evaluation of a transition system for

Evaluation of a Transition System for

MASH Test Level 4

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Introduction

• The purpose of this project was to evaluate the crash performance of an existing approach guardrail transition (AGT) design for the MassDOT.

• The evaluation was performed using FEA based on evaluation procedures set forth in the AASHTO Manual for Assessing Safety Hardware (MASH) for Test Level 4 (TL4).

• The AGT system is used to transition from a 31-inch tall w-beam guardrail to a 42-inch tall steel open-faced bridge rail.

2

42”31”

Background

• This system was previously full-scale crash tested at the Texas Transportation Institute (TTI) under NCHRP Report 350 for TL-4, in which the system met all performance criteria.

• There have been no changes to the system’s design.

• However, it was of interest to the MassDOT to determine if the system meets the strength and safety criteria of the current crash testing standards of MASH TL-4, which involve higher impact severities for each of the required test cases.

3

• MASH specifies three (3) tests for assessing TL-4 crash performance for transitions:

– Test 4-20 (Optional): Involves a 2425-lb passenger car (1100C vehicle) impacting the critical impact point at a nominal speed and angle of 62 mph and 25 degrees.

– Test 4-21: Involves a 5,000-lb ½-ton quad-cab pickup truck (2270P vehicle) impacting the critical impact point at a nominal speed and angle of 62 mph and 25 degrees.

– Test 4-22: Involves a 22,000-lb single unit truck (SUT) (10,000S vehicle) impacting the critical impact point at a nominal speed and angle of 56 mph and 15 degrees.

MASH Test Level 41100C

2270P

10000S

NCHRP Report 350 vs. MASH

0

20

40

60

80

100

120

140

160

180

Report 350 (TL-4)AASHTO '98 (PL-2)

MASH(TL-4)

Imp

act

Seve

rity

(ki

p-f

t)

Test Procedure

small car test

pick-up test

SUT test

54%

Test ConditionsReport 350 /

AASHTO ‘98MASH

22 kip56 mph15 deg.

18 kip50 mph15 deg.

2400 lb62 mph25 deg.




Objectives and Scope

• Two design options were evaluated: 1. Curb-mounted option in which the

bridge rail and AGT are mounted with an 8-inch tall curb, and

2. Sidewalk mounted option in which the bridge rail and AGT are mounted onto the top of a 5-ft wide sidewalk with an 8-inch curb face.

7

8”Deck Surface

Curb

Soil Grade for Transition Posts

42”

32.25”

Deck Surface8”

1.5% slope

Soil Grade for Transition Posts

42”

32.25”

60”

Sidewalk

Objectives and Scope

• The focus of this evaluation was on the transition to the shaped buttress.

• The analysis cases involved approach from both directions: – approach from the transition section leading into the

shaped-concrete buttress, and – approach from the bridge rail section leading into the

concrete buttress.

8

35 ft

Basic Design

• The AGT design includes four primary elements:1) 10-gauge w-beam to thrie-beam transition with decreased

post-spacing, 2) A two-layer, 12-gauge thrie-beam section with further

decreased post spacing, 3) 10-gauge end-shoe, and 4) a shaped concrete buttress.

9

Shaped Buttress (2 layers) 12 ga. thrie beam

Basic Design• Materials

– Thrie-beam: AASHTO M180 Class A Type II steel– Wood: Pine (Grade 1)– Buttress: modeled as rigid

6”x8”x78” Timber Posts6”x8”x84” Timber Posts

1 post-space at 75”

4 post-spaces at 37.5”

3 post spaces at 18.75”

Basic Design• A key aspect of this design is the

shaped buttress, which serves to transition from the thrie-beam rail to the bridge rail.

• The top surface on the leading end of the buttress gradually tapers from 31 inches tall at the thrie-beam end to 42 inches tall as it approaches the bridge rail.

• The buttress also includes a double taper on the front face at the leading end to mitigate potential snag points for the vehicle during impacts.

• A collapsible tube spacer block is placed between the thrie-beam and the tapered face.

• The location of the spacer block results in 31.2 inches of unsupported length of thrie-beam between the spacer block and the tangent section of the buttress.

Vertical taper (1V:4H)

Face Taper (1L:4H)

Face Taper (1L:1H)

CollapsibleTube

BearingPlate

18.75”31.2” 18.75”

Basic Design

Collapsing Tube Assembly• Tube

– 6” Dia. x 0.28” thick x 16.5” long– A53 Grade B steel.

• Bent plate – A709 Grade 50 steel.

