Inelastic Web Crushing Performance Limits of High- Strength-Concrete Structural Walls

Transcription

1 Inelastic Web Crushing Performance Limits of High- Strength-Concrete Structural Walls Rigoberto Burgueño, Ph.D. Assistant Professor of Structural Engineering Department of Civil and Environmental Engineering Michigan State University

2 Presentation Outline Overall Aim Project Basics Team and Facilities Use Research Objectives Background Work Plan Work to Date Research Impact

3 Research Team Researchers Rigoberto Burgueño, Ph.D. (PI), Michigan State Univ. Eric M. Hines, Ph.D., P.E. (Co-PI), LeMessurier, Tufts Univ. Xuejian Liu (Graduate Student), Michigan State University External Advisory Board Evan Bentz, Ph.D., University of Toronto Alessandro Dazio, Ph.D., ETH Zurich Julio Ramirez, Ph.D., P.E. Purdue Univ.

4 Experimental Facilities NEES Facility Multi-Axial Subassemblage Testing (MAST) Laboratory University of Minnesota Twin Cities Non-NEES Facility Civil Infrastructure Laboratory Michigan State University

5 Overall Research Objective To investigate and establish rational performance levels for the development of seismic assessment and design approaches to high-strength-concrete (HSC) structural walls based on ductile shear failure mechanisms.

6 Motivation and Scope Box-Girder Building Structural Wall I-Girder Bridge Piers East Oakland Bay Carquinez Benecia Martinez

7 SFOBB Current & Potential Pier Designs Current Design Potential Design

8 Web Crushing Capacity The term web crushing was coined in the 1960s describing the behavior of thin webbed concrete beams whose compression struts crushed inside the web region under high diagonalcompression stresses. Web crushing generally requires both the presence of a stable compression boundary element and a web that is significantly thinner than the boundary element.

9 Web Crushing Capacity The adverse effects of deformation demand on web crushing capacity have been recognized for some time. Yet, since the 1970s the ACI Code addresses web crushing capacity by limiting shear stresses on an effective cross sectional area to: ' vu 10 fc

10 Web Crushing Capacity The code approach has three flaws that lead to false conclusions about the actual web crushing capacity of a reinforced concrete structural wall: 1. Web crushing capacity is not affected by deformation demand on the member. 2. Web crushing capacity is related to the tensile strength of concrete. 3. Web crushing capacity is purely a function of the member's shear behavior and not its flexural behavior.

11 Web Crushing Capacity Oesterle et al. and Paulay addressed the first two flaws in their studies on wall behavior. Oesterle et al. ( ): v wc = ' 1.8 fc δ Paulay (1982, 1992) N A f g ' c > o ' ' vu φ = fc < 0.16 fc 870 μ Δ psi

12 Truss Analogy Model for Web Crushing 3 Oesterle et al., ACI Str. J., 1984

13 UCSD Studies on Hollow Piers Seismic Behavior and Design 1 Hines, Dazio and Seible, SSRP Rpt. No. 2001/27, UC San Diego

14 Strut Realignment in Plastic Hinge P P P V' y V y V u flexure-shear web crushing zone cracks realign in plastic hinge region V' y V y V u T T C T C C (a) μ Δ < 1 elastic behavior (b) 1 < μ Δ < 4 initial spread of plasticity (c) μ Δ = 4 full inelastic mechanism 1 Hines, Dazio and Seible SSRP Rpt. No. 2001/27 UC San Diego

15 Observed Flexure-Shear Web Crushing Behavior 1 Hines, Dazio and Seible SSRP Rpt. No. 2001/27 UC San Diego

16 Flexure-Shear Web Crushing Capacity P V Standard Shear Flexure- Shear V C jd T 2 Hines and Seible, ACI Str. J., 101(4) 2004

17 Behavior of Wall with Confined Boundary Elements Actuator force [kn] Drift Ratio Δ / L (%) Test Unit 3A F y F' y (in.) Displacement [mm] -F' y -F y P&P O&al. μ Δ = H&S ACI (kips) 1 Hines, Dazio and Seible SSRP Rpt. No. 2001/27 UC San Diego

18 Effect of Concrete Softening Factor (k) on Web Crushing Capacity Curve Shape

19 Specific Objectives/Work Plan Investigate and establish the web-crushing performance limits of HSC structural walls at moderate ductility Investigate the bi-directional seismic performance of structural wall assemblies in the context of hollow piers Develop analytical modeling and analysis procedures for structural walls with boundary elements Develop simple assessment models for HSC structural walls.

