Recommended Guidelines for the Selection of Test Levels 2 Through 5 Bridge Railings (2021) / Chapter Skim
Currently Skimming:
Pages 3-70
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 3... ...
3 LITERATURE REVIEW According to a Federal Highway Administration (FHWA) sponsored study in the 1980's, there are about 500,000 bridges in the U.S., about half of them on the National Highway System.
|
From page 4... ...
4 Figure 2. Miles of Urban and Rural Bridges.
|
From page 5... ...
5 suggest the single-unit truck left the roadway on the right and then crossed two lanes before striking the bridge railing on the left. [Alberson04]
|
From page 6... ...
6 carries 250,000 vehicles/day, for over 9 hours. Such long delays affecting such large numbers of people create a significant travel delay cost.
|
From page 7... ...
7 bridge rail penetrations and rollovers, passenger vehicles can also vault or roll over bridge railings. Avon, Colorado, 2012 Sunday, May 13, 2012 at 9:45 AM in Avon, Colorado, a tandem trailer truck lost control in the I-70 westbound lane and penetrated the Avon Road overpass.
|
From page 8... ...
8 Montreal, Quebec, 2011 On Wednesday, December 28th, 2011 a pickup truck traveling west on the Sainte Anne de Bellevue Road near the entrance to Highway 20 lost control and left the roadway. The vehicle flipped off an overpass and fell onto railway tracks, where it was then hit by a train.
|
From page 9... ...
9 Bronx, New York, 2012 On April 29th, 2012, a white 2004 a white Honda Pilot minivan "…was traveling southbound at about 70 mph in a 50-mph zone of the Bronx River Parkway when the 12:30 p.m accident occurred." [NYDN01] The minivan lost control while driving southbound on the Bronx River Parkway and hit the single-slope median barrier.
|
From page 10... ...
10 Grand Prairie, Texas, 2013 On August 3rd, 2013 a tractor-trailer was traveling westbound on Interstate 30 in Grand Prairie, Texas when the truck veered off the right shoulder. The truck penetrated the guardrail, then struck the bridge abutment and continued down the embankment in between the guardrail and abutment until it crashed down onto State Highway 161 below.
|
From page 11... ...
11 Figure 7. Close-Up of Bridge Rail Type (upper left)
|
From page 12... ...
12 Figure 8. Gates Bridge, Galesburg, IL.
|
From page 13... ...
13 Fort Sumner, New Mexico, 1972 On December 26, 1972, a school bus transporting 34 people was traveling westbound while a tractor-trailer truck transporting cattle was eastbound on US-60 near Fort Sumner, New Mexico.
|
From page 14... ...
14 railing of the curved bridge, landing on its roof. Twenty nine people were fatally injured in the crash.
|
From page 15... ...
15 94 feet of bridge railing, caused damage to the bridge deck, a column supporting the I-610 overpass was sheared off and guardrails on US-59 were damaged. As a result of this crash, the NTSB recommended that the FHWA "in consultation with state and local governments, establish highway design criteria for the selection, location and placement of traffic barrier systems that will redirect and prevent penetration when struck by heavy vehicles.
|
From page 16... ...
16 The barrier on the I-95 overpass, shown in Figure 10, was a 32-inch tall concrete safety shape bridge railing installed adjacent to a four-ft. shoulder on the overpass.
|
From page 17... ...
17 fatalities, 17 serious injuries, 17 minor injuries and three bus occupants were uninjured. The bus driver was ejected in the initial crash and four passengers were either fully or partially ejected when the bus struck the ground below.
|
From page 18... ...
18 Figure 12. Site of a motorcoach bus crash in Sherman, TX, 2008.
|
From page 19... ...
19 H-09-25: "Work with the FHWA to establish performance and selection guidelines for bridge owners to use to develop objective warrants for high-performance Test Level Four, Five, and Six bridge railings applicable to new construction and rehabilitation projects where railing replacement is determined to be appropriate, and include the guidelines in the Load and Resistance Factor Design (LRFD) Bridge Design Specifications." H-09-26: Revise Section 13 of the LRFD Bridge Design Specifications to state that bridge owners shall develop objective warrants for the selection and use of high-performance Test Level Four, Five, and Six bridge railings applicable to new construction and rehabilitation projects where railing replacement is determined to be appropriate.
|
From page 20... ...
20 welding details, and reinforcement development)
|
From page 21... ...
21 1989 AASHTO Guide Specification for Bridge Railings The 1989 AASHTO Guide Specification for Bridge Railings (GSBR) recommended that all bridge railings should be evaluated in full-scale crash tests to verify that a given bridge rail design meets the desired impact performance criteria.
|
From page 22... ...
22 Figure 13. Instrumented crash wall.
|
From page 23... ...
23 km/h (50 mph) and 15 degrees.
|
From page 24... ...
24 Manual for Assessing Safety Hardware (MASH) Since the publication of NCHRP Report 350 in 1993, changes have occurred in vehicle fleet characteristics, operating conditions, technology, etc.
|
From page 25... ...
25 Texas Department of Transportation is currently sponsoring research to determine the minimum barrier height and design impact load for MASH TL4. [Sheikh11]
|
From page 26... ...
