NEES Small-Group Research Project: Seismic Behavior, Analysis and Design of Complex Wall Systems

1. University of Illinois 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

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 0.1Agfc’.

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

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

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

10. Response of PW 4: No Splice

11. Final Damage States for Planar Walls Wall 1: Vb = 3.6f’c 1.5% drift (3rd story) 2.1% drift (10th story) Wall 2: : Vb = 5.0f’c 1.5% drift (3rd story) 1.8% drift (10th story) Wall 3: Vb = 4.5f’c 1.25% drift (3rd story) 1.6% drift (10th story) Wall 4: Vb = 4.6f’c 1.0% drift (3rd story) 1.4% drift (10th 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. • Boundary Element • rlong = 3.5% • rtrans = 1.4% • Web • rlong = 0.27% • rhorz = 0.27% • Coupling beams: • aspect ratio = 2.0 • rdiag = 1.25% • Vn =

15. Construction

16. Testing of the Coupled Wall Specimen Fz,total My,total Dx,Fx,total • ∆x • - prescribed (i.e. disp. control) • Fz,total = constant • - chosen as 0.1fcAg • My,total = k*Fx,total • - k is defined by chosen lateral load dist. • - Fxmeasured in lab for given Dx (edited image)

17. Testing of the Coupled Wall Specimen • ∆x = (∆x1 + ∆x2)/2 • - prescribed (i.e. disp. control) • Fz1 + Fz2 = constant • - chosen as 0.1fcAg • My,total = k*(Fx1 + Fx2) • - k is defined by chosen lateral load dist. • Fx2 – Fx1 = f(Fx,tot) • - f(Fx,tot) is determined by analysis before testing • θy1 = n*∆x1; θy2 = 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 3rd 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 Principal concrete compressive strain field at 0.75 in. lateral displacement bottom 3 stories of 10-story prototype 3-story test specimen

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:

22. Simulation Models and Software • OpenSees fiber-type beam-column models • Force-based, distributed plasticity element without flexure-shear interaction1 and with linear, calibrated shear flexibility2 • Displacement-based, lumped-plasticity with flexure-shear interaction3 • Two-dimensional continuum model • Modified compression field theory as implemented in VecTor24 Neuenhofer and Filippou (1997, 1998), Taucer et al. (1991), Spacone and Filippou (1992) Oyen (2006) Massone et al. (2006), Massone (2006) http://www.civ.utoronto.ca/vector/, Wong and Vecchio (2003)

23. Ratio of Simulated-to-Observed Response

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

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:

26. Damage States / Method of Repair

27. Engineering Demand Parameters • Maximum Drift • displacement at top of specimen / specimen height • Maximum 1st Story Drift • Assume full-scale is a story height of 10 ft. and wall thickness of 12 in. • Assume stiffness above the 1st of the wall is defined by 0.10GcAcv (shear) and average EcIg for the entire wall. • 1st 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 Lw • Assume stiffness of the remaining height of the wall is defined by 0.50EcIg (flexure) and 0.10GcAcv (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

29. Investigation of the Impact of Design Parameters on Damage Progression • Objective: Develop suites of fragilities for walls with different design parameter values 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 3rd floor was much smaller than 1st and 2nd.

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. NEESR Wall Coupling Beam Reinforcement Ratio

35. Evaluation of Response Using Local Instrumentation Data

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

37. Wall 4 Shear Strain from Krypton Data