SHOTCRETE OR FRP JACKETING OF CONCRETE COLUMNS FOR SEISMIC RETROFITTING

Transcription

1 SfP PROJECT 9773: SEISMIC ASSESSMENT AND REHABILITATION OF EXISTING BUILDINGS INTERNATIONAL CLOSING WORKSHOP ISTANBUL, 3 MAY-JUNE, 5 SHOTCRETE OR FRP JACKETING OF CONCRETE COLUMNS FOR SEISMIC RETROFITTING S.N. BOUSIAS, M.N. FARDIS, A.-L. SPATHIS, D. BISKINIS Structures Laboratory, Department of Civil Engineering, University of Patras, Greece

2 RC Jacketing is widely used & cost-effective for RC buildings: familiar to engineers & construction industry; suitable for repair of damage; jacket can encapsulate members & joints providing structural continuity; multiple effects on stiffness, flexural/shear resistance, deformation capacity, anchorage & continuity of reinforcement. FRP wrapping of member ends is becoming the method of choice: very effective for confinement & shear strengthening; less disruption of building use by retrofitting.

3 Part I: Tests on individual columns w/ or w/o shotcrete or FRP jackets; Design expression or rules for: strength, stiffness & deformation capacity of columns w/ shotcrete or FRP jacket, including effect ect of lap splicing in original column.

4 EXPERIMENTAL CAMPAIGN ON RETROFITTING OF RC COLUMNS Total of 39 tests on RC columns, w/ ribbed (deformed) or smooth/hooked bars, w/ or w/o bar lap-splicing in the plastic hinge, cyclically tested to ultimate deformation under const. axial load: 9 unretrofitted controls; 5 columns retrofitted w/ or 4 layers of CFRP at different heights from base; 5 columns retrofitted w/ full-height concrete jacket,, including investigation of different connection at the interface of jacket & old column. Results supplemented w/ data from the literature (mainly on retrofitted columns w/o bar lap-splicing) to derive/calibrate expressions for: The flexural & shear force resistance of retrofitted columns, M y, V R ; The effective stiffness of retrofitted columns at incipient yielding, EI eff =M y L s /3 as determined from the yield moment M y and the chord rotation at yielding, The ultimate chord rotation of flexure-controlled retrofitted columns, as affected by any lap-splices of bars in original column. u y, y ;

5 Φ Φ Φ Φ Φ Φ 5 ~85 8/ ~ ~ / 8 CFRP Retrofitting 75 mm Shotcrete Retrofitting

6 E u,mσ E.75 u,m- E y E.75 um Check only if Near Collapse (NC) Limit State not checked, using NC criteria with V E from analysis σ u,mσ Example of possible use of results: RC member verifications in terms of chord rotation at yielding or ultimate EN Annex Limit State:Damage Limitation Significant Damage Member: ductile secondary brittle secondary E, V E y um : ductile primary brittle primary Near Collapse E um V E V Rd,EC, V E V Rd,EC8 /.5 V E V Rm,EC, V E V Rm,EC8 chord rotation & shear force demand from analysis (if linear, V E from capacity design); chord rotation at yielding; expected value of ultimate chord rotation; mean-minus-sigma ultimate chord rotation; V Rd, V Rm shear resistance, w/ or w/o material safety factors, respectively; V R,EC V R,EC8 shear resistance in monotonic loading; shear resistance in cyclic loading after flexural yielding.

7 EN998-3 Annex A: Chord-rotation at member yielding Ls + z h db f y Beams, rect. columns: y = φy φ y 3 + L + s fc L d s + z Ls b f y Walls: y = φy +. max[, ] +. 3φ y 3 8h fc φ y : yield curvature (via st principles, adapted to median M y ); L s = M/V: shear span at member end (~L/); z~.9d: tension shift (= if member not diagonally cracked by shear at flexural yielding: M y /L s ); h : section depth; f y, f c : MPa; d b : bar diameter; Last term: Due to bar slip from anchorage zone beyond member end (omitted if such slippage not possible)

8 α EN998-3 Annex A: Seismically-detailed members w/ rect. web Expected value of ultimate chord rotation (% drop in resistance) α st,pl :.45 for hot-rolled ductile steel or heat-treated (tempcore);.75 for brittle cold-worked steel; α wall : for shear walls; ω, ω': mechanical ratio of tension (including web) & compression steel; ν: N/bhf c (b: width of compression zone; N> for compression); L s /h : M/Vh: shear span ratio; s : confinement effectiveness factor : α = h s h ρ sx : A sh /b w s h : transverse steel ratio // direction (x) of loading; bc h ρ d : ratio of diagonal reinforcement. Non-seismically detailed members w/o lap splices - cyclic loading Plastic part, pl um = ( )( ν.4a. ) = + α 5 um y st, pl wall um - y max max (., ') (., ω ).3 f.35 yw αρ ω L sx. s f c f c 5, of ultimate chord rotation is multiplied by.85. h c ( ρ ).75 d b i 6bch c

