AASHTO Subcommittee on Bridges and Structures Annual Meeting

NCHRP 12-90 Chuck A. Plaxico, Ph.D.

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

AASHTO Subcommittee on

Bridges and Structures Annual

Meeting April 21, 2015

Saratoga Springs, NY

Limited Use Document

This Presentation is furnished only for review by members of the NCHRP

project panel, AASHTO SCOBS and AASHTO TCRS and is regarded as fully

privileged. The opinions and conclusions expressed or implied in this

presentation are those of the researchers performing the research and are

not necessarily those of the Transportation Research Board, the National

Research Council, or the program sponsors. This research project is funded

under the National Cooperative Highway Research Program; however, this

presentation has not gone through the full review for publication according to

procedures established and overseen by the Transportation Research Board

and approval by the Governing Board of the National Research Council.

Dissemination of information included herein must be approved by NCHRP.

6th Edition of the LRFD Bridge Design Specifications in Article 3.6.5.1 says if the choice is to design for structural resistance (rather than shielding) …

Equivalent static force of 600 kips force applied 5-ft above the ground at 0-15 degrees from the edge of lanes.

Is 600-kips the appropriate equivalent static force?

How do we translate from the force domain to the energy domain?

Validate FEA reinforced concrete model with scaled impact tests

◦ Design and construct 1/3rd scaled circular and square columns.

◦ Perform material characterization tests on cored samples from the columns to calibrate material properties.

◦ Perform pendulum impact tests on the scaled column designs and

◦ Validate an LS-DYNA finite element model of the scaled impact experiments.

Validate tractor-trailer model with TTI crash test

◦ The model developed by NCAC/Battelle/ORNL was revised for head-on high energy impacts.

◦ The model was validated by comparing results to a full-scale tractor-trailer test into a 36” diameter rigid column at TTI.

Develop LS-DYNA models of five representative bridge piers

◦ Calculate quasi-static shear capacity of 5 representative designs.

◦ Determine the dynamic impact loads and failure characteristics of those 5 representative designs.

◦ Relate the quasi-static shear capacity to the dynamic failure loads/failure modes.

60”

8”

8”

24”

A A

B B

Section A-A Section B-B

Spiral Steel

Longitudinal

Steel

Lap

Steel

Concrete

Cover

12”

F'c

Max Agg

Size

(in)

Cover

(in) Bar Size

Number of

Bars

Spiral

Diameter

(in) Bar Size

Pitch

(Spacing)

(in)

1 6 0.75 1.5 #4 6 9 #3 1-3/8 5

2 6 0.75 1.5 #3 11 9 #3 1-3/8 3

3 6 0.75 1.5 #3 11 9 #3 8.6 3

Spiral/Shear Steel

Design

No.

Longitudinal SteelConcrete

Num

Articles

Spiral Column Designs

Cases 1 and 2 meet ACI and LRFD requirements but use a different size and number of longitudinal steel.

◦ Evaluate effects of longitudinal steel on the lateral impact resistance for a given volume ratio of steel reinforcement to concrete.

Case 3 includes the same longitudinal steel design as Case 2, but uses a larger pitch for the spiral steel (i.e., 8.6” vs. 1.375”).

◦ This will allow for evaluating the effects of the amount of shear steel on the lateral impact resistance for spiral columns for a given spiral-bar size.

60”

8”

8”

24”

A A

B B

12”

F'c

Max Agg

Size

(in)

Cover

(in) Bar Size

Number of

Bars

Spiral

Diameter

(in) Bar Size

Pitch

(Spacing)

(in)

1 6 0.75 1.5 #4 6 9 #3 1-3/8 5

2 6 0.75 1.5 #3 11 9 #3 1-3/8 3

3 6 0.75 1.5 #3 11 9 #3 8.6 3

Spiral/Shear Steel

Design

No.

