CFRP repair for connections in steel structure
Department of Civil and Environmental Engineering
Steel Structures Laboratory
Academic Advisor: Associate Professor Takeshi Miyashita
Daniel Rodriguez Amaton
Introduction and backgroundIs well known that corrosion is one of the main
problem steel bolted joints have due to it leads todegradation. The usual reinforcement method forsuch cases is using splice plates. However, to installsuch reinforcement, heavy machinery for thereparation method is needed, making it acomplicated task. Also, by opening holes for thenew splice plate’s bolts, leads to a reduction on thecross section of the member on reparation,compromising its integrity as well.
To make the reparation method on such members aneasier task, using CFRP was proposed due to its lightweight,
highstrengthandanti-corrosive
characteristics, eliminating the need of heavymachinery, also this method doesn’t compromise themember’s integrity as well, and its workability makes
it an efficient reparation method. Image 1 shows thestandard reinforcement method used by NEXCO toreinforce steel bolted joints using CFRP. Showing usa taper length with a proportion of 1 to 10, a
determinate fixing length of 200mm and for every
Carbon Fiber Sheet used there must be a slide lengthof 25mm for each sheet.

Image 1. – Standard method to reinforce steel joints
with CFRP
Objectives and research flow

This research focus on CFRP repair andreinforcement for connections in steel
structures. There were conducted bending

tests on different experimental cases of steel girder
beams with corrosion near
the splice plates with the objective of confirming therepair effect by CFRP, the influence of the taperlength and the position of the high elasticity putty.
In this research, the target steel members are bolted
connections with corrosion damage near the splice
plate and the taper length. All the specimens used inthis research were fabricated under the specificationsof NEXCO Construction Manual.
Healthy specimen. The first step of this research
was to obtain the behavior of a healthy specimen(neither corrosion nor reduced cross-section) under
bending forces.
Specimen damaged by corrosion. After this, thenext step was focus on obtain data using a damaged
specimen by corrosion, in the same way as theprevious one, compressive forces on steel members
were applied.
CFRP reinforced specimen. Finally, on the lastspecimen, obtain data for a damaged specimen but
reinforced with 9 layers of CFRP Sheets, applied as
the current manual related to the CFRP bonding
standard indicates. In order to try recovering ahealthy state.
On this last specimen, there was not enough area toattach the CFRP sheets as planned, because of thefact that the length of CFRP sheets and the length ofthe loading range was limited.
Therefore, to supplement this research, using thefinite element software, an analysis was conductedin which the last specimen has attached not 9 layers
but 18 layers in order to see the real CFRP repair
effect.
Experiment results and conclusions
After conducting the bending experiments,
principally we obtain the next results on this research:
About the bearing load capacity: We can appreciate that the maximum load
reached for a healthy specimen before slipping is
obtained over the 650 kN point. Therefore, fromthis range we can conclude the results of thefollowing two specimens.
As for the damaged specimen by corrosion, it
barely obtained its maximum load on the rangeof 630 kN. Making clear the effect that aspecimen suffers when having its cross section
reduced and corroded by corrosion.
As for the CFRP reinforced experiment themaximum load was reached at a point near 680
kN surpassing the maximum load of the healthyspecimen.



800
700
600
Case S

Load (kN)

500400Case N

Case S_CF

300
200
10000 10 20 30 40Deformation
50 60 70(mm)80 90 100110

Graph 1.-Load-Deformation Relation
Healthy specimen (orange), Specimen damaged bycorrosion(green), CFRP reinforced specimen(purple).
Graph 1 shows the comparison between themaximum load on each experiment in this research.
About the Stress Reduction:
Since one of the objectives of this research is confirm
the stress reduction, in a representative way the stress
distribution was measured on a cross sectional
direction across the girder beam on each experimentalcase.
We can appreciate the obtained results for the stress
distribution on the next graph., which also include
the results obtained on the finite element analysis
conducted on this research.

Graph 2.- Reduced cross section stress distribution
upper part

As we can appreciate on the graph, the reinforced
with 9 layers of CFRP sheets specimen gray line isnot even close to the healthy specimen blue line wecan conclude that the stress of a healthy specimen was
not recovered with this amount of layers of CFRP.
However, we can appreciate that after conducting ananalysis with 18 layers on the last specimen.
We can see that the 18 layers CFRP sheet reinforced
specimen green line of stress is very close to thehealthy specimen blue line, therefore from this fact
we can confirm that the stress of a healthy specimen
was very close to being recovered.
In general, since characteristics such as the loaddisplacement curve, the maximum load, the fracture
behavior and the stress distribution can be obtained
and compared, based on these results, we canconclude that the FEA can be considered as valid todetermine the validity of the repair effect of CFRP on
steel structure.
References
1.-K.Morihisa, REINFORCEMENT OF CORODEDCONTINUOUS STEEL STRUCTURES USINGCARBON FIBER SHEETS, 2017.3 (in Japanese)
2.-NEXCO Construction Manual for Maintenancewith Carbon Fiber Sheets, Nippon Expressway
Research Institute Company Limited, 2013.10 (inJapanese)