Structural Analysis of PostTensioned Concrete Containment Building Repair using 3d Finite Elements

1
Structural Analysis of Post-Tensioned Concrete
Containment Building Repair using 3-d Finite
Elements
Peter R. Barrett, P.E., Computer Aided
Engineering Associates Inc., Daniel B. Fisher
Jr. P.E., AREVA Group
2
Background on Computer Aided Engineering Assoc.

• Engineering consulting firm.
• Engineering seminars including customized on-site
  classes tailored to your specific needs.
• WebEx interactive training available in your
  office via the Web.
• Custom software development.
• Provide ANSYS hotline support.
• Website www.caeai.com.

3
CAEAI Technical Staff

• Nicholas M. Veikos, Ph.D., President
• Peter R. Barrett, M.S.C.E., P.E., Vice President
• Michael Bak, Ph.D., Project Manager
• Patrick Cunningham, M.S.M.E., Project Manager
• Steven Hale, M.S.M.E., Project Manager
• James Kosloski, M.S.M.E., Project Manager
• Hsin-Hua Tsuei, Ph D. CFD Manager
• George Bauer, M.S.M.E., Project Manager
• Lawrence L. Durocher, Ph.D., Director

4
Problem

• Replacement of steam generators in nuclear power
  plants may require a construction opening
• A major design challenge is to develop an
  efficient tendon de-tensioning and subsequent
  re-tensioning plan.
• Stresses and displacements must be monitored
  throughout the repair sequence.
• The method should simulate potential stress
  mismatch between the existing wall and the patch.

5
Solution

• Nonlinear finite element analysis is simulated
  using ANSYS
• The sequential construction simulation includes
• Explicit modeling of the tendons and concrete
  including the tendon-concrete load interaction.
• Tendon tensioning, tendon loss, de-tensioning and
  subsequent re-tensioning
• Direct modeling of the construction opening and
  repair
• Modeling method captures local bending response
  in the patch that can be neglected in simplified
  models

6
Procedure

• Scripted Input Files are used to
• Model a symmetric portion of the building
  (typically 180 degrees or less)
• Model the hoop and vertical tendons explicitly
  with truss elements.
• Model the equipment hatch area and evaluate its
  contribution to the buildings overall state of
  stress.
• Model the removal of individual tendons (hoop or
  vertical).
• Vary an individual tendons force (hoop or
  vertical)
• Include the effects of tendon loss for both
  vertical and horizontal tendons
• Scripted input allows for
• Quick What-if design changes
• Optimization of tendon tensioning and
  de-tensioning

7
Finite Element Modeling

• 3-d brick elements model the concrete building
• Capture nonlinear through-thickness stresses
• 1-d truss elements model the tendons
• Explicit modeling of hoop and vertical tendons
• Stiff Spring elements connect the
  prepatch-building Interface
• Used in the pre-patch analysis to simulate a
  continuous building
• Contact elements simulate the patched-building
  repair
• Use to simulate the reduced patch-wall bond
  strength

8
Example Simulation

• The remaining presentation represents the
  trypical response that one may see in evaluating
  a post-tensioned nuclear containment building.
• The geometry and loading do not represent any
  real building.
• The purpose of the example is to demonstrate the
  response that may be seen in actual containment
  buildings

9
Sample Parametric Input

• ! Loads to be solved 1 solved 0 skipped
• !
• LS_11 ! 1.0 Building Dead Load 1.0
  Tendons 1.0 Crane
• !
• LS_21 ! 1.0 Dead 1.0 Tendons 1.0
  Crane 1.5 pressure
• LS_61 ! Hole in Wall
• ..
• LS_140 ! 1.0 DL 1.09v1.24H
  1.5pressure
• !
• D_scal1.01 ! global scaling dome loads
• H_scal1.01 ! global scaling hoop tendons
• V_scal1.01 ! global scaling vert tendons
• !
• !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  !!!!!!!!!!!!!!!

