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MASH Railing Load Requirements for Bridge Deck Overhang (2023)

Chapter: Appendix A - Agency Survey Results

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Page 246
Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Page 252
Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Page 253
Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Page 253
Page 254
Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Page 255
Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
×
Page 255
Page 256
Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
×
Page 256
Page 257
Suggested Citation:"Appendix A - Agency Survey Results." National Academies of Sciences, Engineering, and Medicine. 2023. MASH Railing Load Requirements for Bridge Deck Overhang. Washington, DC: The National Academies Press. doi: 10.17226/27422.
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Page 257

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246 Agency Survey Results A survey of four state DOTs from each of the four AASHTO regions was performed in September and October 2020 to identify key aspects and trends of deck overhang design to inform the proceeding analytical and testing programs (Figure 355). The survey collected data regarding the material, dimensions, bridge rail characteristics, and design methodologies for deck overhangs. Deck Overhang Material The proceeding analytical and physical testing programs were expected to include only concrete deck overhangs. To evaluate the appropriateness of this assumption, percentages of bridge deck inventories composed of various materials were collected from state DOTs. The results, shown in Table 21, indicate that the overwhelming majority of bridge deck overhangs are composed of concrete. A P P E N D I X A Figure 355. States participating in agency survey.

Agency Survey Results 247   State Concrete Steel Timber Other CA 85 2 2 11 DE 100 0 0 0 FL 99 1 0 0 IL 98 1 1 0 IN 100 0 0 0 LA 88 2 10 0 MA 83 2 1 14 MN 100 0 0 0 NE 100 0 0 0 NJ 95 5 0 0 NY 53 5 7 35 OH 72 1 1 26 SC 100 0 0 0 TX 100 0 0 0 VA 100 0 0 0 WA 75 20 5 0 1 CA other: segmental construction. 2 MA other: historic bridges not tracked in inventory system. 3 NY other: “other,” “open,” and “none” in state inventory system. Table 21. Percentage of decks in state inventories by deck material. Additionally, construction details for the concrete deck overhangs in the surveyed states’ inventories were collected. Construction details of interest included whether the deck overhang was cast-in-place or precast, and if it was cast-in-place, whether removable or stay-in-place forms were used. While many states indicated some extent of stay-in-place form use, stay- in-place forms were never used outside of the fascia girder. Percentages of deck overhang types by their construction details are summarized in Table 22. As shown, nearly all concrete deck overhangs are cast-in-place overhangs with removable formwork. A small sampling of State Cast-in-Place with Removable Forms Cast-in-Place with Stay-in-Place Forms Precast Other CA 99 0 1 0 DE 92 0 8 0 FL 99 0 1 0 IL 99 0 1 0 IN 100 0 0 0 LA 90 0 10 0 MA 98 0 2 0 MN 99 0 1 0 NE 99 0 1 0 NJ 95 0 5 0 NY 98 0 2 0 OH 100 0 0 0 SC 100 0 0 0 TX 99 0 1 0 VA 100 0 0 0 WA 95 0 5 0 Table 22. Percentage of concrete deck overhangs in inventory by construction details.

248 MASH Railing Load Requirements for Bridge Deck Overhang CA 2 12 4 2 10 4.5 DE 1 3.75 NA 1 3.75 NA FL 3 4.5 3.5 3 4.5 3.5 IL 1.75 4.5 3.25 1.75 4.25 3.25 IN 1.5 3 2 2 4 2.5 LA 3.5 5 4 3.5 5 4 MA 1.67 3 3 2 3 2.5 MN 0.5 6 3.25 0.5 6 3.25 NE 0.67 3.5 3.5 0.67 4.5 NA NJ NA NA NA 2.5 4.5 2.5 NY NA NA NA 2 4 NA OH 1.5 4 2.5 1.5 4 4 SC 2.25 4.5 3.25 2.25 4.5 3.25 TX 0.5 6 3 0.5 4.5 3 VA 1.5 3 3 1.5 3 3 WA 3 6 4 3 6 4 Table 23. Deck overhang widths. states, including Delaware, Louisiana, and Washington, indicated a significant level of precast overhang use. Deck Overhang Dimensions Minimum, maximum, and typical deck overhang dimensions were collected to inform the analytical and physical testing programs. Specifically, deck overhang widths and thicknesses were collected, and responses were separated into past and current practices to identify potential differences between historic and recent construction. Additionally, thickness variations, including overhang thickening, overhang thinning, and the use of curbed edges or elevated sidewalks, were identified. Overhang Width and Thickness Minimum, maximum, and typical deck overhang widths provided by the surveyed state DOTs are shown in Table 23 and Figure 356. Responses ranged from 0.5 ft to 10 ft, and the typical or preferred overhang widths, denoted in Figure 356 as black dots, ranged from 2.5 ft to 4.5 ft. Graphical representation of the provided overhang widths includes only current practice. Deck overhang widths are commonly dependent upon girder spacing or girder depth. Exceptionally long overhangs were noted by California for segmental bridge construction. The manner in which the width of deck overhangs is measured is dependent upon the shape of the fascia girder. The majority of surveyed states indicated that deck overhang widths are measured from the centerline of I-shaped girders and from the face of box-shaped girders. The Nebraska and Virginia DOTs indicated that, for I-shaped girders, deck overhang widths are measured from the quarter-point of the girder flange. The Illinois DOT also indicated that the quarter-point of the flange is used as a reference point, but only for concrete bulb tee