Longitudinal SteelConcrete

Num

Articles

Spiral Column Designs

60”

8”

8”

C C

Section C-C

12”

Square Column Design

2 equal space

12”

Concrete cover = 1.5”

Ties: #3 bars 2 equal spaces

8 #4 bars

at corners

F'c

Max Agg

Size

(in)

Cover

(in) Bar Size

Number of

Bars

Tie

Outside

Length

(in) Bar Size

Tie

Spacing

(in)

4 6 0.75 1.5 #4 8 9 #3 8 3

Num

Articles

Spiral/Shear Steel

Design

No.

Concrete Longitudinal Steel

Design meets ACI and LRFD requirements.

◦ Compare to spiral columns designs 1 and 2

The preliminary model entailed:

◦ Diameter: 12 inches

◦ Length: 69 inches

◦ Longitudinal bars: 9 #3 bars

◦ Spiral steel: W2.3 ASTM A82

◦ Pitch: 1.3”

◦ Concrete cover: 1”

Concrete Material

◦ 5ksi concrete with preliminary material parameters provided by Len Schwer for material types:

*MAT_CSCM_CONCRETE

*MAT_RHT

*MAT_WINFRITH_CONCRETE

*MAT_PSEUDO_TENSOR

*MAT_CONCRETE_DAMAGE_REL3

*MAT_CDPM

Steel Rebar

◦ ASTM A615 Grade 60 modeled using *MAT_PIECEWISE_LINEAR_PLASTIC in LS-DYNA with material properties characterized from tensile tests of #4 rebar performed at the Turner-Fairbank Highway Research Center (TFHRC)

Concrete

Characterization Tests

◦ TFHRC Labs: (Specimen poured 6” diameter x 12” tall cylinders)

Unconfined Compression Tests at TFHRC labs

Split Cylinder Tests

◦ ARA Labs: (Specimen cored 1-7/8” diameter cylinders)

Unconfined compression tests

150 MPa confined triaxial tests

300 MPa confined triaxial tests

◦ Others tests we would like to perform but are out of our budget include:

Hydrostatic compression tests

Uniaxial strain tests

Concrete

Preliminary shear failure surface data for a 5 ksi concrete

Implemented in *MAT_272 (MAT-RHT) in LS-DYNA

Steel Rebar

ASTM A615 Grade 60

Stress-strain data obtained from:

Zachary B. Haber, Ph.D Bridge Research Engineer Professional Service Industries, Inc. (PSI) FHWA / TFHRC

Analysis conducted using four different material models.

All resulted in approximately the same peak loading, BUT …

◦ CSCM and the Winfrith stronger and more brittle behavior.

◦ RHT and the Concrete Damage REL3 lower strength after the peak loading and more ductile behavior.

*MAY_CSCM

*MAT_RHT

*MAT_CD_REL3

*MAT_Winfrith

*MAT_RHT *MAT_Concrete_Damage_REL3 *MAT_CSCM

CSCM

RHT

CD_REL3

Winfrith

Time = 0.000 seconds

*MAT_Winfrith


CSCM

RHT

CD_REL3

Winfrith


Showing cracks

*MAT_Winfrith


CSCM

RHT

CD_REL3

Winfrith


Showing cracks

Run Terminated

Prematurely

*MAT_Winfrith

Tractor trailer model developed by NCAC/Battelle/ORNL (version 10-0308).

Used to simulate full-scale crash test 429730-2 conducted at the Texas Transportation Institute (TTI)

Assess validity of the model.

TTI Test No. 429730-2

NCAC/Battelle/ORNL

FE Model Version 10-0308

Impact Weight = 79,520 lb

Impact Speed = 50.1 mph

Impact Angle = 90°

Impact Location: Center Line

The test vehicle was ballasted with unrestrained bags of sand in paper bags resting on wooden pallets.

The FE model included sand bags resting directly on the trailer floor.

The sand was modeled using MAT_005 in LS-DYNA with properties based on calibration tests provided in:

Fasanella, E.L., R.K.H. Lyle, and K.E. Jackson, “Developing Soil Models for Dynamic Impact Simulations,” NASA Langley Research Center, 2009.