9 ω α ρ ω α Test- um model comparison (# 4, median=., C.o.V=3.3%) Members w/ or w/o seismic detailing, w/ ribbed bars lap-spliced over l o in plastic hinge region Compression reinforcement counts as double. For yield properties M y, φ y, y : f y of tension steel multiplied x l o /l oy,min if l o <l oy,min =(.3f y / For ultimate chord rotation um = y +pl um : pl um x l o /l ou,min if l o <l ou,min =d b f y /[( rs f y, f c in MPa, sx = sx f yw /f c : mech. transverse steel ratio // loading, rs =(-s h /b o )(-s h /b o )n restr /n tot (n restr /n tot restrained-to-total lap-spliced bars). f c )d b sx ) f c ], Test-M y model comparison (# 8, median=.5, C.o.V=.9%) 4 Test- y model comparison (# 6, median=.5, C.o.V=8.9%) M y 9 8 y 9 8 u 7 7 M y,exp (knm) 8 6 u,exp(%) u,exp(%) UoP test b&c other sources walls M y,pred (knm) UoP test b&c other sources walls u,pred (%) Test-EI eff model comparison (# 6, median=.975, C.o.V=3.3%) UoP test b&c other sources walls u,pred (%)

10 Concrete Jackets

11 Concrete Jackets (continued/anchored in joint; w/ or w/o lap splices in old member) Calculation assumptions: Full composite action of jacket & old concrete assumed (jacketed member: monolithic ), even for minimal shear connection at interface (roughened interface, steel dowels epoxied into old concrete: useful but not essential); f c of monolithic member = that of the jacket (avoid large differences in old & new f c ) Axial load considered to act on full, composite section; Longitudinal reinforcement of jacketed column: mainly that of the jacket. Vertical bars of old column considered at actual location between tension & compression bars of composite member (~ web longitudinal reinforcement), with its own f y ; Only the transverse reinforcement of the jacket considered for confinement; For shear resistance, the old transverse reinforcement taken into account only in walls, if anchored in the (new) boundary elements. Then: M R & M y of jacketed member: ~% of y of jacketed member for pre-yield (elastic) stiffness: if roughening of interface ~5%, if no roughening ~% of Shear resistance of jacketed member: Flexure-controlled ultimate deformation u : ~9% of ~% of those of monolithic member calculated w/ assumptions above. Concrete Jackets w/ bars not continued/anchored in joint: Jacket considered only to confine the full old section.

12 # 54 members w/ or w/o lap splices: test-to-calculation after RC-jacketing M y,exp/ M y,th M. y. a Present tests: Other tests: ± stand. deviation bounds, pure scatter ± stand. deviation bounds, monolithic members no laps 5db plain 3db plain continuous jacket bars group average 5db deformed 5db plain 45db deformed discontinuous jacket bars standard deviation of group mean y,th y,exp/ y EI exp / EI th *y) u pl + u,exp / ( EI eff. a b c d e f g h i j k a b c d e f g h i j k a: no treatment, b: no treatment, predamaged, c: welded U-bars, d: dowels, e: roughened, f: roughened, predamaged, g: U-bars & roughened, h: U-bars & roughened, predamaged, i: roughened & dowels, j: roughened & dowels, predamaged, k: monolithic.4. u

13 FRP Jackets

14 ρ ε ε ε ε FRP Jackets (not continued/anchored in joint; w/o lap splices in old member Rectangular X-section w/ continuous longitudinal bars (no lap splices): M R & M y, pre-yield (elastic) stiffness EI eff of RC member: not significantly enhanced by FRP jacket (increase neglected); Flexure-controlled ultimate deformation, u : confinement factor due to stirrups enhanced due to FRP confinement by f f f,e/f c f =t f /b w : FRP ratio; f f,e : FRP effective strength: f f,e min fu,f, ε u,f E f.7 min fu,f, εu,f E where: f u,f, E f : FRP tensile strength & Modulus; u,f: FRP limit strain; CFRP, AFRP: u,f=.5; GFRP: u,f=.; polyacetal FRP: ( h R) + ( b R) α = 3bh ρ α ρ f ( ) ( ) f f = c u,f=.3; confinement effectiveness: b, h: sides of X-section; R: radius at corner

15 u,exp(%) _ # FRP-wrapped members w/o lap splices: test-to-calculated ratio 5 3 M y.5 y # median=.4 C.o.V=8.8% M y,exp (knm) 5 # 5 median=. C.o.V=35.8% y,exp(%) _ M y,pred (knm) y,pred (%) 3 EI eff u # 5 median=. C.o.V=9% EI exp 5 5 # 9 median=. C.o.V=3.% EI pred upl + y (%)