Agency Survey Results 249   girders. The Texas DOT uses the AASHTO LRFD BDS, Article 4.6.2.1.6 to determine the critical section of the fascia girder. As overhang width measurement depends on the shape of the fascia girder, data on the use of different fascia girder types were collected from state DOTs. Fascia girder types used by the surveyed state DOTs are shown in Table 24. Similarly, minimum, maximum, and typical deck overhang thicknesses provided by the surveyed state DOTs are shown in Table 25 and Figure 357. Responses ranged from 7 in. to 14 in., and the typical or preferred overhang widths, denoted in Figure 357 as black dots, ranged from 7 in. to 11.5 in. Twelve of the surveyed states, or 75% of the sample, indicated preferred deck overhang thicknesses between 8 in. and 9.5 in. Graphical representation of the provided over- hang widths includes only current practice. It should be noted that the thicknesses described herein correspond to the thinnest portion of the deck overhang and do not include the effects of overhang thickness variation. Thickness Variations and Curbs It is common for deck overhangs to feature thickness variations in the form of additional concrete on the bottom or top face of the overhang. As these details may affect the behavior of the deck overhang in an impact event, information was gathered to describe common types of thickness variations, including overhang tapers and elevated curbs or sidewalks. A summary of thickness variations on the underside of the deck overhang is shown in Table 26. Nine of the surveyed states indicated the use of a linear thickening from the field edge to the face of the supporting element to cover the haunch and fascia girder flange. Similarly, information was gathered on thickness variations on the top of the overhang, including brush curbs and elevated sidewalks. Typical curb heights, curb height ranges, and elevated region widths are shown in Table 27. Additionally, estimated percentages of inventories featuring elevated curbs or sidewalks were collected. Figure 356. Deck overhang widths (current practice).

250 MASH Railing Load Requirements for Bridge Deck Overhang State Supporting element type Monolithic Concrete 1 Concrete Box Precast Girder Steel I-Beam Steel Box Steel Tub Timber CA DE FL IL IN LA MA MN NE NJ NY OH SC TX VA WA 1 Deck overhang and fascia girder cast in the same pour. CA 7 9 8 8 9 8.5 DE 8.5 8.5 8.5 8.5 8.5 8.5 FL 7.5 8 7.5 8 8 8 IL 8 9.5 9 9.5 9.5 9.5 IN 8 12 9 8 12 9 LA 8 9 8 8 9 8 MA 9 11 9.5 9 11 9.5 MN 7 10 8.5 9 11.25 9 NE 6.5 7.5 7 8 8 8 NJ NA NA NA 8.5 10 NA NY NA NA NA 11.5 12.5 11.5 OH 10.5 12.5 10.5 10.5 12.5 10.5 SC 6.5 12 8 8 14 8 TX 6 12 8 8.5 12 8.5 VA 7.5 9 8 7.5 9 8 WA 7 7 7 7 7 7 Overhang thicknesses shown correspond to the deck thickness at the field edge of the overhang. Table 24. Types of fascia girders on bridge inventories. Table 25. Deck overhang thicknesses.

