Investigation of Material Requirements for Highway Guardrail Systems (2022)

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3   2.1 History of AASHTO M 180 The guardrail that is specified in AASHTO M 180 was originally developed in the 1950s and was incorporated by several states into their standard plans and specifications around that time (Ohio Bureau of Highways 1956). By 1961, the M 180 guardrail was sufficiently common that AASHTO included it in the 8th edition of the AASHTO Materials Specifications. AASHTO M 180 has since appeared in every subsequent edition of the AASHTO Materials Specification, including the latest 2018 edition (AASHTO 2018b). The first version of M 180 was published in 1960 and was included in the 1961 AASHTO Materials Specifications (AASHTO 2018b). The first version of the M 180 specification was 3 pages long, including a 1-page drawing with the face and side views of a standard W-beam and terminal end section, dimensioning the recommended 5⁄8-in.-diameter bolts and nuts as well as dimensioning a typical splice connection. Two classes of beam were specified; Class A beams were 10 gauge, and Class B beams were 12 gauge. The following material properties were included in this first publication of M 180: (1) galvanized coating of at least 2.0 oz. per square foot, (2) an elongation of 12%, and (3) tensile strength of 100,000 lb for Class A and 80,000 lb for Class B. Additionally, bend testing was specified for both classes of sheet steel. Inspection, sampling and rejecting, and method of testing sections were also included. An update to M 180 was published in 1965 as M 180-65. The only modification in M 180-65 was the addition of a section on manufacturer marking, which required marking of the manu- facturer name or brand, the gauge or weight of the metal, the weight of galvanizing, and the manufacturer heat number. In 1968 the Interim Specification for Corrugated Sheet Steel Beams for Highway Guardrail was published as M 180-68I. The interim specifications maintained the same Class A and B des- ignations as the 1965 version, but rather than specifying the gauge, a nominal thickness for each class was specified. Four types of guardrail were defined in M 180-68I based on coating applied. (Types 1 and 2 were zinc coated, Type 3 was painted, and Type 4 was corrosion-resistant steel.) The 1968 interim specification added a section on the basis of purchase as well as updated base- metal mechanical properties. From M 180-68I to M 180-18, the following mechanical properties have been used: Yield Point minimum 50,000 psi Tensile Strength minimum 70,000 psi Elongation 2 in., minimum 12% Additionally, the 1968 specification includes a table for beam thicknesses (Table I) and weight of coating (Table II) for each class and type. These thickness, tolerance, and weight values have remained the same from M 180-68I through the current M 180-18 specification. Sections were C H A P T E R   2 Literature Review

4 Investigation of Material Requirements for Highway Guardrail Systems added in the 1968 specification for sheet width, corrosion-resistant beams, end or buffer sec- tions, fabrication, connections and splices, washers and backup plates, and basis of acceptance. The manufacturers’ marking paragraph from M 180-65 was reconfigured into a new section with additional requirements, including stating the class and type; this convention remains through M 180-18. A new reference was included requiring ASTM A307 material type for the splice and post bolts. New details were added to the W-beam drawing in M 180-68I, including the buffer end and beam washers. The 1970 AASHTO M 180-70 specification only contains two modifications from M 180-68I. The first is the addition of the note in the sheet width section: The requirements of paragraph 5.1 are intended to define the minimum width sheet permissible. Calcula- tion of exact width dimensions from Figure 1 shows that the finished product may slightly exceed 19 inches. However, the dimensions of Figure 1 can be met within allowable tolerances by using the 19-inch width. Use of sheets slightly greater than 19 inches wide is permissible provided the tolerances in Figure 1 are met. (AASHTO 180-70, p. 332) This note has remained mostly unchanged (i.e., some changes to the wording were made when thrie beams were added in 1978) through M 180-18. The second addition to M 180-70 from M180-68I was a description of how to use a stout knife and considerable pressure to test the adherence of the zinc coating. This procedure description has remained in the specification through M 180-18. In 1974, AASHTO M 180-74 was published. The most notable change in this version was the addition of International System of Units (SI) measurements and units. Additionally, the galvanizing specification was changed from ASTM A153 to AASHTO M 232. AASHTO M 232 was officially added to the AASHTO Materials Standards in 1972 (AASHTO 2018b). Currently, ASTM A153 is an identical standard to AASHTO M 232. Some substantial changes came in the M 180-78 specification. The largest change was the addition of (1) the thrie beam, and (2) the symmetrical W-beam to thrie-beam transition section. There are multiple places in the specification where new language and figures were added to cover the addition of the thrie beam and the transition sections. The material properties, how- ever, remained consistent with the standard W-beam from previous versions, and the classes and types remained the same for all shapes. The material properties of the end and buffer sec- tions were added in M 180-78 and specify: Yield Point minimum 33,000 psi Tensile Strength minimum 45,000 psi Details for an additional button-head bolt (i.e., Alternative 2) with two flat edges on opposing sides of the bolt head to allow for the use of a wrench were added to the original bolt detail (i.e., Alternative 1). An additional section was included in M 180-78 that covered galvanizing repair after damage. The next update to M 180 came in 1979, AASHTO M 180-79. In M 180-79, the only change was to some wording in Section 9.1, which covers end or buffer sections. The end or buffer sec- tion galvanizing clause from M 180-78, which allowed “the same or greater weight of coating as the beam,” was removed in M 180-79. Broad structural and editorial changes were implemented in the 1984 revision of the speci- fication. Aside from these changes, most of the content remained consistent with M 180-79. A summary of the organization changes is provided here: • The scope section was reduced in size (most of the content moving to the classification section). • Descriptions of the class and type of guardrail were moved to a new section called “Clas- sification – §3.”

Literature Review 5   • A new section was added for applicable documents – §2 (i.e., AASHTO, ASTM, federal, and military standards). • The Basis of Purchase section was renamed “Ordering Information – §4.” • The Basis of Acceptance section was moved from the end of the document (§15) to the front of the document (§5). • All individual material sections were consolidated into a single, all-encompassing section called “Materials – §6” (base metal, zinc, bolts and nuts, washers, end sections, etc.). • The fabrication section was renamed “Manufacture – §7.” • The mechanical properties were consolidated into a single new section called “Mechanical Properties – §8.” • The individual galvanizing/coating sections were consolidated into a single, all-encompassing section called “Coating Requirements – §9” (e.g., beams, bolts and nuts, repairs). • The Beam Thickness and Sheet Width sections were combined into a new section called “Dimensions – §10.” While more content has been added to the M 180 specification since 1984, the sections and their order in the current M 180-18 are the same as in M 180-84. The next update, AASHTO M 180-00, came in 2000. The main change in M 180-00 from M 180-84 was the change to SI units being the standard unit of measure. This resulted in changes to number format and table layout, but none of the values changed. Additionally, a new figure was added (Figure 4) to provide detail for the 16-mm post or splice metric bolt and nut. The final minor changes in M 180-00 were that Section 2 was renamed “Referenced Documents” from “Applicable Documents,” and the page layout was changed to three-column newspaper style. An interim update was made to M 180-00 in 2008, AASHTO M 180-00(2008). The changes in M 180-00(2008) were all formatting and layout changes. The three-column newspaper layout was changed back to a single full-page-width column of text, and the order of the figures and tables was changed, which was likely an attempt to improve the flow of the document. Minor changes were made in 2011 in AASHTO M 180-11. The main change in M 180-11 was the addition of specific ASTM galvanizing standards based on whether the beams are galvanized before fabrication (ASTM A653/A653M) or after fabrication (ASTM A123/A123M). Some style changes (e.g., font type and commas after the hundreds place in large numbers) were also made. The next revision, AASHTO M 180-12, came in 2012. The majority of the content remained the same as that of M 180-11, but new references for galvanizing and coating were included. The zinc standard in the materials section changed from M 120 to ASTM B6. The post-fabrication galvanizing of sheet changed from ASTM A123/A123M to AASHTO M 111 M/M 111, which are identical standards. The reference for mechanical zinc coating of bolts and nuts changed from AASHTO M 298 to ASTM B695; however, the class and type remained consistent through this specification change. An interim update was made to M 180-12 in 2017, but no changes from M 180-12 could be identified based on a review of the documents. Significant changes were made in 2018 in the latest revision, AASHTO M 180-18. The most significant change is that two additional types of beam coating were included; both types are zinc-aluminum-magnesium alloys of different weights (Type V: 245 g/m2, Type VI: 305 g/m2). This change led to several other changes: • Addition of new §6.3 for zinc-aluminum-magnesium alloy referencing ASTM A1046/ A1046M. • Addition of Types V and VI to §6.5.1, which discusses washers and backup plates.

6 Investigation of Material Requirements for Highway Guardrail Systems • Addition of a new Table 1 – Coating Thickness Correction, which includes Types I, II, V, and VI. • Addition of new §9.4 and new weight of coating table, which mirrors the new §9.1 for Types I and II. • Expanded Table 4 – Finished Beam or Sheet Thickness to cover Types V and VI. A few more minor changes also appeared in M 180-18. Steel manufactured in an open hearth was removed from the base-metal subsection. The test specimen preparation for mechanical testing was changed from ASTM A653/A6563M to ASTM A924/A924M. A note was added to the weight of coating tables (Tables 2 and 3) describing the coating thickness testing procedure. A new note was added to Table 4 referencing the new Table 1 for coating correction values for the different coating types. 2.2 Review of Current AASHTO M 180 Specification AASHTO M 180 specifies guardrail and associated components that are nonproprietary, meaning that the components can be produced by and are interchangeable with those of any manufacturer that conforms to the M 180 specification. AASHTO M 180 guardrail components are manufactured by various large- and small-scale mills and fabricators. The current M 180 specification essentially covers five main topics related to sheet beams used for highway guardrail and some of the components: (1) materials and mechanical properties, (2) manufacture, (3) coating requirements, (4) drawings and dimensions, and (5) marking. 2.2.1 Materials and Mechanical Properties 2.2.1.1 Corrugated Steel Guardrail AASHTO M 180-18 requires that the base metal for corrugated sheet steel used for beams, transitions, and end sections be electric arc or basic oxygen furnace steel. A specific material type with chemical composition is not defined in M 180-18. This is because the galvanizing process is dependent on the interaction between the base metal and the zinc (or zinc alloy) used for galvanizing. ASTM A385/A385M, Standard Practice for Providing High-Quality Zinc Coatings (Hot Dip), states: [t]he production of a galvanized coating has as its basis the metallurgical reaction between the steel and the molten zinc. . . . A problem with steel chemistry is not usually apparent until after an item has been galvanized. Not all combinations of silicon, phosphorus, carbon, and manganese can be galvanized successfully. . . . The experience of the steel supplier, designer, manufacturer, and galvanizer should deter- mine the steel selection. Although steel chemistry requirements are not defined in the specification, the required mechanical properties are defined in Section 8 of M 180-18. The base-metal strength require- ments from M 180-18 are summarized in Table 1. As will be shown later in Figures 9 and 10, Beams and Transitions End and Buffer Sections Yield strength 345 MPa (50 ksi) 227 MPa (33 ksi) Tensile strength 483 MPa (70 ksi) 310 MPa (45 ksi) Elongation in 50 mm (2 in.) 12% N/A Table 1. Minimum mechanical property requirements for corrugated steel components.