12

54.9 ft

6’-6” (typ)5’

Basic DesignBridge Rail• A 54.9-ft section of the S3-TL4

bridge rail was developed• Post spacing was set to maximum

allowable • Materials

– Posts - ASTM A709 Grade 50 steel– Tube Rails - A500 Grade C

13

Basic Design

• Base Plate:– 12” x 10” x 1.5” – ASTM A709 Grade 50

• Anchor Bolts:– Five anchors– 1-1/8” diameter x 12” long– ASTM A449 (120 ksi)

14

1-1/8” Dia. A449 (TYP)

*Constrained_Spotwelds

Rigid Deck

Rigid nuts and washers (TYP)

12” x 10” x 1.5”

Slide 20

1”

8”12”

25-7

/8”

7.5”

2”

7”3”1-1/8” Dia. A449

7/8” Dia. A325(TYP)

3” 42-1/8”

12”

25

-7/8

”7.

5”

2”

7”3”1-1/8” Dia. A449

42-1/8”

Sidewalk Surface

(b)(a)

15” 7” at safety curb)

13”

11.5”

Base Plate and Anchor Bolts

Basic Design

Concrete Sidewalk / Deck• Impact cases on AGT

transitioning to buttress– Concrete modeled with rigid

properties

• Impact cases on the bridge rail transition to buttress – Concrete modeled *Mat_RHT

in LS-DYNA– Default material properties

based on an unconfined compressive strength of 4,000 psi

– The material properties for the reinforcing steel conformed to ASTM A615 Grade 60.

15

Element Side Length = 1”(concrete)

12” Spacing(TYP)

10” Spacing(TYP)

#6 Bars#4 Bars

#5 Bars#5 Bars

6 #5 bars (longitudinal)

Element Side Length = 1”(concrete)

6” Spacing(TYP)

Test 4-20 Test 4-21 Test 4-22

Curb-Mounted 3.6 ft4.3 ft

5.5 ft5.5 ft

Sidewalk-Mounted 3.6 ft

4.3 ft

5.5 ft

5.5 ft

7.1 ft

5.5 ft

7.5 ft

10.0 ft

Curb-Mounted - - -

Sidewalk-Mounted - 4.3 ft 5.0 ft

* Allowing tire deflation

Transition to Buttress

Critical Impact Points

AGT SystemImpact Direction

Bridge Rail to Buttress

Analysis Matrix

16

*

≈ 13.5 ftSidewalkSidewalk

3.6 ft

Sidewalk-Mounted Transition to ButtressTest 4-20

• Impact Conditions– Impact Speed = 62.1 mph– Impact Angle = 25 degrees– Impact Point = 3.6 ft upstream

from the point where the buttress begins to flare

– Vehicle Model:• YarisC_V1L_R160407.k• Vehicle Mass = 2,595 lb

18

8”

5’


MOVIES


20

MOVIES


(mm)

Lateral

Displacement

Maximum displacement = 5.11 in (129 mm)

0

5

10

15

20

25

30

35

40

45

OIV-x OIV-y THIV

OIV

(Ft/

s)

OIV

T4-20 (SW)

0

2

4

6

8

10

12

14

16

18

20

ORA-x ORA-y PHD

Max

OR

A (G

's)

ORA

T4-20 (SW)

0

0.5

1

1.5

2

2.5

ASI

ASI

T4-20 (SW)

0

2

4

6

8

10

12

14

16

18

20

50 acc-x 50 acc-y 50 acc-z

Max

Acc

ele

rati

on

(G's

)

50-ms Average Accelerations

T4-20 (SW)


Max Criteria

Preferred Limit

Max Criteria

Preferred Limit

Occupant Risk Metrics

X Acceleration at CG

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0-25

-20

-15

-10

-5

0

5

Time (sec)

Lo

ng

itu

din

al A

cc

ele

rati

on

(G

)

Time of OIV (0.19442 sec) 10-msec average

Y Acceleration at CG

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0-30

-20

-10

0

10

Time (sec)

La

tera

l A

cc

ele

rati

on

(G

)


Roll and Pitch Angles

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0-15

-10

-5

0

5

10

15

Time (sec)

An

gle

s (

deg

rees)

Roll Pitch

• Roll and Pitch < 75 degrees



Evaluation Factors Evaluation Criteria Results

Structural Adequacy

A

Test article should contain and redirect the vehicle or bring the vehicle to a controlled stop; the vehicle should not penetrate, underride, or override the installation although controlled lateral deflection of the test article is acceptable.

Pass

Occupant Risk

D

Detached elements, fragments, or other debris from the test article should not penetrate or show potential for penetrating the occupant compartment, or present undue hazard to other traffic, pedestrians, or personnel in a work zone. Deformations of, or intrusions into, to occupant compartment should not exceed limits set forth in Section 5.2.2 and Appendix E.

