1. U.S. ARMY CORPS OF ENGINEERS
Analysis and Design of Large-Scale Civil Works Structures Using LS-DYNA®
PRESENTED BY THE
U.S. ARMY CORPS OF ENGINEERS
David Depolo, M.S., P.E.
Structural Engineer
Sacramento & Philadelphia Districts
Thomas Walker, P.E.
Sacramento District
Eric Kennedy, P.E.
Structural Engineer
Sacramento District
Ryan Tom
American River Design
NON-PRESENTING CO-AUTHORS
LSTC International Users’ Conference
June 7, 2010

2. Introduction Project overview The JFP model Designing from the model
Properties
Troubleshooting & Lessons Learned
Designing from the model
Running the model
Seismic input

5. The Folsom JFP LS-DYNA Model Overview
Control Structure
Reservoir
(*MAT_NULL)
Foundation
(*MAT_ELASTIC, E = 3500ksi)
Backfill
(*MAT_PSEUDO_TENSOR)
Shear Zone
(*MAT_ELASTIC, E = 324ksi)

6. The Folsom JFP LS-DYNA Model Control Structure
Non-Flow Monoliths
Flow-Through Monoliths
Non-Flow Monolith

7. The Folsom JFP LS-DYNA Model Flow-Through Monoliths
Headwall
Piers
(Designed using LS-DYNA output)
Trunnion Girders
Pier Struts
(Designed using LS-DYNA output)
Radial Gates
(Rigid, defined individually)
Invert Slab
Gate Arms

8. Rigid Bodies & SOFT
Symptom Unrealistic spikes in forces at the radial gate
Corrected
Peak force/length along pier during earthquake

9. Rigid Bodies & SOFT
Reasons Gates defined using *MAT_RIGID Reservoir is merged with the gate to obtain correct hydrostatic pressures
Solution Optional Card A: SOFT = 0 uses a penalty formulation, interface stiffness is based on the bulk modulus

10. Reservoir Contacts
Symptom During an earthquake, some fluid elements lose pressure
Reason Structure displacements created a free surface

11. Reservoir Contacts Solution 1. Split the reservoir at monolith joints
2. Define a contact surface between reservoir parts

12. Reservoir Contacts
For troubleshooting, split contacts so you can focus on problem areas (each conduit has its own set of contacts)
For verification, split contacts into pieces that are easily replicated with a calculator HSF = 0.5*γ*H2*b

13. Hydrostatic Pressures
Complex topography can cause incorrect pressures
Idealized geometry ensures the loads to the structure are more realistic

14. Post-Tensioned Anchorage
Option 1: Constrained Nodes
Each trunnion girder is constrained to nodes that represent the dead ends of the anchors
*CONSTRAINED_EXTRA_NODE_SET
Pros
Simple, easy to implement
Transfers all forces directly to the slab
Cons
Ignores elastic behavior of anchors
Creates a rigid plane in the slab

15. Post-Tensioned Anchorage
Option 2: Beam Elements
Hughes-Liu (Type 1) or Truss (Type 3)
Tied Node-to-Surface contacts at both ends
More realistic than constrained nodes – pressure between trunnion girder and pier changes during the earthquake

16. Post-Tensioned Anchorage
Hughes-Liu beams use *INITIAL_STRESS for post-tensioning
100% Applied initialization – no option to ramp with gravity loads
Truss elements require pressure loads on surfaces to simulate post-tensioning
Stress in beam is the change from the post-tensioning stress

17. Design
Nodal contact forces recorded at pier/slab interface and two higher contacts
Force and moment demands calculated for each nodal group at each output time (dt = 0.01sec)

18. Design Site constraints required an optimized reinforcing design
Generate an interaction diagram for each reinforcing pattern
Axial force determines moment capacity and affects shear capacity
This design would have been much more difficult without LS-DYNA

19. Running the Model Step 1 Run the model with gravity loads first
Use *LOAD_BODY_PARTS to apply gravity to everything except the foundation
Apply Single Point Constraints (SPCs) at all boundaries
*DATABASE_SPCFORC

20. Running the Model Step 2 Apply the equilibrium forces to the model
*LOAD_NODE_POINT with output in the spcforc database
Ramp these forces on the same load curve as the gravity loads
*BOUNDARY_NON_REFLECTING should replace all SPCs
This allows the seismic waves to exit the model, simulating an unbounded condition

21. Running the Model Step 3 Apply the seismic loads
*LOAD_SEGMENT_SET_NONUNIFORM
Each direction of motion has its own load curve

22. Seismic Input Selection of Time Histories
Characterize Design Earthquake Magnitude
Distances from source to site
Subsurface conditions
Duration of Strong Shaking
Available Records or Simulated Time Histories
Deterministic and Probabilistic
Deterministic MCE’s (3 records/per direction)
Probabilistic OBE’s (3 records/per direction)

23. Non-Reflecting Boundary
Seismic Input
Seismic Input Methods
Displacement Time History
Velocity Time History
Acceleration Time History
Force (or Stress) Time History (preferred)
Non-Reflecting Boundary
DAM
HORIZONTAL PLANE FOR GROUND MOTIONS
Ground

24. Seismic Input Seismic Input Location and Minimum Foundation Size
Plane within foundation (*NODE_SET)
Deconvolved ground motions
Methods used to Deconvolve (Typ. 2D) NR
Note: If model is too narrow seismic energy will exit through side of model.

25. Seismic Input Modifying Time Histories to Develop Design Records
Simple (Uniform) Scaling
Determine Natural Period of Structure
Deconvolved earthquake applied to foundation model w/o structure to develop response spectrum
Compare recorded and smooth design spectrums
Apply single factor so that response spectrum of scaled motion is a close match to design spectrum at the natural period
Disadvantages
More EQ records required (min. of 3)
Natural Period of structure must be determined
Agreement of response spectrums could vary significantly at other periods
Scaling for different directions of motion (1 factor for all directions vs. different factors for each direction)

26. Seismic Input Spectral Matching (preferred method) Advantages
Modifying frequency content of input motion so that recorded response spectrum is a close match to the design response spectrum at all periods
Deconvolved vs. Free Field Motion
Advantages
Sufficient to have one time history for each direction
Multiple structures at a site with varying periods would not need scaling for each structure
The energy of the time history is not greatly altered

27. Seismic Input Precautions
Ensure the character of the scaled record in the time domain is fairly similar in shape, sequence, and number of pulses with respect to the original time history.

28. Seismic Input Spectral Matching Procedure
Outcrop acceleration time history for each component
FFT of Outcrop acceleration time history
Apply Outcrop motion at depth in model as force time history and record acceleration of node on surface of foundation model
FFT of computed acceleration time history
Compute correction factor in Frequency Domain as the ratio of the Outcrop to Computed motion amplitudes
Apply correction factor to the input motion in the frequency domain
Inverse FFT of corrected motion to return to time domain
Compute corrected force time history
Repeat procedure if necessary

29. Seismic Input
Example of Spectrally Matched Ground Motions

30. Seismic Input
Example of Spectrally Matched Ground Motions