Agency Survey Results 251   Figure 357. Deck overhang thicknesses (current practice). CA 90 4 Linear variation from field edge to cover haunch and flange DE Unknown 2 Linear variation from field edge to cover haunch and flange FL 0 NA NA IL 100 1.5 Vertical step outside of fascia girder IN 80 2-3 Linear variation or uniform thickness outside of fascia girder LA Unknown 2-3 Linear variation from field edge to cover haunch and flange MA 0 NA NA MN 99 3-6 Linear variation from field edge to cover haunch and flange NE Unknown 0.5-0.75 Extension to act as drip bead at field edge of deck overhang NJ 100 2-3 Uniform thickness outside of fascia girder NY Unknown NA NA OH Unknown 1.5 Linear variation from field edge to cover haunch and flange SC 100 2-3 Linear variation from field edge to cover haunch and flange TX 1 2-3 Linear variation from field edge to cover haunch and flange VA 0 NA NA WA 100 2 Linear variation from field edge to cover haunch and flange Table 26. Deck overhang thickness variations.

252 MASH Railing Load Requirements for Bridge Deck Overhang CA 20 9 9–12 2–5 DE 10 6 4–8 3–9 FL 20 6 6–9 2–3 IL 10 8 8 5–7 IN 15 8 8–12 2–8 LA 20 10 6–10 2–6 MA 100 8 8–12 2–6 MN 37 6 6–10 1–17 NE 0 NA NA NA NJ 70 6 6–9 1.6–6 NY 49 6 6 5–6 OH 12 8 8–10 1–5 SC 33 6 6–10 5–17 TX Unknown 6 6–18 6–7 VA Unknown 6 6–10 > 6 WA 10 6 6 3–6 Table 27. Brush curb and elevated sidewalk dimensions. Bridge Rail Characteristics To assist in selecting the most appropriate conditions for the physical testing program, informa- tion was gathered on the characteristics of bridge rails in the surveyed states’ bridge inventories. Surveyed characteristics included MASH test levels and bridge rail types. Nearly all states indicated that only a minor portion of their existing bridge rail inventories were confirmed through testing or evaluation to meet a MASH test level. Most existing bridge rails on state inventories are rails that either complied with a previous testing standard, such as NCHRP Report 230 or NCHRP Report 350, or were not associated with any testing standard. As such, states provided ideal or expected test level shares for new construction and expected MASH equivalencies, as shown in Table 28. For example, Caltrans specifies that, for new con- struction, bridges with posted speeds greater than or equal to 45 mph use MASH TL-4 rails, and those with posted speeds less than 45 mph use MASH TL-2 rails. The state DOT representative indicated that roughly 75% of state bridges have posted speeds greater than or equal to 45 mph, leading to the distribution shown in Table 28. In Minnesota, many existing bridge rails meet NCHRP Report 350 TL-4 criteria but do not meet the MASH TL-4 height requirement. Con- sequently, it is expected by the surveyed Minnesota DOT representative that the majority of their existing inventory is equivalent to MASH TL-3 criteria. In sum, the data shown in Table 28 do not represent shares of existing bridge rails by MASH test level, but instead show a mixture of ideal, preferred, and equivalent MASH test levels and roughly demonstrate interest or future implementation of each. On average, MASH TL-4 is the most commonly preferred test level, at an average preferred share of 59%. MASH TL-2, TL-3, and TL-5 each share a significantly smaller portion of interest, at average preferred shares of 11%, 17%, and 13%, respectively. States that noted high percentages of TL-3 rails were typically referring to downgraded TL-4 rails. MASH TL-1 or TL-6 bridge rail use was rare and considered negligible. Shares are also