20 1. Structural Walls Investigate and establish elastic and inelastic web-crushing performance limits of HSC structural walls at moderate ductility. 48" [1219] 12" [305] 24" [610] 12" [305] 4" [102] 1/2" [13] cover 12" [305] #6 [19] 14 tot. #3 [10] #3 [10] ties 11" [279] o.c. #3 [10] 5" [127] o.c. Cross-Section

21 1. Structural Walls Test Setup Test Setup at CIL-MSU

22 1. Structural Walls Test Setup 1219mm [48"] Reference Column Rotational Device Hollow Core Jack Load Cell Reaction Frame Displacement Transducer Transducers & Diagonals for Shear Deformation Measurement Hydraulic Actuator Footing 914 mm [36"] 3048 mm [120"] Wall Test Unit Transducers for Curvature Measurement Strong Floor

23 1. Structural Walls Test Matrix Test Matrix Test ID f' c MPa (ksi) ρ l Loading UCSD 3A * 34 (5) tested M5m1 34 (5) monotonic M51 34 (5) cyclic M10m1 69 (10) monotonic M (10) cyclic M (15) cyclic M (15) cyclic M (20) cyclic M (20) cyclic * Benchmark test done at UCSD by co-pi 1 1 Hines, Dazio and Seible SSRP Rpt. No. 2001/27 UC San Diego

24 2. Wall Assemblies Investigate the three-dimensional web crushing behavior of structural wall assemblies within the context of a hollow pier. 2 Test Units ~ ¼ Scale 34 and 137 MPa (5, 20 Ksi) μ Δ ~2 and ~6 Biaxial Loading Protocol 1219 mm [48"] 610 mm [24"] 102 mm [4"] 102 mm [4"] 305 mm [12"] Cross-Section

25 2. Wall Assemblies Test Setup Test Setup at UMN-MAST

26 2. Wall Assemblies - Multi-Axial Loading Protocol A μ Δ Longitudinal Direction D E G F H B C SFOBB Displacement History μ Δ Transverse Direction SFOBB Biaxial Loading Protocol

27 3. Predictive and Diagnostic Analyses Develop analytical modeling and analysis procedures for simulation and assessment of shear behavior in structural walls. 3D Finite Element Models ABAQUS Built-in Concrete and Steel material models 2D Finite Element Models OpenSees Phenomenological Constitutive Models Continuum/Fiber-Based (?)

28 4. Assessment and Design Tools Develop simple assessment and design models for HSC structural walls. Validation and enhancement of flexural analysis tools to evaluate force-displacement behavior Strain limits Extend M-φ based approach to account for multi-axial loading Evaluate fiber-based NL beam-column elements Cast validated process in a strut-and-tie approach Assess both spread of plasticity and web-crushing capacity Strut demands/capacities dependent on plastic deformations Try to be consistent with current ACI-318 recommendations

29 Activities to Date Evaluation of fiber-based nonlinear beam-column elements for assessing structural wall response Analysis and design of single wall test units/setup Three-dimensional multi-axial response of wall assemblies Studies on the effect of loading path dependence on the response and capacity of wall assemblies Evaluation of dynamic data visualization schemes

30 Analysis of Benchmark Wall H P=171 kip 3" [76] 6" [152] 3" [76] 48" [1219] 24" [610] 4" [102] 3" [76] 6" [152] 3" [76] 3" [76] 120" 1/2"[13] cover #6[19] 12 tot. #3[10] spiral 11"[279]o.c. #3[10] #3[10] 5"[127]o.c. 4" [102] 6" [152] 3" [76] y-coord (in) z-coord (in)

31 Analysis of Benchmark Wall Force (kip) ` OS(flx) -200 OS(flx+sp) -250 Experimental Displacement (in)

32 Analysis of Benchmark Wall Force (kip) ` OS(shr) -150 OS(shr+sp) -200 Experimental -250 Displacement (in)

33 Web Crushing Capacity Curves Modified UCSD Shear Force (kn) ACI Standard WC Predicted Response Direct Tension WC Shear Force (kips) Displacement Ductility (μ Δ ) 0

34 Test Unit Analysis/Design Inelastic Web Crushing [f' c = 34MPa (5ksi)] Inelastic Web Crushing [f' c = 103MPa (15ksi)] Inelastic Web Crushing [f' c = 137MPa (20ksi)] Shear Force (kn) ACI [f' c = 137MPa (20 ksi)] Response [f' c = 137MPa (20ksi)] Response [f' c = 34MPa (5ksi)] Shear Force (kips) ACI [f' c = 34MPa (5ksi)] Displacement Ductility (μ Δ )

35 Emerging Issues Element Formulation Shear deformations/degrading shear stiffness Limit strains Material Models Concrete tension stiffening Concrete degradation due to crack misalignment Steel strain hardening Modeling Wall sliding behavior

36 Wall Assembly Analyses SFOBB Tests SFOBB Test Setup ABAQUS/ANACAP-U

37 SFOB DPT Longitudinal Response

38 SFOBB Numerical Investigations H P=1370 kip 276" A 25 μ Δ Longitudinal Direction D E G H B C y-coord (in) F μ Δ Transverse Direction z-coord (in)

39 SFOBB Numerical Investigations Longitudinal force (kips) Experiment -600 OpenSees -800 Longitudinal displacement (in.)

