Investigation of Material Requirements for Highway Guardrail Systems (2022)

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112 Introduction Many guardrail failures are a result of the corrugated rail element rupturing during vehicle collisions. Several examples of such failures have been documented in full-scale crash-test reports (Buth et al. 2006, Fleck 2008, Polivka et al. 2000). In almost all those test cases, the rupture tended to propagate from a tear that initiated at a splice-bolt hole, a post-bolt hole, or a cut on the outer edge of the rail, thus illustrating the importance of ductility in the corrugated sheet steel. Some test photos of rail ruptures that initiated from bolt holes in the splice connection during full-scale crash testing are shown in Figure G-1. No other component of a guardrail system is as critical to system performance as the railing component (i.e., W-beams and thrie beams), since rupture of the rail element leads directly to complete failure of the system. Table G-1 shows the current AASHTO M 180-18 mechanical property specifications for corrugated sheet beams and end sections. To the authors’ knowledge, based on a literature search and communication with several crash test facilities, material certification documents were not included in crash test reports prior to the adoption of MASH. Therefore, material properties for corrugated rail in guardrail systems tested prior to the year 2009, such as those shown in Figure G-1, are not generally available. The research team has identified 11 cases tested under MASH conditions that resulted in par- tial or complete rupture of the rail element; those cases are listed in Table G-2, which includes the corresponding mechanical properties as provided on the mill certification documents. Five of the entries in Table G-2 correspond to recent tests for which test reports are not yet available; those reports will hopefully be provided soon. From the six available test reports, the mechanical properties of the ruptured rail were well above M 180 minimum specifications. In each of these cases, the rupture initiated at either a splice-bolt hole or at a post-bolt hole location, as shown in Figures G-2 through G-7. From a review of the test reports, the cause of the failure was generally attributed to higher than expected forces in the rail resulting from rail pocketing during approach to a relatively stiff post (e.g., post in concrete, post in rocky ter- rain, transition post, and long-span rail) or combined vertical and tensile loading on the rail (e.g., curbs placed in front of rail producing vertical trajectory of vehicle). In the cases where the rupture occurred at a splice, the rail elements on both sides of the splice were of the same material (same heat number), except for Test MWTC-1, in which a W-beam rail (left photo in Figure G-6) was spliced to an asymmetrical transition beam (right photo in Figure G-6) (Winkelbauer et al. 2014). In that case, the W-beam side of the splice ruptured, but there appeared to be some minor tears in a few of the splice-bolt holes of the transition beam. (A portion of the ruptured W-beam (rail 9) is still attached to the transition beam (rail 10) in Figure G-6, partially obstructing the view.) One thing of note is that the tensile strength for the W-beam in that case was 27% greater than that of the transition beam (89,432 psi versus 70,300 psi), while the percent A P P E N D I X G Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 113   elongation was 61% less than that of the transition beam (19.8% versus 32%). However, it cannot be ascertained whether relative differences in mechanical properties were the cause of the W-beam failing instead of the transition beam. For example, in almost all the splice ruptures in Table G-2, with the exception of Test 608551-2, the rail on the upstream side of the splice failed. In general, tensile strength and toughness are considered the primary attributes that affect material rupture under dynamic loading conditions. Tensile strength is a measure of how much stress a material can support without rupture (and indirectly, how much force it can support), and toughness is a measure of how much strain energy a material can absorb before rupturing. Toughness is measured as the area under the stress–strain curve for a material, as illustrated in Figure G-8, and is therefore a function of both strength (i.e., stress magnitude) and plastic deformation (i.e., strain or elongation) of the material. Typically, toughness is measured under dynamic loading conditions such as defined in Charpy or Izod tests. As strain rates increase, most materials respond with higher stress mag- nitudes, while maximum strain magnitudes tend to decrease under higher loading rates. For example, Figure G-9 shows a series of tensile tests performed on W-beam material at various loading rates, in which it is apparent that the strain energy (the area under the curve) tends to increase with strain rate, at least up to strain rates of 1/s. Beyond this rate, the maximum strain magnitude begins to decrease, which counteracts the increase in stress. (c)(b)(a) Figure G-1. Rail rupture initiated at downstream splice bolts in (a) test NEC-1, (b) test 405160-1-1, and (c) test C08C3-027.1 (Buth et al. 2006, Fleck 2008, Polivka 2000). Beams and Transitions End and Buffer Sections Yield strength (minimum) 345 MPa (50 ksi) 227 MPa (33 ksi) Tensile strength (minimum) 483 MPa (70 ksi) 310 MPa (45 ksi) Elongation in 2 in. (minimum) 12% N/A Table G-1. Minimum mechanical property requirements for corrugated steel components in M 180.

114 Investigation of Material Requirements for Highway Guardrail Systems Notes: *Report not published; values not available; MGS = Midwest Guardrail System. Reference Test No Test Date System tested MASH Test # Test House Failure Mechanism Rosenbaugh et al. 2019a MGSCO-1 8/28/2017 MGS guardrail w/6-in curb omitted post MASH Test 3-10 MWRSF Rail rupture at splice (upstream side) Sheikh et al. 2019 608551-2 12/5/2017 W-beam w/wood posts in concrete mow strip MASH Test 3-11 TTI Rail rupture at splice (downstream side) Bligh et al. 2019 469468-12-1 8/21/2018 MBGF w/wood posts in rocky terrain MASH Test 3-11 TTI Rail rupture at post- bolt Ronspies et al. 2020 MGSC-7 11/7/2017 MGS w/6-inch curb MASH Test 3-10 MwRSF Rail rupture at splice (upstream side) Winkelbauer et al. 2014 MWTC-1 8/10/2012 W-to-thrie transition with 4-inch curb MASH Test 3-20 MwRSF Rail rupture at splice (upstream side) Bullard et al. 2010 RF476460-1-5 3/4/2009 Wood-post guardrail MASH Test 3-11 TTI Rail rupture at splice (upstream side) Asadollahi Pajouh et al. 2020 CMGS-1 12/1/2017 MGS on shallow box- culvert MASH Test 3-10 MwRSF Partial tear at splice (downstream side) Kovar et al. 2022 610211-01-3 2/18/2019 MGS at 37.5-in. post spacing MASH Test 3-11 TTI Rail rupture at splice (downstream side) Kovar et al. 2022 610211-01-4 11/27/2018 MGS trans from 75-in. to 18.75-in. post spacing MASH Test 3-21 TTI Rail rupture at splice (upstream side) Report not published 609971-01 * MGS at 7:1 flare MASH Test 3-10 TTI Rail rupture at post Report not published 609971-03-2 * MGS at 11:1 flare MASH Test 3-11 TTI Rail rupture mid- span Table G-2. List of guardrail tests that resulted in complete or partial rupture of rail element. Heat#= 9411949 Yield = 56527 psi Tensile= 75774 psi %elong.= 27.15 % Figure G-2. Splice rupture in Test MGSCO-1 (Source: Rosenbaugh et al. 2019b). Heat#= 184178 Yield = 59960 psi Tensile= 78570 psi %elong.= 24.7 % Figure G-3. Splice rupture in Test 608551-2 (Source: Sheikh et al. 2019).

