Malcolm H. Ray, P.E., Ph.D.Christine E. Carrigan, P.E., Ph.D.

Chuck A. Plaxico, Ph.D.

1. Develop risk-based guidelines that quantify when bridge piers should be investigated for vehicular collision forces per AASHTO LRFD Bridge Design Specifications or be shielded with a longitudinal barrier considering as a minimum: site condition, traffic, bridge design configurations, geometry of the roadway section passing beneath a bridge, operations characteristics, and benefit/cost and

2. Develop guidelines for barrier selection, length-of-need, and placement for shielding bridge piers and protecting the traveling public.

1. Develop risk-based guidelines that quantify when bridge piers should be investigated for vehicular collision forces per AASHTO LRFD Bridge Design Specifications or be shielded with a longitudinal barrier considering as a minimum: site condition, traffic, bridge design configurations, geometry of the roadway section passing beneath a bridge, operations characteristics, and benefit/cost and

2. Develop guidelines for barrier selection, length-of-need, and placement for shielding bridge piers and protecting the traveling public.

1. Develop risk-based guidelines that quantify when bridge piers should be investigated for vehicular collision forces per AASHTO LRFD Bridge Design Specifications or be shielded with a longitudinal barrier considering as a minimum: site condition, traffic, bridge design configurations, geometry of the roadway section passing beneath a bridge, operations characteristics, and benefit/cost and

2. Develop guidelines for barrier selection, length-of-need, and placement for shielding bridge piers and protecting the traveling public.

PHASE ACTIVITY STATUS

I Survey, Literature Review, 1st

Interim Report, Etc.) COMPLETE

II Developing necessary input data and procedure structure

COMPLETE

III Developing the detailed guidelines Just Started

IV Final report and final guidelines 31 Jan 2017

A Forest of Unshielded Pier ColumnsGuidelines will consider:- New and existing bridge piers- Median and roadside applications- Divided and undivided roadways.

Using RSAPv3 to assess risk

Two Step Process:1.Protect bridges from collapse due to truck

impacts with piers LRFD.2.Protect vehicle occupants from serious harm

in pier impacts RDG.

Guideline Process: LRFDStep Action

LRFD

A

FIND NADJ (i.e., highway characteristic adjustment factors)

LRFD

B

FIND AF_CUSP as a function of L3, HV_AADT, heavy vehicle mix and road characteristics (i.e., NADJ from LRFD A).

IF AF_CUSP <AF_BCcritTHEN Finished. Shielding is not required for pier protection. Check RDG for vehicle occupant protection

guidance.ELSE AF_CUSP ≥AF_BCcritTHEN Go to Step LRFD C

LRFD

C

FIND AF_BC as a function of AF_CUSP, RCPC, QCT, ϕS PR, ϕSU SC, highway functional classification where:

AF_BC = AF_CUSP � PC �1 − ϕS PR

0.15�

1 − ϕSU SC

0.20

IF AF_BC≥AF_BCcrit

THEN Shield with MASH TL5 barrier for pier protection. Go to Step LRFD D.

OR Change RCPC, ϕS PR, ϕSU SC then repeat Step LRFD C.

ELSE AF_BC<AF_BCcrit

THEN Finished. Shielding is not required for pier protection. Check RDG for vehicle occupant protection guidance.

LRFD

D

FIND Look up selection and layout guidelines for shielding the pier from heavy vehicle impacts.

IF Barrier is requiredTHEN Choose a 42-inch tall MASH TL5 barrier with appropriate run-out length. Refer to tables in Step

LRFD D for placement and run-out length guidance.ELSE Finished. Check RDG for vehicle occupant protection guidance.

Guideline Process: LRFD Step ALR

FD

AFIND NADJ (i.e., highway characteristic

adjustment factors)Adjust for:Posted SpeedLane WidthHorizontal CurvatureAccess DensityNumber of LanesGradeNADJ=fACC∙fLN∙fLW∙fG∙fHC∙fPSL

NADJ adjusts the expected number of lane departures (encroachments).

