Structural Analysis of Bridge Gusset Plates:
Steel vs. Composite
By: Stephen Ganz
MANE 6980
Master’s of Engineering Project Proposal
Abstract
Bridges play a vital role in transportation networks the world over. Spanning up to
several thousand feet and towering up to several hundred feet high, these manmade engineering marvels allow for safe, convenient passage for people and their
cargo. Most bridges are based on truss designs to efficiently transmit load back to
their foundations. Gusset plates are integral to truss based bridge design because
they serve as the attachment point for these structural members. Gusset plates have
become the focal point of much research since the 2007 collapse of the I-35 bridge
in Mississippi, in which the National Transportation Safety Board (NTSB) reports
that the probable cause is due to inadequate plate design. This paper will focus on
performing structural analyses of gusset plates. The goal here is compare the
performance differences in metallic and composite plates.
Background
Gusset plates are commonly found in many different structures including bridges,
crane supports, crane booms, building frames, roofing etc. Basically they are used in
any structural joint which connects beams together using either rivets or welding.
In doing so, these plates are subjected to significant loads which make their design
paramount to the safety of the whole structure.
Figures 1 a, b, c - Top left, a typical
bridge gusset plate. Top right, an aerial
view of Mississippi’s I-35 bridge collapse.
Left, the Moodna Viaduct, the longest and
tallest railroad bridge east of the
Mississippi river.
In the case of bridges, loading mainly comes from three components: dead load,
dynamic load and live load. Dead load is the weight of the structure itself, dynamic
loads such as wind and live load from passing vehicles and snow.
Modeling truss joints in Finite Element Analysis (FEA) software is an attractive
alternative to destructive testing. And while no simulation is advanced enough to
perfectly mimic real world testing, FEA has become increasingly accurate in
predicting stresses and at the very least it is a valuable tool, supplemental to the
design development and verification process
Problem Description and Methodology
Stress and deflection analyses will be performed in Finite Element Analysis (FEA)
software based on loads calculated by method of joints for a Warren Truss bridge. A
bridge model will be constructed in Abaqus consisting only of Gusset Plates and
boundary conditions. This will eliminate unnecessary computation of involving
trusses. Next, a mesh study will be performed by running the analysis with different
mesh densities.
Then the analysis will be run again using plates made from
structural steel and composite materials.
Finally, results will be compared and
conclusions will be made regarding the advantages/disadvantages of composite
materials in this application.
Loading will come from dead load (bridge weight) and live load (vehicles, snow)
based on building requirements in accordance with DOT rules and regulations.
Transverse forces (wind) will be ignored since these plates are not significantly
loaded in transverse bending and to permit the use of shell elements for 2D analysis.
A full 3D analysis is beyond the capability of the resources I have access to and that
failures of these joints are more commonly associated with tensile and buckling
failure. This should provide enough information to make a structural comparison.
Figure 2 – Warren Truss Bridge
Figure 3 – Generalized free body diagrams of gusset plates. The arrows indicate forces
applied which can be in tension or compression.
Resources Required
For this project 3 main resources are needed
1. Microsoft Office
2. Abaqus/CAE
3. Mathcad
All of the modeling and Finite Element Analysis will be performed using
Abaqus/CAE 6.9 or newer. This program enables the user to completely model
components, assign section properties, constraints, loads and view results. Abaqus
is available at my workplace. Microsoft office will be used to assemble reports and
Mathcad is will be used to perform any hand calculations necessary.
Expected Outcomes
A composite gusset plate may offer possible strength advantages over steel.
Milestones
5/21
Submit proposal draft
5/26
Complete Research and Develop Loads
6/4
Create 2-D model complete mesh study
6/11
Submit First Progress Report
6/19
Create composite model and compare to metals
7/2
Submit Second Progress Report
7/9
Tabulate Results
7/16
Submit Final Draft
7/30
Preliminary Final Report
8/6
Submit Final Report
Resources
1. 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 I35W 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.
8. Beer, Johnston. “Vector Mechanics for Engineers Statics and Dynamics 7th 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>