Importance of retrofitting Beam column joint and methods are described in this ppt

1. “RETROFITTING OF REINFORCED CONCRETE
BEAM COLUMN JOINTS”
Presented by
Miss. Mule Disha Pradip

2. CONTENTS
 Introduction
 Beam column joints
 Jacketing
 Case study 1
 Case study 2
 Case study 3
 Concluding remarks
 References

3. Introduction
 Retrofitting is Upgradation of certain building system
(existing) to make them more resistant to seismic activity.
 Structure can be - Earthquake damaged.
- Earthquake vulnerable.
 Proves to be better economic and immediate shelter to
problems rather than replacement.

4.  There are considerable members of RC structures in India
that do not meet the requirement of current design
standards because of inadequate design or construction
errors which need structural upgradation specially to meet
seismic design requirement
 In recent earthquakes all over the world has highlighted the
consequences of poor performance of beam-column joints.
 Failure is because of shear failure in beams, bar slip and
shear failure of beam-column joints.
Introduction

5. Introduction
 Retrofitting of RC structure
1. Strengthening existing member
- RC Jacketing
- Steel Plate Bonding and Jacketing, Steel section
caging : FRP
- Plate Bonding And Jacketing

6. Introduction
2.Adding new member.
- Shear walls.
- Frames (moment resisting frames and braced
frames)
- Bracing.
-Buttresses.

7. Retrofitting techniques
Global
6.Mass reduction
4.Addition of wing wall / buttresses
3.Addition of bracing
1. Addition of shear wall
5.Wall thick ceiling
7.Supplimental damping and base isolation
2.Addition of infill
Local
3. Jacketing of beam column joint
2. Jacketing of columns
1. Jacketing of beams
4. Strengthening individual bldg

8. Beam column joint
 Since construction materials have limited strength , the
joint have limited force caring capacity
 When force larger than this are applied during earthquake ,
joints are severely damaged.
 Repairing damaged joint is difficult , so the damaged must
be avoided. Thus the beam column joint must be design to
resist earthquake effect.

9. Objective
The beam-column joint rehabilitation is to-
1. Strengthen the shear and bond-slip resistance in order
to eliminate the brittle failure.
2.To ensure that the ductile flexural hinging will take
place in the beam.
 A joint should maintain its integrity and must be designed
stronger than the members framing to it.

10. Jacketing
 Most popular method for strengthening of building
columns.
 Purpose of jacketing-
1.To increase concrete confinement.
2.To increase shear strength.
3.To increase flexural strength.

11. Concrete jacketing
 involves addition of longitudinal bars, closely spaced ties,
and a layer of concrete.
 The jacket increases both flexural strength and shear
strength of concrete .
 The usual practice consists of first assembling the jacket
reinforcement cages, arranging the formwork and then
placing the concrete jacket.
 But it is cost effective.

12. Concrete jacketing
 Concrete jacketing disadvantages-
1.Cost effective
2.Requires intensive labour
3.Detailing of steel in the form of digital collars
4.Incrases Dimensions of structure
5.Incrases weight of structure

14. Steel jacketing
 Steel jacketing refers to encasing the member with steel
plates and filling the gap with non-shrink grout.
 The jacket enhances both flexural strength and shear
strength of concrete.
 Steel jacketing disadvantages –
1.Complicated working procedure.
2.Inner surface corrosion .
3. Heavy weight.
4.C/S increases.

16. Fiber Reinforced Polymer( FRP)
 Fiber reinforced polymer (FRP) is a composite material
consisting of polymeric resin reinforced with high strength
fibers.
 Composite materials are available in the form of sheets,
pre-formed shapes and bars.
 The FRP sheets are thin, light and flexible enough to be
inserted.

17. Fiber Reinforced Polymer( FRP)
 The fibers can be of glass, carbon, aramid.
 Glass fibers have lower stiffness and cost compared to
carbon fibers.
 They are suitable in low cost seismic retrofit applications.

18. Fiber Reinforced Polymer( FRP)
 The FRP composites are useful for repair, rehabilitation and
retrofit of structures for the following reasons:
1.The FRP sheets are light and flexible, which facilitate
installation. It does not need drilling of concrete or
masonry.
2.The curing time required is less
3.The sheets are thin and hence there is no marginal increase
in the size of retrofitted member.

19. Fiber Reinforced Polymer( FRP)
 The material is chemically inert and has resistance against
electro-chemical corrosion.
 There is good fatigue strength, which is suitable for
fluctuating loads.

21. Case study -1
 Retrofitting of RC beam column joint using RC jacketing
by Tsonos .G (2009).
 Objective: To improve strength, stiffness and ductility of
the element.
 Experimental evidences by Tsonos, G., (2009), shows that
strengthening schemes are effective in transforming the
brittle joint shear failure mode of reference specimen into a
more ductile failure mode in case of the strengthened
specimens.

22. Test specimen
 The test specimens are 1:2 scale models of the
representative 40 cm x 40 cm beam-column joints.
 The comparison of the load-deflection curves of the
original subassemblage and the retrofitted sub assemblage
is done.
 The dimensions and cross sectional details of the original
specimen are as shown in Fig. 1.
 As shown in Fig. 2, the retrofitted specimen had a four-
sided jacket, 14 longitudinal bars at each corner of the
column.
 Which were connected by; 8 supplementary ties at 70 mm.

23. Fig -1

24. Fig -2

25. Experimental setup
 The general arrangement of the experimental setup by
Tsonos, G., (2009) is shown in Fig.3.
Fig -3

26. Test Results
 The original sub assemblage is subjected to a cyclic lateral
load history, so as to provide the equivalent of severe
earthquake damage.
 The specimen experienced brittle shear failure at the joint
region.
 Damage occurred both in the joint area and in the critical
regions of columns, while the beam remained intact.
 Failure mode of the strengthened specimen involved the
formation of a plastic hinge in the beam near the column
juncture.
 Damage of the specimen occurred mainly in the critical
region of the beam and also in the joint area.