Literature Review 7   the percent elongation for W-beam and thrie-beam rails used in full-scale crash testing over the past 10+ years has ranged from 16.3% to 31.1%, and only one of those cases was less than 19.8%. The average percent elongation for W-beam and thrie-beam rails was 25% and 27.8%, respectively. Considering the fact that many (if not most) guardrail failures result from rail rup- ture (particularly at splice connections), improving strength properties and ensuring material toughness would likely result in improved guardrail performance. 2.2.1.2 General Bolt Hardware (Splice and Post Bolts, Nuts, and Washers) AASHTO M 180-18 specifies the material property requirements for bolts and nuts by refer- encing ASTM A307. This reference to ASTM A307 covers base material, chemical composition, and mechanical properties. ASTM A307 is a standard that primarily applies to externally threaded connectors (e.g., bolts, threaded rods), so it is not an appropriate reference to specify requirements for nuts. A more appropriate specification for nuts is ASTM A563, which, like ASTM A307, defines materials, chemical composition, and mechanical properties for carbon and alloy steel nuts. Speci- fication for washers in M 180-18 consists only of the drawings for rectangular beam washers pro- vided in Figures 3 and 4. AASHTO M 180-18 does not provide any base material or mechanical property requirements for washers; however, it does state that the washers shall be galvanized in accordance with AASHTO M 232M/M 232. 2.2.2 Manufacture Section 7 of AASHTO M 180-18 discusses the manufacturing requirements for guardrail components but provides only minimal guidance regarding specific manufacturing processes. AASHTO M 180-18 includes references to figures for shaping, punching, and drilling; it also specifies that beams shall be shop curved to the appropriate curvature of the installation when beams are to be erected on curves with a radius of 150 ft or less. Through discussions with industry personnel and examination of responses to the survey of practice (Appendix F), it was learned that fit-up problems are often experienced during field installation. This is particularly true when connecting three or more layers of nested rail com- ponents together (e.g., connecting transition or terminal connectors to nested thrie beams), where it is often difficult to achieve proper alignment of bolt holes and slots. The problem is often exacerbated when these components are fabricated using different manufacturing methods. For example, terminal connectors and transition rails are typically press formed, while main guard- rail panel elements are roll formed; these two manufacturing methods often result in different amounts of springback of the part after fabrication, which is a source of non-alignment and fit-up problems. AASHTO M 180-18 states, in Section 7, that the end and transition sections “shall be ready for assembly when delivered. Only drilling or cutting necessary for special connections and for sampling will be permitted in the field” (AASHTO M 180-18, p. 7). This statement seems to “imply that the parts should fit up without field modifications so installers, right or wrong, have the perception and expectation that they will not have to drill or modify splice-bolt holes” in the field (Radice, personal communication). Although M 180-18 discourages field modification, modifications are often needed, especially when bolt holes are not adequately aligned. Research into this problem was recently conducted at Texas A&M Transportation Institute (TTI) and resulted in improved slot-design options for the terminal connector. The alternatives identified included (1) adding longitudinal slots along the hills and valleys of the corrugated portion of the terminal connector to promote increased flexibility of the part, (2) using vertical slots (rather than horizontal slots) to facilitate alignment of connection hardware, and (3) using larger-diameter holes to facilitate alignment of connection hardware (Abu-Odeh et al. 2017).

8 Investigation of Material Requirements for Highway Guardrail Systems 2.2.3 Coating Requirements As discussed in Section 2.1, six types of guardrail are specified by M 180-18. The types of guardrail are differentiated by coating type and thickness. The coating specification require- ments for each guardrail type are summarized in Table 2. Section 8.1.3 of M 180 references ASTM A924/A924M for preparation for test specimens for mechanical property testing. Sec- tion 8 of A924/A924M is Tests for Coating Properties and describes both the weigh-strip-weigh and X-ray fluorescence methods for coating thickness measurement. Both single-spot and triple- spot testing are described for both test methods. Additional information on the weigh-strip- weigh method is found in AASHTO T 65M/T 65 (ASTM A90/A90M), which is referenced in M 180-18. AASHTO M 180-18 specifies that end sections and transitions must be of the same type and class that are specified for the main guardrail panels. Type I guardrail is essentially the type that has been specified in M 180 since 1960. In M 180-60, the requirement was for a galvanized coating mass of 2.0 oz/ft2. AASHTO M 180-18 requires a minimum single-spot galvanizing mass of 1.8 oz/ft2, slightly less than what was required in 1960. In the M 180 1968 interim revision, Types I and II were defined for the first time. The minimum single-spot coating mass has remained the same for Types I and II from 1968 through M 180-18 (Type I = 1.8 oz/ft2, Type II = 3.6 oz/ft2). AASHTO M 180-18 allows for galvanizing of Type I and II beams before fabrication using the continuous hot-dip galvanizing process according to ASTM A653/A653M or after fabrication using the batch hot-dip galvanizing process according to AASHTO M 111M/M 111 (ASTM A123/A123M). AASHTO M 180-18 specifies that zinc used to coat Type I and Type II beams conform to ASTM B6 with a grade of Prime Western. Types III and IV guardrail were also included for the first time in AASHTO M 180-68I. Type III beams are intended to be painted and, prior to leaving the manufacturing facility, they are required to “be cleaned and shop painted with one coat of rust-inhibitive primer” (AASHTO M 180-18). This primer step is required to ensure that surface corrosion does not occur before final top coating can be applied. No process or paint specifications for the final painted coating are provided in M 180-18. Type IV beams are manufactured from corrosion-resistant steel (e.g., cor-ten, weathering steel, ASTM A588/A588M steel, ASTM A606/A606M steel), which by design is uncoated and relies instead on a thin layer of surface oxidation that builds up when exposed to weather and acts as a protective coating. AASHTO M 180-18 requires that Type IV beams not be painted or galvanized and that, in a continuous run of guardrail, they do not show a distinctive color differ- ential. For many years, there has been concern about catastrophic corrosion in certain environ- ments, which can lead to the barrier becoming ineffective. In the late 1990s and early 2000s, the New Hampshire DOT (NHDOT) performed an in-house study on the condition of its Type IV guardrail beams. Regarding weathering steel, NHDOT found that “after 10–15 years in service, 50% of lap connections and 25% of the rail at mid-span were inadequate. Furthermore, after 15–20 years in service, 71% of lap connections were failing while the mid-span rate of failure remained at 25%” (NHDOT 2003). Additionally, the FHWA, on its Frequently Asked Questions site, lists the question “Is it OK to use weathering steel in longitudinal barriers?” FHWA’s answer is “[n]o, the use of weathering steel guardrail should be limited. Where aesthetic concerns are primary, weathering steel guardrail may be used if the owner agency adopts a frequent periodic inspection and replacement schedule” (FHWA 2018). Types V and VI guardrail were added to M 180 in the most current version, AASHTO M 180-18. Types V and VI use a zinc-aluminum-magnesium alloy coating rather than the zinc- only coating used for Type I and Type II beams. The minimum single-spot coating weights of Types V and VI are lower than the Type I and Type II equivalents (Type V = 0.80 oz/ft2, Type  VI = 1.00 oz/ft2). AASHTO M 180-18 allows for galvanizing prior to roll forming or

Type Base Metal Mech. Testing Coating Coating Mass (Min. Single- Spot) Coating Procedure 1-Spot Coating Check 3-Spot Coating Check Coating Mass Test Procedure Class A Class B Finished Thickness Under Tolerance Finished Thickness Under Tolerance I Electric arc or basic oxygen furnace ASTM A924 ASTM B6 zinc 550 g/m2 1.80 oz/ft2 ASTM A653 or ASTM A111 550 g/m2 1.80 oz/ft2 610 g/m2 2.00 oz/ft2 AASHTO T 65M or ASTM E376 2.74 mm 0.108 in. 0.23 mm 0.009 in. 3.51 mm 0.1380 in. 0.25 mm 0.010 in. II 1100 g/m 2 3.60 oz/ft2 1100 g/m2 3.60 oz/ft2 1220 g/m2 4.00 oz/ft2 2.82 mm 0.111 in. 0.23 mm 0.009 in. 3.58 mm 0.1410 in. 0.25 mm 0.010 in. III Rust- inhibitive primer N/A Cleaned, shop painted, and one coat of primer N/A N/A N/A 2.67 mm0.105 in. 0.23 mm 0.009 in. 3.43 mm 0.1350 in. 0.25 mm 0.010 in. IV As approved by engineer (A588) None N/A None N/A N/A N/A 2.67 mm0.105 in. 0.23 mm 0.009 in. 3.43 mm 0.1350 in. 0.25 mm 0.010 in. V Electric arc or basic oxygen furnace ASTM A1046 Zn-Al-Mg alloy 245 g/m2 0.80 oz/ft2 ASTM A1046 245 g/m2 0.80 oz/ft2 275 g/m2 0.90 oz/ft2 AASHTO T 65M or ASTM E376 2.71 mm 0.1066 in. 0.23 mm 0.009 in. 3.47 mm 0.1366 in. 0.25 mm 0.010 in. VI 305 g/m 2 1.00 oz/ft2 305 g/m2 1.00 oz/ft2 350 g/m2 1.15 oz/ft2 2.72 mm 0.1070 in. 0.23 mm 0.009 in. 3.48 mm 0.1370 in. 0.25 mm 0.010 in. Table 2. Specifications for each type of guardrail specified in AASHTO M 180-18.

