RPI Master’s Project Second Progress Report Stephen Ganz – 6/5/2012

Structural Analysis of Bridge Gusset Plates:Steel vs. Composite

Problem Description• The objective of this project is to compare the performance differences in

metallic and composite plates by performing structural analyses on the vertical section of a Warren truss bridge

Material performance is based on stresses and deflections

• The materials chosen are A36 Carbon Steel and HexPly 8552 IM7 prepreg composite

• This will be accomplished by comparing results from computer generated Finite Element Analyses.

• Requirements for the bridge is based on federal and state regulations

Steps to Completion• Develop Bridge Model

• Develop Gusset Plate Detail Dimensions

• Calculated loads based on bridge model

– Dead Load

– Live load

• Constructed a working 2D FEA model of a Warren truss bridge

• Perform a Mesh Study

• Determine Best Evaluation Method to Analyze Composite Plates

• Run Analyses & Compare Results based on FS and Deflections

Bridge and Plate Details• As previously mentioned, the vertical section is a Warren Truss with verticals. It’s length was

arbitrarily chosen, but it’s height and width are based on state and federal requirements

• Gusset plates were selected to be 2 inches thick

Loads• Loads were based on the overall dimensions of the bridge model as well as state and federal

requirements for vehicles. This included weights of the trusses, sidewalks, snow, vehicles and road deck.

Total Load (W) is 576,636 lbs

Total Dead Load 297,201 lbs

• Trusses – 101,721 lbs• Sidewalk – 43,500 lbs• Roadway – 205,200 lbs• Floor and Roof Joists – 98,759 lbs

Total Live Load – 279,435 lbs

• Vehicles – 188,235 lbs• Snow – 182,400 lbs

Model Development

• The best way to produce accurate results is to include the truss members

– By using a coarse mesh for the trusses their presence comes at very little computing cost

– Tie constraints bond the the trusses to the plates to simulate a weld

A B

C

D

E

F

G

H

Ii

J

K

L

W 5

W 5

W 5

W 5

W 5

Pinned End Roller End

Loads were applied as surface tractions (psi) at the 5 locations shown

Surftract 1153psi

Mesh Study & Failure Method• Mesh studies were carried for both steel and composite models

– This was done by varying the mesh density of the plates until a convergence of stress or TSAI-WU criteria was observed

• Developing an accurate way of calculating Factors of Safety for the composites (CFAILURE)

Plate C

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0 200 400 600 800 1000 1200

Elements

TS

AIW

CFAILURE• This field output request has been selected as the tool to provide the

necessary results from FEA to base composite failure on

• CFAILURE is a built in feature in Abaqus that can allow the user to view results based on Maximum Stress Theory, Maximum Strain Theory, Tsai-Hill and Tsai-Wu criterion

Factors of safety are calculated as 1/TSAIW for each layer

• Defining the failure stresses in Abaqus (Edit Material -> Suboptions -> Fail Stress)

FEA Results• A36 Steel Model • Composite Models

[0 15 30 45 60 75 90]S

[0 45 90]S

[0 90]S

Shown here are the maximum values for stress in the A36 Steel Model and maximum TSAIW values in the composite models

Factors of Safety for Steel are based on Von Mises stress

Factors of Safety for Composite model are based on TSAIW values

Deflections Illustrated x100

• A36 Steel Model • Composite Models

[0 15 30 45 60 75 90]S

[0 45 90]S

[0 90]S

The best performing composite model deformed nearly twice as much as A36 steel.

Factors of Safety

The table below lists the factors of safety based on failure for all the FEA models. The factors of safety are based on peak stresses or maximum TSAIW values for that particular model

Steel displayed the highest factor of safety, outperforming the best composite by approximately 30%.

Table 4: Factors of Safety

Steel Model Von-Mises Stress Max allowable FS

A36 Carbon Steel 12668 58000 4.58

Composite Models TSAIW Max allowable FS

HexPly [0 90]S 0.296 1 3.38

HexPly [0 45 90]S 0.286 1 3.50

HexPly [0 15 30 45 60 75 90]S 0.400 1 2.50

Deflections Illustrated x100

The best performing composite model deformed nearly twice as much as A36 steel.

Table 5: Deflections

Steel Model U magnitude U1 U2

A36 Carbon Steel 0.454 0.180 -0.447

Composite Models

HexPly [0 90]S 0.890 0.329 -0.879

HexPly [0 45 90]S 0.833 0.331 -0.816

HexPly [0 15 30 45 60 75 90]S 0.944 0.377 -0.921

Lowest % over steel 183% 183% 183%

Outcomes

• The A36 Carbon Steel Gusset plates outperformed those made from HexPly 8552 IM7 composite material based on failure margin and deflections

• This is primarily due to ther orthotropic nature of composites– HexPly 8552 IM7 is much stronger than steel when loaded longitudinally, but it is only

about half as strong as A36 in the transverse directions.

• Composites do have desirable qualities, but they are not suited for this application in which a plate is loaded in up to 6 different directions.

References1. State of Connecticut Department of Transportation. “Bridge Design Manual.” Newington, CT 2003.

2. Kinlan, Jeff. “Structural Comparison of a Composite and Steel Truss Bridge.” Rensselaer Polytechnic Institute, Hartford, CT, April, 2012. http://www.ewp.rpi.edu/hartford/~ernesto/SPR/Kinlan-FinalReport.pdf

3. Abaqus/CAE 6.9EF-1. “Abaqus User Manual.” Dassault Systèmes, Providence, RI, 2009.

4. Budynas, Richard G. and Nisbett, J. Keith. “Shigley’s Mechanical Engineering Design 9th Edition.” McGraw-Hill, New York, NY, 2011. 

5. Abaqus Technology Brief TB-09-BRIDGE-1. “Failure Analysis of Minneapolis I-35W Bridge Gusset Plates,” Revised: December, 2009.

6. Gibson, Ronald F. “Principles of Composite Material Mechanics Second Edition.” Boca Raton, FL: Taylor and Francis Group, 2007.

7. Najjar, Walid S., DeOrtentiis, Frank. “Gusset Plates in Railroad Truss Bridges – Finite Element Analysis and Comparison with Whitmore Testing.” Briarcliff Manor, New York, 2010.

References8. Beer, Johnston. “Vector Mechanics for Engineers Statics and Dynamics 7 th Edition.” New York,

NY. McGraw-Hill, 2004.

9. Kulicki, J.M. “Bridge Engineering Handbook.” Boca Raton: CRC Press, 2000.

10. Meyers, M. M. “Safety and Reliability of Bridge Structures.” CRC Press, 2009.

11. Portland Cement Association. Unit Weights, 2012. http://www.cement.org/tech/faq_unit_weights.asp