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 115   Heat#= 209337 Yield = 61740 psi Tensile= 79690 psi %elong.= 26 % Figure G-4. Rail rupture at post-bolt in Test 469468-12-1 (Source: Bligh et al. 2019.) Yield = 56527 psi Tensile= 75774 psi %elong.= 27.15 % Figure G-5. Partial splice rupture in Test MGSC-7 (Source: Ronspies et al. 2020). Heat#= 4614 Yield = 67993 psi Tensile= 89432 psi %elong.= 19.8 % Heat#= 1106510 pg 160 Yield = 50400 psi Tensile= 70300 psi %elong.= 32 % W-beam rail W-thrie transition Figure G-6. Splice rupture in Test MWTC-1 (Source: Winkelbauer et al. 2014). Heat#= 116021 Yield = 59690 psi Tensile= 78030 psi %elong.= 25.3 % Figure G-7. Splice rupture in Test RF476460-1-5 (Source: Bullard et al. 2010).

116 Investigation of Material Requirements for Highway Guardrail Systems The issue of ductility was also corroborated by members of prominent full-scale crash-test organizations [i.e., TTI, MwRSF, and the Center for Collision Safety and Analysis (CCSA)] (cor- respondence through email and discussions at the 99th annual meeting of the Transportation Research Board in Washington, DC). ASTM A370-20 (Standard Test Methods and Definitions for Mechanical Testing of Steel Products) provides procedures for conducting Charpy tests on subsize specimens with thicknesses as small as 0.098 in. (2.5 mm). The research team is not aware of any such testing being performed on corrugated sheet steel used in guardrail; therefore, no Charpy data were available for this review. 0 10 20 30 40 50 60 70 80 90 100 0 0.05 0.1 0.15 0.2 0.25 Tr ue S tr es s (k si ) True Strain Toughness W-Beam material Figure G-8. Typical true stress versus strain for M 180 material (Source: Wright and Ray 1996). Figure G-9. Nominal stress–strain curves for M 180 material under various loading rates (Source: Wright and Ray 1996).

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 117   Objective The research team reviewed the material properties of corrugated sheet steel used in guardrail to determine if changes are warranted for mechanical property specifications in M 180, and if such changes are practical. The current mechanical property specifications for corrugated sheet steel in M 180-18 were summarized in Table G-1. The focus of the review was to assess whether minimum strength or toughness specifications could be updated to better ensure guardrail per- formance without imposing a significant burden on mills and suppliers. Methodology A request was sent to several transportation agencies to provide mill certification information for W-beam and thrie-beam rails used in nonproprietary guardrail installations in their states. A total of three states responded to the request: Florida, Maine, and Ohio. The reports included a total of 382 cases for W-beam rail and 53 cases for thrie-beam rail from four different guard- rail suppliers: Gregory Highway Products, Highway Safety Corp., R.G. Steel Corp., and Trinity Industries. The yield strength, tensile strength, and percent elongation were extracted from each of the mill reports, and the properties from a given heat number were not repeated unless they were used in a separate state project installation (e.g., a separate run of guardrail). Two additional material attributes related to material toughness were calculated and reported: (1) ratio of tensile strength and yield strength (T/Y ratio) and (2) a pseudo-strain energy. The T/Y ratio is used in other ASTM specifications, namely ASTM A992, which has a minimum T/Y ratio specifica- tion of 1.18. As mentioned previously, strain energy is a direct measure of toughness; however, since stress–strain curves were not available from the mill reports, a pseudo-strain energy was approximated using the properties provided (i.e., yield strength, tensile strength, and percent elongation). The stress–strain curve was approximated by assuming a linear tangent modulus, and the tensile strength (i.e., maximum stress value) was assumed to coincide with maximum elongation, as illustrated in Figure G-10. The pseudo-strain energy was then computed as the area under the approximated stress–strain curve, as illustrated by the shaded region in Figure G-10. St re ss (k si ) Strain True Stress (upper line) Nominal Stress (lower line) Yi el d St re ng th Te ns ile S tr en gt h %Elongation Pseudo Strain Energy Figure G-10. Calculating pseudo-strain energy using yield strength, tensile strength, and percent elongation from mill reports.