27. Plots of applied shear versus drift angle for the
strengthened specimen
Plots of applied shear versus drift angle for
original specimen

28. Conclusion of case study-1
 The control specimen, representing an existing beam-
column sub assemblage, performed poorly under reversed
cyclic lateral deformations.
 The connection of the control specimen exhibited
premature shear failure during the early stages of seismic
loading and damage was concentrated in the joint region.
 The performance of reinforced shotcrete jacketed sub
assemblage showed a vast improvement.
 Damage to the strengthened specimens is concentrated
mainly in the beam critical region and also in the joint
area.

29. Case study -2
 Strengthing of RC beam column joints using CFRP by
Alsayed et al., (2005).
 Objective: To upgrade the shear strength and ductility of
seismically deficient exterior beam-column joint.
 The seismic performance of beam-column joints is
investigated and is compared to that of a CFRP
strengthened specimen.

30. Test Specimens
 Two specimens were cast and were subjected to cyclic
loading, so as to provide the equivalent of severe
earthquake damage.
 The schematic diagram of the joint specimen is as shown in
Fig.4.
 The damaged specimen is then repaired using CFRP sheets.
 The repaired specimen was again subjected to the similar
lateral cyclic load history.

31. Fig -4

32. Fig -5

33.  Figure 5 shows the general arrangement of experimental
set up used by Alsayed et al., (2007) for testing of interior
beam-column joints.
 The bottom of the column surface is attached to a base
pivot using 4, high strength threaded rods.
 The base pivot, in turn, is fastened to a strong steel I-beam.
 To apply the simulated seismic type cyclic load on the
specimen, a 500-kN servo-controlled hydraulic actuator is
connected to a reaction steel frame, which stands on a
strong concrete floor
Test Specimens

34. Test Results
 The hysteretic behavior of exterior joints is examined in
terms of shear strength and deformation capacity.
 The ultimate load for repaired specimen is substantially
higher than its corresponding original (before repair) .
 This is primarily due to the increased confinement of joint
resulting from externally bonded CFRP sheets.

35. Load-displacement hysteretic plot for CFRP
upgraded specimen
Load-displacement hysteretic plot for
control specimen

36. Conclusion of case study-2
 CFRP repaired specimen is compared with its
corresponding specimen tested before repair and, in
general, it was observed that provision of CFRP sheets
improved the shear resistance and ductility of the RC joint
to a great extent.
 The effectiveness of CFRP sheets in upgrading deficient
exterior beam-column joints is established.

37. Case study-3
 Strengthening of RC beam column joints using GFRP by
El-Armoury and Ghobara, (2002).
 Objective: To strengthen the shear and bond-slip resistance
in order to eliminate those types of brittle failure and
ensure instead that ductile flexural hinges would develop
in the beam.
 El-Armoury and Ghobara, (2002) have proposed
techniques for upgrading reinforced concrete beam column
joints using GFRP.

38. Test specimen
 In the experimental study conducted, three reinforced
concrete beam column joints were tested.
 The beam-column joints are designed assuming that points
of contra flexure occur at the mid height of columns and
the mid-span of beams.
 No transverse reinforcement was provided in the joint
region.
 The dimensions and reinforcement details of the specimen
are as shown in Fig.6.

39. Fig -6

40. Test Specimen
 The rehabilitation scheme proposed by the authors
consisted of a system for upgrading the shear strength of
the joint.
 The joint is wrapped with two U-shaped composite layers.
 The first layer was bi-directional sheet and the second was
unidirectional sheet.
 The ends of the sheets are anchored using steel plates and
tie rods driven through the joint.
 Four unidirectional glass fiber sheets were applied to the
beam bottom face for a horizontal distance of 1000 mm and
extended along the inner column face vertically for a
distance of 500 mm, as shown in Fig.7.

41. Fig -7

42. Fig -8

43. Experimental setup
 The specimens are tested with the column in the vertical
position, hinged at the top and bottom column ends and
subjected to a cyclic load applied at the beam tip as shown
in Fig.8.
 The beam-tip displacement and the column lateral
displacement are measured using potentiometers.
 Two diagonal linear voltage differential transformers
(LVDTs) were attached to the joint to measure the joint
shear deformation.

44. Test results
 The retrofitted specimen is subjected to the same loading
sequence as in the control specimen.
 The strain values showed that the fiber sheets attached to
the beam face are carrying most of the developed tensile
forces, indicating that the glass fiber fabric was working
effectively.
 Severe pinching and stiffness degradation occurred in the
last two cycles following the fracture of the weld

45. Load-displacement hysteretic plot for
retrofitted specimen
Load-displacement hysteretic plot for control
specimen

46. Conclusion of case study-3
 The control specimen with no shear reinforcement in the
joint and with inadequate anchorage for the beam, showed
a brittle joint shear failure.
 Using GFRP jacketing, the concrete integrity is maintained
by confinement.
 The ductility and the load-carrying capacity of the
rehabilitated joint are significantly improved.

47. Concluding remarks
 By retrofitting, the concrete integrity is maintained by
confinement and has significantly improved the ductility
and the load-carrying capacity of the rehabilitated joint.
 Short Crete jacketing improves the strength, stiffness and
ductility of the joints. The method is also cost effective.
 However, jacketing needs skilled and intensive labour due
to difficulties in placing of the additional reinforcement.
 Joint rehabilitation using fiber-reinforced polymers (FRP)
has the advantages of simplicity of application, less need
for skilled labour, corrosion resistance, not excessively
increase the dimensions of the sections of structural
elements.

48. Thank You