10 Investigation of Material Requirements for Highway Guardrail Systems pressing the shape using the continuous hot-dip galvanizing process (i.e., using the method described in ASTM A1046/A1046M). AASHTO M 180 specifies that the zinc alloy used to coat Type V and Type VI beams conform to ASTM A1046/A1046M Coating Bath Composition (Table 6) Type 1 with 5%–13% aluminum, 2%–4% magnesium, and up to 1% total additional alloying elements. Specifying coating requirements for bolts, nuts, and washers goes back to the first version of M 180 in 1960, which referenced AASHTO M 111 M/M 111. The current reference for coating hardware is to use the batch hot-dip process according to AASHTO M 232M/M 232 (ASTM A153/A153M) Class C, which has been the case since M 180-68I. AASHTO M 180-18 also allows for mechanical zinc coating according to ASTM B695, Class 50, Type 1 for bolts and nuts only. ASTM A307 recommends mechanically zinc-coating bolts in accordance with ASTM B695 Class 55, which is different from the recommendation in M 180-18 for Class 50. The M 180 specification regarding galvanizing repair goes back to 1978. Since AASHTO M 180-78, the reference for galvanizing repair has been TT-P-641 or DOD-P-21035, which specifies two coats of zinc dust/zinc oxide paint. Additionally, M 180-18 allows for re-galvanizing. Some common reasons for requiring galvanizing repair are field practices such as widening holes and slots to facilitate bolting of nested elements, drilling and cutting for special connections, and damage during transport. An additional concern with coatings, which was brought to the research team’s attention by a manufacturer survey respondent, is that AASHTO M 111 M/M 111 (ASTM A123/A123M) specifies a “minimum average thickness of coating for any individual specimen is one coating grade less than that required in Table 1.” In order to ensure that manufacturers hit the M 180-18 coating thickness requirements, it may be necessary to include a note prohibiting this clause in M 111 M/M 111 (ASTM A123/A123M) in an update to M 180-18. 2.2.4 Drawings and Dimensions AASHTO M 180-18 defines component dimensioning using figures. The following compo- nents are illustrated using engineering drawings in M 180-18: • 5⁄8-in. post or splice bolt (alt no. 1 and 2) • 5⁄8-in. post or splice nut • 16-mm post or splice bolt • 16-mm post or splice nut • W-beam sheet • W-beam end section • W-beam buffer end section • W-beam splice pattern • W-beam post-bolt pattern (for wood posts) • Thrie-beam sheet • Thrie-beam end section • Thrie-beam buffer end section • Thrie-beam splice pattern • Thrie-beam post-bolt pattern (for wood posts) • Symmetrical transition section • Beam washer (shown in both Figures 3 and 4) Figure 1 in M 180-18 shows the 15.88 (5⁄8-in.) post bolt or splice bolt and nut. The image used in M 180-18 has been unchanged since M 180-00(2008), but other versions go back to the 1978 edition. The dimensions and notes for the 5⁄8-in. post bolt or splice bolt have been consistent

Literature Review 11   in all figures through all editions of M 180 since 1978. Figure 1 in M 180-18 is clear and easy to read; all dimensions are present, except for the bolt length, which is specified “as required.” Additionally, Section 6.4.2 requires that the bolts and nuts “conform to or exceed the require- ments of ASTM A307” (AASHTO M 180-18). By citing ASTM A307, the threads per inch and class are implied; however, more explicit details of these features (e.g., 5⁄8-in.-11 Class 2A bolt) would lead to more clarity. Figure 2 in M 180-18 shows the 16-mm metric post bolt, splice bolt, and nut. The image used in M 180-18 has been unchanged since M 180-00(2008) but has existed in previous versions of M 180 back to the 2000 edition. The dimensions and notes for the metric bolt and nut have been consistent in all figures through all editions of M 180 since 2000. The only difference seems to be in the bolt length/threaded length table. In the 2000 version, the designator column is an alphanumeric identifier beginning with “FBB,” which was adopted from the AASHTO-ARTBA- AGC Task Force 13 (TF13) Hardware Guide (hereafter referred to the TF13 Guide). Since M 180-00(2008), these designators have begun with “F 88.” It is assumed that this was a mistake that originated from the low-quality image published in M 180-00 that has persisted through subsequent updates. This table, within M 180 Figure 2, contains useful information, but the implied reference to the TF13 Guide is no longer appropriate. For more discussion on the TF13 Guide and M 180, see Section 2.3. Figure 3 in M 180-18 shows the W-beam and W-beam end components. The image used in M 180-18 has been basically unchanged since M 180-00 except that the radius of the outer cor- rugation was removed between the 2011 and 2012 publications. Figure 3 has existed in one form or another in previous versions of M 180 back to the first publication in 1960. The dimensions called out in the W-beam figure have been consistent all the way back to 1960. In addition to the W-beam itself, additional callouts are made for the (fishtail) end section, buffer end, beam washers, beam splice, and beam erection. An obvious missing element in this figure is the commonly used W-beam to rigid barrier terminal connector. Additionally, the beam washer is depicted in both the W-beam figure and thrie-beam figure. This is redundant and creates an opportunity for inconsistencies between drawings to occur. In the erection callout, wood posts are illustrated rather than steel posts, and mid-span splices are not illustrated or mentioned, although they are the norm for current guardrail installations. Figure 4 in M 180-18 shows the thrie beam and thrie-beam end components. The image used in M 180-18 has been basically unchanged since M 180-00(2008) but has existed in previous versions of M 180 back to 1978. The dimensions called out in the thrie-beam figure have been consistent from 1978 through the latest edition. In addition to the thrie beam itself, additional callouts are made for the (fishtail) end section, buffer end, beam washer, beam splice, and beam erection. An obvious missing element in this figure is the commonly used thrie-beam to rigid barrier terminal connector. As mentioned previously, the beam washer is depicted in both the W-beam figure and thrie-beam figure, which is redundant and creates an opportunity for inconsistencies between drawings to occur. Figure 5 in M 180-18 shows the symmetrical thrie-beam to W-beam transition panel. The image used in M 180-18 has been basically unchanged since M 180-78. The dimensions called out in the thrie-beam figure have been consistent from 1978 through the latest edition of M 180. There are inconsistencies between the transition section drawing and the W-beam and thrie- beam figures that it references. In the W-beam and thrie-beam figures, the dimension callout from the center of the post-bolt slot to the center of the splice-bolt slots is 108 mm, while in the transition figure, this dimension is listed as 110 mm. Similarly, in the W-beam and thrie-beam figures, the dimension from center of splice-bolt hole to edge of the panel is 50.8 mm, while in the transition figure, the dimension is listed as 50 mm. Additionally, Figure 5 only provides SI units, while all other figures in M 180-18 show both metric and U.S. customary units.

12 Investigation of Material Requirements for Highway Guardrail Systems The asymmetrical transition that has been in circulation in the roadside safety literature for many years and used in many nonproprietary guardrail systems is not present in M 180-18. Tolerances are discussed throughout M 180-18. Tolerances are mentioned in the notes sections of M 180-18, Figures 1 through 4, which state that “[a]ll dimensions are subject to manufacturer’s tolerances except where allowable tolerances are shown” (AASHTO M 180-18). Tolerances are also mentioned in M 180-18, Table 4, for finished beam thickness, and in §10.2.1 in the sheet width discussion. Tolerances are not explicitly stated for bolt-hole/slot patterns for splices, post attachments, and end/transition sections. 2.2.5 Marking A section on marking of components has been present in M 180 since 1968 in M 180-68I. In 1968, M 180 required that beams be identified using the fields shown in the top section of Fig- ure 1 of this report. This list remained unchanged until the 2000 revision, where it changed to the text shown in the lower left section of Figure 1. This new list was recreated in the 2008 update (see the lower right section of Figure 1) and has remained consistent in every version of M 180 since. By breaking item b from the 1968 list into two new bullet points, two fragments have been created. It is assumed by the research team that the change in 2000 was to split the heat treatment number and coating lot number into two separate lines; however, this is not clear. The remainder of the marking section focuses on basic “rules” for marking beam elements. To summarize the end of the marking section: W-beam and thrie-beam sections shall have readily available markings directly applied, while end sections and backup plates may not have readily available markings directly on them (i.e., they may be labeled as a bundle, not individually). There are no marking requirements mentioned in M 180 for other hardware such as posts and fasteners. Including marking of the coating lot on sheet steel components is not necessary, and in some cases (e.g., when using batch hot-dip galvanizing) can be an undue burden on manufacturers. If manufacturers maintain internal records for all components included in each coating lot, mark- ing the pieces is somewhat redundant. The manufacturer brand and coating type, which are suf- ficient for tracing the component back to the manufacturer and identifying coating information in most cases, are already included in the required marking information. Without providing coating lots directly to the sheet steel component, the manufacturer would assume responsi- bility for tracing any/all other components included in the coating lot. For example, if it were determined via test samples that a shipment of guardrail beams had inadequate coating, then Figure 1. Marking section of M 180-68I (top), M 180-00 (lower left), and M 180-00(2008) (lower right).