118 Investigation of Material Requirements for Highway Guardrail Systems Although this methodology does not provide precise calculation of strain energy, the pseudo- strain energy value should represent a reasonable comparison of material toughness between the various heats, since the stress–strain curves for each material heat for M 180 guardrail are expected to have the same basic shape. Results General Statistics A summary of material property statistics for M 180 W-beam rail from the data collected in this study is shown in Table G-3, with additional details provided in Addendum G-1. Likewise, a summary of mechanical properties for M 180 thrie-beam rail is shown in Table G-4, with additional details presented in Addendum G-2. The addenda include cumulative distribution plots for each material property as well as the general correlation of each material property cross-plotted against each of the others. A total of 382 data points were collected for W-beam rail. As shown in Table G-3, the yield strength ranged from 46,682 psi to 77,974, with a mean of 61,232 psi and standard deviation of 4,094 psi. The tensile strength ranged from 62,400 psi to 95,000 psi, with a mean of 81,296 psi and standard deviation of 4,425 psi. The percent elongation ranged from 12% to 45.6%, with a mean of 24.5% and standard deviation of 3.4%. The median was of the same general magnitude as the mean in all cases. Additional statistics regarding T/Y ratio and pseudo-strain energy are also provided in Table G-3. Of the 382 data points collected for W-beams, 380 met the current specifications of M 180-18. The two cases that did not meet specifications were one with a yield strength of 46,682 psi (e.g., <50 ksi) and another with tensile strength of 62,400 psi (e.g., <70 ksi). The mechanical property data for thrie-beam rail (refer to Table G-4) were similar to those of the W-beam data; however, in the 53 data points collected for the thrie-beam material, the yield and tensile strength tended to be slightly lower than those of the W-beam, while the percent elongation was slightly higher. All the thrie-beam cases met required minimum specifications. The resulting mechanical properties for W-beam and thrie-beam rail based on a 95% confidence interval are provided in Table G-5 and are shown graphically in Figure G-11. Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 382 Max 77,974 95,000 45.6 1.6 32.95 Min 46,682 62,400 12.0 1.07 10.22 Mean 61,232 81,296 24.5 1.33 17.41 Std Dev 4,094 4,425 3.4 0.05 2.17 95% CI (+/-) 411 444 0.34 0.005 0.22 Median 61,480 80,415 25.0 1.32 17.66 Mode 62,000 89,000 26.0 1.33 14.81 10th Percentile 56,131 77,107 20.0 1.29 14.83 5th Percentile 54,731 75,530 19.0 1.28 13.81 2nd Largest 73,600 94,900 33.0 1.5 25.95 2nd Smallest 50,000 70,308 13.0 1.1 10.38 %Elong. T/Y Ratio Table G-3. Material property statistics for M 180 W-beam rail.

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 119   Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 53 Max 65,000 83,940 30.1 1.5 20.17 Min 53,900 70,650 16.3 1.25 15.86 Mean 60,316 79,233 25.7 1.31 18.09 Std Dev 3,080 3,071 2.4 0.04 1.45 95% CI (+/-) 829 827 0.64 0.010 0.39 Median 61,400 79,830 25.7 1.31 18.20 10th Percentile 54,884 73,610 22.7 1.28 16.61 5th Percentile 54,524 72,742 21.7 1.28 16.37 2nd Largest 64,700 83,490 29.8 1.4 19.85 2nd Smallest 53,960 72,000 20.8 1.3 16.26 %Elong. T/Y Ratio Table G-4. Material property statistics for M 180 thrie-beam rail. The 5th percentile yield strength value for the W-beam was 54,731 psi (9.4% higher than the minimum value specified in M 180-18), the 5th percentile tensile strength value was 75,530 psi (7.9% higher than minimum specification in M 180-18), and the 5th percentile for percent elonga- tion was 19% (8% higher than minimum specification in M 180-18). Likewise, the 5th percentile value for yield strength for the thrie-beam was 54,884 psi (9.7% higher than minimum specification), the 5th percentile value for tensile strength was 72,742 psi (3.9% higher than minimum specification), and the 5th percentile for percent elonga- tion was 21.7% (80.8% higher than minimum specification). Correlation Between Various Mechanical Properties for M 180 Sheet Steel The strength of the correlation between various properties was assessed based on the criteria provided on the DM STAT webpage (http://www.dmstat1.com/res/TheCorrelationCoefficient Defined.html#:∼:text=Values%20between%200.7%20and%201.0,shared%20between%20 the%20two%20variables.%E2%80%9D) and on visual inspection of the scatter plots, where R2 values of 0.7–1 were considered a strong correlation, 0.3–0.7 were considered a moderate correlation, 0.1–0.3 were considered a weak correlation, and values of less than 0.1 were con- sidered to have very weak or no correlation. Mechanical Property W-Beam Rail Thrie-Beam Rail Yield strength 61,232 ± 411 psi 60,316 ± 829 psi Tensile strength 81,296 ± 444 psi 79,233 ± 827 psi Percent elongation 24.5 ± 0.34% 25.4 ± 0.64% T/Y ratio 1.33 ± 0.005 1.31 ± 0.01 Pseudo-strain energy (σε) 17,410 ± 220 psi 18,090 ± 390 psi Table G-5. Average mechanical property values with 95% confidence interval.

120 Investigation of Material Requirements for Highway Guardrail Systems As shown in the cross-plots in Addenda G-1 and G-2, several of the mechanical properties exhibited a moderate-to-strong linear relationship with each other, while others showed weak or no relationship at all. For example, tensile strength had a moderate-to-strong correlation with yield strength, but had a weak correlation to percent elongation, and had no correlation to T/Y ratio or strain energy. The latter was somewhat surprising, since increasing strength would intuitively tend to increase strain energy; however, as shown in Figure G-20, the percent elon- gation tends to decrease as strength increases, thereby counteracting any potential increase in strain energy. Tables G-6 and G-7 provide a summary of the findings regarding the relationships between mechanical properties of M 180 sheet steel for W-beam rail and thrie-beam rail, respec- tively. The arrows in the table indicate whether the correlation was positive (≠) or negative (↑). The shaded cells in the table indicate the material attributes that exhibited moderate-to-strong correlation. Yield strength exhibited a moderate-to-strong positive correlation to tensile strength (i.e., tensile strength increases as yield increases) and had a moderate negative correlation with T/Y ratio (i.e., T/Y decreases as yield increases). The only mechanical property that showed a 50000 52000 54000 56000 58000 60000 62000 64000 W-Beam Rail Thrie-Beam Rail Yi el d St re ng th (p si) Yield Strength 70000 72000 74000 76000 78000 80000 82000 84000 W-Beam Rail Thrie-Beam Rail Te ns ile S tr en gt h (p si) Tensile Strength 20 21 22 23 24 25 26 27 28 29 30 W-Beam Rail Thrie-Beam Rail % el on ga tio n %elongation Figure G-11. Average mechanical property values with 95% confidence interval.