Guideline Process: LFRD BLR

FD B

FIND AF_CUSP as a function of L3, HV_AADT, heavy vehicle mix and road characteristics (i.e., NADJ from LRFD A).

IF AF_CUSP < AF_BCcritTHEN Finished. Shielding is not required for pier

protection. Check RDG for vehicle occupant protection guidance.

ELSE AF_CUSP ≥ AF_BCcritTHEN Go to Step LRFD C

How many collisions would occur in a year with an unshielded pier with these traffic conditions and highway characteristics at this offset?

Guideline Process: LRFD B

Guideline Process: LRFD CLR

FD C

FIND AF_BC as a function of AF_CUSP, RCPC, QCT, ϕS PR, ϕSU SC, highway functional classification where:

AF_BC = AF_CUSP � PC �1 − ϕS PR

0.15�

1 − ϕSU SC

0.20IF AF_BC ≥ AF_BCcrit

THEN Shield with MASH TL5 barrier for pier protection. Go to Step LRFD D.

OR Change RCPC, ϕS PR, ϕSU SC, repeat Step LRFD C.ELSE AF_BC < AF_BCcritTHEN Finished. Shielding not required for pier

protection. Check RDG for vehicle occupant protection guidance.

Guideline Process: LRFD C

Guideline Process: LRFD DLR

FD D

FIND Look up selection and layout guidelines for shielding the pier from heavy vehicle impacts.

IF Barrier is requiredTHEN Choose a 42-inch tall MASH TL5 barrier with

appropriate run-out length. Refer to tables in Step LRFD D for placement and run-out length guidance.

ELSE Finished. Check RDG for vehicle occupant protection guidance.

Guideline Process: RDGStep Activity Action

RDG

A

FIND Find NADJ (i.e., highway characteristic adjustment factors) and AF_PVENCR (i.e., the modified number of annual passenger vehicle encroachments) as a function of PV_AADT and L3.

IF AF_PV ENCR < AF_A+Kcrit

THEN Pier may remain unshielded based on vehicle occupant protection.

ELSE AF_PV ENCR ≥ AF_A+Kcrit

THEN Proceed to Step RDG B

RDG

B

FIND AF_A+K as function of AF_PVENCR, barrier type and barrier height.

IF AF_A+K≥AF_A+Kcrit

THEN Shield with a MASH TL3 barrier for vehicle occupant protection.ELSE AF_A+K<AF_A+KcritTHEN Pier may remain unshielded based on vehicle occupant

protection.

RDG

C FIND Look up selection and layout guidelines for shielding the pier for vehicle occupant protection in Step RDG C tables.

Guideline Process: RDG ARD

G A

FIND Find NADJ (i.e., highway characteristic adjustment factors) and AF_PVENCR (i.e., the modified number of annual passenger vehicle encroachments) as a function of PV_AADT and L3.

IF AF_PV ENCR < AF_A+KcritTHEN Pier may remain unshielded based on vehicle

occupant protection.ELSE AF_PV ENCR ≥ AF_A+KcritTHEN Proceed to Step RDG B

Guideline Process: RDG A

Guideline Process: RDG A

Guideline Process: RDG BRD

G B

FIND AF_A+K as function of AF_PVENCR, barrier type and barrier height.

IF AF_A+K ≥ AF_A+Kcrit and pier protection is not required based on the LRFD process

THEN Shield with a MASH TL3 barrier for vehicle occupant protection.

ELSE IF AF_A+K ≥ AF_A+Kcrit and pier protection isrequired based on the LRFD process

THEN Shield with a MASH TL5 barrier for pier and vehicle occupant protection.

ELSE AF_A+K < AF_A+KcritTHEN Pier may remain unshielded based on vehicle

occupant protection.