Pass

FThe vehicle should remain upright during and after collision. The maximum roll and pitch angles are not to exceed 75 degrees.

Pass

HThe longitudinal and lateral occupant impact velocity (OIV) shall not exceed 40 ft/s with a preferred limit of 30 ft/s

Pass

IThe longitudinal and lateral occupant ridedown acceleration (ORA) shall not exceed 20.49 G, with a preferred limit of 15.0 G

Pass

Conclusions

OCI = 3.14” at lower right-front corner of

door < 9” critical

Max roll = 11.7 deg.Max pitch = 7.7 deg.

Max OIV = 32.5 ft/s

Max ORA* = 6.5 g

Deformation = 5.1” (at 17 inches upstream from

tangent section of buttress)

* Note: the ORA values would be much higher if the OIV occurs a few milliseconds sooner.

≈ 14.8 ftSidewalk


25

• Impact Conditions– Impact Speed = 62.1 mph– Impact Angle = 25 degrees– Impact Point 5.5 ft

• Vehicle Model– 500_SIlveradoC_V3a_170804.k– Vehicle Mass = 5,007 lb

Sidewalk-Mounted Transition to ButtressTest 4-21• Impact Conditions

– Impact Speed = 62.1 mph– Impact Angle = 25 degrees– Impact Point 5.5 ft

• Vehicle Model– 500_SIlveradoC_V3a_170804.k– Vehicle Mass = 5,007 lb

26

Sidewalk

5.5 ft


MOVIES


Dynamic displacement = 6.22 in (158 mm)

Permanent displacement = 5.11 in (130 mm)

Lateral Displacement

(mm)

42”

0

5

10

15

20

25

30

35

40

OIV-x OIV-y THIV

OIV

(ft/

s)

OIV

No Deflation

0

5

10

15

20

ORA-x ORA-y PHD

Max

OR

A (G

's)

ORA

No Deflation


Max Criteria

Preferred Limit

Max Criteria

Preferred Limit



0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-15

-10

-5

0

5

Time (sec)

Lo

ng

itu

din

al A

cc

ele

rati

on

(G

)



0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-25

-20

-15

-10

-5

0

5

10

Time (sec)

La

tera

l A

cc

ele

rati

on

(G

)


Roll and Pitch Angles

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-20

-10

0

10

20

Time (sec)

An

gle

s (

deg

rees)

Roll Pitch

• Roll and Pitch < 75 degrees



Evaluation Factors Evaluation Criteria Results

Structural Adequacy

A


Pass

Occupant Risk

D


Pass

FThe vehicle should remain upright during and after collision. The maximum roll and pitch angles are not to exceed 75 degrees.

Pass

HThe longitudinal and lateral occupant impact velocity (OIV) shall not exceed 40 ft/s with a preferred limit of 30 ft/s

Pass

IThe longitudinal and lateral occupant ridedown acceleration (ORA) shall not exceed 20.49 G, with a preferred limit of 15.0 G

Pass

Conclusions

OCI = 1.5” at wheel-well floor pan < 9” maximum

Max roll = 13.7 deg.Max pitch = 18.8 deg.

Max OIV = 26.9 ft/s

Max ORA = 15.6 g

Dynamic = 6.22 in

Permanent = 5.11

32


• Impact Conditions– Impact Speed = 56 mph– Impact Angle = 15 degrees– Target Impact Point

• 5.5 ft• 7.5 ft• 10 ft

33

• Vehicle Model– F800.k– Vehicle Mass = 22,046 lb

≈ 22 ftSidewalk


• Impact Conditions– Impact Speed = 56 mph– Impact Angle = 15 degrees– Target Impact Point

• 5.5 ft• 7.5 ft• 10 ft

34

• Vehicle Model– F800.k– Vehicle Mass = 22,046 lb

5.57 ft

6.6 ft

5.5 ft

7.5 ft

10 ft


35

Report 350 (Test) MASH (FEA)

IP = 5.5 ftIP = 5.5 ft


MOVIES

36


IP = 5.5 ftIP = 5.5 ft


MOVIES

37


IP = 5.5 ftIP = 5.5 ft

Comparison

38

3.3 inches

5.3 inches

3.0 inches

Impact PointMax Wheel

Penetration

IP = 5.5 ft

IP = 7.5 ft

IP = 10.0 ft

Comparison

39

3.3 inches

5.3 inches

3.0 inches

Impact PointMax Wheel

Penetration

IP = 5.5 ft

IP = 7.5 ft

IP = 10.0 ft


0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-20

-10

0

10

20

Time (sec)

Lo

ng

itu

din

al A

ccele

rati

on

(G

)



0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-15

-10

-5

0

5

10

Time (sec)

Late

ral A

ccele

rati

on

(G

)


0

5

10

15

20

25

30

35

40

OIV-x OIV-y THIV

OIV

(ft/

s)

OIV

Cabin C.G.

