1. NEES Small-Group Research Project: Seismic Behavior, Analysis and Design of Complex Wall Systems (NSF Grant CMMI-0421577) Laura Lowes, Dawn Lehman, Anna Birely, Joshua Pugh, UW Dan Kuchma, Chris Hart, Ken Marley, UIUC UNIVERSITY of ILLINOIS

2. Research Objective Establish the seismic performance of modern reinforced concrete walls and develop the response and damage-prediction models required to advance performance- based design of these systems Photo courtesy of MKA Seattle

3. Research Activities to Date Experimental testing: – Testing of four planar walls completed in 2008 – Testing of a planar coupled wall to be completed Nov. 2010 – Testing of three c-shaped walls to be completed in 2011 Simulation: development, calibration and evaluation of – Elastic, effective stiffness models – Fiber-type beam-column models w/ and w/o flexure-shear interaction – Two-dimensional continuum models Performance-prediction models: – Development of data relating damage and demand – Development of fragility functions for walls

4. Experimental Testing Of Planar Walls

5. Experimental Test Program Prototype structure Experimental test matrix Core Wall under Construction (Courtesy of MKA, Seattle)

6. NEES Experimental Testing Bottom three stories of 10-story of a planar prototype wall. Shear and moment applied to simulate lateral load distribution in 10-story prototype Target axial load of 0.1A g f c ’.

7. Planar Wall Test Specimens 1/3-scale with details reflecting modern construction practice. Boundary Elements (3.5%) Splice at Base of Wall Full Scale: 12’ high/18 in. thick Lab: 4’ high/ 6 in. thick

8. Planar Wall Test Matrix Moment-to Shear Ratio Distribution of Reinforcement Splices? STUDY PARAMETERS Wall 1 Wall 2 Wall 3 Wall 4 M b = 0.71hV b V b = 2.8  f’c = 0.7V n UNIFORM NO YES BE at EDGE YES M b = 0.50hV b V b = 4.0  f’c = 0.9V n M b = 0.50hV b V b = 4.0  f’c = 0.9V n M b = 0.50hV b V b = 4.0  f’c = 0.9V n

9. Global Response: Base Moment v. 3 rd Floor Drift MnMn % Drift M, k-ft MnMn MnMn MnMn

10. Response of PW 4: No Splice

11. Final Damage States for Planar Walls Wall 1: V b = 3.6  f’c 1.5% drift (3 rd story) 2.1% drift (10 th story) Wall 2: : V b = 5.0  f’c 1.5% drift (3 rd story) 1.8% drift (10 th story) Wall 3: V b = 4.5  f’c 1.25% drift (3 rd story) 1.6% drift (10 th story) Wall 4: V b = 4.6  f’c 1.0% drift (3 rd story) 1.4% drift (10 th story)

12. Experimental Testing of a Coupled Wall

13. Objective: To determine what is the seismic behavior of a modern coupled wall Review inventory of modern coupled walls – 17 buildings with coupled-core wall systems designed for construction in CA or WA in last 10 years. – Information collected included geometry, aspect ratios, reinforcement ratios, degree of coupling, shear demand-capacity ratio, pier wall axial demand-capacity ratio, etc. Review previous experimental tests – Numerous tests of coupling beams with different reinforcement layouts, ratios and confinement details. – Only seven (7) coupled-wall tests found in the literature. – Coupled wall test specimens are not representative of current design practices. Design and evaluate multiple 10-story planar coupled walls – Design walls following the recommendations of the SEAOC Seismic Design Manual, Vol. III, using ASCE 7-05, and meeting requirements of ACI 318-08. – Progression of yielding and failure mechanism was evaluated via continuum finite- element analysis using VecTor2. – Design was updated to ensure yielding of coupling beams and wall piers.