Agency Survey Results 253   demonstrated in Figure 358 in which average shares are shown as bars and maximum state shares are shown as brackets. Percentages of state bridge rail inventories by rail type are shown in Table 29. Unlike Table 28, which demonstrated ideal, preferred, or equivalent shares by MASH test level, the values in Table 29 correspond to actual, existing bridge rail inventories. Ten of 16 surveyed states indicated that 50% or more of their bridge rail inventory consists of concrete barriers. The average share of state bridge rails made up of barriers was 58%, though this was reduced significantly by Nebraska and New York in which concrete barriers are uncommon. Concrete post-and-beam bridge rails were the second-most common bridge rail type, at an average state inventory share of 16%, followed by top-mounted and side-mounted metal post-and-beam bridge rails, at average state CA 0 25 0 75 0 0 DE 0 0 60 30 10 0 FL 0 0 25 75 0 0 IL 0 0 20 70 10 0 IN 0 20 40 0 40 0 LA 0 0 0 100 0 0 MA 0 25 5 50 20 0 MN 0 30 60 10 0 0 NE 0 0 0 80 20 0 NJ 0 0 10 50 40 0 NY 0 0 0 90 10 0 OH 0 38 2 27 33 0 SC 0 0 0 100 0 0 TX 0 30 40 20 10 0 VA 0 10 10 70 10 0 WA 0 0 0 90 10 0 Average 0 11 17 59 13 0 1 Values indicate ideal, preferred, or equivalent MASH test level distribution. Table 28. Ideal or expected percentage of bridge rails on state inventories by MASH test level. 0% 25% 50% 75% 100% TL-1 TL-2 TL-3 TL-4 TL-5 TL-6 Sh ar e of S ta te In ve nt or y MASH Test Level of Bridge Rail Figure 358. Ideal or expected percentage of bridge rails on state inventories by MASH test level.

254 MASH Railing Load Requirements for Bridge Deck Overhang inventory shares of 9% and 7%, respectively. Hybrid post-and-beam made up an average inven- tory share of 7%, while deformable guardrail-style and timber bridge rails are very uncommon, with average state inventory shares of 2% and 0.4%, respectively. Only Massachusetts and Texas indicated significant use of deformable guardrail-style bridge rails. Use of GFRP Reinforcement As the physical and analytical testing programs were expected to include only steel-reinforced deck overhangs, state DOT representatives were surveyed on their states’ use of glass-fiber- reinforced polymer (GFRP) reinforced deck overhangs. It was expected that the use of GFRP reinforcement would be uncommon, justifying its exclusion from the proceeding testing program. None of the surveyed states indicated that shares greater than 1% of their state bridge inventories use GFRP reinforcement. However, seven states (Illinois, New York, Ohio, South Carolina, Texas, Virginia, and Washington) expressed a desire to increase the number of bridges using GFRP reinforcement in future construction. Overhang Design Philosophies The design aids by which state DOTs evaluate and design their bridge deck overhangs are summarized in Table 30. An overwhelming majority of states (fifteen of sixteen) use the ana- lytical methods of the AASHTO LRFD BDS, Section 13 in some capacity. Likewise, fourteen CA 75 10 2 12 0 1 0 DE 96 1 0 0 1 1 1 FL 65 35 0 0 0 0 0 IL 70 0 20 10 0 0 0 IN 65 0 5 10 20 0 0 LA 50 30 10 8 2 0 0 MA 40 0 15 32 1.5 1.5 10 MN 70 10 10 0 10 0 0 NE 17 73 0 0 10 0 0 NJ 40 5 0 20 30 0 5 NY 1 13 5 3 34 1 3 2 OH 63 0 37 0 0 0 0 SC 42 48 2 5 3 0 0 TX 35 25 5 5 20 0 10 VA 90 WA 100 0 0 0 0 0 0 Average 58 16 7 9 7 0.4 2 NY inventory not accounted for in the table (39%) includes chain-link, steel balustrade, concrete balustrade, generic steel, aluminum, continued highway guardrail, and picket rails. Table 29. Percentage of bridge rails on state inventories by type.

Agency Survey Results 255   of the sixteen surveyed states use crash testing to determine the adequacy of bridge deck overhangs. Ten of the states indicated that their state DOT bridge design manual contains deck overhang design information not contained in the AASHTO LRFD BDS and therefore significantly guides the overhang design procedure. Only two states indicated use of the NHI course no. 130081, LRFD for Highway Bridge Superstructures, which provides guidance on load distributions and design sections, and no states indicated use of the PCI Bridge Design Manual. State DOT Concerns with Existing AASHTO LRFD BDS To inform future revisions of the AASHTO LRFD BDS Section 13, state DOT representa- tives provided commentary on observed shortcomings of the current bridge deck overhang evaluation methodology. In this free-response question, several common concerns were noted by multiple states. Common concerns raised by various state DOT representatives are summarized in Table 31. In order of the frequency with which they were noted, concerns included: • Overconservatism of designing the deck overhang for Mc of the bridge rail (nine states), • Absence of MASH design parameters (five states), • Unspecified distribution pattern of impact demands into the deck overhang (five states), and • Overconservatism of one-way bending assumption for the deck overhang (two states). Additional concerns noted by one state DOT representative included: • Absence of design examples, • Absence of guidance for overhangs supporting side-mounted post-and-beam rails, • Absence of guidance for overhangs supporting metal post-and-beam rails mounted on curbs, • Congestion of deck reinforcement due to overconservative overhang demands, and • Effects of anchor rod epoxy coating on deck overhang damage. CA DE FL IL IN LA MA MN NE NJ NY OH SC TX VA WA Table 30. Design aids used by state DOTs.

