Barriers, Parapets, and Railings Arielle Ehrlich State Bridge Design Engineer May 17, 2017 Bridge Office mndot.gov/bridge
MnDOT Vocabulary Is it a barrier, a parapet or a railing? BARRIER. It is concrete and does not have a vertical front face. 5/17/2017 Bridge Office mndot.gov/bridge 2
MnDOT Vocabulary Is it a barrier, a parapet or a railing? PARAPET. It is concrete and has a vertical front face. 5/17/2017 Bridge Office mndot.gov/bridge 3
MnDOT Vocabulary Is it a barrier, a parapet or a railing? RAILING. It is steel. 5/17/2017 Bridge Office mndot.gov/bridge 4
MnDOT Vocabulary Barriers: Concrete, sloped or safety shape Parapets: Concrete, vertical face Railings: Steel (ornamental, fencing, structural) AASHTO calls these all bridge rails! 5/17/2017 Bridge Office mndot.gov/bridge 5
Vocabulary Is it a barrier, a parapet or a railing? RAILING and PARAPET. This is the T 1 railing on the P 2 parapet. 5/17/2017 Bridge Office mndot.gov/bridge 6
Why Barriers? 5/17/2017 Bridge Office mndot.gov/bridge 7
Purpose of Crash Testing Crashworthiness is determined by: Strength ability to contain a vehicle Geometry ability to redirect a vehicle Occupant safety ability to minimize risk to vehicle s occupants 5/17/2017 Bridge Office mndot.gov/bridge 8
Crash Testing 5/17/2017 Bridge Office mndot.gov/bridge 9
History of Crash Testing Standards Highway Research Board (HRB) Circular 482 (1962) only one vehicle! Several other documents produced: NCHRP Report 153 (1974) TRB Circular 191 (1978) NCHRP Report 230 (1981) Publications refined the process and the vehicles 5/17/2017 Bridge Office mndot.gov/bridge 10
History of Crash Testing Standards NCHRP 350 Recommended Procedures for the Safety Performance Evaluation of Highway Features Publication in 1993 Implementation in 1998 5/17/2017 Bridge Office mndot.gov/bridge 11
History of Crash Testing Standards Manual for Assessing Safety Hardware (MASH) Originally published in 2009 Second edition published in 2016 All new hardware must be tested to MASH (not NCHRP 350) starting January 1, 2011 5/17/2017 Bridge Office mndot.gov/bridge 12
MASH Implementation FHWA/AASHTO Implementation Plan January 7, 2016: Bridge barriers must be tested to MASH (2016) On National Highway System (NHS) Projects let after December 31, 2019 New installation or full replacement 5/17/2017 Bridge Office mndot.gov/bridge 13
MASH Implementation FHWA/AASHTO Implementation Plan January 7, 2016: Bridge barriers must be tested to MASH (2016) Existing systems do not need to be replaced Agencies are encouraged to develop a policy for non NHS routes and other types of projects (such as mill and overlay projects) Full testing is required; finite element analysis alone is insufficient to validate NCHRP 350 devices meets MASH 5/17/2017 Bridge Office mndot.gov/bridge 14
MASH Implementation Deadlines for other safety devices: December 31, 2017: W beam barriers, CIP concrete barriers June 30, 2018: W beam terminals December 31, 2018: Cable barriers and terminals, crash cushions December 31, 2019: Transitions, all other longitudinal barriers (including portable barriers), terminals, sign supports, breakaway hardware 5/17/2017 Bridge Office mndot.gov/bridge 15
MASH Implementation NCHRP 20 07/Task 395 Work being done by Texas Transportation Institute (TTI) Determining commonly used barriers around the country Trying to determine which rails need to be retested to MASH and which can be approved based on previous evaluation Maintaining a database of MASH tested hardware and wish list for hardware to be tested https://www.roadsidepooledfund.org/mash implementation/ NCHRP is considering a new project in FY 18 to continue the work of this project 5/17/2017 Bridge Office mndot.gov/bridge 16
Test Levels Test Level AASHTO Article 13.7.2 Description MnDOT Usage TL 1 TL 2 TL 3 Work zones with low posted speeds, very low ADT, low speed local streets Work zones and local collector roads with favorable site conditions, small number of heavy vehicles, posted speeds are reduced High speed arterial highways with low mixtures of heavy vehicles and with favorable site conditions N/A Low speed High speed on approach panels; guardrail 5/17/2017 Bridge Office mndot.gov/bridge 17
Test Levels Test Level AASHTO Article 13.7.2 Description MnDOT Usage TL 4 TL 5 High speed highways, freeways, expressways, and interstates with a mixture of trucks and heavy vehicles Similar to TL 4, but where large trucks are a significant portion of ADT High speed on bridges Pier protection; historically on the outside of curved decks TL 6 Applications where tanker type trucks or other high center of gravity vehicles are anticipate, especially with unfavorable site conditions N/A 5/17/2017 Bridge Office mndot.gov/bridge 18
