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PROJECT No. 20-07 / Task 395MASH Equivalency of
NCHRP 350-Approved Bridge Railings
2018 AASHTO SCOBS T-7 Committee Meeting, Burlington Vermont
June 27, 2018William Williams, P.E.
Acknowledgements
• Waseem Dekelbab, PhD, PE, PMP, Senior Program Officer
• Project Panel
– SCOBS T7, TCRS, State DOTs, Consultants
2
Research Team
• Roger Bligh, P.I.
• William Williams, Co-P.I.
• Chiara Silvestri Dobrovolny
• Sana Moran
• Nathan Schulz
Research Objectives• Identify and prioritize bridge rail systems
• Determine MASH equivalent test levels
• Determine whether individual bridge rails can be submitted to FHWA for determination of federal-aid reimbursement eligibility or whether testing is needed.
4
Tasks
5
Task 1. Identification and Prioritization
Task 2. Develop Methodology for Bridge Rail Analysis
Task 3. Analysis of Bridge Rails
Task 4. MASH Coordination Effort
Task 5. Eligibility Letters
Task 6. Presentations
Task 7. Final Report
Task 1 – Collect Bridge Rail Information
6
• Electronic survey of State DOT personnel:
Type of bridge rails used
Relative frequency of use
Prior test information
Intended future use
• Categorize and prioritize systems
Bridge Rail Prioritization
7
34 survey responses (33 DOT Agencies and FHWA Federal Lands)
Responses organized based on bridge rail categories and
subcategories:
Concrete-Only
o Vertical profile
o Post and beam
o New Jersey profile
o Single Slope profile
o F-Shape profile
Metal-Only
o Deck-Mounted
o Side-Mounted
Combination Traffic-Pedestrian
o With Sidewalk
o Without Sidewalk
Metal on Concrete Curb/Parapet
With Curb
o 3 metal members
o 2 metal members
o 1 metal member
With Parapet
o 3 metal members
o 2 metal members
o 1 metal member
Wood-Only
Noise Wall-Only
Retrofit-Only
Weighted Frequency of Use (WFofU)
8
Prioritization by WFofU
9
WFofU10 - 19
WFofU≥ 20
Task 2 - Assess Analysis Methodologies
• Assess methodologies previously used/accepted by FHWA
• Develop methodology for evaluating MASH compliance of existing bridge rails– Crash tested and/or FHWA eligible railings
• Consider:– Previous level of testing
– MASH impact severity
– MASH evaluation criteria
Simulation Study for MASH TL-3 Bridge Rail Analysis
• Finite element simulations were conducted to determine minimum rail height and lateral impact loads for MASH Test Level 3
– Rigid vertical wall
– MASH 2270P vehicle
27-inch Rail Height
29-inch Rail Height
Global Equivalencies• Stability
Minimum Rail Height (in)
Test Level NCHRP 350a MASH
3 27 29b
4 32 36
5 42 42a AASHTO LRFD Bridge Design Specifications, Section 13b Resulting minimum rail height from simulation analysis
Global Equivalencies• Strength
Test
Level
NCHRP 350a MASH
Lateral
Impact
Force (kips)
Resultant
Force
Height (in)
Moment
(kip-in)
Lateral
Impact
Force (kips)
Resultant
Force
Height (in)
Moment
(kip-in)
TL-3 54 24 1296 71 19.5 1385
TL-4 54 32 1728 68b 25b 1700
a AASHTO LRFD Bridge Design Specifications, Section 13b Impact force and resulting height corresponds to 36 in tall barrier
• AASHTO LRFD Bridge Design Specifications
– Figures A13.1.1-2 and A13.1.1-3
Rail Geometrics
Global Equivalencies• Rail Geometrics – Pickup Truck Crash Test Data
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 2 4 6 8 10 12
Rat
io o
f R
ail C
on
tact
Wid
th t
o H
eigh
t
Post Setback Distance (in)
Post Setback Criteria
350 TL-3
MASH TL-3
350 TL-4
MASH TL-4
MASH TL-5
350 Failed Tests
MASH Failed Tests
Not Recommended
Preferred
Oregon Bridge Rail (Crooked River)
F411
NY (2-member)
T4(A) Bridge Rail
T77
T101
Caltrans ST-10T131
Global Equivalencies• Rail Geometrics – Pickup Truck Crash Test Data
0
5
10
15
20
25
30
0 2 4 6 8 10 12 14
Ver
tica
l Cle
ar O
pen
ing
(in
)
Post Setback Distance (in)
Snag Potential
350 TL-3
MASH TL-3
350 TL-4
MASH TL-4
MASH TL-5
350 Failed Tests
MASH Failed Tests
