof crush with pole and hardware height and weight and aid in determining critical pole configurations, and (b) dropping poles with associated hardware of varying height and weights onto vehicles as a precursor to full-scale crash testing. The findings will be used to identify improvements to vehicle computer models to better simulate crash testing roof crush. Additionally, this research will investigate if the criterion of a 4-in. tall object on a 5- ft chord is still applicable to the current vehicle fleet. This objective should include (a) reviewing procedures used to develop the 4-in. tall on 5-ft chord criteria, (b) determining if modifications or improvements to the procedure can be implemented, and (c) conducting an analysis of procedures with the current vehicle fleet. Note that the primary emphasis will be on meeting the objectives of Project 17-105, considering how the new findings can contribute to the goals of Project 22-43 (i.e., identifying a critical reduced matrix for MASH evaluation of luminaire poles with TB1-17 transformer base). Breakaway Steel Luminaire Pole with Aluminum TB1-17 Frangible Transformer Base Two full-scale crash tests, test nos. TBLP-1 and TBLP-2, were conducted on luminaire poles with a TB1-17 transformer base under MASH 3-60 impact conditions at an angle of 0 degrees with impact at the vehicle’s center point. Simulation indicated that center impacts were deemed more critical than impacts at the right or left quarter points. Additionally, an impact angle of 0 degrees would increase the likelihood of the pole landing on the center of the roof, which has less crush stiffness. In test no. TBLP-1, the 50-ft tall pole with dual 15-ft long mast and a weight of 1,015 lb arm was impacted by a 1100C small car, and the base was activated but the test failed MASH criteria due to excessive occupant impact velocity (OIV). In test no. TBLP-2, the 30-ft tall pole with a single 30-ft long mast arm and a weight of 824 lb was impacted by a 1100C small car, but the desired activation of the TB1-17 transformer base did not occur and the test failed MASH criteria. The LS-DYNA models were then updated and validated to match the test results. Next, simulations were conducted on various pole configurations with a wide range of design parameters, including pole height and mast arm length with single and dual mast arms, under 1 PRE-PUBLICATION DRAFT—Unedited Text and Graphics 

PRE-PUBLICATION DRAFT—Unedited Text and Graphics MASH 3-60, 3-61, and 3-62, with varying vehicle impact points. The validated simulations showed the potential for evaluating the crashworthiness of poles in terms of OIV. However, the inconsistent behavior of poles after base fracture observed in various full-scale crash tests presents a challenge in predicting roof crush through simulation. Additionally, inaccuracies in the vehicle roof model introduce additional complexity to the problem. As part of the continuation of the current project, these challenges will be further investigated under NCHRP Project 17-105. The full-scale crash tests and simulations revealed a series of trends in crash performance of poles with various configurations. The highlights of these trends include: • None of the simulations or full-scale crash tests exceeded MASH maximum limits for ORA values, lateral and longitudinal values, or roll and pitch values. • Critical measures for evaluating luminaire poles include ensuring the pole base breaks away upon impact, limiting longitudinal OIV to below 16 ft/s, limiting maximum intrusion into the occupant compartment (i.e., roof crush) to less than 4 in., and preventing any part of the luminaire from penetrating the vehicle. • MASH 3-60 impacts appeared to be more critical in terms of roof crush compared to MASH 3-61 and 3-62 impacts. Center impacts were generally found to be more critical than right- or left-quarter impacts for roof crush, primarily due to the longitudinal