Guideline Process: RDG B

Guideline Process: RDG B

Guideline Process: RDG CRD

G C

FIND Look up selection and layout guidelines for shielding the pier for vehicle occupant protection in Step RDG C tables.

Critical Acceptance Values Traffic Mix and Heavy Vehicle Properties Load and Impact Conditions Shielding Options

Definition #1:… the inability of the superstructureto carry its live and dead load.AF_BC = AF_CUSP � PC � 1−ϕS PR

0.15� 1−ϕSU SC

0.20Pier Redundancy and Superstructure ContinuityR = 1.00 for redundant pier systemR = 0.85 for non-redundant pier systemSC = 1.00 if super structure is continuous over

the pier of interestSC = 0.80 If the superstructure is not

continuous over the pier of interest

Definition #2: … the inability of the critical pier component to support its design live and dead loads.

AF_BC = AF_CUSP � PC

YES YES

NO NO NO

What should the number be?◦ LRFD C3.6.5.1(Vehicle Collisions) “Design for

vehicular collision force is not required if AFHBP is less than 0.0001 for critical or essential bridges or 0.0010 for typical bridges.”◦ LRFD 3.14.5 (Vessel Collisions) “Design for

collision force is not required if AFHBP is less than 0.0001 for critical or essential bridges or 0.001 for typical bridges.”

Recommendation:◦ 0.0001 for critical/essential bridges◦ 0.0010 for typical bridges

What should the number be? NCHRP 22-12(03) (Bridge Railing

Selection Guidelines) used a critical risk of:◦ 0.01 A+K/1000-ft /30 yrs◦ 0.0018 A+K/mi/yr

For a point hazard like a bridge pier this is equivalent to:◦ 0.0001 A+K/Pier/yr◦ Trajectories leaving the road 300 ft

upstream of the leading edge of the pier. Recommendation: 0.0001 A+K/Pier/yr

Rural Urban

FHW

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1 Motorcycles 0.00 0.00 0.00 0.002 Pass. Cars 0.75(1-PT) 0.75(1-PT) 0.80(1-PT) 0.80(1-PT)3 Pickups, Vans and SUVs 0.25(1-PT) 0.25(1-PT) 0.20(1-PT) 0.20(1-PT)

5-7 Single-Unit Truck 0.20(PT) 0.60(PT) 0.30(PT) 0.70(PT)8-10 Single-Trailer Truck 0.70(PT) 0.30(PT) 0.60(PT) 0.20(PT)11-13 Multi-Trailer Truck 0.05(PT) 0.00 0.05(PT) 0.00

Percent trucks (PT) can be varied between 0 and 40% so…

MASH Test Vehicles

VEHICLE CHARACTERISTICS

Vehicle Type FHWA Class

RSAP Vehicle Type

Weight Length Width C.G. Long.

C.G. Height

lbs ft ft ft ftPassenger Cars 2 C 3,300 15.00 5.40 6.00 2.00Pickup Trucks 3 PU 5,000 19.75 6.50 8.50 2.30Light Single Unit Truck 5-7 LSUT 11,500 35.00 7.77 11.60 3.40Average Single Unit Truck 5-7 ASUT 15,000 35.00 7.77 12.25 3.83Heavy Single Unit Truck 5-7 HSUT 22,000 35.00 7.77 14.17 4.70Extra-Heavy SUT 5-7 EHTT 50,600 35.00 7.77 16.50 6.19Light Tractor Trailer 8-10 LTT 27,000 61.30 8.50 24.58 3.73Average Tractor Trailer 8-13 ATT 50,000 61.30 8.50 28.75 4.83Heavy Tractor Trailer 8-13 HTT 80,000 61.30 8.50 30.88 5.42Extra-Heavy Tract. Trailer 8-13 EHTT 105,000 61.30 8.50 31.75 6.00

MASH Test Vehicles

6th Ed. of the LRFD states …◦ “where the design choice is to provide structural resistance, the

pier or abutment shall be designed for an equivalent static force of 600 kip, which is assumed to act in a direction zero to 15 degrees with the edge of the pavement in a horizontal plane, at a distance of 5.0 ft above the ground.”