Literature Review 13   it is likely that other guardrail components included in that lot would also be suspect and may need to be rejected or tested. 2.3 Task Force 13, A Guide to Standardized Highway Barrier Hardware 2.3.1 Background According to the Task Force 13 (TF13) website, “Task Force 13 develops, recommends, and promotes standards and specifications for bridge and road hardware used by highway and trans- portation agencies on the nation’s roadways” (TF13 2019). TF13 has been a presence in the roadside safety industry for over 48 years. It was previously a task force of a joint committee of AASHTO, the Associated General Contractors of America (AGC), and the American Road and Transportation Builders Association (ARTBA). The AASHTO-ARTBA-AGC Joint Com- mittee sunset TF13 in September 2015. The Joint Committee’s original intent had been for a task force to perform specific tasks and then disband when the tasks were complete. TF13 was the longest serving task force of the AASHTO-ARTBA-AGC Joint Committee. TF13 has since been re-established as an independent, charitable, educational organization chartered in Ohio and is composed of volunteers that continue the same basic mission as the original joint committee. TF13 members are unofficial (i.e., there is no particular process or requirement for becoming a member), and they are primarily associated with industry, academia, and highway agencies. In the past, TF13 accomplished its mission by developing and publishing guides that essen- tially served as a catalog of components and systems for all types of roadside hardware, includ- ing guardrails, guardrail terminals, crash cushions, small sign supports, luminaire supports, bridge railings, and transitions. These guides have been used by transportation agencies, includ- ing DOTs, to help standardize the roadside hardware industry with respect to drawing details and specifications of common roadside devices. The current version of the TF13 Guide is a web-based content management system originally developed by Roadsafe LLC and currently maintained by TF13. It is open (i.e., accessible) to the public, but only registered users can submit materials or participate in reviews of the guide’s content. The content of the guide is for informational purposes only and does not constitute a standard, specification, or regulation. The following is a brief summary of the TF13 Guide’s history. The first of the TF13 guides was the popular “Guide to Standardized Barrier Rail Hardware,” published in 1971 and then updated in 1973 and 1979 (AASHTO and Association of American Road Builders 1971; AASHTO and American Road and Transportation Builders Association 1979). TF13 also developed separate guides for small sign supports, work-zone channeling devices, drainage products, bridge railings, general hardware components, transitions, and lumi- naire supports, although these were not as widely used as the former (AASHTO 1990; AASHTO 1995; AASHTO 1999; AASHTO and American Road and Transportation Builders Associa- tion 1980). Unfortunately, it became increasingly difficult for the all-volunteer TF13 to manage the pub- lications, such that by the late 1980s the TF13 guides were largely out-of-date. In addition, the state DOTs had been directed to switch to SI units and, of course, all the guides were in U.S. customary units. New crash-testing guidelines appeared in the early 1980s, spawning a great deal of innovation and change in the roadside safety hardware industry. All these changes made it imperative for TF13 to update its guides and find more effective update and distribution procedures. NCHRP Project 22-10 was initiated in 1991 to update both the Hardware Guide and the Small Sign Support Guide, and a contract was awarded to Momentum Engineering to perform the work. The principal objectives were to survey the state DOTs for design details,

14 Investigation of Material Requirements for Highway Guardrail Systems present materials in SI units, and develop an update process to allow for continuous updating. By the end of the project, new technology was becoming available to allow for distribution of documents on CD-ROMs and for making materials available on the World Wide Web. The task force attempted to switch from an all-paper guide to digital media; however, AASHTO was not quite ready for the change in 1996 when NCHRP Project 22-10 was completed. As an interim informal measure, M.H. Ray posted both the Hardware Guide and the Sign Support Guide on the web as PDFs and provided a front-end interface, making it easy to browse the documents for the component of interest. Many TF13 members liked the accessibility of the material on the web, and after working with AASHTO and NCHRP over several years were able to obtain funding to update the Hardware Guide and put it on the web (TF13 2019). In 2005, Ray officially put the Hardware Guide online as a part of NCHRP Project 20-7(196). As a result, the content of the Hardware Guide was greatly expanded to include drawings, photographs, links to manufacturer web pages, and FHWA eligibility letters. Also, the whole process of submitting, updating, and approving drawings was put online, including commenting and draft web pages that are visible to all members of the roadside safety community. Although the TF13 Guide is not a standard, specification, or regulation, many states reference the TF13 Guide in their standard specifications and standard details. The informality of TF13 makes it easy and efficient to post information for new hardware systems and components as they become available, which is useful for quickly disseminating and sharing new designs with other states. In fact, from 2010 to 2017, the FHWA required that all new hardware designs being submitted for federal-aid eligibility review include drawings in TF13 format to facilitate inclu- sion into the TF13 Guide; thus, the content of the guide for a time was largely comprehensive and current. For components of these systems, however, it is necessary that the drawings and specifications be reliable and consistent from system to system. In that regard, standards for the system components, particularly for components that are common across many systems, should be issued through a formal standards-issuing body such as AASHTO so that the user can have absolute confidence in the organization’s competence and authority. 2.3.2 Guardrail Components Included in the TF13 Hardware Guide At the time of this review, there were 46 nonproprietary guardrail systems and six median barrier systems listed in the TF13 Guide that used corrugated W-beams or thrie beams as the main longitudinal rail member. Thirty-five of those systems are no longer eligible for new instal- lations on federally funded roadways because they either failed to meet the current crash-testing standards of the AASHTO Manual for Assessing Safety Hardware (MASH; AASHTO 2009) or have not yet been tested to that standard. There are also six nonproprietary transition systems listed in the TF13 Guide that use W-beams or thrie beams as the main longitudinal rail compo- nent, of which five meet current crash-test standards. In addition, there are several proprietary guardrail terminals that use M 180 guardrail components, as well as some nonproprietary bridge and culvert railings. Appendix E provides a partial listing of W-beam and thrie-beam guardrail components that are included in the TF13 Guide. Not included in this list are various terminal components such as anchor cables, bearing plates, foundation tubes, and swage fittings. Material and coating spec- ifications for each of these components are also provided. Many of the components in the TF13 Guide did not directly include a specifications page; those cases are denoted with a dash in the tables of Appendix E. In several of those cases, however, the drawing page referenced another component that did include a specification page.

Literature Review 15   2.3.2.1 W-Beam and Thrie-Beam Components Appendix E lists all the W-beam and thrie-beam corrugated components in the TF13 Guide. Each of those components either directly or indirectly references M 180 material specifica- tions for Type II or IV corrosion protection. ASTM A588/A588M, ASTM A606/A606M, or M 222M/M 222 are also allowed as an alternative for Type IV (i.e., corrosion-resistant steel). 2.3.2.2 Bolt Hardware Appendix E lists all the hardware components in the TF13 Guide. The bolt hardware section in the TF13 Guide includes standard dimensions for nine button-head bolts. The TF13 bolts FBB01-05 are consistent with M 180 bolts F8801-F8805 (table within M 180-18, Figure 2), and TF13 bolts FBB06-07 are more or less consistent with AASHTO M 180, Figure 1, except that M 180 does not specify a minimum thread length. TF13 bolts FBB08-09, which are used to fasten timber guardrail systems to sound-barrier walls, are not included in M 180. All the button-head bolts in the TF13 Guide reference M 180 for geometric and material specifications. The galva- nized bolts are ASTM A307 Grade A with a minimum yield strength of 36 ksi and a minimum tensile strength of 60 ksi, with zinc coating conforming to M 232M/M 232 for Class C and M 289 for Class 50. The corrosion-resistant bolts are specified as ASTM A325 Type 3, with a minimum yield strength of 92 ksi and a minimum tensile strength of 120 ksi. 2.3.2.3 Steel Posts Appendix E lists all the steel post components in the TF13 Guide. AASHTO M 180-18 does not provide specifications for posts, but the TF13 Guide does provide drawings and material specifications. For galvanized steel posts, TF13 references multiple material specifications, including ASTM A36/A36M, AASHTO M 270M/M 270 (ASTM A709/A709M) Grade 36 or 50, and ASTM A992/A992M. Six post components specify steel with a minimum yield strength of 36 ksi, five post components specify steel with a minimum yield strength of either 36 ksi or 50 ksi, and one post component specifies steel with a minimum yield strength of 50 ksi (i.e., PSF01). In all cases, the zinc coating is to be hot-dip galvanized in accordance with AASHTO M111 M/M 111 v (ASTM A123/A123M). For corrosion-resistant steel posts, the TF13 Guide also references multiple specifications, including AASHTO M 270/M 270M (ASTM A709/A709M) Grade 50W (345W), with the excep- tion of supplementary requirements and A588/A588M. The portion of the post embedded in soil is to be zinc coated according to AASHTO M 111 M/M 111 (ASTM A123/A123M), while the portion of the post above soil is not to be zinc coated, painted, or otherwise treated. 2.3.2.4 Steel Blockouts Appendix E lists all the steel blockout components in the TF13 Guide. For galvanized steel blockouts, the TF13 Guide references AASHTO M 270M/M 270 (ASTM A709/A709M) Grade 36 with zinc coating conforming to AASHTO M 111 M/M 111 (ASTM A123/A123M). For corrosion-resistant steel blockouts, the material is to conform to AASHTO M 270M/M 270 (ASTM A709/A709M) Grade 50. To the authors’ knowledge, there are no steel blockouts used in current Test Level 3 or greater guardrail designs. 2.3.2.5 Wood Posts Appendix E lists all the timber post components in the TF13 Guide. There are several wood- post components that include both round and rectangular cross-sections. The round cross- section posts used in weak-post guardrail systems (e.g., PDE11) have a diameter of 5.5 in., while those used in strong-post guardrail systems have nominal diameters ranging from 7.1 in. to

16 Investigation of Material Requirements for Highway Guardrail Systems 9.125 in. The species of wood specified for these components include southern yellow pine, Douglas fir, ponderosa pine, and white pine; however, for most of the wood-post components, the species is not specified. In most cases, either the material specification ANSI 05.1 is refer- enced, or a minimum stress grade of 1,160 psi – 1,200 psi is specified. Only one component drawing (PDE21-22) specifies both a minimum and maximum groundline diameter for the post. Component PDE21-22 also provides additional specifications regarding manufacture; groundline location; size; scars; shape and straightness; splits, checks, and shakes; knots; treat- ment; decay; holes; slope of grain; compression wood; and ring density. The specification for preservation treatment references M 133 in all cases except for two round post components (i.e., PDE17 and PDE21-22), which reference either American Wood Protection Association (AWPA) BOS U1-05 or AWPA BOS T1-05. 2.3.2.6 Wood Blockouts Appendix E lists all the timber blockout components in the TF13 Guide. These components generally have rectangular cross-sections, although the side contacting the post is routed in some cases to fit flush with the face of the post (e.g., round posts) or to mitigate post rotation on wide-flange posts. The dimensions are the primary distinguishing feature between the various blockout components. The blockout depth, which defines the offset distance between the post and longitudinal rail elements, ranges from 2 in. (PDB03) to 12 in. (PDB18), with the most common depth being 7⁷⁄₈ in. The width of the blockout components ranges from 3.94  in. (PDB03-06) to 6 in., with 6 in. being the most common, while the height generally depends on the rail type. For example, for W-beam systems, the blockout height ranges from 13⁷⁄₈ in. to 14¼ in., with the most common height being 14¼ in. There is one component listed that has a depth of 1911⁄16 in. (PDB08); this component is only used in the W-beam bull-nose system, which has never met NCHRP Report 350 crash performance criteria and is no longer being installed (at least to the authors’ knowledge). For thrie-beam systems, the blockout depth ranges from 19 in. to 20 in. One blockout component has a taper on the lower half of the front face (PDB12) and is used in the thrie-beam bull-nose end terminal. The minimum stress grade for the blockout material is specified as either 1,160 psi or 1,200 psi in almost all cases. The grading is to be in accordance with the rules of the West Coast Lumber Inspection Bureau, Southern Pine Inspection Bureau, or other appropriate timber association. For those components with a minimum stress grade of 1,200 psi, a minimum southern yellow pine Grade 1 is additionally specified. The specification for preservation treatment references AASHTO M 133 in all cases except for two (PDB03-07 and PDB08), which do not include any specifications. 2.3.2.7 Composite Material Blockouts Composite blockouts are a common component in many guardrail systems. They are not covered in the TF13 Guide or M 180-8 because they are proprietary to the manufacturers who make them. 2.3.3 Discrepancies Between the TF13 and AASHTO M 180 Drawings The drawings in M 180 have some inconsistencies when compared to those in the TF13 Guide. For example, Figure 2 of this report shows the cross-section drawings of the W-beam compo- nent in M 180 compared to the drawing in the TF13 Guide (RWM02). One basic difference is that TF13 rounds metric units to the nearest millimeter integer, while AASHTO rounds to the nearest 0.1 mm. Also, the dimensions in the TF13 drawing for the W-beam component are more clearly indicated. For example, as highlighted in Figure 2, the radius of the outer corrugation is not defined in M 180-18 (e.g., it was last included in M 180-11). The dimension lines defining

