Post on 10-Dec-2021
Advancing Steel and Concrete
Bridge Technology
Manual For Finite Element
Analysis
Presentation to T-5
July 2012
John M. Kulicki
Task Team
• FHWA
– Dr. Brian D. Kozy, PE
– Mr. Reggie Holt
• Prime – ALTSS Center, Lehigh University
– Dr. Richard Sause, PE
– Dr. Chad Kusko
• Task Leader – Modjeski and Masters, Inc
– Dr. John Kulicki, PE
– Dr Thomas Murphy, PE
Objectives and Approach
• Provide greater consistency in application
of FEA to bridge structures
– Raise the level of basic understanding to
encourage wider application of FEA
– Avoid blunders
– Understand behavior
– Introduce economies
Refined Analysis Tasks
• Deliverables are a manual of refined
analysis, AASHTO LRFD provisions, and
example (benchmark) problems.
• Spread across Task 1 and Task 2.
How?
• Produce instructional manual over two Tasks
• Task 1 – first 7 sections and examples
– Application basics
– Not material specific
– bridge type specific guidelines for steel and
concrete
– Proposed Spec changes to more directly use
results of FEA
How?
• Keep flexible
• Encourage initiative and creativity
• Avoid deep mathematics
• Concentrate on application
• Don’t overwhelm with too much “Big
Bridge Stuff”
• Avoid software specifics to extent possible
– try to stay generic
1. Refined Methods of Analysis in
AASHTO LRFD (T1)
• FEA as one refined method of analysis
permitted by LRFD
• 1D, 2D grid vs. 3D FEA compared
• Areas in LRFD where refined methods are
suggested/permitted (which are FEA
applicable)
• Compatibility of analysis and specification
provisions
2. Fundamentals of FEA (T1)
• General capabilities of modern software –
not a commercial
• Typical input and output
• Shape functions and degrees of freedom
• Typical element families and usage
• Handling torsion – and warping in
particular
4. Model Verification (T1)
• Model and software verification
• Learning the software
• Vetting the design process
• Retrofitting bridges
• Examples – results of incorrect BC’s Posit ive Moment - S10N 0.5L - BF Stresses
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7 8
Lusas St ress (Ksi)
Fie
ld S
tre
ss (
Ksi
)
Case 5
Case 6
Case 7
Case 8
Field=Lusas
Linear
(Field=Lusas)
Live Load Moment in Exterior Box Girder
-10000
-8000
-6000
-4000
-2000
0
2000
4000
6000
8000
0 200 400 600 800 1000
Distance (ft)
Mo
men
t (k
-ft)
5. Evaluation of Stresses with
Shell Elements (T1)
• Integrating stresses
• Effective flange width
• Automatic slicing
• Staged loading/construction and stress
evaluation
6. Live Load Application (T1)
• What does AASHTO LRFD require?
• When is more required?
• How is live load modeled?
• How does program go from wheels to
nodes?
• Verifying automated
loaders
7. Composite Section Analysis (T1)
• Effective flange widths
• Red Herrings (axial forces in bending
members)
8. Examples
• Comparison of 1D, 2D and 3D analyses
for load distribution
– Steel bridges
– Concrete bridges
– Guidance on when refined analysis is
beneficial or needed
9. Concrete Bridges (T2)
• Modeling creep and shrinkage
• Made continuous for live load
• Secondary PT effects
• Linear elastic analysis vs. cracked
concrete material
• See staging elsewhere
-0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0 0 200 400 600 800 1000
Time (days)
Dis
pla
cem
en
t (i
nc
hes)
10. Prestressing and Post-tensioning (T2)
• Is prestressing a resistance or a load?
• Service vs. ultimate
• Applying P/T in an FEA – trajectory or
equivalent loads
11. Steel Bridges (T2)
• Handling mixed materials
• Cross-frames and diaphragms
• Picking the geometric positioning and
associated modeling issues
• Layover
• Deck construction
• Staged construction
• Hot spot fatigue analysis
13. Steel Bridges (continued)
• Initial imperfections, e.g. web flatness
• Camber
• Distortion-Induced Fatigue - stiffness vs.
flexibility – modeling issues
12. Steel Connections (T2)
• Actual stress distributions vs. typical
design assumptions vs. FEA
• Localized yielding and redistribution
13. Stability Analysis (T2)
• Imperfections and initial stresses, e.g.
residual stresses
• What the design equations account for
and what is typically modeled.
14. Nonlinear Considerations (T2)
• When is nonlinear analysis required?
• Material
• Geometric
• Combined
• Lift-off, i.e. changed boundary conditions
during analysis
• Slip-stick
15. Dynamic Analysis (T2)
• Look to Seismic Guide Spec and current
provisions
• Mass and stiffness modeling
– Mass moment of inertia
• How many modes are enough?
• Using the mass participation percentage
• Time history, modal (spectral) analysis
• Special requirements for seismic analysis
of girder bridges
16. Examples (T2)
• Curved multi-beam bridge – static and
dynamic analysis
• Stability example
• Time-dependent
example