• !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  !!!!!!!!!!!!!!!!!!!
• ! Pressure Loading - By Load Step
• !
• P_sc_ls288.51.4 ! Press Loading (psi) for
  load step 2
• P_sc_ls31e-9 ! Press Loading (psi) for
  load step 3
• P_sc_ls1488.51.4 ! Internal Pressure
  Loading (psi) for load step 14
• !
• ! Define Bottom Elevation for Hole
• !
• !bot_hole-1 ! use -1 for no hole
• bot_hole859.75
• !
• ! Define Top Elevation of for Hole
• !
• !top_hole-1 ! use -1 for no hole
• top_hole859.7523.41667
• ..

10
Brick elements - building, abutments, patch
11
1-d truss elements to model the tendons
This is modeled explicitly for each tendon using
an initial strain approach that produces the
corresponding tendon force.
12
1-d truss elements to model the tendons
Solid and Truss Nodes line-up for coupling in
non-axial directions
Axial Tendon Displacements are fixed
13
1-d truss elements to model the tendons
Max. Tendon Load at Abutment
14
Example Solution Sequence

• LS 1 Dead Load Tendon Loads Equipment
  Loading
• LS 2 Dead Tendons Equipment Accident
• LS 3 Dead Tendons Equipment
• LS 4 Tendons de-tensioned in hole only -
  vertical and horizontal
• LS 5 Tendons de-tensioned locally away from
  the hole
• LS 6 Create the hole in the wall
• LS 7 Remaining vertical tendons detensioned as
  necessary
• LS 8 Patch installed stress free
• LS 9 Patch installed and contact elements
  activated
• LS 10 Springs removed
• LS 11 Partially re-tension verticals tendons
• LS 12 Partially re-tension hoop tendons
• LS 13 Fully re-tension hoop and vertical tendons
• LS 14 Fully re-tensioned hoop and vertical
  tendons Accident

15
Vertical Stress - Gravity Tendon Loads LS1
16
Hoop Stress Gravity Tendon Loads LS1
17
Vertical Stress Hole Reduced Tendons LS7
18
Hoop Stress Hole Reduced Tendons LS7
19
Hoop Stress Repair Re-Tension LS13
20
Vertical Stress Repair Re-Tension LS13
21
Non-linear Contact Response
22
Time History Solution
23
Comparison to Path Independent Loading
Path Dependent Step-by-Step
Path Independent All loads applied at once
24
Summary of Path Dependent Loading

• Time History Simulation illustrates loading
  sequence
• Comparison between path dependent solution and
  path independent solution show
• Reduction in compressive hoop stress in the patch
  region caused by the repair sequence
• Potential vertical tensile stresses in the patch
  region that are predicted only by including the
  sequential loading
• Higher tendon re-tensioning is often required in
  the patch to design for this effect.

25
Sequential Illustration Simple Wall Model

• Load the wall under uniform axial displacement
  (The axial compression replicates the effect of
  the tendon loads) - Measure the stress state in
  the pre- repaired wall.
• Reduce the displacement and create a hole in the
  wall simulating the creation of the construction
  opening.
• Patch the hole under the same reduced
  displacement (Use element birth)
• Increase the loads (uniform axial displacement)
  back to its original values (This replicates the
  re-tensioning of the tendons) and compare with
  original wall

26
Illustration Load, Hole, Patch Re-load
27
Sequential Illustration Simple Wall Model
28
Conclusions

• A nonlinear incremental finite element based
  stress analysis predicts stresses that would not
  be captured using a non-path dependent simulation
• Explicit modeling of the tendons and abutments
  accurately capture force, displacement and stress
  results.
• Step-by-step loading provide the ability to
  extract intermediate results
• Using element Birth and Death captures the true
  response of creating and repairing construction
  openings.
• An automated analysis file with user-friendly
  input parameters allow the designer to perform
  design iterations without becoming an analysis
  expert