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 121   strong correlation with material toughness (i.e., pseudo-strain energy) was percent elongation, with a positive correlation R2 value of 0.85. Conclusions No other component of a guardrail system is as critical to system performance as the corru- gated beam rail, where rail rupture leads directly to system failure. For a given guardrail design, tensile strength and toughness are the primary material attributes that affect the ability of the rail to resist rupture. It is therefore important to ensure that these attributes are sufficiently maxi- mized to reduce potential for failure. The results of the study showed that these two attributes were not directly related to each other, at least for M 180 sheet steel (refer to Figures G-13 and G-14 in Addendum G-1 and Figures G-19 and G-20 in Addendum G-2). Specifying a minimum toughness criterion, similar to that of ASTM A370-20, would ensure that the material would undergo sufficient plastic deformation before initiating a tear; however, component testing was not within the scope of this project. Since toughness data for guardrail sheet steel were not available, a pseudo-toughness metric was developed instead based on an approximated strain energy using yield strength, tensile strength, and percent elongation (i.e., typical mechanical properties provided on mill reports). This pseudo-toughness was computed for all of the surveyed data, and the results indicated a direct correlation between toughness and percent elongation. Thus, simply ensuring that the percent elongation property is sufficiently high will likewise ensure that the material has adequate toughness, without including additional mechanical property specifications, tests, or calculations. Increasing the percent elongation requirement for corrugated rail is proposed since W-beam rail has percent elongation values consistently above the current specification of 12%. For example, 16% elongation corresponds to the 1st percentile value for W-beam rail and corresponds to a 0th percentile for thrie-beam rail (i.e., no thrie-beam rail in the survey had a percent elongation value of less than 16.3%). Increasing minimum percent elongation to 16% would increase the Yield Strength ↑ Moderate correlation (i.e., R2 = 0.685) ↓ Weak correlation (i.e., R2 = 0.132) ↓ Moderate correlation (i.e., R2 = 0.343) ↑ No correlation (i.e., R2 = 0) Tensile Strength ↓ Weak correlation (i.e., R2 = 0.285) ↓ No correlation (i.e., R2 = 0.001) ↓ No correlation (i.e., R2 = 0.035) %elongation ↓ No correlation (i.e., R2 = 0.015) ↑ Strong correlation (i.e., R2 = 0.849) T/Y ratio ↓ Very Weak correlation (i.e., R2 = 0.078) %elongation T/Y ratio σεTensile Strength Table G-6. Correlation between various mechanical properties for M 180 W-beam rail. Yield Strength ↑ Strong correlation (i.e., R2 = 0.725) ↓ Weak correlation (i.e., R2 = 0.143) ↓ Moderate correlation (i.e., R2 = 0.429) ↑ No correlation (i.e., R2 = 0.008) Tensile Strength ↓ Weak correlation (i.e., R2 = 0.277) ↓ No correlation (i.e., R2 = 0.026) ↓ No correlation (i.e., R2 = 0.005) %elongation ↓ No correlation (i.e., R2 = 0.005) ↑ Strong correlation (i.e., R2 = 0.846) T/Y ratio ↓ Very weak correlation (i.e., R2 = 0.07) %elongation T/Y ratio σεTensile Strength Table G-7. Correlation between various mechanical properties for M 180 thrie-beam rail.

122 Investigation of Material Requirements for Highway Guardrail Systems minimum pseudo-strain energy value 33% compared to current specifications, as illustrated in the calculations that follow. Current baseline properties (70–50–12) [i.e., (tensile  70 ksi, yield  50 ksi, %elongation  12%)] 50 70 2 0.12 7.2 ksi( )σε = + ∗ = Increasing %elongation to 16% (70–50–16) 50 70 2 0.16 9.6 ksi (e.g., a 33% increase)( )σε = + ∗ = Further increasing the minimum percent elongation to 19% would increase the minimum pseudo-strain energy value 58% compared to current specifications. The percent elongation of 19% corresponds to the 5th percentile value for W-beam rail and corresponds to the 1st percen- tile for thrie-beam rail in this study. Increasing %elongation to 19% (70–50–19) 50 70 2 0.19 11.4 ksi (e.g., a 58% increase)( )σε = + ∗ = Increasing the tensile strength from 70 ksi to 75 ksi was another revision that was considered. The 5th percentile value for tensile strength was 75,530 psi for W-beam rail and 72,743 psi for thrie-beam rail. Increasing the minimum percent elongation to 16% and the minimum tensile strength to 75 ksi would increase the minimum pseudo-strain energy by 39%. Further increasing the minimum percent elongation to 19% and the minimum tensile strength to 75 ksi would increase the minimum pseudo-strain energy 65%. These calculations are illustrated in the following. Increasing tensile strength to 75 ksi and %elongation to 16% (75–50–16) 50 75 2 0.16 10 ksi (e.g., a 39% increase)( )σε = + ∗ = Increasing tensile strength to 75 ksi and %elongation to 19% (75–50–19) 50 75 2 0.19 11.9 ksi (e.g., a 65% increase)( )σε = + ∗ = It was also of interest to determine how many cases would have been rejected based on the option of increasing both the minimum percent elongation and tensile strength requirements. For the case of 16% minimum percent elongation and 75 ksi minimum tensile strength (e.g., 70–50–16), 19 of the current 380 compliant W-beam cases would not meet the new require- ments, which would correspond to 5% being rejected. For the case of 19% minimum percent elongation and 75 ksi minimum tensile strength (e.g., 70–50–19), 32 of the current 380 com- pliant W-beam cases would not meet the new requirements, which would correspond to 8.4% being rejected. It should be noted, however, that the average difference between yield strength and tensile strength for M 180 sheet steel is approximately 20 ksi. So, increasing the minimum tensile strength to 75 ksi would in effect also result in the minimum yield strength being increased to 55 ksi. Further, for a given material chemistry, the percent elongation generally decreases as