Modified NCAC/Battelle/ORNL model ◦ Version 10-0308

Modifications Included: ◦ Changed failure strain for u-bolts to 0.16 ◦ Repositioned u-bolts to eliminate initial penetrations ◦ Updated material properties for u-bolts based on material tests performed at Battelle

01/13/2009 ◦ Re-meshed front components of tractor for impact with rigid pole ◦ Re-meshed the fifth-wheel ◦ Changed nodal rigid body (NRB) connections to generalized- weld-with-failure for all

frame-bracket connections ◦ Changed connection of cabin to frame rails to constrained joints with failure conditions ◦ Changed several NRB connections to spotweld with failure conditions ◦ Included failure strain for all materials (HSLA steel failure set to 0.2) ◦ Corrected thickness of drive shaft. ◦ Removed steel plates behind the cabin (these were included on the original model to

replicate the mounting plates installed for mounting the data acquisition equipment on the FOIL vehicle).

◦ Changed engine material from elastic to elasto-plastic. ◦ Changed mass of engine to match the weight of a Detroit DD15 14.8L plus 45 quarts of oil. ◦ Added mass to the floor and firewall to make up for the reduction in engine mass from

previous change.

Major Differences

between

Crash Test Vehicle

And

FEA Model

• Wheel base length of FEM

tractor is 16.2 inches

shorter than test vehicle.

• Empty weight of FEM

vehicle is 6.3k less than test

vehicle (17% less).

• FEM ballast is 6.6k greater

than test vehicle (15%

greater).

0

200

400

600

800

1000

1200

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)

Test No. 429730-2 -- Total Force

Test 10-ms avg. Test 25-ms avg. 0.016 s - Frame

0.030 s - Engine 0.232 s Truck Cab Sqeezed 0.276 s - Front-Wall of Trailer Fails

0.380 s - Cargo Compresses Cabin 0.393 s - Direct Contact of Trailer Cargo FEA 10-ms avg.

FEA 25-ms Avg.

FEA

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)

Test No. 429730-2 -- Total Force on Column

Test 429730-2 10-ms avg. FEA 10-ms avg.

Time = 0.03 seconds

• Test: Engine impacts against the

column, resulting in a force spike of

approximately 830 kips.

• FEA: Engine impacts against the

column resulting in a force spike of

928 kips (11% higher than test).

Event:

928 kip

830 kip

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)



Time = 0.10 seconds

• Cabin mounts fail in both the test and

simulation resulting in sudden drop in

load on the column.

Event:

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)



Time = 0.17 seconds

• Resistance on column again drops as

cabin is at rest (waiting on impact from

trailer).

Event:

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)




• Truck sleeper contacts trailer and

begins to be squeezed.

Event:

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)




• Test: Engine wedges between the rigid

column and the tandem axle or fifth wheel

of the tractor. The sudden stop of the fifth

wheel results in high stress on connections

at the joint between the trailer side walls

and the kingpin box, which subsequently

fails.

• FEA: The engine is wedged between the

rigid column and the left side of the tandem

axel on the tractor. Failure not modeled for

the trailer materials.

Event:

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)




• Test: After the trailer fails, there is a

sudden drop in force on the column.

The force reaches a second peak

when the front of the trailer make

contact with the column.

• FEA: No failure of trailer. The tractor

and trailer continue to press forward

under relatively constant load.

Event:

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)




• Test: The peak force in the test due to

trailer and ballast was 513 kips.

• FEA: The peak force in the FEA due to

trailer and ballast was 462 kip (10%

less).

• This test/simulation used sand ballast.

You could get a much higher 2nd peak

if the cargo was rigid.

Event [Continued]:

513 kip

462 kip

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)

Test No. 429730-2 -- Total Force


0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)



No mass redistribution Mass redistributed by

increasing cabin floor

thickness

0

100

200

300

400

500

600

700

800

900

1000

0 0.1 0.2 0.3 0.4 0.5 0.6

Forc

e (

kip

s)

Time (seconds)



Mass redistributed by

increasing density of cabin

floor.

The load response on the column due to the trailer and ballast (i.e., after the truck is crushed) is affected by where the back of the engine impacts the rear of the tractor.

