Investigation of Material Requirements for Highway Guardrail Systems (2022) / Chapter Skim
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From page 39... ...
39 The proposed updates and revisions presented in the following sections will bring M 180 into conformance with current requirements and the state of practice for providing highway guardrail components. Additionally, the proposed changes should result in a more thorough, consistent, and up-to-date specification document that will improve consistency in guardrail specifications among transportation agencies, manufacturers, and suppliers.
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40 Investigation of Material Requirements for Highway Guardrail Systems 4.2 Transition Beams The symmetrical transition beam was introduced in M 180-78 and has been included in all subsequent updates of M 180 since (refer to Section 2.1 for details)
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Deficiencies and Proposed Updates to AASHTO M 180-18 41 for guardrails increased from 28 in.
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42 Investigation of Material Requirements for Highway Guardrail Systems 4.4 Steel Guardrail Posts Steel guardrail posts have never been included in M 180 (see Table 14)
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Deficiencies and Proposed Updates to AASHTO M 180-18 43 The proposed mechanical properties are listed in the following and are consistent with ASTM A36/A36M, which has historically been the standard for steel guardrail posts. • Yield point, minimum, 36 ksi (250 MPa)
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44 Investigation of Material Requirements for Highway Guardrail Systems The only limitation in most cases is the proposed maximum tensile strength requirement of 80 ksi. This requirement is included to prevent supplying over-strength posts, and it is proposed that this specification be preserved in M 180 until data are provided (e.g., full-scale testing with higher-strength posts)
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Deficiencies and Proposed Updates to AASHTO M 180-18 45 with wood, as indicated in Appendix F The timber species used for blockouts, as with timber posts, was determined to be too varied to justify inclusion in M 180.
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46 Investigation of Material Requirements for Highway Guardrail Systems considered for inclusion in the update. To the authors' knowledge, however, HSS tubes are not commonly used for guardrail or transitions, and the only two systems that the authors are aware of that use this component are the weak-post box-beam guardrail (which is not MASH compliant)
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Deficiencies and Proposed Updates to AASHTO M 180-18 47 In M 180-18, all fasteners are discussed in level 2 subsections (e.g., Section 6.4 – Bolts and Nuts and Section 6.5 – Washers and Backup Plates)
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48 Investigation of Material Requirements for Highway Guardrail Systems with the TF13 Guide for part FWC12b-36b, except for a suspected typo in the TF13 Guide of ASTM A436 (i.e., Standard Specification for Austenitic Gray Iron Castings) ; the correct specification is ASTM F436/F4366M.
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Deficiencies and Proposed Updates to AASHTO M 180-18 49 The current mechanical property specifications in M 180-18 for corrugated sheet steel are provided in Table 1 of M 180-18. Revisions that were considered herein included: • Increase yield strength or tensile strength, • Increase minimum percent elongation, • Add a maximum yield-to-tensile-strength ratio criterion (similar to that of ASTM A992/ A992M)
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50 Investigation of Material Requirements for Highway Guardrail Systems (e.g., a separate run of guardrail)
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De ciencies and Proposed Updates to AASHTO M 180-18 51 stress–strain curve, as illustrated by the shaded region in Figure 28. Although this methodology does not provide precise calculation of strain energy, the pseudo-strain energy value should represent a relative comparison of internal energy capacity for these materials, since the stress– strain curves for all M 180 guardrail beam material are expected to have the same basic shape.
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52 Investigation of Material Requirements for Highway Guardrail Systems yield and tensile strength) or imposing a significant burden on mills and suppliers.
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Deficiencies and Proposed Updates to AASHTO M 180-18 53 for guardrail sheet steel components, the ability of producers to supply properly coated steel with the desired mechanical properties could be affected. For Type IV beams (corrosion-resistant material)
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54 Investigation of Material Requirements for Highway Guardrail Systems For metallic-coated steels (Type I, II, V, and VI) , the finish thickness as specified in Table 4 of M 180-18 corresponds to: Finish Thickness(Nominal)
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Deficiencies and Proposed Updates to AASHTO M 180-18 55 Appendix F)
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56 Investigation of Material Requirements for Highway Guardrail Systems as small as 5 ft, and that curved rail is typically supplied in radius increments of 5 ft. Due to the flexibility of the uninstalled rail, it is possible for installers to make fine adjustments between the 5-ft increments in the field.
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Deficiencies and Proposed Updates to AASHTO M 180-18 57 with no additional information. When multiple sources of the same information exist within the same standard specification, there is an opportunity for contradictions to arise if one source is updated and the other source is not.
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From page 58... ...
58 Investigation of Material Requirements for Highway Guardrail Systems influence the amount of galvanizing available for protection once the galvanized piece is put into service. White rust is relatively easy to prevent by taking specific actions when storing the materials, such as stacking arrangements that encourage air flow and eliminate standing water.
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Deficiencies and Proposed Updates to AASHTO M 180-18 59 (ASTM B695)
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60 Investigation of Material Requirements for Highway Guardrail Systems maintain adequate internal records for all components included in each coating lot, then marking the pieces is somewhat redundant. The manufacturer brand and coating type are already included in the required marking information, and this is sufficient for tracing the component back to the manufacturer and identifying coating information.
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Deficiencies and Proposed Updates to AASHTO M 180-18 61 Since a larger suite of fasteners is proposed to be added to M 180, markings for these parts should be included in the update. It is proposed that M 180 simply include a reference to the specific standard for each fastener type for marking requirements, which would avoid future contradictions if the referenced ASTM and ANSI/ASME standards are updated.
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62 Investigation of Material Requirements for Highway Guardrail Systems Figure 31. Suggested marking for traceability of steel guardrail posts.
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Deficiencies and Proposed Updates to AASHTO M 180-18 63 of components (as discussed in the previous section)
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64 Investigation of Material Requirements for Highway Guardrail Systems but seems to contain a misspelling of the original designators (e.g., F 8801 in M 180-18 versus FBB01 in M 180-00 and TF13)
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Deficiencies and Proposed Updates to AASHTO M 180-18 65 Figure 32. Typical methods for dimensioning slots.
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66 Investigation of Material Requirements for Highway Guardrail Systems As discussed in Section 4.2, the asymmetrical transition beam, which has been a standard component in many nonproprietary guardrail systems for many years, is proposed to be added to M 180. The drawing for this component has been added to the transition figure in the proposed M 180 update (see Figure 4 in Appendices A and B)
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From page 67... ...
Deficiencies and Proposed Updates to AASHTO M 180-18 67 proprietary systems is so numerous that, if added to M 180, the document would become more of an assembly guide than a material specification. Although some components covered under the M 180 specification are used for proprietary systems, a disclaimer is proposed to be added to the scope section to acknowledge that M 180 covers nonproprietary components and does not purport to cover all components used in proprietary systems.
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68 Investigation of Material Requirements for Highway Guardrail Systems • Add ASTM A572/A572M to define material properties for steel guardrail posts. • Add ASTM A576 to define material properties for swage fittings used in guardrail anchors.
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From page 69... ...
Deficiencies and Proposed Updates to AASHTO M 180-18 69 and to be as specific and unique as possible. It also recommends avoiding general terms and any part of the publication's title.
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