Y

UTA

N

AGAO

, [e-mail]

K

ENTARO

M

ATSUMOTO

M

ASAHIRO

S

AKANO

, [e-mail]

Department of Civil and Environmental Engineering, Kansai Universit

y

H

IRONORI

N

AMIKI

,

Kyobashi Mentec Ltd.

STEEL PLATE PRE-STRESSING REINFORCEMENT FOR COPED

STEEL GIRDER ENDS

WZMOCNIENIE PRZEZ WSTĘPNE SPRĘśENIE NAKŁADKI STALOWEJ

STOSOWANE W DŹWIGARACH STALOWYCH

Z PODCIĘTĄ STREFĄ PODPOROWĄ

Abstract In this study, the fatigue reinforcing effect of coped steel girder end reinforced by the steel
plate pre-stressing method is investigated through loading tests. The principal results obtained through
this study are as follow; it was verified that sufficient compressive pre-stress can be introduced into
the web in the coped girder end using the steel plate pre-stressing method. So, it is expected this
reinforcing effect that fatigue crack is prevented from propagating to the web.

Streszczenie W niniejszym studium przedstawiono badanie za pomocą obciążeń próbnych dźwigarów
stalowych z podciętą strefą podporową, w których zastosowano metodę wstępnego sprężenia nakładki
stalowej w celu uzyskania wzmocnienia na zmęczenie. Zasadnicze efekty uzyskane na podstawie badań
są następujące: potwierdzono, że wystarczające wstępne sprężenie ściskające może zostać wprowadzone
do środników dźwigara o podciętej strefie podporowej stosując metodę wstępnego sprężenia nakładek
stalowych. Przewiduje się, że ten sposób wzmocnienia pozwoli zapobiec propagacji pęknięć zmęczenio-
wych w środniku.

1. Introduction

Recently, it has been voluminously reported that fatigue cracks have been detected at

coped steel girder ends, which were reinforcing by using ribbed steel plate. However,
the conventional reinforcement method has the case that the size of the reinforcing plate
cannot always be sufficient, due to limited little space in the coped steel girder end. And it
has also case that sufficient friction grip connection can not be produced by the reinforcing
plate rib when the reinforcing plate is fixed on to the web. So, it has been reported that
fatigue cracks were again propagated after reinforcement.

In the previous study, we proposed the steel plate pre-stress reinforcement method

for coped girder end as an alternative for conventional method. Steel plate pre-stress reinfor-
cement method fixes angle iron on the web of coped girder end and bottom flange by high-
strength bolts, and introduce compressive pre-stress into the web. This reinforcement effect
can be expected to the prevention of fatigue crack. And, it is shown to be more effective than
conventional reinforcement. However, this reinforcement method cannot show enough
reinforcement effects depending on the development direction of the fatigue crack.

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Steel plate pre-stressing reinforcement for coped steel girder ends

In this study, the fatigue reinforcing effect of coped steel girder end reinforced by

the steel plate pre-stressing method is investigated through static loading tests.

2. Steel plate pre-stressing reinforcement

Fig. 1 shows the fatigue crack and the principal stress distribution in the coped steel

girder end in the previous study. In the coped steel girder specimen, the fatigue crack occurs
from the fillet weldment between bottom flange and web of coped corner, and propagates to
the web. The direction of fatigue crack propagation in the web is almost perpendicular to
the direction of maximum principal stress.

Steel plate pre-stress reinforcement is that fatigue crack is prevented that fatigue crack by

introducing compressive stress perpendicular to the direction of propagating crack at
the web. Previous steel plate pre-stress reinforcement method could not be introduced
compressive stress perpendicular to the direction of propagating crack at the web, because
angle steel of the reinforcing member is installed both web and bottom flange.

Fig. 1. The fatigue crack and the principal stress distribution in the previous study

In the reinforcing method of this study, small steel plates as reinforcing members are
installed on the face and back of the web, and compressive stress introduced perpendicular to
the direction of propagating crack at the web. Hence, reinforcing plate fixes on 45 degrees
that is referred to the course of fatigue crack of coped girder end by other study.

1)

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Fig. 2. Basic concept of steel plate pre-stress reinforcing method for the coped steel girder end

3. Experiment method

3.1 Specimen

Fig. 3 shows the configuration and dimensions of the coped steel girder specimen.