fall of the pole on the vehicle’s roof. • Roof crush concerns were noted for poles weighing over 500 lb in MASH 3-60 impacts. As a result, it is recommended to conduct one full-scale crash test on any pole configuration to evaluate its performance under this critical impact condition. • In some cases that involve left- or right-quarter impacts at a 25-degree angle, the base did not break away, resulting in high OIV values. This behavior could be attributed to modifications that strengthened the base’s corners. Validation through full-scale crash testing under these conditions is necessary to assess OIV criteria. • MASH 3-61 impacts did not result in vehicle contact or intrusion into the occupant compartment. • OIV values increased as the total system weight increased in MASH 3-61 impacts, particularly for heavy poles weighing over 800 lb. Full-scale crash testing is required to determine specific critical pole characteristics. • Center impacts at a 0-degree impact angle in MASH 3-61 appeared to be suitable for assessing OIV. • MASH 3-62 impacts generally resulted in lower OIV values than MASH 3-61 impacts, suggesting that luminaire poles should be evaluated only under MASH 3-61 to meet OIV criteria. • None of the MASH 3-62 impacts led to vehicle contact or intrusion into the occupant compartment. Full-scale crash tests may not be necessary for these conditions. • Low-speed pickup truck tests are not included in existing MASH standards. Further research is needed to assess their necessity and compare their criticality with MASH 3-60 and MASH 3-61 tests. Note that the LS-DYNA simulations were significantly improved in predicting the impact behavior of luminaire poles. However, the validation process is incomplete without running the full set of tests. For instance, simulations for poles representing MASH 3-61 and 3-62 impact conditions lack full-scale crash test data for validation, which makes it challenging to develop guidelines and 2 PRE-PUBLICATION DRAFT—Unedited Text and Graphics 

PRE-PUBLICATION DRAFT—Unedited Text and Graphics recommend modifications to MASH for these systems. Thus, the concept of identifying a family and utilizing a reduced test matrix to determine crashworthiness could not be fully demonstrated. Using the available full-scale crash tests and updated simulations, preliminary guidelines for MASH evaluation of pole with TB1-17 base were drafted, as shown in Table 1. To validate these recommendations and to further refine the pole categories, a series of full-scale crash tests are necessary, as shown in Table 2, and would also provide data for further validation of the simulations. 3 PRE-PUBLICATION DRAFT—Unedited Text and Graphics 

PRE-PUBLICATION DRAFT—Unedited Text and Graphics Table 1. Draft Guidelines Recommended for MASH Evaluation of Luminaire Poles with TB1-17 Transformer Base – (Not Applicable before Validation) Pole Configuration MASH 3-60 MASH 3-61 MASH 3-62 ►One test needed for roof crush evaluation: 3-60-CE-0 No test needed No test needed Short Poles (H≤20 ft & W≤450 lb) ►One test needed for OIV evaluation: 3-60-RQ/LQ-25 ►One test needed for roof crush evaluation: 3-60-CE-0 No test needed No test needed Medium Poles (20 ft <H<40 ft & W≤800 lb) ►One test needed for OIV evaluation: 3-60-RQ/LQ-25 ►One test needed for roof crush ►One test needed for evaluation: 3-60-CE-0 No test needed Tall Poles (H≥40 ft & W>800 lb) OIV evaluation: ►One test needed for OIV 3-61-CE-0 evaluation: 3-60-RQ/LQ-25deg Table 2. Full-Scale Crash Tests Required to Validate Recommendations – Luminaire Poles with TB1-17 Transformer Base Pole Configuration MASH 3-60 MASH 3-61 MASH 3-62 One test needed: Short Poles (H≤20 ft & W≤450 lb) No test needed No test needed 3-60-CE-0 (Roof Crush) Two tests needed: One test needed: Medium Poles (20 ft <H<40 ft & W≤800 lb) 3-60-CE-0 (Roof crush) No test needed 3-61-CE-0 (OIV) 3-60-LQ/RQ-25 (OIV) One test needed: One test needed: One test needed: Tall Poles (H≥40 ft & W>800 lb) 3-60-LQ/RQ-25 (OIV) 3-61-CE-0 (OIV) 3-62-CE-0 (OIV) 4 PRE-PUBLICATION DRAFT—Unedited Text and Graphics 