NCHRP 350 vs. MASH Test vehicles are updated to reflect the 85th percentile of the United States passenger vehicle fleet. Impact condition criteria were modified to correct inconsistencies Evaluation criteria were modified to be more objective 5/17/2017 Bridge Office mndot.gov/bridge 19
NCHRP 350 vs. MASH 5/17/2017 Bridge Office mndot.gov/bridge 20
NCHRP 350 vs. MASH Significant differences at TL 4 350 MASH 5/17/2017 Bridge Office mndot.gov/bridge 21
NCHRP 350 vs. MASH Significant differences at TL 4 Single unit truck values have changed substantially Value NCHRP 350 MASH W (kips) 18.0 22.0 G (in) 49 63 Speed (mph) 50 55 Minimum Height of TL 4 Barrier NCHRP 350 32 MASH 36 5/17/2017 Bridge Office mndot.gov/bridge 22
MnDOT Type S Barriers 32 F shape doesn t meet minimum height for MASH TL 4 New series of barriers developed: Type S 5/17/2017 Bridge Office mndot.gov/bridge 23
MnDOT Type S Barriers Minimum height based on crash testing is 36 ; 32 F doesn t meet MASH Based on Texas DOT SSTR Rail Designed to meet or exceed strength of TxDOT SSTR 10.8 o slope Three heights: 36, 42, 54 All MASH TL 4 Working on eligibility letter with TTI 5/17/2017 Bridge Office mndot.gov/bridge 24
New MnDOT MASH TL 2 Parapet Current parapet (P 1, Fig. 5 397.166) doesn t meet MASH TL 2 when mounted on a sidewalk Developing a replacement based on Caltrans Type 732SW Low speed only Proposed parapet meets MASH TL 2 on a sidewalk 5/17/2017 Bridge Office mndot.gov/bridge 25
Other MnDOT Barriers T 1 railing with P 2 parapet (Fig. 5 397.157) Not currently tested to MASH Meets 36 height, so possible it will meet MASH TL 4 May be crash tested in the future F shape will remain on repair projects where barrier isn t being replaced 5/17/2017 Bridge Office mndot.gov/bridge 26
Barrier Design Interior Section Yield Line End Section Yield Line Yield line does not extend into the deck. Deck needs adequate strength to force the yield line to stay in the barrier. 5/17/2017 Bridge Office mndot.gov/bridge 27
Barrier Design What if the segment length is less than L c? Diagonal yield line can t develop L Design for yield line at the joint between the parapet and the deck. 5/17/2017 Bridge Office mndot.gov/bridge 28
Loads Values are for NCHRP 350 only. No MASH values determined yet. Recommended values for MASH TL 4 are too high Biggest issue is for overhang design; Barriers can be physically tested. MnDOT standards still showing NCHRP 350, although barriers meet MASH and deck is expected to 5/17/2017 Bridge Office mndot.gov/bridge 29
Pedestrian and Bicycle Railings Current MnDOT height requirement: 54 Higher than minimum in AASHTO Article 13.8.1 May need to be higher over interstates and railroads 5/17/2017 Bridge Office mndot.gov/bridge 30
Pedestrian and Bicycle Railings Design loads: 50 plf + 200 lb point load per AASHTO Article 13.8.2 For posts, apply the load at the lower of the top horizontal rail or 5 feet above the top of the walkway surface 5/17/2017 Bridge Office mndot.gov/bridge 31
Pedestrian and Bicycle Railings Maximum clear opening size: 4 in lower 27 6 above 27 Opening sizes are more restrictive than AASHTO 5/17/2017 Bridge Office mndot.gov/bridge 32
Ornamental Metal Railings Two standard ornamental metal rails: T 3 (includes chain link fence) T 4 (no chain link fence) Curb and parapet mount standards available Low speed applications only At 40 mph, ornamental metal rails must be protected by a traffic barrier At lower speeds, can be mounted on a sidewalk or behind a traffic barrier 5/17/2017 Bridge Office mndot.gov/bridge 33
Chain Link Fence AASHTO Article 13.8.2 includes 0.015 ksf wind load on chain link fence Wind load does NOT need to be applied simultaneously to live load Wind load is applied for both design of fencing and for the posts 5/17/2017 Bridge Office mndot.gov/bridge 34
References AASHTO LRFD Bridge Design Specifications Chapter 13 MnDOT LRFD Bridge Design Manual Section 13 http://www.dot.state.mn.us/bridge/pdf/lrfdmanual/section13.pdf MnDOT Bridge Details Manual Part II http://www.dot.state.mn.us/bridge/bridgedetails2.html 5/17/2017 Bridge Office mndot.gov/bridge 35
Thank you! Arielle Ehrlich arielle.ehrlich@state.mn.us 651.366.4506 5/17/2017 Bridge Office mndot.gov/bridge 36