Literature Review 17   the position of the outer edges of the W-beam and the center base are also not clearly dened in M 180, whereas the TF13 drawing clearly shows that the outside edges of the W-beam extend beyond (below) the base. In the M 180 drawing, the labeling of the 1⁄16-in. distance between the outside edges and the base is redundant. e M 180 drawing also does not include the tolerance specication on the ats at the edges of the W-beam. All of these issues are present for the thrie- beam drawing in M 180, except that the radii of the outer corrugations are dened in that case. e erection drawings for the W-beam and thrie-beam systems in M 180 only include two lengths for the corrugated rails, which correspond to 2-space and 4-space rail elements. e TF13 Guide, on the other hand, provides drawings for 1-space, 2-space, 3-space, 4-space, 6-space, and 8-space options. Figure 3 shows the M 180-18 erection drawing for the W-beam; the erection drawing for the thrie beam is similar. AASHTO M 180 also does not specify blockouts, nor does it include the option for moving the splices to the mid-span, which corresponds to the common MASH-tested 31-in. guardrail design and the weak-post W-beam guardrail designs. Addition- ally, bolt locations for fastening corrugated rail to steel posts (i.e., oset to avoid the post web) are not included in the M 180-18 gure for W-beams or thrie beams. In Note 3 of the M 180 drawing, it is stated that “rectangular plate washers are optional only in transition sections. (a) AASHTO M 180 Figure 3 (b) TF13 Drawing RWM02 Radius not provided Redundant and no tolerance specified Not clear which dimension line corresponds to the outer edge and which is for the base Tolerance not provided Figure 2. Comparison of W-beam cross-section dimensions specied in (a) M 180 and (b) TF13 drawing RWM02. Figure 3. AASHTO M 180-18 W-beam erection drawing.

18 Investigation of Material Requirements for Highway Guardrail Systems They are not to be used in the main section of strong post-post guardrail” (AASHTO M 180-18). The research team is not aware of any transition section that still uses washers with the post bolts, but they are still used in some weak-post guardrail designs (e.g., SGR02 and SGR02b). 2.3.4 Markings in TF13 Guide The TF13 Guide currently has no specifications for markings of components, but members are actively working to establish such standards for certain components. For example, TF13 has recently been working in conjunction with guardrail post fabricators to establish a “standardized drawing” for markings on over-length guardrail posts. Since there is no AASHTO standard for these markings, several agencies have been developing their own standards, and each of those standards is different (Gripne and Task Force 13 2019). TF13 proposed a simple marking to be required only for the common W6×8.5 and W6×9 guardrail posts. Other posts, such as the S3×5.7 used in weak-post guardrail and the W6×15 used in transition systems, are excluded. Further, only posts with oversize lengths would require marking. In other words, any post that is used as the minimum-length post specified by an agency would be excluded from the marking process. The markings proposed by TF13 are to be made by stamping a single number on one side of the post that indicates the length of the oversized post in feet. For a post length that falls within a half-foot increment, the integer would be underlined. For example, a 7½-ft post would be marked as 7. The stamp is to be located between 3 in. and 9 in. from the top of the post. The height of the stamp is to be ¾ in., which is consistent with the specification in M 180-18 for stamping guardrail panels. Further, the TF13 proposed marking is to be stamped prior to galva- nizing, legible after galvanizing, permanent, and to remain visible in the field after final assembly (Gripne and Task Force 13 2019). 2.4 States’ Use States typically reference M 180 in their standard details and specifications for various material and geometry requirements of guardrail designs. The following sections present a comparison of how states are, or are not, using M 180 to specify details regarding manufacture, requisition, and assembly of guardrail components. Throughout this literature review, the standard specification and standard details from various states are compared to form an understanding of the current state of the practice in specifying guardrail components. The standard specifications and details from 18 geographically diverse states were selected as a representative sample, as indicated in Figure 4. This selection of states represents diversity of population density and terrain types. Additional information from some of the states’ specifications engineers is included in Appendix F (survey of practice). 2.4.1 References in State Standard Specifications and Standard Details Figures 5 and 6 illustrate the references found in each of the reviewed states’ standard speci- fications and details. It is consistent across the states that M 180 is the standard reference in the standard specifications for sheet steel used in the W-beam and thrie-beam guardrail and transi- tion sections. It is less common for M 180 to be referenced in the standard details for sheet steel; instead, the TF13 Guide was more commonly referenced. The same trend can be seen when looking at references for splice and post hardware. In the splice and post hardware category, there is noticeably less reference to M 180 in both standard specifications and details. This is curious since splice-bolt specifications have been included in M 180 since its first publication in 1960 and have remained essentially unchanged since the 1978 version.

Literature Review 19   Figure 4. States’ standard specifications and details reviewed by the project team. Note: MGS = Midwest Guardrail System. Figure 5. Comparison table of states’ reference to M 180 and other publications in their standard specifications and details.

20 Investigation of Material Requirements for Highway Guardrail Systems 2.4.2 Splice, Post, and Terminal Connector Hole/Slot Patterns Figure 7 illustrates the published bolt-hole/slot patterns for W-beam and thrie-beam rail from M 180 as well as W-beam and thrie-beam terminal connectors from the TF13 Guide. Figure 8 illustrates the splice, post, and terminal connector hole/slot dimensions found for each of the reviewed states’ standard details for both W-beams and thrie beams. Most states have the same dimensioning as M 180 for the post and splice connection, which is intuitive since M 180 has published dimensions for these component parts. AASHTO does not, on the other hand, have a published standard detail for terminal connectors. For the sake of simplicity, the TF13 Guide drawings for RWE02a-b (for W-beams) and RTE01b (for thrie beams) were regarded as the “published” dimensions for terminal connectors. In Figure 8, the figure key indicates when a state’s standard details matched the TF13 Guide for terminal connector dimensions and when a state’s standard details were similar but varied in some way from the TF13 Guide. Figure 6. Comparison of states’ reference to M 180 and other publications in their standard specifications and details.

Literature Review 21   2.4.3 Galvanizing Process Preference From the sample of states’ standard specifications, it was found that for galvanization of steel guardrail beams, most states specify something similar to the Wyoming Department of Trans- portation (WYDOT) standard, which requires manufacturers to “provide and use 12-gauge [2.51 mm] corrugated steel sheet beams in accordance with AASHTO M 180, type 1, class A” (WYDOT 2010). That is to say that most of the states allow for galvanizing prior to or after fabrication. However, five of the states in the sample specify M 180 but go on to require that the panels be galvanized after fabrication using the batch hot-dip galvanizing process refer- encing AASHTO M 111 M/M 111 (ASTM A123/A123M). In addition, NHDOT specifies that “[g]alvanized steel rail elements and terminal sections shall be treated with a solution of sodium dichromate or other approved chemical solutions so as to prevent or reduce storage stain” (NHDOT 2016). Of the states reviewed, New Hampshire was the only one to require this proce- dure, although it is a common practice in the galvanizing industry to use these and other treat- ments to reduce the possibility of wet storage stain (American Galvanizers Association 2017). (d) Thrie Beam Terminal Connector Holes and Slots (a) W-Beam Splice and Post Slots (b) Thrie Beam Splice and Post Slots (c) W-Beam Terminal Connector Holes and Slots Figure 7. Bolt and slot patterns for (a) W-beam splice and post (AASHTO M 180-18), (b) thrie-beam splice and post (AASHTO M 180-18), (c) W-beam terminal connector (TF13 2019), and (d) thrie-beam terminal connector (TF13 2019).

22 Investigation of Material Requirements for Highway Guardrail Systems NCHRP Project 20-07/Task 333 included research to compare the corrosion performance of batch hot-dip galvanizing and continuous hot-dip galvanizing (Elzly Technology Corporation 2014). The study looked at the performance at both Type I and Type II coating weights for both galvanizing methods on straight guardrail samples, lapped guardrail samples, and small test coupons over 120 cycles in an accelerated corrosion test chamber. It was determined that parts coated using batch hot-dip galvanization are typically supplied at higher coating weights than M 180 requires, and these higher coating weights lead to better corrosion performance; how- ever, the authors specified that “this should not be misinterpreted to mean that [batch hot-dip galvanizing] is intrinsically better than” continuous hot-dip galvanizing (Elzly Technology Cor- poration 2014). An additional finding was that the corrosion performance between batch and continuous hot-dip galvanizing was similar for each galvanizing weight. This finding held true even on the factory edges of the test samples, which, by nature of the process, are coated in the batch hot-dip galvanizing process and uncoated in the continuous hot-dip galvanizing process. 2.4.4 Torque Requirements for Bolts Bolt torque specifications are not covered in M 180-18. A review of the standard specifications from the sampled states revealed that bolt torque specifications are present but are relatively general in nature. For example, as shown in Table 3, bolt torque is most often specified simply as “snug tight” or “drawn tight,” where the Virginia Department of Transportation (VDOT) provides the following definition of snug tight: Figure 8. Comparison of states’ detail for bolt hole/slot punching of beams and terminal connectors.