14. Coupled Wall Test Specimen Specimen is bottom three stories of a 10-story planar coupled wall. Coupling beams have aspect ratio of 2.0 and diagonal reinforcement. Seismic loading results in yielding in coupling beams and wall piers. Pier walls are capacity- designed for shear. Coupling beams:  aspect ratio = 2.0  diag = 1.25% V n = Boundary Element  long = 3.5%  trans = 1.4% Web  long = 0.27%  horz = 0.27%

15. Construction

16. Testing of the Coupled Wall Specimen ∆ x - prescribed (i.e. disp. control) F z,total = constant - chosen as 0.1f c A g M y,total = k*F x,total - k is defined by chosen lateral load dist. - F x measured in lab for given  x (edited image)  x,F x,total M y,total F z,total

17. Testing of the Coupled Wall Specimen ∆ x = (∆ x1 + ∆ x2 )/2 - prescribed (i.e. disp. control) F z1 + F z2 = constant - chosen as 0.1f c A g M y,total = k*(F x1 + F x2 ) - k is defined by chosen lateral load dist. F x2 – F x1 = f(F x,tot ) - f(F x,tot ) is determined by analysis before testing θ y1 = n*∆ x1 ; θ y2 = n*∆ x2 - n is determined by analysis before testing (edited image)

18. Validation of the Loading Protocol Compare simulated response of 10-story prototype and 3-story laboratory test specimen 3 rd story load versus displacement response prototype specimen

19. Validation of the Loading Protocol Compare simulated response of 10-story prototype and 3-story laboratory test specimen bottom 3 stories of 10-story prototype 3-story test specimen Principal concrete compressive strain field at 0.75 in. lateral displacement

20. Simulation: Model Development and Evaluation

21. Experimental Database 66 wall tests from 13 different test programs 60% are slender (AR > 2); 40% are squat (AR < 2) 78% tested cyclically; 22% tested monotonically Failure modes – Slender walls: 85% in flexure; 10% in shear; 5% in flex-shear – Squat walls: 40% in flexure; 60% in shear Design parameters: ParameterAverageMin.Max. f ’ c (psi) 5400237010250  vert (%) 1.900.403.00  horz (%) 0.600.001.70 P/A g f ’ c 0.040.000.20 V u  f ’ c (psi) 5.701.1312.80

22. Simulation Models and Software OpenSees fiber-type beam-column models – Force-based, distributed plasticity element without flexure-shear interaction 1 and with linear, calibrated shear flexibility 2 – Displacement-based, lumped-plasticity with flexure-shear interaction 3 Two-dimensional continuum model – Modified compression field theory as implemented in VecTor2 4 1.Neuenhofer and Filippou (1997, 1998), Taucer et al. (1991), Spacone and Filippou (1992) 2.Oyen (2006) 3.Massone et al. (2006), Massone (2006) 4.http://www.civ.utoronto.ca/vector/, Wong and Vecchio (2003)http://www.civ.utoronto.ca/vector/

23. Ratio of Simulated-to-Observed Response Wall Config. Stiffness to YieldMaximum StrengthDisplacement Capacity Force- Based Flex- Shear 2D Force- Based Flex- Shear 2D Force- Based Flex- Shear 2D Rect. Slender (30/66) 0.91 (0.21) 1.23 (0.21) 1.02 (0.23) 0.99 (0.17) 1.07 (0.13) 1.09 (0.08) 0.66 (0.36) 1.00 (0.38) 1.14 (0.32) Barbell Slender (9/66) 1.55 (0.12) 1.72 (0.16) 1.36 (0.10) 1.00 (0.08) 1.18 (0.11) 1.01 (0.08) 0.41 (0.29) 2.23 (0.33) 1.12 (0.30) Rect. Squat (15/66) 0.89 (0.20) 1.63 (0.12) 1.28 (0.20) 1.00 (0.17) 1.01 (0.12) 1.02 (0.07) 1.11 (0.42) 0.65 (0.28) 0.69 (0.33) Flanged Squat (12/66) --- 3.99 (0.52) 1.57 (0.37) 1.25 (0.13) 2.49 (0.53) 0.49 (0.65) 0.66 (0.53)

24. Damage Prediction Models Initial spalling Spalling at base Steel fracture

25. Experimental Database 66 wall tests from 18 different test programs 100% are slender with AR > 2 83% tested cyclically; 17% tested monotonically 92% tested uni-directionally, 8% tested bi-directionally Design parameters: ParameterAverageMin.Max.Std. Dev. Scale0.40.25.00.5 f ’ c (psi) 55003000113002000  be (%) 3.50.811.42.0  web (%) 0.60.12.30.6  horz (%) 0.50.21.40.2 P/A g f ’ c 0.10.00.20.05 V u  A cv  f ’ c ) (psi) 4.81.011.02.0 VuVnVuVn 0.70.21.40.3