26 recommended for the 51-in. tall barrier having top barrier widths of 11 in.
|
From page 27... ...
27 Table 3. Summary of test information for selected heavy tractor-trailer crash tests.
|
From page 28... ...
28 Guidelines and Specifications FHWA and AASHTO AASHTO Standard Specifications for Highway Bridges Historically, design of bridge rails has followed guidance contained in the AASHTO "Standard Specifications for Highway Bridges." Prior to 1965, the AASHTO specification required very simply that "substantial railings along each side of the bridge shall be provided for the protection of traffic." It was specified that the top members of bridge railings be designed to simultaneously resist a lateral horizontal force of 150 lb/ft and a vertical force of 100 lb/ft applied at the top of the railing. The design load on lower rail members varied inversely with curb height, ranging from 500 lb/ft for no curb to 300 lb/ft for curb heights of 9 in.
|
From page 29... ...
29 These bridge rail design procedures were retained through numerous editions of the specifications. In fact, the provisions in the 17th edition of the AASHTO "Standard Specifications for Highway Bridges" published in 2002 are essentially the same as the specification adopted in 1965.
|
From page 30... ...
30 from the edge of travel 8 feet, a PL1 railing is appropriate for traffic volumes up to 3,700 vpd; a PL2 bridge railing is recommended for traffic volumes between 3,700 and 31,900 vpd and a PL3 bridge railing is recommended for traffic volumes greater than 31,900 vpd. These recommendations presume that the highway section is straight with no grade, a deck height above the surface of 35 ft or less and the bridge does not pass over a sensitive or occupied area.
|
From page 31... ...
31 below the adjustment factors would be 2.0, 2.0 and 1.8. The ADT would be adjust to 18,000 ∙ 2.0 ∙ 2.0 ∙ 1.8 = 129,600 vpd which would place the railing into the PL3 category.
|
From page 32... ...
32 method for steel were used, 67 percent of the strength of the steel is assumed. In both cases, the designer is neglecting a significant portion of the capacity of the structure.
|
From page 33... ...
33 velocity truck impacts would tend to reach the capacity too early and the rollover algorithm was under conservative, penetrations were over predicted and rollovers under predicted. Mak and Sicking revised the rollover algorithm and adjusted the bridge railing capacities upward as shown in Table 5 and re-ran their analysis.
|
From page 34... ...
34 Table 6. Revised selection guidelines for bridge railings based on NCHRP 22-08.
|
From page 35... ...
35 RDG section 5.3 lists the following three subjective criteria that should be used in choosing an appropriate test level barrier: 1. Percentage of heavy vehicles, 2.
|
From page 36... ...
36 This 2004 FHWA report cites a 1997 FHWA policy memorandum which formally adopted NCHRP Report 350 as the guideline for testing bridge railings. This 1997 memorandum summarized over a decade of crash tests conducted on bridge railings, providing a complete list of all the crash-tested bridge railings, the guidelines used to test the bridge railings (e.g., NCHRP 230, NCHRP 350, etc.)
|
From page 37... ...
37 specific railings under certain situations, specify particular test levels for certain roadways and discuss retrofit polices. The Bridge or Structures Design Manuals from many different States have been reviewed and are discussed in this section.
|
From page 38... ...
38 • Approach and trailing end treatments (guardrail, crash cushion or rigid shoulder barrier)
|
From page 39... ...
39 Table 7 Summary of Minnesota "TABLE 13.2.1: Standard Rail Applications" [MNDOT06] Description Test Level Speed Limit Application Comment Concrete Barrier (Type P-1)
|
From page 40... ...
40 New York State DOT The New York State DOT uses the following recommendations for each performance level, as outlined in the New York State DOT Bridge Manual: [NYSDOT10]
|
From page 41... ...
41 retrofitted with guardrail if there is a safety walk or allowed to remain in place as is. If the bridge railings do not meet the NCHRP230 or later criteria, the railings are upgraded.
|
From page 42... ...
42 "engineering judgment and/or analysis" is used to determine the need for additional crash testing.
|
From page 43... ...
43 • "Non-NHS routes, • Design speeds less than or equal to 45 mph, or • In conjunction with a sidewalk." [NCDOT10] NCDOT suggests the use of vertical concrete barrier rail for bridges on NHS and non-NHS routes.
|
From page 44... ...
44 Nevada DOT Nevada DOT provides guidance to designers on the general application of TL3 through TL6 bridge railings in its Structures Manual.[NDOT08] TL1 and TL2 bridge rails "have no application in Nevada." Specific warrants for TL3 and higher bridge railings are not provided but the following general application guidance is offered for each test level: • TL3 bridge railing is the minimum acceptable performance level.
|
From page 45... ...
45 containment levels; containment "T" for low-angle containment consistent with many temporary applications; containment "N" for the normal level on most roads; containment H for high containment levels and the H4 level for very high containment. Containment level T is not appropriate for selecting bridge railings but the other three containment levels are shown below in Table 8 with the nearest MASH test level in terms of the target energy.
|
From page 46... ...
46 based on the geometry of the bridge and land use up to a containment level of H2 (i.e., roughly TL4)
|
From page 47... ...