Literature Review 23   Snug tight is defined as the tightness attained when a power wrench begins to impact solidly or when the bolts are firmly hand tightened with a spud wrench such that the complete area of the connecting surfaces are brought into firm contact with each other. Snug tightening shall progress systematically from the most rigid part of the connection to the free edges, and then the bolts of the connection shall be retightened in a similar systematic manner as necessary until all bolts are simultaneously snug tight and the connection is fully compacted. (VDOT 2016) The Uniform Standard Specifications and Details for Public Works Construction document of the Maricopa Association of Governments (Phoenix, AZ) includes guidance for torque values for hardware used in guardrails that is shown after this paragraph. Similar guidance exists in other state standard specifications; however, those tables apply to high-strength bolts only, rather than general guardrail ASTM A307 type bolts. Unless otherwise shown on the plans, bolts shall be torqued as follows: State Bolt Torque Specification State Bolt Torque Specification Alabama Drawn tight New Hampshire Drawn tight Alaska Not specified Ohio Drawn tight Arizona Securely tightened Oregon Drawn tight Arkansas Workmanlike manner Iowa Fully tight Colorado Drawn tight Rhode Island Drawn tight Georgia Firmly tightened Texas Not specified Maine Drawn tight Vermont Drawn tight Massachusetts Drawn tight Virginia Snug tight fit Minnesota Not specified Wyoming Snug tight Table 3. Bolt torque specifications for reviewed states. Diameter of Bolt Torque, Foot/Pounds 5/8” 45–50 3/4” 70–75 7/8” and larger 120–125 All bolts, other than those specified to be torqued, shall be securely tightened. (Maricopa Association of Governments 2019) 2.4.5 Marking of Components When the standard specifications for the sampled states were reviewed in regard to require- ments for marking steel guardrail beams, the project team found that most states specify some- thing similar to the Colorado Department of Transportation (CDOT) standard, which states that, “[t]he rail elements shall be corrugated sheet steel beams conforming to the requirements of AASHTO M 180 of the designated class and type” (CDOT 2017). Thus, most states require that the marking specifications of M 180 be followed, while some states (e.g., Texas) include additional marking requirements, and others (e.g., New Hampshire) do not specify any mark- ing. For example, in addition to the M 180 marking specifications, the Texas Department of Transportation (TxDOT) standards also require manufacturers to “permanently mark all curved sections of metal beam rail element with the radius of the curved section in the format ‘R = XX ft.’ Markings must be on the back of the metal beam rail section away from traffic and visible after erection” (TxDOT 2014). On the other hand, NHDOT standards specify that “steel rail elements, terminal sections . . . shall conform to AASHTO M 180 (except that paragraph 11, Marking, shall not apply)” (NHDOT 2016). The NHDOT standard specification does not specify what, if any, information should be marked on the guardrail elements.

24 Investigation of Material Requirements for Highway Guardrail Systems 2.5 Manufacturer Use Manufacturers’ use of M 180 is, in general, as specified by their customers. Due to the propri- etary nature of many private manufacturing companies, there is little publicly available docu- mentation describing the precise manufacturing processes they use. Manufacturers were a target group for the survey of practice. In the survey of practice (Appendix F), many manufacturers provided valuable information regarding how their organizations use and refer to M 180 in their design processes. 2.6 Survey of Practice A survey of practice was developed and distributed to users of the AASHTO M 180 specifica- tion. The survey contained 31 multiple-choice and short-answer questions. The questions were developed in such a way that the respondents had an opportunity to provide feedback on how they use M 180 and to identify any known or perceived deficiencies that should be addressed in the update to M 180. The survey included images to make some questions easier to answer, and most questions on the survey could be answered using radio buttons, check boxes, or selec- tions from drop-down lists. The use of essay questions was limited. The survey took an average of 45 minutes for each respondent to complete. A total of 65 AASHTO M 180 users responded to the survey. A breakout of how many respondents came from each survey group collector is shown in Table 4. Full details on the survey, discussion of results, and metrics on the responses are presented in Appendix F. 2.7 Equivalent Material Types 2.7.1 AASHTO M 180 W-Beam and Thrie-Beam Materials AASHTO M 180-18 specifies mechanical properties and basic manufacturing requirements (e.g., produced from an electric arc furnace or basic oxygen furnace) for sheet steel used for guardrail W-beam and thrie-beam elements; however, chemical composition requirements are not specified. One reason for this is that the chemical composition may vary greatly depending on what type of guardrail is specified. Different grades and types of steel react differently to the various coating processes (particularly galvanizing) defined in M 180; therefore, the chemical composition of the base metals vary, as seen in Table 5. 2.7.2 High-Strength Bolts From the survey of practice (results presented in Appendix F), high-strength bolts used in guardrail hardware are typically specified using either ASTM A449 or ASTM A325. Materials Survey Group Number of Responses AASHTO Committee on Materials and Pavements 24 State specification engineers and manufacturers 16 TRB Standing Committee on Roadside Safety Design (AKD20) 14 Task Force 13 9 Additional survey collectors 2 Table 4. User group responses to M 180 survey.

Notes: Ga. = gauge. Blank cells represent undetectable levels of that chemical. Table 5. Chemical composition of guardrail base metal from various MASH crash tests.

26 Investigation of Material Requirements for Highway Guardrail Systems specified in ASTM A449 and ASTM A325 (AASHTO M 164) have a minimum yield strength of 92 ksi and a minimum tensile strength of 120 ksi; there is no maximum tensile strength specified for these materials. The chemical composition is also similar for each of these materials. ASTM F1554 (AASHTO M 314) is less commonly used and has a minimum yield strength of 105 ksi, minimum tensile strength of 125 ksi, and maximum tensile strength of 150 ksi. ASTM F1554 (AASHTO M 314) specifies a minimum elongation of 15%, while ASTM A449 and ASTM A325 (AASHTO M 164) specify a minimum elongation of 14%. All elongation values are based on tensile specimens with 2-in. gauge length. Chemical composition of the metals used for high- strength bolts can be seen in Table 6. 2.7.3 Shapes and Plates States are specifying several different types and grades of steel for various steel shapes and plates used in guardrail components. For example, based on a review of standard specifications from several states, 18 different specifications were identified. Table 7 provides detailed mechan- ical properties and chemical compositions for various materials; these material specifications include minimum yield strength values ranging from 36 to 50 ksi and minimum tensile strength values ranging from 58 to 80 ksi. As indicated in Table 7, many of these material specifications have similar mechanical properties and chemical compositions. For example: • ASTM A709 Grade 50 and AASHTO M 270 Grade 50 are identical and are similar to ASTM A572 Grade 50. • ASTM A709 Grade 50S and AASHTO M 270 Grade 50S are identical to ASTM A992. ASTM A769 is also similar to this group. • ASTM A709 and AASHTO M 270 Grade 50W Types A and B are equivalent to ASTM A588 Grades A and B, respectively. Most of these do not have a maximum yield strength specified for materials, with the exception of AASHTO M 270 (ASTM A709/A709M) Grade 50S, and ASTM A992/A992M, which states that “a maximum yield strength of 70 ksi is permitted for structural shapes that are required to be tested from the web location” (ASTM A992/A992M). Maximum tensile strength, on the other hand, is specified, either directly or indirectly, by most material specifications; the one excep- tion is ASTM A242/A242M. For example, ASTM A36/A36M, ASTM A709/A709M Grade 36, and AASHTO M 183M/M 183 specify a maximum tensile strength of 80 ksi, and ASTM A529 specifies maximum tensile strength of 100 ksi. Other specifications reference ASTM A6/A6M as an optional “supplemental requirement” that states that tensile strength shall not exceed the minimum specified tensile strength by more than 30 ksi (see note I in Table 7). Although some states still reference M 183M/M 183, this specification is no longer active and was replaced by ASTM A36/A36M and ASTM A709/709M Grade 36. ASTM A36/A36M material is becoming more difficult to find but is still offered by some manufacturers as a special order from the mill. ASTM A709/A709M was developed for use on bridges. Accordingly, standard in-ground instal- lations of guardrail and median barrier posts will likely not require ASTM A709/A709M, and ASTM A992/A992M may be a better choice. ASTM A992/A992M is now the preferred material specification in the structural steel industry for wide-flange sections, including those commonly used for guardrail posts (e.g., W6×9, W6×8.5, W6×15 and W6×25) (Tavarez 2018). In addition to the availability and cost-effectiveness of ASTM A992/A992M, it has several other notable advantages, including well-defined ductility and weldability. As stated by J. Cattan in Modern Steel Construction, “The major advantage of A992 is its better material definition. It has an upper limit on yield strength of 65 ksi, a minimum tensile strength of 65 ksi, a specified maximum yield-to- tensile ratio of 0.85, and a specified maximum carbon equivalent of 0.47%” (Cattan 1999).

Notes: Ga. = gauge. Blank cells represent undetectable levels of that chemical. *Comply with ASTM A325 Yield Min Min Max (ksi) (ksi) 2-in Ga. 8-in Ga. C Mn Si V Nb P S A449 Type 1 .. 1/4" to 1" 92 120 - 14 0.3-0.52 0.6 0.15-0.35 0.035 0.04 A325 1/2" to 1" / F3125 92 120 - 14 0.3-0.52 0.6 0.15-0.35 0.035 0.04 * AASHTO M164 92 120 - 14 0.3 0.6 0.15-0.4 0.035 0.04 F1554 1/2" to 3" 105 105 125 150 15 12 0.27 0.6-0.9 0.04 0.05 M314 same as F1554 105 105 125 150 15 12 0.27 0.6-0.10 0.04 0.05 Chemical Composition (%)High-Strength Bolts Spec Grade Tensile Strength % Elong. Table 6. Mechanical properties and chemical compositions for various materials currently used for high-strength bolts for guardrail.