PRE-PUBLICATION DRAFT—Unedited Text and Graphics Single 2¼-in. 12-Gauge PSST Steel Sign Support The second type of device selected for analysis and evaluation under this project was the PSST sign support system. This system was found to be widely used across the nation, and based on the NCHRP Project 03-119 survey, had a high ranking and percentage of use by state departments of transportation (DOTs). The analyses began with model validations of the PSST sign support system using available full- scale crash tests. Upon completing the validations, a matrix of simulations was set up and conducted to investigate the effects of different parameters on MASH performance within a family of PSST sign support systems. Table 3 highlights the various parameters that were investigated in the matrix of simulations. PSST systems with various panel sizes were analyzed, ranging from 1 ft x 1½ ft to 4 ft x 5 ft. Gauge thicknesses of 0.08, 0.1, and 0.12 in. were used for the sign panels, with aluminum assigned as the material for all models. The post size for this family of devices was selected to be a 2¼-in. x 2¼-in. cross-section with a gauge thickness of 12. A 7-ft mounting height to the bottom of the sign panel, the most common configuration, was used for all models. The anchor size was selected to accommodate the post sizes (2¼ in. x 2¼ in. by 12-gauge thickness), using ASTM A1011 Grade 50 steel for both the post and anchor. The anchor embedment was set at 36 in. into the ground in all models. These parameters were chosen based on what was commonly used by state DOTs under NCHRP Project 03-119. MASH standard soil was used for the ground surrounding the anchor. Models at three MASH impact configurations (3-60, 3-61, and 3-62) were employed in the matrix of simulations. Additionally, different impact locations (center, driver-side offset, and passenger-side offset) and different impact angles (0, +25, and -25 degrees) were incorporated into the matrix of simulations. Table 3. PSST Sign Support Configurations Analyzed Device Family 2¼-in. 12-gauge Single PSST Sign Support Identical, Critical Structural Sign support section and size 2¼-in., 12-gauge PSST Feature 1 ft x 1½ ft; 2 ft x 2 ft; Sign panel size 2½ ft x 2½ ft; 3 ft x 3 ft; (if applicable, a lower smaller 3 ft x 4 ft; 4 ft x 5 ft advisory panel may potentially (recommended from be considered) NCHRP 03-119) 7 ft (recommended from Sign panel mounting height Potential Parameters that Provide NCHRP 03-119) Similar Safety Performance under Aluminum MASH Impact Conditions Sign panel material (recommended from NCHRP 03-119) 0.08 in., 0.10 in., 0.120 Sign panel thickness in. Support embedment/foundation 36 in. With and without wind Presence of wind beams beams Close to 400 simulations were performed and analyzed, generating a considerable amount of information. The critical MASH metrics for the PSST system were the OIV, windshield intrusion, 5 PRE-PUBLICATION DRAFT—Unedited Text and Graphics 

PRE-PUBLICATION DRAFT—Unedited Text and Graphics and roof deformation. Excessive windshield penetration was by far the most common cause of failure for the PSST systems. The results from the simulations were used to select full-scale crash tests to validate the analyses and establish guidelines for potential incorporation into MASH for testing a family of sign support devices. Five full-scale crash tests were conducted on PSST systems. All five tests utilized the same post: a 2¼-in. 12-gauge single PSST post, which is a criterion for belonging to the same family of devices. The five tests were diversified in terms of impact configuration (MASH test nos. 3-61 and 3-62), panel size (1 ft x 1.5 ft, 4 ft x 5 ft, and 3 ft x 3 ft), impact location (center and offset), and impact angle (0 and 25 