26. Damage States / Method of Repair Damage State DescriptionMethod of Repair DS 1 Initial cracking Initial yielding of reinforcement Cosmetic Repair DS 2 Concrete crack widths > 1/16 in.Epoxy Injection of Cracks DS 3 Spalling that does expose long. reinforcement Epoxy Injection of Cracks and Patching of Concrete DS 4 Exposed longitudinal reinforcement Vertical cracks/splitting Cracks ≥ 1/8” Replace Concrete DS 5 Core crushing Bar buckling and/or fracture Web crushing Bond slip failure Shear failure Replace Wall

27. Engineering Demand Parameters Maximum Drift – displacement at top of specimen / specimen height Maximum 1 st Story Drift – Assume full-scale is a story height of 10 ft. and wall thickness of 12 in. – Assume stiffness above the 1 st of the wall is defined by 0.10G c A cv (shear) and average E c I g for the entire wall. – 1 st story drift is then calculated using displacement measured at the top of the wall specimen and above assumptions. Maximum Rotation Demand for a Lumped-Plasticity Model – Hinge at base of the wall has a hinge length of ½ L w – Assume stiffness of the remaining height of the wall is defined by 0.50E c I g (flexure) and 0.10G c A cv (shear) – Hinge rotation is then calculated using displacement measured at the top of the wall specimen and above assumptions.

28. Fragility Functions for Slender Walls Damage state – demand data are used to calibrate lognormal CDF Lognormal Distribution Parameters Damage State Median Drift (%) Dispersion DS10.090.78 DS20.630.85 DS30.960.50 DS41.100.64 DS51.600.59

29. Investigation of the Impact of Design Parameters on Damage Progression Objective: Develop suites of fragilities for walls with different design parameter values ParameterImpact Axial load ratioSignificant Shear demandSignificant Aspect ratio / shear span (M base /V base /L w )Significant Displacement history (uni- versus bi- directional) Apparently significant* Shape (planar, flanged, c-shaped, etc.)Minimal ScaleMinimal Shear demand-capacity ratioMinimal DS versus drift with data grouped by axial load ratio * Too few test specimens with bi-directional displacement histories

30. Conclusions Laboratory testing of rectangular planar walls – Drift capacity of rectangular concrete walls with modern detailing and representative load distributions ranges from 1.0% to 1.5% (1.4% to 2.0% at roof of 10-story structure). – Damage was concentrated in the first story; other stories cracked but otherwise pristine. – Drift was due to base rotation (15-25%), flexure (55-60%), and shear (~25%). Flexural deformation of 3 rd floor was much smaller than 1 st and 2 nd.

31. Conclusions Simulation – Strength Planar walls: All models provide accurate and precise simulation of strength The continuum model also provides acceptable accuracy and precision for flanged, squat walls – Stiffness to yield For rectangular, slender walls the models provide reasonably accurate and precise simulation of stiffness: error in simulated stiffness ranges from 23% to 2% with a cov of approximately 20% The continuum model provides the best accuracy and precision for all of the wall configurations considered – Displacement capacity None of the models does a particularly good job of simulating displacement capacity for all of the wall configurations considered The continuum models provides acceptable accuracy and precision for slender walls; errors are less than 15% with a cov of approx. 30%

32. Conclusions Performance-based design – For slender walls, the median drift at which wall replacement is required is 1.6%

33. THANK YOU! Questions?

34. Coupling Beam Reinforcement Ratio NEESR Wall

35. Evaluation of Response Using Local Instrumentation Data

36. Krypton and Disp. Transducer Data Drift at top of specimen Wall 1 Wall 2 Wall 3Wall 4 Cracking Yielding 3 rd floor shear 2 nd floor shear 1 st floor shear 3 rd floor flexural 2 nd floor flexural 1 st floor flexural Base rotation Base slip Contribution to total drift (%)

37. Wall 4 Shear Strain from Krypton Data