0

2

4

6

8

10

12

14

16

18

20

ORA-x ORA-y PHD

Max

OR

A (G

's)

ORA

Cabin C.G.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

ASI

ASI

Cabin C.G.

0

1

2

3

4

5

6

7

50 acc-x 50 acc-y 50 acc-z

Max

Acc

ele

rati

on

(G's

)

50-ms Average Accelerations

Cabin C.G.


Max Criteria

Preferred Limit

Max Criteria

Preferred Limit

IP = 5.5 ft

40

CabinCabin


0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-15

-10

-5

0

5

10

Time (sec)

Late

ral A

ccele

rati

on

(G

)



0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-15

-10

-5

0

5

10

Time (sec)

Lo

ng

itu

din

al A

ccele

rati

on

(G

)


0

5

10

15

20

25

30

35

40

OIV-x OIV-y THIV

OIV

(ft/

s)

OIV

Cabin C.G.

0

2

4

6

8

10

12

14

16

18

20

ORA-x ORA-y PHD

Max

OR

A (G

's)

ORA

Cabin C.G.


Max Criteria

Preferred Limit

Max Criteria

Preferred Limit

41

CabinCabin

IP = 7.5 ft

0

5

10

15

20

25

30

35

40

OIV-x OIV-y THIV

OIV

(ft/

s)

OIV

Cabin C.G.

0

2

4

6

8

10

12

14

16

18

20

ORA-x ORA-y PHD

Max

OR

A (G

's)

ORA

Cabin C.G.


Max Criteria

Preferred Limit

Max Criteria

Preferred Limit

IP = 10 ft


0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-15

-10

-5

0

5

10

Time (sec)

Late

ral A

ccele

rati

on

(G

)



0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6-20

-10

0

10

20

Time (sec)

Lo

ng

itu

din

al A

ccele

rati

on

(G

)


42

CabinCabin


0

20

40

60

80

100

120

140

160

180

200

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Imp

act

Forc

e (k

ips)

Time (sec)

60Hz Filter

25ms moving average

50ms moving average61k

54k

82k

73k

Analysis with IP = 5.5 ftResultant Forces

0

20

40

60

80

100

120

140

160

180

200

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Imp

act

Forc

e (k

ips)

Time (sec)

60Hz Filter

25ms moving average

50ms moving average


Analysis with IP = 7.5 ft

123k

96k

75k

67k

Resultant Forces

0

20

40

60

80

100

120

140

160

180

200

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Imp

act

Forc

e (k

ips)

Time (sec)

60Hz Filter

25ms moving average

50ms moving average


Resultant Forces Analysis with IP = 10.0 ft

138k

105k

76k

65k


Summary of Results

Max. Disp. Wheel Pen Long. Lat. Resultant OIVx OIVy ORAx ORAy Roll Pitch

ft (in) (in) (kip) (kip) (kip) (ft/s) (ft/s) (g) (g) (deg) (deg)

5.6 Pass 5.8 3.0 45 67 82 9.5 15.1 19 9.3 17.1(2) 8.7(2) Pass

7.5 Pass 5.6 3.3 59 91 123 10.8 15.1 10.2 7.2 7.4 4.8 Pass

10 Pass 8.0 5.3 70 103 138 11.2 14.1 16.7 9.6 24.2(2) 7 Pass

Structural Adequacy Maximum 25ms-avg. Forces Occupant Risk Metrics Vehicle Stability

Overall

ResultContain

CIP

<< 40

Non-critical in all cases


Conclusions

OCI (negligible)

Max roll = 24 degMax pitch = 7 deg.

Deflection = 8”

47

Evaluation Factors Evaluation Criteria – MASH Test 4-12 Results

Structural Adequacy

A


Pass

Occupant Risk

D


Pass

GIt is preferable, although not essential, that the vehicle remain upright during and after collision.