47 Table 10 Alberta Canada Roadside Design Guide Bridge Rail Specifications Test Level Application TL2 For use on local roads. TL4 Preferred bridge rail for most applications.
|
From page 48... ...
48 encroachment calculation is easily converted into a simple factor. The multi-lane factor accounts for encroachments from other lanes.
|
From page 49... ...
49 Table 11. Bridge Height and Occupancy Factors Bridge Height Above Ground (m)
|
From page 50... ...
50 Figure 16. Portion of the Alberta bridge rail severity index selection table.
|
From page 51... ...
51 Germany The bridge railing selection guidelines for Germany are provided in RPS 2008 in section 3.5.1.1 and are summarized below in Table 12. The German selection guidelines generally segregate bridges into those that pass over sensitive areas, populated areas or other transportation infrastructure.
|
From page 52... ...
52 Table 13. Composition of Traffic by Category.
|
From page 53... ...
53 While the Selby crash involved the approach guardrails to the bridge, there have been other very similar cases involving penetrating bridge rails over rail lines in the UK. For example, a concrete mixer truck penetrated a brick bridge parapet near the town of Oxshott in Surey, England at about 3:30 pm on November 5th, 2010.
|
From page 54... ...
54 • Where the existing bridge or structure cannot meet the containment level derived from RRRAP, further assessment is conducted to determine the level of containment possible without strengthening. • If the risks associated with the provision of the lower level of containment determined through the RRRAP, then the lower containment level is provided.
|
From page 55... ...
55 Table 15. Summary of R350 Bridge Railing Selection by Highway Function.
|
From page 56... ...
56 Table 16. Summary of R350 Bridge Rail Selection Guidelines for Heavy Vehicle Accommodation.
|
From page 57... ...
57 Table 18. Summary of R350 Bridge Rail Selection Guidelines by Geometric Design Considerations.
|
From page 58... ...
58 Unfortunately, the authors did not separate out different barrier types so it is believed that the data in Table 19 include bridge railings, transitions and guardrails. Similarly, it is not clear if there is a distinction between rollover back onto the roadway or rolling over the bridge railing and off the bridge.
|
From page 59... ...
59 were examined for all reported bridge departures (i.e., penetrations and rollovers)
|
From page 60... ...
60 Table 20. Penetration and rollover percentage in Texas bridge railing crashes.
|
From page 61... ...
61 open concrete, New Jersey, and F-shape concrete bridge rails. With the exception of bridges over railroad tracks, almost all existing Kansas bridge rails are 32 inches high and fall into the TL3 category under the new MASH criteria.
|
From page 62... ...
62 multiplied by their associated probabilities of occurrence. The crash costs for each encroachment were estimated based on the severity of the encroachment (i.e., the consequences of impacting the bridge rail at the prescribed encroachment conditions)
|
From page 63... ...
63 𝐹 = 𝑊 𝑉 𝑠𝑖𝑛 𝜃2𝑔(𝐴 sin𝜃 − 𝐵2 (1 − cos 𝜃)
|
From page 64... ...
64 Hb = The height of the barrier in feet and Θ = The impact angle. This formulation assumes that the vehicle forces act at the center of gravity of the vehicle and that the barrier forces act at the very top of the barrier.
|
From page 65... ...
65 Table 21. Crash Costs used in BCAP.
|
From page 66... ...
66 RSAP are really risk-based probabilistic analysis tools where mathematical models of probabilities and risk are manipulated in order to estimate the frequency and severity of crashes. RSAP uses these four modules to assess the cost-effectiveness of a design: • Encroachment Module, • Crash Prediction Module, • Severity Prediction Module, and • Benefit/Cost Analysis Module.
|
From page 67... ...
67 Where: B/C Ratio 2-1= Incremental B/C ratio of alternative 2 to Alternative 1 CC1, CC2, = Annualized crash cost for Alternatives 1 and 2 DC1, DC2, = Annualized direct cost for Alternatives 1 and 2 RRRAP The RRRAP is a software program developed in the UK to aid in the implementation of the "Design Manual for Roads and Bridges," TD 19/06.
|
From page 68... ...
68 Risk Analysis Another approach not often used explicitly in roadside safety but common in many other types of engineering fields is risk analysis. In risk analysis the risk of experiencing a particular type of event is quantified using probabilistic models.
|
From page 69... ...
69 reported by the media or investigated by NTSB occurred at sites that would likely not have been considered to be particularly susceptible to a heavy vehicle crash. While some of the crashes certainly occurred at sites with the three risk factors noted in the RDG and the 1989 AASHTO GSBR (i.e., adverse geometry, percent of trucks and adverse consequences of penetration)
|
From page 70... ...
70 There is, therefore, a need to develop more specific recommendations on where different test level bridge railings should be used. While the general guidance provided by the 1989 AASHTO GSBR and the Roadside Design Guide are sound, States and designers need more specific characteristics like what percentage of trucks constitute "large truck traffic," or what traffic volume might be considered "high volume," or what degree of curvature constitutes a "sharp curve." Providing these more specific answers is one of the objectives of this research project.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.