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 123   tensile strength increases, as shown in Figure G-13 in Addendum G-1, and the additional cost to produce the high-strength, low-alloy (HSLA) chemistry needed for higher strength levels while achieving high elongation may not be reasonable. Recommendations Table G-8 shows a summary of the current and proposed mechanical property requirements for W-beam rail. Ninety-nine percent of the materials surveyed already meet the proposed spec- ifications of Option 1, while 95% of the surveyed materials were found to meet the proposed specifications of Option 2. Thus, these recommendations are basically just catching M 180 up to the reality of what is currently being provided. As shown in Table G-9, the project panel ulti- mately approved Option 1 for inclusion in the proposed updates to M 180 for the mechanical property specifications for corrugated sheet steel used for guardrail beams, transition beams, and terminal connectors. Adopting these recommendations will improve minimum strength and toughness of these components and reduce the potential for poor guardrail performance without imposing a significant burden on mills and suppliers. Appendix G References Asadollahi Pajouh, M., Bielenberg, R.W., Rasmussen, J.D., Bai, F., Faller, R.K., and Holloway, J.C. Dynamic Test- ing and Evaluation of Culvert-Mounted, Strong-Post MGS to TL-3 Guidelines of MASH 2016. 2020. Bligh, R.P., Menges, W.L., Griffith, B.L., Schroeder, G.E., and Kuhn, D.L. MASH Evaluation of TXDOT Roadside Safety Features – Phase II, Report 0-6946-R2. Texas A&M Transportation Institute, College Station, Texas. 2019. Current Proposed Option 1 Option 2 Yield strength (minimum) 50 ksi (345 MPa) 50 ksi (345 MPa) 50 ksi (345 MPa) Tensile strength (minimum) 70 ksi (483 MPa) 70 ksi (483 MPa) 70 ksi (483 MPa) Elongation in 2 in. (minimum) 12% 16% 19% Resulting (minimum) 7.2 ksi 9.6 ksi (33% increase) 11.4 ksi (58% increase) * is a calculated value and not a direct test result. Table G-8. Proposed mechanical property specifications for corrugated steel rail. Panel Approved % Increase Yield strength (minimum) 50 ksi (345 MPa) – Tensile strength (minimum) 70 ksi (483 MPa) – Elongation in 2 in. (minimum) 16% 33% Resulting σε (minimum) 9.6 ksi 33% is a calculated value and not a direct test result. Table G-9. Panel-approved mechanical property specifications for corrugated steel rail.

124 Investigation of Material Requirements for Highway Guardrail Systems Bullard, D.L., Jr., Bligh, R.P., Menges, W.L., and Haug, R.R. NCHRP Web-Only Document 157: Volume I: Evaluation of Existing Roadside Safety Hardware Using Updated Criteria—Technical Report. Transportation Research Board of the National Academies, Washington, DC. 2010. Buth, C.E., Menges, W.L., and Schoeneman, S.K. NCHRP Report 350 Test 3-11 of the Long-Span Guardrail with 5.7 m Clear Span and Nested W-Beams Over 11.4 m. Report/Test No.405160-1-1. Texas A&M Transporta- tion Institute, College Station, Texas. May 2006. Fleck, J. 1997 Chevrolet C2500 Pickup Impact with the Strong Steel Post W-Beam Guardrail – Part 2. Test Report C08C3-027-2. MGA Research Corporation, Burlington, WI. 2008. Kovar, J.C., Bligh, R.P., Menges, W.L., Schroeder, G.E., Schroeder, W., Wegenast, S.A., Griffith, B.L., and Kuhn, D.L. MASH Crash Testing and Evaluation of the MGS Guardrail System With Reduced Post Spacing. Texas A&M Transportation Institute Proving Ground, College Station, TX. 2022. Polivka, K.A., Faller, R.K., Sicking, D.L., Rohde, J.R., Reid, J.D., and Holloway, J.C. Guardrail and Guardrail Terminals Installed Over Curbs. Final Report to the Midwest States’ Regional Pooled Fund Program. MwRSF Research Report No. TRP-03-83-99, Project No. SPR-3(017)-Year 8, Midwest Roadside Safety Facility, University of Nebraska–Lincoln. 2000. Ronspies, K., Bielenberg, R.W., Rosenbaugh, S., Faller, R.K., and Stolle, C.S. Evaluation of the MGS Placed 6 in. Behind a 6-in. Tall AASHTO Type-B Curb to MASH TL3. Report No. TRP-03-390-20. Midwest Roadside Safety Facility, Lincoln, Nebraska. 2020. Rosenbaugh, S. K., Stolle, C. S., Ronspies, K. B., University of Nebraska–Lincoln, Nebraska Department of Roads, and Federal Highway Administration. MGS with Curb and Omitted Post: Evaluation to MASH 2016 Test Designation No. 3-10. MwRSF. 2019a. Rosenbaugh, S.K., Stolle, C.S., and Ronspies, K.B. MGS with Curb and Omitted Post: Evaluation to MASH 2016 Test Designation No. 3-10. Report No. TRP-03-393-19. Midwest Roadside Safety Facility, Lincoln, Nebraska. 2019b. Sheikh, N.M., Menges, W.L., and Kuhn, D.L. MASH TL-3 Evaluation of 31-inch W-Beam Guardrail with Wood and Steel Posts in Concrete Mow Strip. Report No. 608551-1-4. Texas A&M Transportation Institute Proving Ground, College Station, Texas. 2019. Winkelbauer, B.J., Rosenbaugh, S.K., Bielenberg, R.W., Putjenter, J.G., Lechtenberg, K.A., Faller, R.K., and Reid, J.D. Dynamic Evaluation of MGS Stiffness Transition with Curb. MwRSF Research Report No. TRP-03-291-14. Midwest Roadside Safety Facility, Lincoln, Nebraska. 2014. Wright, A.E. and Ray, M.H. Characterizing Guardrail Steel for LS-DYNA3D Simulations. Transportation Research Record, No. 1528, 1996.

