FRP Seismic Strengthening of Columns in Frames

Transcription

1 FRP Seismic Strengthening of Columns in Frames Dr Mihaela-Anca Ciupala (EU Marie Curie Research Fellow) Dr Kypros Pilakoutas (Reader) Professor Nicolae Taranu Centre for Cement and Concrete Department of Civil & Structural Engineering The University of Sheffield, UK

2 Acknowledgments This research has been supported by a Marie Curie Fellowship of the European Community programme Human Potential under contract number HPMF-CT The financial support of : EU TMR Network ConFibreCrete EU Ecoleader project University of Sheffield EU Craft project CurvedNFR is also gratefully acknowledged.

3 Outline Introduction and Context of work Design procedure FRP confinement models Test frame Strengthening design example Conclusions

4 Context of work Centre of Cement and Concrete - The University of Sheffield, UK EU TMR Network ConFibreCrete EU Ecoleader research project Full scale 3D two storey RC frames Tamaris Laboratory, CEA Saclay, France

5 Introduction Use of FRP in columns Confinement objective Difficulties: most existing models for confined concrete and strengthening design guidelines are based on steel confinement confinement of rectangular sections is not always dealt properly by models developed for circular sections joint confinement is not always easy to achieve

6 Design procedure for plastic hinge confinement Target μ Δ μ φ 1+ μ 1 3( L / L) / p p = Δ ( 1 0.5L L) μ φ L = 0.08L f d p y l f y d l ε cu Required = μ φ φ y x Required thickness of FRP - Confinement model

7 Conventional ductility Curvature in plastic hinge region in constant Plastic hinge region estimated roughly Yield penetration at plastic stage only

8 Ductility issues Curvature in plastic hinge region varies if bars are fully bonded due to high confinement Plastic hinge region depends on moments Yield penetration at yield and plastic stage V L L p My φy My Yield penetration zone φy Ls Mult Yield penetration zone a) b) c) d) φult L s Moments and curvatures at yielding Moments and curvatures at maximum response (ultimate state)

9 Ductility equations μ φ = where μ Δ (1 0.5λ ) 0.9 (1 15α ) ( 2 2 ) 1.3λ + 42αβ + 294α β 0.9 (1 15α ) pl pl λ pl =1 M M y ult d α = L f y 500 β = f f ult y

10 Design procedure for plastic hinge confinement Target μ Δ μ φ ε cu Required = μ φ φ y x Required thickness of FRP - Confinement model

11 Models for FRP-confined rectangular columns Wang & Restrepo f ' ' cc = α1α 2 f co Spoelstra & Monti ε cu = ε cc E E sec sec, u ( E E ) c ( E E ) c sec, u sec E 1 sec Ec ' f cu = E sec, u ε cu Lam & Teng ε cc / ε co = m( f ' l / f ' co ) ' cc ' ' ' / fco = 1 2 fl / fco f + CEB-FIB Model Code 1990 ε * c, 85 = αω wd

12 Rectangular columns Mander s model modified by several researchers FRP jacket Effectively confined concrete core Unconfined concrete b =b-2r b r d =d-2r d Lateral stress is not calculated and effective stress not properly addressed Energy approach! Spoelstra and Monti calculate lateral stress Model code 90 model simple

13 RC frame 3 RC frames to be tested by the Ecoleader project 3.3 m 30 Φ6/200 Φ14 Designed using old standards 3.3 m b=260 d=260 Strengthening with FRP after damaging on shaking table 4.0 m Pushover analysis of the frame was carried out to determine the failure mechanism 4.0 m Base shear (kn) collapse First yielding Top displacement (m)

14 Design procedure for plastic hinge confinement Target μ Δ μ φ ε cu Required = μ φ φ y x Required thickness of FRP - Confinement model

15 Strengthening design example for columns Confinement of plastic hinge region Jacket thickness of 1, 2, 3 fibre sheets Table 1. Fibre properties Fibre type t j (mm) E j (MPa) f ju (MPa) ε ju (%) CFRP GFRP AFRP μ Δ Strengthening objective = 8 Effective column length is 1.65 m and the expected L p =301 mm Required curvature ductility is μ =15 resulting in a required = φ ε cu

16 Axial stress for 1L of CFRP confinement Rectangular Circular Normalised axial stress (fcc/fco) Wang&Resprepo Spoelstra&Monti Lam&Teng Model Code 1990 Unconfined concrete Normalised axial stress (fcc/fco) Lam&Teng Spoelstra&Monti Test Axial strain Axial strain

17 Normalised strength enhancement ( / ) ' f cc f co ' CFRP GFRP AFRP 1L 2L 3L 1L 2L 3L 1L 2L 3L Wang& Restrepo Spoelstra &Monti Lam& Teng fib Model code

18 Ultimate strain (%) fib Model code Lam& Teng Spoelstra &Monti Wang& Restrepo 3L 2L 1L 3L 2L 1L 3L 2L 1L AFRP GFRP CFRP ε cu

19 Estimated displacement ductility fib Model code Lam& Teng Spoelstra &Monti Wang& Restrepo 3L 2L 1L 3L 2L 1L 3L 2L 1L AFRP GFRP CFRP μ Δ

20 Conclusions FRP strengthening differs in behaviour (and design) from steel jacketing FRP jacketing can enhance bond slip characteristics and lead to different plastic hinge lengths The main design parameter for confinement strengthening is maximum concrete axial strain Many models, but not enough accuracy Results of design dominated by the model inaccuracy More research to be done at the element and structural level