40 SFOB DPT Longitudinal Response Longitudinal force (kips) Experiment -600 ABAQUS OpenSees -800 Longitudinal displacement (in.)

41 SFOB DPT Transverse Response Transverse force (kips) Experiment ABAQUS -600 OpenSees -800 Transverse displacement (in.)

42 SFOB DPT Longitudinal Response

43 SFOB DPT Longitudinal Response Longitudinal Force (kips) Longitudinal Displacement (in.)

44 Loading Path Effects on Response

45 Loading Path Effects on Response SL1H0 SL1H6 SL1H12 SL1H24 LCSE12Bstrain L2-Strain Longitudinal Force (kips) Longitudinal Bar Strain (micro strain)

46 Emerging Issues Element Formulation Torsion deformations/degrading torsion stiffness Validation Instrument selection for model validation Data acquisition settings

47 Near Future Activities Continue analysis effort Testing of first 2 test units (f c = 34 MPa) by September 2006 Testing of next 2 test units (f c = 69 MPa) by December 2006 Design first wall assembly test unit by December 2006

48 Research Impact Increased understanding of earthquake design principles has become robust. Advancement in materials, structural behavior and analysis seem proper to migrate towards improvements in efficiency without sacrificing safety. Establishing performance limits for HSC structural walls behaving in alternative ductile modes of failure is expected to contribute to the next stage in seismic design of thin-webbed elements/systems.

49 NEESR-II II-05 Inelastic Web Crushing Performance Limits of High- Strength-Concrete Structural Walls Rigoberto Burgueño, Ph.D. (PI) Michigan State University Eric M. Hines, Ph.D., P.E. (Co-PI) LeMessurier Consultants, Tufts University

50 NEESR-II II-05 Inelastic Web Crushing Performance Limits of High- Strength-Concrete Structural Walls Rigoberto Burgueño (PI) Michigan State University Eric M. Hines (Co-PI) LeMessurier Consultants, Tufts University

51 Web Crushing Capacity Expressing concern that overuse of stirrups for resisting shear might lead to shear failure mechanisms related to the concrete, an early ASCE Committee (1912) recommended that total shear stresses be limited to: ' vc fc 248 psi A second ACI-ASCE joint committee raised the limit to: v c ' 0.12 fc with no limit to the value of f c but limiting the allowable stress taken by the steel stirrups to 75 psi.

52 Web Crushing Capacity In 1962, ACI-ASCE Joint Committee 326 on shear and diagonal tension proposed recommendations for limiting shear stresses on reinforced concrete member sections have remained in the ACI Specifications since Committee 326 made the switch to limiting total shear stresses according to sqrt(f c ) instead of the traditional f c emphasizing the desire to safeguard against diagonal tension.

53 Web Crushing Capacity The document included no description of web crushing per se and proposed to limit shear stresses as v u ' 8 fc for the case where only vertical stirrups were used to resist shear and ' vu 10 fc where of the total shear was carried by bent-up longitudinal bars or diagonal stirrups placed at an angle of α<70 o from the longitudinal axis of the member.

54 PCA Studies Oesterle et al. ( ) 79)

55 PCA Studies Oesterle et al. ( ) 79) v wc = kf cos β sin β ' c = 0.5kf ' c k 3.6 = 2 1+ ε γ = δ 0.52 γ m 0 N ' A g f c

56 Web Crushing in Structural Wall with Confined Boundary Elements P V Standard Shear Flexure- Shear V C jd T

57 Regions of Active Shear Transfer P P P V V V L L L V C < _ α L pr α V V T C T C α x c x c (a) (b) (c) L pr T L pr

58 1. Wall Assemblies 102 mm [4"] 1219 mm [48"] 610 mm [24"] 102 mm [4"] 305 mm [12"] Cross-Section

59 SFOBB Numerical Investigations

60 Outstanding issues and motivation New structural concepts and systems Employ the inherent in-plane stiffness and strength of FRP laminates New design methods Design structures working under in-plane stress demands Take into account the material-property tailorability of FRP laminates

61 Shape and Material-Property Optimization (Level 1) Objective Minimize Strain Energy: min Design Variables Geometric Parameters (including mass) Lamination Parameters: {V 1A, V 3A, V 1D, V 3D } Constraints Displacements (service): L / 800 Stresses (service): 0.25 σ u f E = 1 2 V σ εdv

62 Laminate Design Optimization (Level 2) Design variables Fiber orientations Objective Minimize the discrepancy between the design and the optimal lamination parameters Minimize f = ( ) V i V i 2 Constraints No constraints are required

63 Acknowledgements The studies presented have been possible through the financial support of: Dept. of Civil and Environmental Engineering MSU Intramural Research Grant Program MSU Research Excellence Fund The National Science Foundation Thanks go to Prof. Frieder Seible for the inspiration and vision that initiated the thought process towards the presented membrane-based concepts.