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 125   Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 382 Max 77,974 95,000 45.6 1.6 32.95 Min 46,682 62,400 12.0 1.07 8.91 Mean 61,232 81,296 24.5 1.33 17.37 Std Dev 4,094 4,425 3.4 0.05 2.17 95% CI (+/-) 411 444 0.34 0.0051 0.22 Median 61,480 80,415 25.0 1.32 17.65 Mode 61,710 83,000 26.0 1.3 14.81 10th Percentile 56,131 77,107 20.0 1.29 14.82 5th Percentile 54,731 75,530 19.0 1.28 13.72 2nd Largest 73,600 94,900 33.0 1.5 25.95 2nd Smallest 50,000 70,308 13.0 1.1 9.89 12-ga W-Beam (M 180 Class A) %Elong. T/Y Ratio y = 0.8944x + 26533 R² = 0.6848 60000 65000 70000 75000 80000 85000 90000 95000 100000 40,000 45,000 50,000 55,000 60,000 65,000 70,000 75,000 80,000 Te ns ile S tr en gt h (p si ) Yield Strength (psi) Tensile Strength vs. Yield Strength y = -0.0003x + 42.951 R² = 0.1318 0 5 10 15 20 25 30 35 40 45 50 40,000 45,000 50,000 55,000 60,000 65,000 70,000 75,000 80,000 % E lo ng ati on Yield Strength (psi) %Elongation vs. Yield Strength y = -7E-06x + 1.7772 R² = 0.3427 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 40,000 45,000 50,000 55,000 60,000 65,000 70,000 75,000 T/ Y Ra tio Yield Strength (psi) T/Y Ratio vs. Yield Strength y = 3E-06x + 17.2 R² = 3E-05 0.6 5.6 10.6 15.6 20.6 25.6 30.6 35.6 40,000 45,000 50,000 55,000 60,000 65,000 70,000 75,000 80,000 σε (k si ) Yield Strength (psi) σε vs. Yield Strength 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 40,000 45,000 50,000 55,000 60,000 65,000 70,000 75,000 80,000 Pe rc en til e Yield Strength (psi) Cumulative Distribution (Yield Strength) Figure G-12. Statistics pertaining to yield strength of M 180 W-beam guardrail. Addendum G-1 Summary of W-Beam Mechanical Properties

126 Investigation of Material Requirements for Highway Guardrail Systems Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 382 Max 77,974 95,000 45.6 1.6 32.95 Min 46,682 62,400 12.0 1.07 8.91 Mean 61,232 81,296 24.5 1.33 17.37 Std Dev 4,094 4,425 3.4 0.05 2.17 95% CI (+/-) 411 444 0.34 0.0051 0.22 Median 61,480 80,415 25.0 1.32 17.65 Mode 61,710 79,770 26.0 1.3 14.81 10th Percentile 56,131 77,107 20.0 1.29 14.82 5th Percentile 54,731 75,530 19.0 1.28 13.72 2nd Largest 73,600 94,900 33.0 1.5 25.95 2nd Smallest 50,000 70,308 13.0 1.1 9.89 %Elong. 12-ga W-Beam (M 180 Class A) T/Y Ratio 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 60,000 65,000 70,000 75,000 80,000 85,000 90,000 95,000 100,000 Pe rc en til e Tensile Strength (psi) Cumulative Distribution (Tensile Strength) y = -0.0004x + 57.883 R² = 0.2853 0 5 10 15 20 25 30 35 40 45 50 60,000 65,000 70,000 75,000 80,000 85,000 90,000 95,000 100,000 % E lo ng ati on Tensile Strength (psi) %Elongation vs. Tensile Strength y = -4E-07x + 1.3626 R² = 0.0012 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 60,000 65,000 70,000 75,000 80,000 85,000 90,000 95,000 100,000 T/ Y Ra tio Tensile Strength (psi) T/Y Ratio vs. Tensile Strength y = -9E-05x + 24.858 R² = 0.0352 0.6 5.6 10.6 15.6 20.6 25.6 30.6 35.6 60,000 65,000 70,000 75,000 80,000 85,000 90,000 95,000 100,000 σε (k si ) Tensile Strength (psi) σε vs. Tensile Strength y = 0.7657x - 1016.9 R² = 0.6848 40000 45000 50000 55000 60000 65000 70000 75000 80000 60,000 65,000 70,000 75,000 80,000 85,000 90,000 95,000 100,000 Yi el d St re ng th (p si ) Tensile Strength (psi) Yield Strength vs. Tensile Strength Figure G-13. Statistics pertaining to tensile strength of M 180 W-beam guardrail.

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 127   Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 382 Max 77,974 95,000 45.6 1.6 32.95 Min 46,682 62,400 12.0 1.07 10.22 Mean 61,232 81,296 24.5 1.33 17.41 Std Dev 4,094 4,425 3.4 0.05 2.17 95% CI (+/-) 411 444 0.34 0.0051 0.22 Median 61,480 80,415 25.0 1.32 17.66 Mode 62,000 89,000 26.0 1.3 14.81 10th Percentile 56,131 77,107 20.0 1.29 14.83 5th Percentile 54,731 75,530 19.0 1.28 13.81 2nd Largest 73,600 94,900 33.0 1.5 25.95 2nd Smallest 50,000 70,308 13.0 1.1 10.38 %Elong. 12-ga W-Beam (M 180 Class A) T/Y Ratio 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 10.0 20.0 30.0 40.0 50.0 Pe rc en til e % Elongation Cumulative Distribution (%Elongation) y = -436.48x + 71911 R² = 0.1318 40000 45000 50000 55000 60000 65000 70000 75000 80000 10.0 15.0 20.0 25.0 30.0 35.0 Yi el d St re ng th (p si ) % Elongation Yield Strength vs. %Elongation y = -694.16x + 98279 R² = 0.2853 60000 65000 70000 75000 80000 85000 90000 95000 100000 10.0 15.0 20.0 25.0 30.0 35.0 Te ns ile S tr en gt h (p si ) % Elongation Tensile Strength vs. %Elongation y = -0.0018x + 1.3748 R² = 0.0151 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 10.0 15.0 20.0 25.0 30.0 35.0 T/ Y Ra tio % Elongation T/Y Ratio vs. %Elongation y = 0.5881x + 2.9812 R² = 0.8492 0 5 10 15 20 25 30 35 10.0 15.0 20.0 25.0 30.0 35.0 σε (k si ) % Elongation σε vs. %Elongation Figure G-14. Statistics pertaining to percent elongation of M 180 W-beam guardrail.