Recommendation◦ Impact load is an equivalent static force of 600 kips.◦ Critical component resistance is either the ultimate inelastic

bending moment or the shear, whichever is lowest.◦ Load acts 0-15 degrees from the edge of pavement.◦ Load acts between 2 and 5 ft above the ground.◦ Evaluate column, cap and foundation capacity.

Based on pendulum tests and FEA analyses:◦ Retain 600 kips force BUT interpret as the smaller of

the ultimate inelastic bending moment or shear:◦ For reinforced columns:

𝑃𝑃𝐻𝐻2 = 𝑓𝑓𝑝𝑝𝐴𝐴𝑏𝑏 𝑛𝑛1𝑑𝑑1 + �𝑖𝑖=2

𝑁𝑁

𝑛𝑛𝑖𝑖𝑑𝑑𝑖𝑖2

𝑑𝑑2(𝐴𝐴 + 𝐵𝐵)2

𝐴𝐴𝐵𝐵

Pier system must resist the lateral load at: Location of impact, Foundation connection and Bent/cap connection.

Load is applied 2 to 5 ft above the ground. While the average loads in the rigid pole test occurred at 5 ft

above the ground, the failure loads in the test and FEA occurred 25 inches above the ground.

12” Dia. 60” Long Columnf’c = 6 ksify = 60 ksi6 #4 long. bars#3 spirals @ 1-3/8” pitch

12” Dia. 60” Long Columnf’c = 6 ksify = 60 ksi11 #3 long. bars#3 spirals @ 1-3/8” pitch

12” Dia. 60” Long Columnf’c = 6 ksify = 60 ksi11 #3 long. bars#3 spirals @ 8.6”pitch

12” Square 60” Long Columnf’c = 6 ksify = 60 ksi8 #4 long. bars#3 ties @ 8” spacing

FiniteElement Analysis

Nominal Shear

UltimateInelastic Bending

Design Force(kips)

Force(kips)

Force(kips)

24” Dia. 5.5 ksi conc. 60 ksi steel 5#9 longit. Bars #3 sprials @ 2.25” 456 297 27730” Dia. 5.5 ksi conc. 60 ksi steel 8#9 longit. Bars #3 sprials @ 2.25” 534 413 55436” Dia. 5.5 ksi conc. 60 ksi steel 9#10 longit. Bars #4 sprials @ 4” 592 548 92448” Dia. 5.5 ksi conc. 60 ksi steel 15#10 longit. Bars #4 sprials @ 4” 623 855 2052

Pier crash severity◦ EFCCR = 0.0784

Passenger Vehicle Protection Only◦ 31-inch tall MASH TL3 w-beam guardrail ◦ EFCCR = 0.0047 PRV=2.0% RR=0.1%

Pier Protection when offset is adequate ◦ 42-inch tall MASH TL5 concrete F Shape ◦ EFCCR = 0.0035 PRV=0.0% RR=1.5%◦ 2 of 9 TT tests came to rest with the trailer

on the field side of the barrier ◦ Assumed to be MASH TL5

Pier Protection when offset is inadequate ◦ 54-inch tall MASH TL5 concrete F Shape.◦ EFCCR = 0.0035 PRV=0.0% RR=1.5%◦ No test experience with 54” F/NJ/SS barriers.

There is a risk of the trailer contacting the pier columns if it rolls to much during the impact.

To what degree should this be prevented?High likelihood of trailer contact

Less likelihood of trailer contact

FEA and TTI crash test showed that the engine mass in the TT tests is what created the failure load in the pier column.

Force of the trailer striking the pier is unlikely to cause forces large enough to fail the pier column unless:◦ There is a rigid piece of cargo weighing more than 3,000

lbs (e.g., a steel coil, machinery, etc.)◦ This is a very rare occurrence.