Likely Pass

But possible that vehicle could roll onto its side

CIP = 10.0 ft

Max. Disp. OIVx OIVy ORAx ORAy Roll Pitch

(mph) (deg) ft (in) Location (in) (ft/s) (ft/s) (g) (g) (deg) (deg)

Test 4-20 62 25 3.6 Pass 3.0 Door (lower) 2.57 25.6 30.2 4.7 11.1 3.7 4.4 Pass

62 25 4.3 Pass 2.6 Wheel well/ Toe Pan 2.9 26.6 26.9 6.2 11.2 17.1 16.1 Pass

62 25 5.5 Pass 2.9 Wheel well/ Toe Pan 3.1 26.9 27.2 6.2 10.5 17.3 14.4 Pass

Test 4-22 56 15 5.5 Pass 4.0 Wheel well/ Toe Pan 1.47 4.9 13.1 11.8 9.6 24.1 4.6 Pass

Test 4-20 62 25 3.6 Pass 5.1 Door (lower) 3.14 30.2 32.5 6.1(1)

6.5(1) 11.7 7.7 Pass

62 25 4.3 Pass * * * 22 25.9 5.9 15.6 38.7 15.3 Pass

62 25 5.5 Pass 6.2 Front-Side Panel 1.5 22.3 26.9 4.2 15.6 13.7 18.8 Pass

62(3) 25(3) 5.5(3) Pass(3) 5.7 Front-Side Panel 1.5(3) 22(3) 26.2(3) 3.7(3) 16.2(3) 11.1(3) 13.1(3) Pass(3)

62 25 7.1 Pass * * * 22 34.8 5.2 12.8 14.6 16.5 Pass

56 15 5.6 Pass 5.8 Front-Side Panel 3.67 9.5 15.1 19 9.3 17.1(2)

8.7(2) Pass

56 15 7.5 Pass 5.6 Front-Side Panel 5.6 10.8 15.1 10.2 7.2 7.4 4.8 Pass

56 15 10 Pass 8.0 * * 11.2 14.1 16.7 9.6 24.2(2) 7 Pass

Sidewalk Test 4-21 62 25 5.1 Pass 1.1 Wheel well/ Toe Pan 2.7 24.9 26.6 10.4 10.8 8.9 7.4 Pass

Sidewalk Test 4-22 56 16.5 5.3 Pass 2.5 Front-Side Panel 5 5.2 16.4 10.5 10 31 4.8 Pass

* Value not evaluated

(1) Maximum ORA occurred on tail-end of a major acceleration pulse. Would have been higher if OIV had occured slightly sooner.

(2) Max angular displacement occurred for SUT cabin, rather than cargo-box.

(3) Analysis performed with tires deflated after debeading during traversal of sidewalk curb.

MASH Test

No.

Mounting

OptionTransition Type

Impact Conditions

Vehicle Stability

RESULTS

Overall

Result

OCI


Speed Angle CIP

Structural Adequacy

Contain

Bridge Rail to AGT

Test 4-21

Test 4-21

Curb

Sidewalk

AGT to Bridge Rail

Test 4-22

Summary• The crash performance of the MassDOT AGT system design was evaluated for

MASH TL-4 using FEA. • Detailed finite element analysis models were developed for each of the proposed

designs, and LS-DYNA was used to simulate the required impact conditions. • The CIP was selected to maximize potential for snagging and/or to maximize the

probability for high vehicle decelerations during the approach to the rigid buttress.• A total of thirteen (14) analysis cases were performed and reported

48

Conclusions

• The barrier successfully contained and redirected the vehicle with minimal to moderate damage to the barrier for all test cases.

• There were no detached elements from the barrier that showed potential for penetrating into the occupant compartment or presenting undue hazard to other traffic.

• For the small car and pickup tests, the vehicle remained upright and did not experience excessive roll or pitch angle displacements; and the OIV and maximum ORA values were within critical limits specified in MASH.

• For the SUT test, the overall stability of the vehicle was uncertain at the termination of the analyses, but it appeared likely that the vehicle would remain up-right. – According to MASH, it is not essential that the vehicle remain upright;

• Based on the analysis results, the barrier is expected to meet all structural and occupant risk criteria in MASH.

49

Recommendations

• Based on the results of this study, it is recommended that the Sidewalk-Mounted AGT be considered for further evaluation via full-scale crash testing under MASH Test Level 4 conditions.

• The sidewalk-mounted AGT resulted in:– Higher OIV and potentially higher ORA for the small car test. – Higher ORA for the pickup truck test. – Greater barrier damage for all TL-4 impact cases

• The recommended critical impact points corresponding to each of the recommended tests are:– Test 4-20 (Optional): CIP = 3.6 feet upstream of the tangent breakpoint

on the buttress,– Test 4-21: CIP = 5.5 feet upstream of the tangent breakpoint on the

buttress,– Test 4-22: CIP = 10.0 feet upstream of the tangent breakpoint on the

buttress.

50

evaluation of a transition system for

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