128 Investigation of Material Requirements for Highway Guardrail Systems Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 382 Max 77,974 95,000 45.6 1.6 32.95 Min 46,682 62,400 12.0 1.07 8.91 Mean 61,232 81,296 24.5 1.33 17.36 Std Dev 4,094 4,425 3.4 0.05 2.17 95% CI (+/-) 411 444 0.34 0.0051 0.22 Median 61,480 80,415 25.0 1.32 17.63 Mode 61,710 79,770 26.0 1.3 14.81 10th Percentile 56,131 77,107 20.0 1.29 14.82 5th Percentile 54,731 75,530 19.0 1.28 13.72 2nd Largest 73,600 94,900 33.0 1.5 25.95 2nd Smallest 50,000 70,308 13.0 1.1 9.89 %Elong. 12-ga W-Beam (M 180 Class A) T/Y Ratio 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 Pe rc en til e T/Y Ratio Cumulative Distribution (T/Y Ratio) y = -46885x + 123573 R² = 0.3427 40000 45000 50000 55000 60000 65000 70000 75000 80000 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 Yi el d St re ng th (p si ) T/Y Ratio Yield Strength vs. T/Y Ratio y = -3033.1x + 85329 R² = 0.0012 60000 65000 70000 75000 80000 85000 90000 95000 100000 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 Te ns ile S tr en gt h (p si ) T/Y Ratio Tensile Strength vs. T/Y Ratio y = -8.1813x + 35.344 R² = 0.0151 10 15 20 25 30 35 40 45 50 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 % E lo ng ati on T/Y Ratio % Elongation vs. T/Y Ratio y = -11.85x + 33.126 R² = 0.0777 0 5 10 15 20 25 30 35 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 σε (k si ) T/Y Ratio σε vs. T/Y Ratio Figure G-15. Statistics pertaining to T/Y ratio of M 180 W-beam guardrail.

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 129   Figure G-16. Statistics pertaining to pseudo-strain energy of M 180 W-beam guardrail.

130 Investigation of Material Requirements for Highway Guardrail Systems § http://www.dmstat1.com/res/TheCorrelationCoefficientDefined.html#:~:text=Values%20between%200.7%20and%201.0,shared%20between%20the%20two %20variables.%E2%80%9D Figure G-17. Strength of linear correlation between material attributes of M 180 W-beam guardrail.

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 131   Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 53 Max 65,000 83,940 30.1 1.5 20.17 Min 53,900 70,650 16.3 1.25 11.26 Mean 60,316 79,233 25.7 1.31 17.89 Std Dev 3,080 3,071 2.4 0.04 1.45 95% CI (+/-) 829 827 0.64 0.0102 0.39 Median 61,400 79,830 25.7 1.31 18.20 10th Percentile 54,884 73,610 22.7 1.28 16.47 5th Percentile 54,524 72,742 21.7 1.28 16.06 2nd Largest 64,700 83,490 29.8 1.4 19.85 2nd Smallest 53,960 72,000 20.8 1.3 14.41 12-ga Thrie-Beam (M 180 Class A) %Elong. T/Y Ratio y = -0.0003x + 43.179 R² = 0.1428 0 5 10 15 20 25 30 35 40,000 45,000 50,000 55,000 60,000 65,000 70,000 % E lo ng ati on Yield Strength (psi) %Elongation vs. Yield Strengthy = 0.8487x + 28042 R² = 0.7245 60000 65000 70000 75000 80000 85000 90000 40,000 45,000 50,000 55,000 60,000 65,000 70,000 Te ns ile S tr en gt h (p si ) Yield Strength (psi) Tensile Strength vs. Yield Strength y = -8E-06x + 1.8028 R² = 0.4291 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 40,000 45,000 50,000 55,000 60,000 65,000 70,000 75,000 T/ Y Ra tio Yield Strength (psi) T/Y Ratio vs. Yield Strength y = 9E-05x + 12.592R² = 0.0312 0.6 5.6 10.6 15.6 20.6 25.6 40,000 45,000 50,000 55,000 60,000 65,000 σε (k si ) Yield Strength (psi) σε vs. Yield Strength 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 40,000 45,000 50,000 55,000 60,000 65,000 70,000 Pe rc en til e Yield Strength (psi) Cumulative Distribution (Yield Strength) Figure G-18. Statistics pertaining to yield strength of M 180 thrie-beam guardrail. Addendum G-2 Summary of W-Beam Mechanical Properties

132 Investigation of Material Requirements for Highway Guardrail Systems Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 53 Max 65,000 83,940 30.1 1.5 20.17 Min 53,900 70,650 16.3 1.25 11.26 Mean 60,316 79,233 25.7 1.31 17.87 Std Dev 3,080 3,071 2.4 0.04 1.45 95% CI (+/-) 829 827 0.64 0.0102 0.39 Median 61,400 79,830 25.7 1.31 18.18 10th Percentile 54,884 73,610 22.7 1.28 16.47 5th Percentile 54,524 72,742 21.7 1.28 16.06 2nd Largest 64,700 83,490 29.8 1.4 19.85 2nd Smallest 53,960 72,000 20.8 1.3 14.41 %Elong. 12-ga Thrie-Beam (M 180 Class A) T/Y Ratio 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 60,000 65,000 70,000 75,000 80,000 85,000 90,000 Pe rc en til e Tensile Strength (psi) Cumulative Distribution (Tensile Strength) y = -0.0004x + 57.764 R² = 0.2766 0 5 10 15 20 25 30 35 60,000 65,000 70,000 75,000 80,000 85,000 90,000 % E lo ng ati on Tensile Strength (psi) %Elongation vs. Tensile Strength y = -2E-06x + 1.4735 R² = 0.0261 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 60,000 65,000 70,000 75,000 80,000 85,000 90,000 T/ Y Ra tio Tensile Strength (psi) T/Y Ratio vs. Tensile Strength y = -3E-05x + 20.499 R² = 0.0048 0.6 5.6 10.6 15.6 20.6 25.6 60,000 65,000 70,000 75,000 80,000 85,000 90,000 σε (k si ) Tensile Strength (psi) σε vs. Tensile Strength y = 0.8537x - 7322.5 R² = 0.7245 40000 45000 50000 55000 60000 65000 70000 60,000 65,000 70,000 75,000 80,000 85,000 90,000 Yi el d St re ng th (p si ) Tensile Strength (psi) Yield Strength vs. Tensile Strength Figure G-19. Statistics pertaining to tensile strength of M 180 thrie-beam guardrail.