For example, the force-time histories shown below are from three different analyses with slightly different tractor model changes (e.g., how the loss of mass from the engine due to the model change was redistributed to the cabin floor).

The primary event that lead to differences in response at 0.28 seconds into the impact was the orientation of the engine and where the engine impacted against the tractor tandem axel.

The model’s response during the first 0.28 seconds of the impact event accurately replicated that of the full-scale crash test.

The model also reasonably replicated the magnitude of the second peak load.

The model did not capture the failure of the trailer’s front wall – in part, because failure was not included in the material definitions for the trailer materials.

Based on these comparisons, the model is considered to be sufficiently valid for simulating the impact load on concrete columns with diameter (or width) of 36 inches or less.

The model will be used in preliminary analyses to investigate the strength/capacity of various bridge pier designs for lateral impact loading.

Note: Prior to use of the model for primary investigations of laterally loaded columns, the trailer materials will be updated to include failure and the validation analysis rerun.

Preliminary analyses were performed to simulate lateral loading on two full-scale column designs.

◦ Design 1: (Standard Ohio Design)

36” diameter

Height = 15’

Concrete cover = 3”

Long. Reinf.: 11 #9 bars

Steel/concrete ratio = 1.08%

Spiral steel: #4 bar w/ 4.5” pitch

◦ Design 2: (common design from the TTI crash investigation study)

30” diameter

Height = 15’

Concrete cover = 2.25”

Long. Reinf.: 8 #9 bars

Steel/concrete ratio = 1.13%

Spiral steel: #2 bar w/ 6” pitch

Spiral SteelBar Size = #2Pitch = 6 inches

Longitudinal SteelEight #9 BarsEqual Spacing

The column was modeled with “cold” joints at the connection points of the pier cap and the foundation.

A portion of the pier cap and footer was explicitly modeled with lap steel at the joints.

The dimensions were based on an existing Ohio design.

Fixed conditions were imposed:

◦ At the bottom and at the four sides of the footer

◦ At the front and back faces of the pier cap (w.r.t. traffic direction)

Concrete modeled using *MAT_RHT

Longitudinal Steel

Spiral Steel

Section A-A

Lap Steel

(Same size

bar as long

steel)

3.33 ft

3 ft

15 ft

5 ft

Fixed

Fixed

6.5 ft

A-A

Based on the Ohio Pier Plan and Elevation Drawing FRA-270-22.42 (see figure on right)

◦ Rectangular footing:

8’-10” footprint based on rebar length

3’ depth

◦ Lap Joint Steel

Same as the column steel with decreased spiral diameter in order to fit inside the pier reinforcement

Extends 6’-6” into pier column

Note:

• The Bar Mark is first identified by letter.

S = superstructure, P = Pier, A =

Abutment, SP = spiral, DS = drilled

shaft

• The number after the letter identifies

the bar size. 4 = #4 bar, 5 = #5 bar, etc.

• The remaining numbers are just unique

numbers to identify each individual bar.

Based on the Ohio Pier Plan and Elevation Drawing FRA-270-22.42

◦ Cap is 36 inches wide, 40 inches tall

◦ 8 #11 bars on bottom

◦ 5 #10 bars on top

◦ 4 #5 bars on the sides

◦ Stirrups not modeled

Two types of loading were evaluated:

1. 80,000-lb tractor-trailer impacting at 50 mph

2. Rigid cylinder moving at constant velocity

Load applied at 5’ above ground

Loading rates: 2, 5 and 20 mph

Load Case 1 Load Case 2

5’

Concrete failure included in analysis

but element erosion not turned on

Concrete failure included in analysis

but element erosion not turned on

Force-Time History Plots

30” column 36” column

2 mph 5 mph 20 mph

2 mph5 mph20 mph

Contour Plots of Effective Plastic Strain Force-Time History Plots

2 mph 5 mph 20 mph

36” Column

30” Column

2 mph5 mph20 mph

These results and the general model response will be further analyzed as we continue to further develop the concrete material model parameters and validate against the scaled column impact tests to be performed at the FOIL.

AASHTO Subcommittee on Bridges and Structures Annual Meeting

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