High Potential
Low Potential
T4(A)Bridge Rail
F411
T77
Oregon Bridge Rail (Crooked
River)
NY (2-member)
T101
T131Caltrans
ST-10
Global Equivalencies• Bridge rail systems were separated into
categories to establish global test equivalency– Solid Concrete Parapet
– Concrete Post and Beam
– Metal Rail • Deck or Side Mounted
– Metal Rail on Curb• Curb height less than or equal to 11 inches
– Metal Rail on Concrete Parapet• Concrete parapet height greater than or equal to 12 inches
Global Equivalencies
* Concrete parapet height greater than or equal to 24 inches
NCHRP 350 Rail
System Type
MASH Test Level
TL-2 TL-3 TL-4 TL-5
Solid Concrete Parapet TL-2TL-3
TL-4TL-5
Concrete Post and
Beam
TL-2
TL-3
TL-4
TL-5
Metal Rail Deck
Mounted
TL-2
TL-3
TL-4
TL-5
Metal Rail on Curb
TL-2
TL-3
TL-4
TL-5
Metal Rail on Concrete
Parapet*TL-2
TL-3
TL-4TL-5
• Analyze existing data to determine if equivalent MASH test levels can be established– Supplemented by limited finite element impact
simulations
• Evaluate prioritized bridge rails (Task 1) using approved methodology (Task 2)– Conservative analysis
– MASH equivalent test level
– Crash testing needed?
Task 3 - Analyze Selected Bridge Rails
Key MASH Considerations
• Structural Adequacy
– Strength
• Rail Height
– Stability
• Rail Geometry
– Occupant risk
Structural Adequacy
• Increased impact severity results in increased impact forces
TestImpact Severity (k-ft) Percent
DifferenceNCHRP 350 MASH
3-10 27.3 55.9 +105%
3-11 101.4 115.2 +13%
4-12 98.5 154.4 +56%
Structural Adequacy
Test
Level
NCHRP 350a MASH
Lateral
Impact
Force (kips)
Resultant
Force
Height (in)
Moment
(kip-in)
Lateral
Impact
Force (kips)
Resultant
Force
Height (in)
Moment
(kip-in)
TL-3 54 24 1296 71 19.5 1385
TL-4 54 32 1728 68b 25b 1700
Rail height
• Minimum height for vehicle stability varies with test level
Test Level
NCHRP 350* MASH
3 27 29
4 32 36
5 42 42* AASHTO LRFD Bridge Design Specifications, Section 13
Rail Geometry
• Rail geometry effects vehicle-barrier interaction– Post setback distance– Vertical clear opening– Contact surface area
• Increased impact severity increases snagging potential
• Applicability of AASHTO LRFD Bridge Design Specification relationships unknown– Different vehicles– Different impact conditions
• AASHTO LRFD Bridge Design Specifications
– Figures A13.1.1-2 and A13.1.1-3
Rail Geometrics
Bridge Rail Analysis Categories
• Analysis templates created for the following categories:
– Solid Concrete Parapet
– Concrete Post and Beam
– Steel Post and Beam
– Combination Steel Post and Concrete Parapet
Strength Analysis• From templates
Note: Yellow cell = input; Green cell = results check
Analyzed Bridge Rails
30
• Coordinate with pooled fund efforts and other research initiatives– Collect available information
– Share information to avoid duplication of effort
– Work toward compiling information on all MASH devices
• Roadside Safety Pooled Fund Program– MASH Implementation Coordination Effort
• Develop and maintain databases for MASH implementation needs and testing
Task 4 – MASH Coordination
MASH Databasewww.roadsidepooledfund.org
Task 5 – FHWA Eligibility Requests
• Prepare necessary documentation and rationale for submission of eligibility requests to FHWA
• Selected, prioritized bridge rail systems
• Methodology and rationale should be applicable to other rail systems
FHWA Eligibility Letter Request & Summary
• Numerous eligibility letters requests were prepared and sent for the systems that passed
• A list of these systems (13 total) are provided in Appendix D of the report.
• Some systems are borderline… TBD
• Some systems will need to be crash tested
• NCHRP 22-35 is currently underway - Evaluation of Bridge Rail Systems to Confirm AASHTO MASH Compliance
Contact Information• William Williams
(979) 862-2297
• Roger Bligh
(979) 845-6375