256 MASH Railing Load Requirements for Bridge Deck Overhang In-Service Performance While eleven of the surveyed states indicated that significant in-service bridge rail damage has been observed, only one state noted one case of significant in-service deck overhang damage. Moreover, for each case in which significant in-service bridge rail damage was noted, this behavior was rare. Descriptions of in-service behavior, particularly that of bridge deck overhang performance, demonstrate high levels of conservatism in the existing methodology. Retrofitting Practices To determine whether retrofit bridge rails should be significantly investigated in the analytical and physical testing programs, state DOT representatives were asked to discuss retrofitting practices within their agency. Of the sixteen surveyed states, fifteen indicated that bridge decks are upgraded only if a bridge is being redecked or if severe environmental deterioration requires removal and replacement of the overhang. Only one state contacted for the survey (Texas) performs bridge rail upgrades independent of resurfacing, restoration, or rehabilitation (3R) projects. Texas was also the only surveyed state that downgraded the test level of attached bridge rails due to insufficient deck overhang capacity. In ten of the surveyed states, entire overhangs are removed and replaced for bridge widening or in cases of severe deterioration. In these cases, bridge rails are not considered to be retrofitted, as the updated overhang and bridge rail are installed at the same time. Several strategies were noted for use when an existing rail is either insufficient for a MASH test level or is being replaced. Commonly, when a bridge rail does not meet a MASH test level, it is simply left in place and downgraded to a lower MASH test level. This is often the case with bridge rails that met NCHRP Report 350 TL-4 criteria but have been downgraded to MASH TL-3 due to the increased height requirement. Four states indicated that bridge rail test levels are down- graded to a MASH-equivalent level and then deemed acceptable for that application. Five states State Primary Concerns with AASHTO LRFD BDS, Section 13 Designing Deck Overhang for Mc of Rail Absence of MASH Design Loads Impact Load Distribution into Overhang One-way Bending Assumption Is Overconservative Absence of Design Examples CA DE FL IL IN LA MA MN NE NJ NY OH SC TX VA WA Table 31. Summary of states’ perceived deficiencies in existing AASHTO LRFD BDS, Section 13.

Agency Survey Results 257   use epoxy or grouting to install new bridge rails on existing deck overhangs. Two states indi- cated that thrie beam is occasionally attached to bridge rails to improve crashworthiness. Additionally, at least two states modified their evaluation criteria for existing bridge deck overhangs. When evaluating new bridge rail installations on existing bridge deck overhangs, Caltrans and the Connecticut DOT reduce the deck overstrength factor from 1.20 to 1.00 (refer to the following synthesis for additional details). This practice reduces tensile and flexural over- hang demands by 20%, allowing for an increased likelihood of overhang damage in favor of the installation of a stronger bridge rail which might otherwise appear incompatible with the overhang. Caltrans also modifies the impact load distribution pattern for bridge rails installed on existing deck overhangs. The pattern, shown in Figure 359b, allows for further longitudinal distribution of impact demands for existing deck overhangs. Consequently, existing deck over- hangs are evaluated using reduced demands relative to new deck overhangs. (a) Load distribution for bridge rails installed on new deck overhangs (b) Load distribution for bridge rails installed on existing deck overhangs Figure 359. Caltrans’ load distribution patterns for new and existing construction.

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State highway agencies across the country are upgrading standards, policies, and processes to satisfy the 2016 AASHTO/FHWA Joint Implementation Agreement for MASH.

NCHRP Research Report 1078: MASH Railing Load Requirements for Bridge Deck Overhang, from TRB's National Cooperative Highway Research Program, presents an evaluation of the structural demand and load distribution in concrete bridge deck overhangs supporting barriers subjected to vehicle impact loads.

Supplemental to the report are Appendices B through E, which provide design examples for concrete barriers, open concrete railing post on deck, deck-mounted steel-post, and curb-mounted steel-post.

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