The specimen was designed the girder ends with the coped corner (radius of 50 mm).
The material used was JIS SM400 Steel.

Fig. 3. Coped steel girder specimen

3.2 Flat bar pre-stressing method

Fig. 4 shows the reinforcing coped steel girder specimen. Reinforcing plate used JIS

SM400 steel, and this size was 80×19×540 mm. Reinforcing plate is fixed on both sides
of web using high strength bolts. And filler plate used between web and steel plate by way
of strain gauge.

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Steel plate pre-stressing reinforcement for coped steel girder ends

Fig.4. Reinforcing the coped steel girder specimen

Pre-stress is introduced by heating and cooling process. Pre-stressing processes are

as follows (see Fig. 5):

Fig. 5. Pre-stress reinforcing method

STEP1: One end of reinforcing plate fixed on the web using high strength bolts.
STEP2: Heat the reinforcing plate using gas burners.

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STEP3: When steel plate elongation reaches the expected value, another end of reinfor-

cing plate installed on the web.

STEP4: Cool the reinforcing plate. During cooling processes, tensile stress should be

introduced into the reinforcing plate and compressive stress should be introduced
into the web.

The steel plate elongation was monitored and controlled by using a dial mater.

3.3 Loading Condition

In the loading condition, the specimen is simply supported and loaded at the point of 2/5

of the span so that a sufficient shearing force and bending moment can be applied in
the coped steel girder end. The maximum load is set to 300 kN, so that the maximum stress
which occurs in the bottom flange may remain within the static allowable stress for
the material. The loading load range is ∆280 kN.

4. Experimental results

4.1 Introduced Pre-stress

Fig. 6 shows the introduced pre-stress distribution in the web near coped corner.

Compressed pre-stress in the web have been introduced to parallel with the steel plate. Pre-
stress have been decrease slowly as separated from the reinforcing plate. It was confirmed
that pre-stress of the compression introduced into the direction of reinforcing bar.

Fig. 6. Pre-stress distribution (∆L

h

= 0.5 mm, pre-stress of bar P = 266 kN)

Fig. 7 shows the relationship of pre-stress between web and reinforcing plate. Fig. 8

shows the relation between pre-stress in the web and extend of steel reinforcing plate.

Introduced pre-stress of the web and steel reinforcing bar become the linear relation.

These relations are making follow:

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Steel plate pre-stressing reinforcement for coped steel girder ends

In this reinforcing specimen, extend of reinforcing plate is decided by understanding

a necessary introduction pre-stress to the web.

Fig. 7. Relationship of pre-stress between web and reinforcing plate

Fig. 8. Relation between pre-stress in the web and extend of reinforcing plate

4.2 Steel plate pre-stressing reinforcement effect

Fig. 9 shows the principal stress distributions in the web near the coped corner when

maximum loading. Before reinforcement (Fig. 9a), the principal stress near coped corner
becomes tensile stress. In the conventional steel plate reinforcement (Fig. 9b), maximum
principal stress have decreased throughout the web. In the specimen with steel flat bar pre-

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stressing reinforcement (Fig. 9c), the maximum principal stress, these have made fatigue
cracking, has change compressive stress by the introduced pre-stress. For these above, when
the fatigue crack in the weld propagated to the web, steel plate pre-stressing reinforcement
have expected the prevention of girder breaking because of the prevention of development
cracking under the reinforcing plate.

Fig. 9. Principal stress distribution: a) Before Reinforcement

Fig. 9. Principal stress distribution: b) Steel Plate Reinforcement

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Steel plate pre-stressing reinforcement for coped steel girder ends

Fig. 9 Principal stress distribution: c) Steel Plate Pre-stressing Reinforcement

5. Conclusions

The principal results obtained through this study are as follow.

It was verified that sufficient compressive pre-stress can be introduced into the web in
the coped girder end using the steel plate pre-stressing method. So, it is expected this
reinforcing effect that fatigue crack is prevented from propagating to the web.

References

1. K.Matsumoto, H.Takahashi, M.Sakano, and H.Namiki(2006): The Proposal of more effective

reinforcement method for coped steel girder ends, JSCE (in Japan)

2. K.Matsumoto, M.Sakano, and H.Namiki(2007): Steel plate Pre-stressing Reinforcement For

Notched Steel Girder ends, Structural Failures, Mięzyzdroje, Poland.