degrees). Upon analyzing the test results and comparing them with the simulation predictions, differences were observed that did not significantly impact the overall conclusions drawn from the simulation analyses. The variances were attributed to soil strength, which affected the separation timing of the post from the base sleeve. After updating the models accordingly, the simulations aligned with the test outcomes. The simulations were rerun, and the summary results were updated. Table 4 shows a summary of all cases, incorporating the results from the updated models. Based on these results, the following observations were noted: • MASH test no. 3-60 was the least critical of the three impacts for the PSST sign support system family being considered. This test could be omitted or reduced to only one test with the largest sign panel. • MASH test no. 3-61 was the most critical of the three tests. It was noted that the size of the panel affects the MASH performance outcome. In some cases, medium sized panels were more critical than smaller and larger sizes. To verify that a system with all panel sizes meets MASH, tests with the smallest and largest sign would need to be performed, and based on the outcome of these tests, an additional test may need to be performed (e.g., if the smallest panel hit the hood and the larger panel hit the roof, a test with a size in between would be needed). • Similar effects were noted for MASH test no. 3-62. The panel size affects the MASH performance, and the middle panel size could be more critical than the smallest and largest sizes. Testing should start with the two extreme cases (smallest and largest sizes) and based on the outcome, additional testing with in-between sizes may be needed. • It was noted that impact locations and impact angle can have an important effect on the outcome of the test. In some cases, offset impacts and impacts at an angle were more critical than the no-offset impact. In other cases, the no-offset impact was more critical. Tests with and without offset are needed. Considering all impacts, none of the analyzed configurations were found to meet MASH criteria for all three tests (3-60, 3-61, and 3-62). This highlights the difficulty of developing a system that meets current MASH criteria. 6 PRE-PUBLICATION DRAFT—Unedited Text and Graphics 

PRE-PUBLICATION DRAFT—Unedited Text and Graphics Table 4. Summary of PSST Computer Simulation Results Impact Panel Size 1' x 1.5' 2' x 2' 2.5' x 2.5’ 3' x 3' 3' x 4' 4' x 5' Impact locations Condition Panel Thickness 0.08 0.10 0.12 0.08 0.10 0.12 0.08 0.10 0.12 0.08 0.10 0.12 0.08 0.10 0.12 0.08 0.10 0.12 and Angle OIV (ft/s) 5.2 5.6 5.6 6.6 7.2 7.2 7.9 8.2 8.2 Center/ Windshield Int. (in) 0 0 0 0 0 0 0 0 0 0-Deg Roof Int. (in) 0 0 0 0 0 0 0 0 0 Driver-Side OIV (ft/s) 5.9 5.9 6.2 7.2 7.5 7.9 7.9 8.5 8.5 8.9 9.2 9.5 9.5 9.8 10.5 11.2 11.5 11.8 MASH Offset/ Windshield Int. (in) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 3-60 0-Deg Roof Int. (in) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Pass. -Side OIV (ft/s) 5.9 5.9 5.9 7.2 7.5 7.9 8.2 8.5 8.9 Offset/ Windshield Int. (in) 0 0 0 0 0 0 0 0 0 0-Deg Roof Int. (in) 0 0 0 0 0 0 0 0 0 OIV (ft/s) 3.3 6.2 6.6 6.2 6.2 6.9 6.2 5.9 6.2 6.2 5.9 3.9 Center/ Windshield Int. (in) 0 0 0 0 0 0 1.2T 4.7T 8.8T 8.2T 4.3T 0 0-Deg Roof Int. (in) 0 0 0 0 0 0 0 2.8 4.3 4.3 3.9 5.9 OIV (ft/s) 5.9 5.6 6.2 6.6 6.2 6.2 6.2 3.0 6.6 6.2 7.2 4.9 Center/ - Windshield Int. (in) 0 0 0 0 0 0.7T 4.3T 1.2T 3.1T 3.1T 6.7T 3.3T 25-Deg Roof Int. (in) 0 0 0 0 0 0 2.362 0 1.6 1.6 3.9 8.0 OIV (ft/s) 4.9 5.9 5.2 5.6 5.6 7.2 7.2 7.9 7.2 7.2 3.3 6.2 MASH Center/ Windshield Int. (in) 0 0 0 0 0 0.4T 1.6T 2.0T 3.1T 1.8T 6.3T 7.9T 3-61 +25-Deg Roof Int. (in) 0 0 0 0 0 0 2.4 0 0 0 3.6 5.1 Driver-Side OIV (ft/s) 3.3 3.6 3.3 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 1.0 Offset/ Windshield Int. (in) 1.2T 1.6T 4.2T 12.4T 6.8T 12.5T 13.0T 11.8T 4.7T 4.7T 