Call Girls Service Nashik Vaishnavi 7001305949 Independent Escort Service Nashik
Retrofitting Reinforced Concrete
1. A new Method for Retrofitting Reinforced Concrete
Columns
School of Civil, Mining & Environmental Engineering
University of Wollongong
M.N.S. Hadi, T.M. Pham, and X. Lei
3. Introduction
FRP has been widely used to strengthen
existing structures;
For concrete columns, FRP is used to wrap the
columns thereby provides confining pressure;
Experimental studies confirmed that FRP
confinement increases the ultimate load and
ductility by a significant amount;
4. Introduction
For square columns, the confinement efficiency
is lower compared with circular columns;
A common solution is to round the sharp
corners, but limited improvement was found.
5. Research Significance
Circularisation – A new technique is proposed
and examined to increase the confinement
efficiency for FRP-confined square columns;
Eccentric loading was incorporated to investigate
the combined load – bending moment behaviour.
6. Research Significance
Circularisation – Ideas:
Four pieces of segmental circular concrete covers were
bond onto the surface of the original column to make
the cross-section from a square to a circular.
Original column
Concrete covers
7. Experimental Program
An experimental program was carried
out at the High Bay Laboratory at the
University of Wollongong.
Features:
• 12 square reinforced columns;
• Half of the specimens were
circularised;
• Confined with CFRP or steel
straps;
• Loading conditions: concentric, 15
mm & 25 mm eccentric.
12. Preparation of Specimens
• Two sets of formworks were used, one for columns and
one for segmental circular concrete covers;
• Foams were used to generate required shape.
Formworks (a) Columns (b) Concrete covers
(a) (b)
15. Construction of External Confinement
FRP
Wet layup
method
3 layers
continuous
confinement
100 mm
overlap for
each rings
Steel
Straps
Special tool
was used to
tighten the
straps
Each band was
fixed by a
buckle
Each ring had
30 mm clear
spacing
17. Loading System
Loading System
(a) Overview
(b) Overhang edge
(c) Loading head
• Eccentricity was created by
placing the overhang edge
into the gauges on the
loading heads;
• Loading was displacement
controlled
• Loading rate was 0.3
mm/min
18. Test Results – Group N
Specimen Yield
Load
(kN)
Corres.
Axial Disp.
(mm)
Ultimate
Load
(kN)
Corres.
Axial Disp.
(mm)
Corres.
Lateral
Disp. (mm)
N-0 707 1.31 506 1.83 -
N-15 563 1.24 492 2.02 3.35
N-25 414 0.96 363 1.27 3.11
Summary of the tested columns, Group N
19. Test Results – Group N
Load - displacement diagrams, Group N
20. Test Results – Group RF
Summary of the tested columns, Group RF
Specimen Yield
Load
(kN)
Corres.
Axial Disp.
(mm)
Ultimate
Load
(kN)
Corres.
Axial Disp.
(mm)
Corres.
Lateral Disp.
(mm)
RF-0 796 1.83 1485 24.5 -
RF-15 635 1.56 583 8.12 34.64
RF-25 515 1.68 477 7.94 33.86
21. Test Results – Group RF
Load - displacement diagrams, Group RF
22. Test Results – Group CF
Summary of the tested columns, Group CF
Specimen Yield
Load
(kN)
Corres.
Axial Disp.
(mm)
Ultimate
Load
(kN)
Corres.
Axial Disp.
(mm)
Corres.
Lateral Disp.
(mm)
CF-0 1478 2.00 2471 13.96 -
CF-15 1202 2.02 1266 9.73 38.97
CF-25 1011 1.69 995 8.63 39.66
23. Test Results – Group CF
Load - displacement diagrams, Group CF
24. Test Results – Group CS
Summary of the tested columns, Group CS
Specimen Yield
Load
(kN)
Corres.
Axial Disp.
(mm)
Ultimate
Load
(kN)
Corres.
Axial Disp.
(mm)
Corres.
Lateral Disp.
(mm)
CS-0 1060 1.85 948 3.48 -
CS-15 905 1.05 779 3.39 7.3
CS-25 766 1.40 655 2.80 8.2
25. Test Results – Group CS
Load - displacement diagrams, Group CS
26. Increase of Column capacity
Nominal average axial stress – strain diagrams
28. Discussions and Conclusions
• Circularisation dramatically increases the
efficiency of FRP confinement. By circularising
square concrete columns, the efficiency of
FRP confinement can be maximised;
• Eccentricity dramatically reduced the ultimate
load of all specimens, regardless of the
technique incorporated;
• Most significantly, test results showed that the
proposed circularisation technique is a viable
and efficient method for strengthening square
RC columns.