16 ρ α ρ α f c in MPa, f=t f /b w : FRP ratio, f f,e : effective FRP strength in MPa, rs=4/n tot (n tot : total lap-spliced bars, only the 4 corner ones restrained). Test-M y model comparison Test- y model comparison Test- um model comparison (#, median=.65, C.o.V=9.%) (#, median=.85, C.o.V=8.9%) (# 6, median=., C.o.V=.7%) FRP Jackets (not continued/anchored in joint; w/ lap splices in old member) Rectangular X-section w/ longit. bars lap-spliced over l o in plastic hinge: Compression reinforcement counts as double. For yield properties M y, φ y, y : f y of tension steel multiplied x l o /l oy,min if l o <l oy,min =(.f y / f c )d b For ultimate chord rotation um = y +pl um : pl um calculated on the basis of confinement by te stirrups alone, multiplied x l o /l ou,min if l o <l ou,min =d b f y /[( rs f f f,e /f c ) f c ], M y.4. y 5 u 4 M y,exp (knm) 8 6 y,exp (%)..8.6 u,exp(%) UoP test other sources. UoP test other sources UoP test other sources M y,pred (knm) y,pred (%) u,pred (%) Test-EI eff model comparison (#, median=., C.o.V=%)

17 ρ ε ρ ρ FRP Jackets Shear resistance in cyclic loading past flexural yielding Shear resistance of FRP-jacketed member: h x V R = min µ + Ls h pl Ls ( N,.55Ac fc ) + (.5 min( 5, ).6 max(.5, ρtot ).6 min 5, fc Ac + Vw V f V f = min( u,f E u,f, f u,f ) f b w z/ contributes to member shear resistance as controlled by diagonal tension f :FRP ratio, f = t f /b w ; f u,f :FRP tensile strength; z : internal lever arm. Test-to-prediction ratio vs. #, median=.4, C.o.V=.9%: Total shear resistance of retrofitted member as controlled by diagonal tension, should not exceed shear resistance of old RC member as controlled by web crushing. Vu,exp / V u,pred ductility

18 Part II: Pseudodynamic test of.7: scale -story unsymmetric structure,, w/ or w/o FRP-retrofitting

19 ŷ d y r x CoG d xˆ R y r r y d x REFERENCE FRAME x ACTUATOR

20 Pseudodynamic tests of structure: Unretrofitted After repair of damage & FRP-wraps at all column ends (top & bottom, both stories). With nd story infilled & FRP-wraps at all column ends. 5sec Herceg-Novi (Montenegro 979) record, modified to fit EC8 spectrum on firm soil w/ PGA:.3g S a (m / s ) EC8 Record Period (s)

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22 Story drifts - Unretrofitted structure at.3g Drift Displacement (m) Drift Displacement (rad) p8x (E->W)-Level - p8x (E->W)-Level Time (sec) Test was stopped before end of record, due to heavy damage at base of ground-story soft-side columns (lap splices): Peak drifts of soft-side columns: p8theta-level Ground story:.9% and.5% in orthogonal direction (simultaneous); nd story:.6% and.% in orthogonal direction (simultaneous). -.5 p8theta-level - Time (sec)

23 Column drifts - Unretrofitted structure at.3g 4 3 p8 Soft column - Lev. Stiff column - Lev..5 Col., Lev. Drift ratio (%) - - i-s Drift Ratio Y (%) Time p8 (sec) 4 Soft column - Lev. 3 Stiff column - Lev i-s Drift Ratio X (%).5 Col., Lev. Drift ratio (%) - - i-s Drift Ratio Y (%) Time (sec) i-s Drift Ratio X (%)

24 FRP-wraps at all column ends (top & bottom, both stories)

25 Story drifts and story force-displacement loops - FRP-wraps.3g.4.3 p px (E->W)-Level - px (E->W)-Level -..5 p ptheta-level - ptheta-level - Drift Displacement (m) Drift Displacement (rad) Time (sec) Time (sec) 6 px (E->W)-Level - 6 px (E->W)-Level Force (kn) - Force (kn) Displacement (m) Displacement (m)

26 Interstory drifts - FRP-wraps.3g (top & bottom, both stories) 4 p 4 p 3 3 Drift ratio (%) - Drift ratio (%) Soft column - Lev. Stiff column - Lev Time (sec) -3 Soft column - Lev. Stiff column - Lev Time (sec)

27 nd story infilled; FRPwraps at all column ends

28 Story drifts - nd story infilled; FRP-wraps at all column ends.6.4 p px (E->W)-Level - px (E->W)-Level - Drift Displacement (m) Time (sec) p.3 ptheta-level - ptheta-level -. Drift Displacement (rad) Time (sec)

29 nd story infilled; FRP-wraps at all column ends 8 6 px (E->W)-Level p Soft column - Lev. Stiff column - Lev. 4 4 Force (kn) - -4 Drift ratio (%) Displacement (m) Time (sec)

30 THANK YOU!