4.1T 0.1 0-Deg Roof Int. (in) 0 0 0.2 3.9 0.2 4.3 3.9 3.9 3.5 3.9 3.3 2.4 Pass. -Side OIV (ft/s) Offset/ Windshield Int. (in) 0-Deg Roof Int. (in) OIV (ft/s) 2.0 2.0 2.3 2.3 2.6 2.3 1.3 2.3 2.3 2.3 2.3 2.3 Center/ Windshield Int. (in) 0 0 0 0 0 0 0 3.9 5.5 0 5.5 3.3 0 3.6 0-Deg Roof Int. (in) 0 0 0 0 0 0 0 4.7 2.4 0 3.0 3.2 0 3.504 OIV (ft/s) 1.6 2.0 2.0 3.0 3.9 3.0 1.6 3.0 1.6 3.3 3.0 3.0 MASH Center/ Windshield Int. (in) 0 0 0 0 0 0 0 3.9 2.8 0 2.4 1.8 0 2.205 3-62 +25-Deg Roof Int. (in) 0 0 0 0 0 0 0 0 0.8 0 1.6 2.8 0 3.0 OIV (ft/s) Center/ - Windshield Int. (in) 25-Deg Roof Int. (in) Meets MASH Criteria Does Not Meet MASH Criteria T Symbol after intrusion number indicates “tearing” is predicted. 7 PRE-PUBLICATION DRAFT—Unedited Text and Graphics 

PRE-PUBLICATION DRAFT—Unedited Text and Graphics A matrix of tests is currently defined in MASH for sign support systems (Table 5). Full-scale testing all configurations in this matrix for a family of PSST systems would be cost-prohibitive. Using the results from the simulations, along with the full-scale crash tests and insights gained from existing literature, the research team developed a revised matrix for MASH testing of a family of PSST sign support systems. Instead of running the three impacts (3-60, 3-61, and 3-62) for each configuration in the family of devices, the new matrix incorporates fewer key tests on select critical configurations. The new matrix reduces the number of required tests without compromising the evaluation and safety of the different configurations within the PSST family of devices. Table 6 depicts the updated test matrix for the analyzed family of PSST systems. Only Test Level 3 (TL- 3) is included in the table, but similar tests can be adopted for the other test levels. The same table can be adopted for other small sign support systems after further analysis and testing. In the revised matrix, the impact speeds, test vehicles, and evaluation criteria remained unchanged from the original MASH recommendations. The impact angles and locations were updated to reflect worst-case scenarios. According to the revised matrix, a minimum of five tests are needed for each family of devices, with the possibility of requiring two additional tests depending on the outcomes of the initial five tests. Detailed justifications for the selection of tests and the updated impact conditions are included in the project’s final report. Table 5. Original MASH Test Matrix for Support Structures (MASH, 2016) Feature Test Vehicle Impact Impact Accept- Impact Evaluation No. Speeda Anglea able KE Point Criteriac mph θ deg. Range, (km/h) kip-ft (kJ) 3-60 1100C 19 (30) 25 ≤34 (41) (c) B,D,F,H,I,N Support Structures 3-61 1100C 62 (100) 25 ≥288 (390) (c) B,D,F,H,I,N 3-62 2270P 62 (100) 25 ≥594 (806) (c)t B,D,F,H,I,N a See MASH Section 2.1.2 for tolerances on impact conditions. b See MASH Table 5-1. c See MASH Figure 2-5 for impact point. Table 6. Recommend Test Matrix for Family of PSST Sign Support Systems Feature Test Vehicle Family Impact Impact Accept- Impact Evaluation No. System Speed Anglec able KE Pointd Criteriae Sizea mph θ deg. Range, kip- (km/h)b ft (kJ) 3-60A 1100C Tallest 19 (30) 25 ≤34 (41) Offset B,D,F,H,I,N 3-61A 1100C Tallest 62 (100) 25 ≥288 (390) Center B,D,F,H,I,N Small 3-61B 1100C Shortest 62 (100) 25 ≥288 (390) Offset B,D,F,H,I,N Sign Support 3-61C 1100C Mid-size 62 (100) 25 ≥288 (390) Offset B,D,F,H,I,N System 3-62A 2270P Tallest 62 (100) 25 ≥594 (806) Center B,D,F,H,I,N 3-62B 2270P Shortest 62 (100) 25 ≥594 (806) Offset B,D,F,H,I,N 3-62C 2270P Mid-size 62 (100) 25 ≥594 (806) Offset B,D,F,H,I,N a See Report Sections 7.2.3 & 7.2.4 for size guidance b See MASH Section 2.1.2 for impact conditions tolerances c See Report Sections 7.2.6 below for impact angle d See Report Sections 7.2.5 below for impact location e See MASH Table 5-1 for evaluation criteria 8 PRE-PUBLICATION DRAFT—Unedited Text and Graphics