Yield Min Min Max (ksi) (ksi) 2-in Ga. 8-in Ga. C Mn Si V Nb P S Cu Ni Cr Mo Al Sn N B Ti Ca A36(1)(2)(3) 36 58 80 21 20 0.26 (see A6) <0.4 0.04 0.05 0.2 A709(1)(2)(3) 36 36 58 80 21 20 0.26 (see A6) <0.4 0.04 0.05 0.2 M183(1) 36 58 80 21 18 A572(1)(2) 42 42 60 Ɨ 24 20 0.21 1.35 0.4 0.01-0.15 0.03 0.03 0.003-0.015 0.006-0.04 A529(1) 50 65 100 21 18 0.27 1.35 0.4 0.04 0.05 0.2 A242(1)(2)(3) 50 70 N.A. 21 18 0.15 1 0.15 0.05 0.2 A572(1)(2)(3) 50 50 65 Ɨ 21 18 0.23 1.35 0.4 0.01-0.15 0.03 0.03 0.003-0.015 0.006-0.04 M270(1)(2)(3) 50 50 65 Ɨ 21 18 0.23 1.35 0.4 0.01-0.15 0.005-0.05 0.03 0.03 A709(1)(2)(3) 50 Same as AASHTO M270 Grade 50 A992(1)(2)(3) 50-65 65 Ɨ 21 18 0.23 0.5-1.6 0.4 0.15 0.05 0.035 0.045 0.6 0.45 0.35 0.15 M270(1)(2)(3) 50S Same as ASTM A992 Ɨ A709(1)(2)(3) 50S Same as ASTM A992 Ɨ A769(1)(2) 50 50 65 Ɨ 12 17 0.26 0.3-1.65 0.6 0.03 0.035 * A588(1)(2)(3) A 50 70 Ɨ 21 18 0.19 0.8-1.25 0.3-0.65 0.02-0.1 0.03 0.03 0.25-0.4 0.4 0.4-0.65 * A588(1)(2)(3) B 50 70 Ɨ 21 18 0.2 0.75-1.35 0.15-0.5 0.01-0.1 0.03 0.03 0.2-0.4 0.5 0.4-0.7 * M270(1)(2)(3) 50W Types A and B are equivalent to Specification A588 Grades A and B, respectively. * A709(1)(2)(3) 50W Types A and B are equivalent to Specification A588 Grades A and B, respectively. Si m ila r Si m ila r Type Dependant Si m ila r Si m ila r Sheet and Plate Steel Chemical Composition (%) Spec Grade Tensile Strength % Elong. Notes: Ga. = gauge. Blank cells represent undetectable levels of that chemical. *Corrosion Resistant; ƗOptional maximum tensile strength to be specified by purchaser on contract per ASTM A6 S18; (1)W6×9 posts; (2)W6×15 posts; (3)W6×25 posts. Table 7. Mechanical properties and chemical compositions for various materials currently used for steel shapes and plates for guardrail.

Literature Review 29   Where corrosion-resistant steel is required, the standard specifications generally require that components fabricated from plates and shapes be manufactured from steel that conforms to ASTM A588/A588M, ASTM A606/A606M, or AASHTO M 270M/M 270 (ASTM A709/A709M) Grade 50W, except for supplemental requirements. 2.8 Documentation of Material Properties for Test Articles per MASH 2.8.1 MASH Requirements Obtaining and documenting material properties for key elements of the test article in a full- scale crash test have been recommended in all standard crash-test procedures documents since NCHRP Report 230, and the current procedure (i.e., MASH) has remained essentially unchanged since NCHRP Report 350 (AASHTO 2009; AASHTO 2016; Michie 1981; Ross et al. 1993). According to Section 2.3.1 in NCHRP Report 350 and Section 3.4.1 in MASH, “the material char- acteristics [e.g., physical and chemical properties] of all the key elements in the test article . . . should be documented in the test report” (AASHTO 2009; AASHTO 2016; Michie 1981; Ross et al. 1993); therefore, the documentation is recommended but not mandated. Both NCHRP Report 350 and MASH further state that “material specifications such as AASHTO, ASTM, and so forth, should be reported for all key elements” and that random samples should be tested to confirm the stated specifications; when materials are marginal or significantly exceed minimum specifica- tions, the testing agency should offer a judgment on the potential effects (AASHTO 2016; Ross et al. 1993). When the material properties are included in the test report, they are typically in the form of mill certification reports, which are added as an appendix to the crash test report with reference to the applicable component(s) of the test article. 2.8.2 Data Collection A literature search was performed to identify research reports and full-scale crash-test reports related to testing of guardrails and transitions as well as other roadside hardware that use typical guardrail components (e.g., W-beams, thrie beams, transition panels, posts, block- outs, hardware, anchorage). All the reports obtained for this review were developed at either TTI or the Midwest Roadside Safety Facility (MwRSF). Table 8 shows a summary of the litera- ture search. To the authors’ knowledge, based on the literature search and communication with the test facilities, neither the material characterization documents nor the mill certification documents were included in crash test reports prior to adoption of MASH. Therefore, the literature search was limited to only those crash test reports that were published after the adoption of MASH in 2009 and that include mill certification documentation. Unfortunately, most guardrail hardware was tested prior to this date, even for the MASH testing; therefore, the mill certifications reports for those test articles were not readily available. There were a total of 22 full-scale crash-test reports reviewed. 2.8.3 Summary of Findings A summary of the material property statistics for several common guardrail components extracted from the mill certification reports of MASH-tested hardware is provided in Table 9. These include W-beams, thrie beams, terminal connectors, guardrail posts, transition posts, soil plates, post sleeves, anchor ground struts, anchor foundation tubes, anchor brackets, anchor bearing plates, and post bolts. Figures 9 through 22 show material statistics as well as

30 Investigation of Material Requirements for Highway Guardrail Systems the cumulative distribution plots for yield strength from the mill certification reports for each component type. For example, Figure 9 shows the cumulative distribution for yield strength of 12-gauge W-beam used in all MASH testing. None of the tested hardware components had a yield strength that was less than the specified minimum of 50 ksi; 60 ksi was the 16th percentile yield strength (e.g., 16% of the tested components had a yield strength of less than 60 ksi), while 65.5 ksi was the 80th percentile yield strength. There may be a few errors in these summaries because it was difficult in some cases to exactly match the mill certification information to the component that was tested. It is expected that many of the mill certification reports correspond to large shipments of components that were used for several different test articles. This was evident in many of the test reports developed by MwRSF, where the material for the component used in the test article was clearly marked in the mill certification report using highlight marking. The highlight marking, however, was the exception rather than the rule. Nonetheless, the mill certification data provided herein are representative of components obtained either for use in the referenced test or for use in other roadside hardware testing. In general, the yield strength for the components of the test articles exceeded specified minimums for all cases except for the terminal connector and the W6×9 post with reference ASTM A992/ A992M. The material classification for the terminal connector for most cases was M 180 Class B, although M 180 does not include specifications for terminal connectors. Since these compo- nents are subjected to the same tensile forces as the adjoining main rails, it is logical that this component be required to have the same material and strength as the main rail component. Reference Test Article Test Facility Test No. Abu-Odeh et al. 2015 Short Radius Guardrail TTI SR-6 Bielenberg et al. 2017 Transition W-Beam Guardrail and Portable Concrete Barriers MwRSF MGSPCB-1, -2, -3 Bligh et al. 2020 Thrie-Beam Transition and W-Beam Guardrail in Concrete Mow Strips TTI 469469-5, -11 Gutierrez et al. 2013 MGS with Southern Yellow Pine Posts MwRSF MGSSYP-1, -2 Haase et al. 2016 MGS with 6ft Posts and 1V-2H Slope MwRSF MGSS-1 Lingenfelter et al. 2016 MGS with omitted post MwRSF MGSMP-1 Meyer et al. 2017 MGS increased span MwRSF MGSLS-1, -2 Asadollahipajouh et al. 2017 MGS and Breakaway Light Pole MwRSF ILT-1 & 2 Rosenbaugh et al. 2011 MGS Approach Guardrail Transition Steel Posts MwRSF MWTSP-1, -2, -3 Rosenbaugh et al. 2015 Weak Post W-Beam in Mow Strips MwRSF MGSMS-1 Rosenbaugh et al. 2019 MGS w/Curb and Omitted Post MwRSF MGSCO-1, -2 Schmidt et al. 2012 MGS Posts MwRSF MH 1-8 Schneider et al. 2014 Weak Post GR on Culverts MwRSF CP6 & 7 Dobrovolny et al. 2017 25-in. TL-2 W-Beam Guardrail TTI 608421 Sheikh et al. 2019 W-Beam Guardrail in Concrete Mow Strips TTI 608551 Schrum et al. 2013 Non-blocked MGS MwRSF MGSNB-1 & 2 Stolle et al. 2012 MGS Maximum Mounting Height MwRSF MGSMRH-1,-2 Stolle et al. 2015 MGS Mounting Height MwRSF MGSMRH-1, -2 Thiele et al. 2009 MGS and 6-in. Curb MwRSF MGSC-5 Thiele et al. 2010 MGS with 6-in. Curb MwRSF MGSC-6 Weiland et al. 2013 MGS Minimum Length MwRSF MGSMIN-1 Note: MGS = Midwest Guardrail System. Table 8. List of full-scale crash-test reports reviewed.

Component Specification Number of Data Points Yield Strength Tensile Strength Percent Elongation Minimum Mill Certification Report Minimum Mill Certification Report Minimum Mill Certification Report Specification Max. Min. Average Specification Max. Min. Average Specification Max. Min. Average (psi) (psi) (psi) (psi) (psi) (psi) (psi) (psi) (%) (%) (%) (%) W-Beam M 180 Class A 111 50,000 70,200 52,520 63,321 70,000 89,432 71,600 78,521 12 30 16.3 25.0 Thrie-Beam M 180 Class A 24 50,000 66,300 53,660 58,838 70,000 81,800 71,390 75,752 12 31.1 24.6 27.8 Terminal Connector M 180 Class B 6 50,000 59,770 33,000 53,235 70,000 78,641 52,100 71,116 12 38 27.4 30.7 W6x9 Posts A 992 18 50,000 60,600 49,600 55,858 65,000 80,500 69,800 74,811 21 33.6 19.3 25.4 W6x9 Posts M 183/A36/ A709 33 36,000 62,600 45,800 54,217 58-80 ksi 78,300 62,000 70,651 21 28.29 20.0 23.5 W6x15 A572 Gr. 50 2 50,000 55,200 54,900 55,050 65,000 73,800 73,300 73,550 21 24.9 24.4 24.7 W3x5.7 A572 Gr. 50 2 50,000 54,800 53,300 54,050 65,000 74,700 74,200 74,450 21 19.5 19.2 19.4 Soil Plate A36 3 36,000 46,660 46,660 46,660 58-80 ksi 73,630 73,630 73,630 21 26.9 26.9 26.9 Post Sleeve A36 12 36,000 69,600 47,292 60,664 58-80 ksi 88,400 62,162 81,519 21 31 23 25.4 Ground Strut A36/A1011 6 36,000 49,500 45,900 47,967 58-80 ksi 69,340 64,020 65,508 21 33.6 32.7 33.0 Foundation Tube A500 Gr. B 33 46,000 70,400 47,297 54,268 58,000 90,800 62,162 70,869 23 50 26.6 31.1 Anchor Bracket A36 19 36,000 68,425 44,500 49,757 58-80 ksi 78,404 60,300 67,945 21 34 25 29.8 Bearing Plate A36 19 36,000 64,700 46,700 50,347 58-80 ksi 79,500 69,900 73,795 21 28 22 24.3 Note: Highlighting denotes component categories with at least one component that did not meet minimum specifications. Table 9. Summary of material properties for MASH-tested hardware components.