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 133   Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 53 Max 65,000 83,940 30.1 1.5 20.17 Min 53,900 70,650 16.3 1.25 15.86 Mean 60,316 79,233 25.7 1.31 18.09 Std Dev 3,080 3,071 2.4 0.04 1.45 95% CI (+/-) 829 827 0.64 0.0102 0.39 Median 61,400 79,830 25.7 1.31 18.20 10th Percentile 54,884 73,610 22.7 1.28 16.61 5th Percentile 54,524 72,742 21.7 1.28 16.37 2nd Largest 64,700 83,490 29.8 1.4 19.85 2nd Smallest 53,960 72,000 20.8 1.3 16.26 %Elong. 12-ga Thrie-Beam (M 180 Class A) T/Y Ratio 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 Pe rc en til e % Elongation Cumulative Distribution (%Elongation) y = -492.23x + 72960 R² = 0.1428 40000 45000 50000 55000 60000 65000 70000 10.0 15.0 20.0 25.0 30.0 35.0 Yi el d St re ng th (p si ) % Elongation Yield Strength vs. %Elongation y = -683.14x + 96781 R² = 0.2766 60000 65000 70000 75000 80000 85000 90000 10.0 15.0 20.0 25.0 30.0 35.0 Te ns ile S tr en gt h (p si ) % Elongation Tensile Strength vs. %Elongation y = -0.0007x + 1.3319 R² = 0.0017 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 10.0 15.0 20.0 25.0 30.0 35.0 T/ Y Ra tio % Elongation T/Y Ratio vs. %Elongation y = 0.5384x + 4.0611 R² = 0.7686 0 5 10 15 20 25 10.0 15.0 20.0 25.0 30.0 35.0 σε (k si ) % Elongation σε vs. %Elongation Figure G-20. Statistics pertaining to percent elongation of M 180 thrie-beam guardrail.

134 Investigation of Material Requirements for Highway Guardrail Systems Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 53 Max 65,000 83,940 30.1 1.5 20.17 Min 53,900 70,650 16.3 1.25 11.26 Mean 60,316 79,233 25.7 1.31 17.88 Std Dev 3,080 3,071 2.4 0.04 1.45 95% CI (+/-) 829 827 0.64 0.0102 0.39 Median 61,400 79,830 25.7 1.31 18.20 10th Percentile 54,884 73,610 22.7 1.28 16.47 5th Percentile 54,524 72,742 21.7 1.28 16.06 2nd Largest 64,700 83,490 29.8 1.4 19.85 2nd Smallest 53,960 72,000 20.8 1.3 14.41 %Elong. 12-ga Thrie-Beam (M 180 Class A) T/Y Ratio 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 1.00 1.10 1.20 1.30 1.40 1.50 Pe rc en til e T/Y Ratio Cumulative Distribution (T/Y Ratio) y = -53041x + 130059 R² = 0.4291 40000 45000 50000 55000 60000 65000 70000 1.00 1.10 1.20 1.30 1.40 1.50 Yi el d St re ng th (p si ) T/Y Ratio Yield Strength vs. T/Y Ratio y = -13051x + 96394 R² = 0.0261 60000 65000 70000 75000 80000 85000 90000 1.00 1.10 1.20 1.30 1.40 1.50 Te ns ile S tr en gt h (p si ) T/Y Ratio Tensile Strength vs. T/Y Ratio y = -2.5583x + 29.051 R² = 0.0017 10 15 20 25 30 35 40 45 50 1.00 1.10 1.20 1.30 1.40 1.50 % E lo ng ati on T/Y Ratio % Elongation vs. T/Y Ratio y = -10.087x + 31.154 R² = 0.0698 0 5 10 15 20 25 1.00 1.10 1.20 1.30 1.40 1.50 σε (k si ) T/Y Ratio σε vs. T/Y Ratio Figure G-21. Statistics pertaining to T/Y ratio of M 180 thrie-beam guardrail.

Review of Mechanical Properties for Corrugated Sheet Steel Used in Guardrail Field Installations 135   Yield Tensile σε (psi) (psi) (ksi) Specified Min. 50,000 70,000 12.0 - - Data Points 53 Max 65,000 83,940 30.1 1.5 20.17 Min 53,900 70,650 16.3 1.25 15.86 Mean 60,316 79,233 25.7 1.31 18.09 Std Dev 3,080 3,071 2.4 0.04 1.45 95% CI (+/-) 829 827 0.64 0.0102 0.39 Median 61,400 79,830 25.7 1.31 18.20 10th Percentile 54,884 73,610 22.7 1.28 16.61 5th Percentile 54,524 72,742 21.7 1.28 16.37 2nd Largest 64,700 83,490 29.8 1.4 19.85 2nd Smallest 53,960 72,000 20.8 1.3 16.26 12-ga Thrie-Beam (M 180 Class A) %Elong. T/Y Ratio 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 10 12 14 16 18 20 22 Pe rc en til e σε (ksi) Cumulative Distribution (σε) y = 191.44x + 56891 R² = 0.0081 40000 45000 50000 55000 60000 65000 70000 10 12 14 16 18 20 22 Yi el d St re ng th (p si ) σε (ksi) Yield Strength vs. σε y = -147.27x + 81868 R² = 0.0048 60000 65000 70000 75000 80000 85000 90000 10 12 14 16 18 20 22 Te ns ile S tr en gt h (p si ) σε (ksi) Tensile Strength vs. σε y = 1.4275x + 0.1475 R² = 0.7686 0 5 10 15 20 25 30 35 10 12 14 16 18 20 22 % E lo ng ati on σε (ksi) % Elongation vs. σε y = -0.0069x + 1.4387 R² = 0.0698 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 1.45 1.5 10 12 14 16 18 20 22 T/ Y Ra tio σε (ksi) T/Y Ratio vs. σε Figure G-22. Statistics pertaining to pseudo-strain energy of M 180 thrie-beam guardrail.

136 Investigation of Material Requirements for Highway Guardrail Systems § http://www.dmstat1.com/res/TheCorrelationCoefficientDefined.html#:~:text=Values%20between%200.7%20and%201.0,shared%20between%20the%20two %20variables.%E2%80%9D Figure G-23. Strength of linear correlation between material attributes of M 180 thrie-beam guardrail.

Abbreviations and acronyms used without denitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration GHSA Governors Highway Safety Association HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

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