There are no tractor trailer tests (i.e., R350 or MASH) of 54” tall NJ/F/SS concrete barriers.

TTI test of 90” tall barrier prevents rollover to the field side but a TL-6 barrier is not practical and the one tested design is a bridge railing.

Shielding OptionsSome bridge piers located very close to the

shoulder will be very difficult to deal with regardless of which choice we make.

6th Ed. of LRFD requires…◦ A 54” high barrier if pier is within 10 ft from back

of barrier.◦ A 42” high barrier if pier is more than 10 ft from

back of barrier. Choices:◦ Ignore offset trailer impacts with the pier

columns will be messy crashes but are unlikely to cause bridge collapse.◦ Including 10-ft offset assumes 54” tall F/NJ/SS

barriers are adequate to keep tractor trailers from coming to rest on the field side of the barrier but there are no such crash tested barriers.

Some bridge pier collisions are the result of length-of-need failures.

Length-of-need and other layout recommendations will be provided in Phase III.

Normal part of RSAPv3 so no additional information needed to be developed in Phase II.

Parameter RangePier Width (Wp)

• 24, 30, 36 and 48-inch RSAPv3 Input

Pier Offset (L3)

• 2-10 ft in 2-ft increments RSAPv3 Input• 15-30 ft in 5-ft increments RSAPv3 Input

Pier Location

• RSAPv3 Input (note: both roadside and median applications are considered).

Pier Capacity (H)

• Capacity #1 Task 6.2A-C• Capacity #2 Task 6.2A-C• Capacity #3 Task 6.2A-C• Capacity #4 Task 6.2A-C• Capacity #5 Task 6.2A-C

Pier System Redundancy (R)

• Cannot accommodate the loss of any pier columns. Task 6.2D• Can accommodate loss of 1 pier column. Task 6.2D• Can accommodate loss of 2 pier columns. Task 6.2D

Bridge Continuity (SC)

• Bridge has continuity over at-risk pier system Task 6.2D• Bridge does not have continuity over at-risk pier system Task

6.2DHighway Type

• Divided RSAPv3 Input• Undivided RSAPv3 Input • One-way RSAPv3 Input

Speed Limit • 45 and 65 mi/hr RSAPv3 InputHorizontal Curvature

• Base guidelines on tangent sections and use the RSAPv3 Horizontal Curve adjustment factor RSAPv3 Default Parameters

Parameter RangeTerrain • 10:1 foreslope RSAPv3 Input Grade • Base guidelines on flat sections and use the RSAPv3 Grade

adjustment factor RSAPv3 Default Parameters Access Density

• Base guidelines on an access density of zero access points /mile and use the RSAPv3 Access Density adjustment factor RSAPv3 Default Parameters

Volume (ADT)

• 500-9,500 veh/day in 500 vpd incr. RSAPv3 Input• 10,000-100,000 vpd in 10,000 vpd incr. RSAPv3 Input

Percent Trucks (PT)

• 0-40 percent in 5% increments RSAPv3 Input

Vehicle Mix • Based on analysis of vehicle mix by roadway type (Task 6.1A) and heavy vehicle properties (Task 6.1B).

Heavy Vehicle Encroachments

• Based on analysis of encroachment rates (Task 6.1C and Trajectories (Task 6.1D) for heavy vehicles.

Barrier Type/Capacity

• 31-inch tall TL3 W-Beam Task 6.4C-E• 42-inch tall TL5 NJ Median Barrier Task 6.4C-E• 54-inch tall TL5 NJ Median Barrier Task 6.4C-E

Barrier Offset (L2)

• 6-12 ft in 2-ft increments RSAPv3 Input

Run-out Length (LR)

• RDG recommended + 0 ft RSAPv3 Input• RDG recommended + TBD in Phase III ft RSAPv3 Input