32 Investigation of Material Requirements for Highway Guardrail Systems Yield Tensile (psi) (psi) Max 70,200 89,432 30.0 Min 52,520 71,600 16.3 Avg 63,321 78,521 25.0 Specified Min. 50,000 70,000 12.0 Data Points 111 12-ga W-Beam (M 180 Class A) %Elong. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 50,000 55,000 60,000 65,000 70,000 75,000 Pe rc en til e Yield Strength (psi) Cumulative Distribution Figure 9. Material property statistics for 12-gauge W-beams used in MASH testing. Yield Tensile (psi) (psi) Max 66,300 81,800 31.1 Min 53,660 71,390 24.6 Avg 58,838 75,752 27.8 Specified Min. 50,000 70,000 12.0 Data Points 24 12-ga Thrie-Beam (M 180 Class A) %Elong. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 50,000 55,000 60,000 65,000 70,000 Pe rc en til e Yield Stress (psi) Cumulative Distribution Figure 10. Material property statistics for 12-gauge thrie beams used in MASH testing. Yield Tensile (psi) (psi) Max 59,770 78,641 38.0 Min 33,000 52,100 27.4 Avg 53,235 71,116 30.7 Specified Min. 50,000 70,000 12.0 Data Points 6 Terminal Connector (M 180 Class B) %Elong. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 30,000 35,000 40,000 45,000 50,000 55,000 60,000 65,000 Pe rc en til e Yield Stress (psi) Cumulative Distribution Figure 11. Material property statistics for terminal connectors used in MASH testing.

Literature Review 33   Yield Tensile (psi) (psi) Max 60,600 80,500 33.6 Min 49,600 69,800 19.3 Avg 55,858 74,811 25.4 Specified Min. 50,000 65,000 21.0 Data Points 18 W6x9 Posts (A992) %Elong. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 40,000 45,000 50,000 55,000 60,000 65,000 Pe rc en til e Yield Strength (psi) Cumulative Distribution - A992 Figure 12. Material property statistics for W639 posts (A992) used in MASH testing. Yield Tensile (psi) (psi) Max 62,600 78,300 28.3 Min 45,800 62,000 20.0 Avg 54,217 70,651 23.5 Specified Min. 36,000 58-80 ksi 21.0 Data Points 33 %Elong. W6x9 Posts (M 183/A36/A709) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 40,000 45,000 50,000 55,000 60,000 65,000 Pe rc en til e Yield Strength (psi) Cumulative Distribution - M 183/A36/A709 Figure 13. Material property statistics for W639 posts (M 183/A36/A709) used in MASH testing. Yield Tensile (psi) (psi) Max 55,200 73,800 24.9 Min 54,900 73,300 24.4 Avg 55,050 73,550 24.7 Specified Min. 50,000 65,000 21 Data Points 2 W6x15 Posts (A572 Gr 50) %Elong. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 50,000 51,000 52,000 53,000 54,000 55,000 56,000 Pe rc en til e Yield Stress (psi) Cumulative Distribution Figure 14. Material property statistics for W6315 posts used in MASH testing.

34 Investigation of Material Requirements for Highway Guardrail Systems Yield Tensile (psi) (psi) Max 54,800 74,700 19.5 Min 53,300 74,200 19.2 Avg 54,050 74,450 19.4 Specified Min. 50,000 65,000 21 Data Points 2 %Elong. W3x5.7 Posts (A572 Gr 50) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 50,000 51,000 52,000 53,000 54,000 55,000 56,000 Pe rc en til e Yield Stress (psi) Cumulative Distribution Figure 15. Material property statistics for W335.7 posts used in MASH testing. Yield Tensile (psi) (psi) Max 46,660 73,630 26.9 Min 46,660 73,630 26.9 Avg 46,660 73,630 26.9 Specified Min. 36,000 58-80 ksi 21.0 Data Points 3 Soil Plate (A36) %Elong. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 40,000 41,000 42,000 43,000 44,000 45,000 46,000 47,000 Pe rc en til e Yield Stress (psi) Cumulative Distribution Figure 16. Material property statistics for soil plates used in MASH testing. Yield Tensile (psi) (psi) Max 69,600 88,400 31.0 Min 47,292 62,162 23.0 Avg 60,664 81,519 25.4 Specified Min. 36,000 58-80 ksi 21.0 Data Points 12 Post Sleeve (A36 / A500 / A53 Gr. B) %Elong. 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 Pe rc en til e Yield Stress (psi) Cumulative Distribution Figure 17. Material property statistics for post sleeves used in MASH testing.

Literature Review 35   Yield Tensile (psi) (psi) Max 68,425 78,404 34.0 Min 44,500 60,300 25.0 Avg 49,757 67,945 29.8 Specified Min. 36,000 58-80 ksi 21.0 Data Points 19 Anchor Bracket (A36) %Elong. 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 Stress (psi) Cumulative Distribution Figure 20. Material property statistics for anchor brackets used in MASH testing. Yield Tensile (psi) (psi) Max 49,500 69,340 33.6 Min 45,900 64,020 32.7 Avg 47,967 65,508 33.0 Specified Min. 36,000 58-80 ksi 21.0 Data Points 6 Ground Strut (A36 / A1011) %Elong. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 40,000 42,000 44,000 46,000 48,000 50,000 Pe rc en til e Yield Stress (psi) Cumulative Distribution Figure 18. Material property statistics for ground struts used in MASH testing. Yield Tensile (psi) (psi) Max 70,400 90,800 50.0 Min 47,297 62,162 26.6 Avg 54,268 70,869 31.1 Specified Min. 46,000 58,000 23.0 Data Points 33 Foundation Tube (A500 Gr. B) %Elong. 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 Pe rc en til e Yield Stress (psi) Cumulative Distribution Figure 19. Material property statistics for foundation tubes used in MASH testing.

36 Investigation of Material Requirements for Highway Guardrail Systems Regarding the W6×9 posts with reference ASTM A992/A992M, one case resulted in a yield strength of 49.6 ksi, which was only slightly below the specified minimum of 50 ksi for this material type. Further, guardrail post components are typically specified using ASTM A36/ A36M, so it is possible that the design engineer specified a lower strength (e.g., A36), and the manufacturer simply provided ASTM A992/A992M because it met the ASTM A36/A36M requirements. There is a lot of overlap between these material standards, which allows for a steel lot/heat/ batch to qualify under multiple standards. For example, A36 requires a minimum yield strength of 36 ksi and tensile strength ranging from 58 to 80 ksi. As such, it has been easier to supply steel guardrail posts under other specifications that meet ASTM A36/A36M mechanical property requirements, including ASTM A992/A992M, M 270M/M 270, ASTM A709/A709M, and ASTM A572/A572M. As shown in Figures 12 through 16, the mechanical properties of guardrail posts supplied to the crash test agencies, regardless of specification, met all conditions of A36, with the exception of a couple of ASTM A992/A992M cases that had maximum tensile strength just over 80 kips (e.g., 80.5 kips). As mentioned previously, ASTM A36/A36M posts are becoming increasingly difficult to obtain. Over the past 5 to 10 years, test agencies have typically received steel specified as ASTM A572/A572M or ASTM A992/A992M when ordering ASTM A36/A36M guardrail posts. In some cases, the test houses have stopped listing grade ASTM A36/A36M steels due to lack of Yield Tensile (psi) (psi) Max 64,700 79,500 28.0 Min 46,700 69,900 22.0 Avg 50,347 73,795 24.3 Specified Min. 36,000 58-80 ksi 21.0 Data Points 19 Bearing Plate (A36) %Elong. 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 Stress (psi) Cumulative Distribution Figure 21. Material property statistics for bearing plates used in MASH testing. Break Strength (psi) Max 81,460 Min 70,550 Avg 77,508 Specified Min. 62,800 Data Points 24 Post Bolt (A307 Gr. A) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 70,000 72,000 74,000 76,000 78,000 80,000 82,000 84,000 Pe rc en til e Break Strength (lbf) Cumulative Distribution Figure 22. Material property statistics for post bolts used in MASH testing.

Literature Review 37   availability and are now specifying ASTM A992/A992M for projects (MwRSF 2016). It has not been determined if, or to what degree, the higher-strength steels affect guardrail performance. For example, steel posts are expected to plastically deform and bend back out of the way, espe- cially when the vehicle makes direct contact with them during impact. Using a higher-yield- strength steel would reasonably affect this behavior, but to what degree is unknown. It is worth noting that almost all the mill reports for guardrail posts reviewed had a yield strength exceeding 50 ksi and tensile strength of as high as 80.5 ksi (refer to Figures 12 and 13). Except for the one instance of the terminal connector, no material had a tensile strength below minimum specification. There were only two sample cases for the W3×5.7 posts, but the mill certification reports for both of those cases showed a percent elongation of the material below specification (e.g., 19.2% versus 21%). All component categories that resulted in at least one component that did not meet minimum specifications (i.e., yield strength, tensile strength, or percent elongation) are marked in high- lighting in Table 9. There was no indication in the test reports of whether these properties had any potential effects on the performance of the test articles. There were also several cases where the material properties of the components were significantly higher than minimum specifications. For example, the W6×9 post with M 183M/M 183 specification had at least one case where the yield strength was 74% higher than the specified minimum. It is worth noting that these tests were successful and, although engineering judgment is often provided for cases involving failed tests, the test reports in these cases did not provide opinions on the potential effects of the sig- nificantly stronger materials.