STEEL PLATE PRE_STRESSING REINFORCEMENT FOR NOTCHED STEEL GIRDER ENDS.pdf

Prof. Masahiro SAKANO, peg03032@nifty.com

Kansai University, Osaka, Japan

Kentaro MATSUMOTO, matsumoto_kentarou@railtec.jp

Railtec Co., Osaka, Japan

Dr. Hironori NAMIKI

Kyobashi Mentec Co.Ltd., Osaka, Japan

STEEL PLATE PRE-STRESSING REINFORCEMENT

FOR NOTCHED STEEL GIRDER ENDS

WST PNE SPR ENIE WZMOCNIENIA RODNIKA D WIGARA STALOWEGO

Z PODCI TYM KO CEM

Abstract The applicability of the steel plate pre-stressing method is investigated for the purpose of preventing fa-

tigue crack propagation to the web in the notched girder end. With the steel plate pre-stress method, it is considered

to be possible for the reinforcing plate to be decreased in size in comparison with the conventional reinforcing

method, since both live load and dead-load can be reduced or changed to compressive stress by compressive pre-

stressing. Monotonic and fatigue loading tests are reported using full-scale girder specimens with notch.

Streszczenie Analizowano mo liwo wst pnego spr enia rodnika podci tego ko ca d wigara stalowego w celu

zapobiegania rozprzestrzeniania si pkni zmczeniowych. Stosujc sprenie rodnika uznano, e moliwe b-

dzie zmniejszenie wymiarów elementów wzmacniajcych w porównaniu z konwencjonalnym wzmocnieniem, gdy

naprenia zarówno od obcienia uytkowego jak i ciaru własnego mog by dziki wstpnemu spreniu ci-

skajcemu zredukowane lub zamienione na naprenia ciskajce. Przedstawiono wyniki bada Pd obcieniem

stałym jak i zm czeniowym z wykorzystaniem d wigarów z podci ciem wykonanych w skali naturalnej.

1. Introduction

It has been extensively reported that fatigue cracks have been detected at notched steel girder

ends, which are reinforced by using ribbed steel plate. However, the conventional reinforcement

method may not always be perfect in its response to actual conditions, since the size of the rein-

forcing plate cannot always be sufficient, due to limited space with stiffeners or various attach-

ment members in the notched girder end. There is also a possibility that sufficient friction grip

connection is not 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 this study, the applicability of the steel plate pre-stressing method is investigated for the

purpose of preventing fatigue crack propagation to the web in the notched girder end. The steel

plate pre-stress method is also considered to have the potential for decrease in size of the rein-

655

forcing plate in comparison with the conventional reinforcing method, since both live load stress

and dead load tensile stress can be reduced or changed to compressive stress by compressive pre-

stressing. In this paper, monotonic and fatigue loading tests are reported using full-scale girder

specimens with notch.

2. Experimental Method

2.1 Specimens

Fig. 1 shows the configuration and dimensions of the notched steel girder specimen. The

specimens were designed so that the girder end with the notch (radius of 80mm) can be ex-

changed, and the other part can be used repeatedly. The material used was JIS SS400 Steel.

Three parts of the girder end were prepared, respectively for three cases of no reinforcement,

steel plate reinforcement and steel plate pre-stressing reinforcement.

900

1325

1100

2350

4650

3325

1-Web PL 800 8 1308

75 85 7 5

Loading Point

1-Web PL 800 8 3308

2-Spl PL 315 8 700

32-H.T.B M22 65 (F10T)

1 5

5 0 200

400

8 0

1 5

950

10 0

3 916.7=2750

150

1500

2850

4350

150

( Unit:mm )

Fig. 1 Notched girder specimen (elevation)

In the loading condition, the specimen is simply supported and loaded at the point of 1/3 of the

span so that a sufficient shearing force and bending moment can be applied in the notched girder

end. The maximum load is set at 300kN, so that the maximum stress which occurs in the bottom

flange may remain within the static allow-

able stress for the material.

1325

Point

2.2 Steel plate reinforcement

Reinforcing Member

In the specimen with steel plate rein-

forcement, the reinforcing steel plate is in-

stalled to the notched girder end by a fric-

tion grip connection using high-strength

bolts (see Fig. 2). Angle steels as reinforc-

ing members (90mm×90mm×670mm) are

installed on the face and back of the web,

and then fixed to both the bottom flange in

the small section and the web in the large

section. This steel plate reinforcing method

is expected to reduce the stress concentra-

185

670

185

5 0 200

185

400

10 0

950

450

150

1500

( Unit:mm )

Fig. 2 Reinforcing the Notched girder Specimen

656

300

tion of notched members and extend the fatigue life, because stress in the bottom flange in the

small section is transmitted to the web in the large section.

2.3 Steel plate pre-stressing method

Pre-stresses are introduced into the notch using a heating and cooling process. Pre-stressing

processes are as follows (see Fig.3).

Step 1: Fix one end of the reinforcing steel plate to the web of the large section side near the

loading-point side using high-strength bolts.

Step 2: Heat the reinforcing plate using gas burners.

Step 3: Fix the other end of the reinforcing plate when its elongation reaches the expected

value.

Step 4: Cool the reinforcing steel plate. During these processes, tensile stress should be intro-

duced into the reinforcing plate and compressive stress should be introduced into the

bottom flange of the reinforced beam.

The elongation of the reinforcing plate was monitored and controlled by using a dial meter.

The reinforcing method should ensure that the stress concentration can be reduced by installing

Step 1

Step 3

Bolting

•

cooling

Shrink

Bolting

Step 2

Step 4

•

L heating

Stretch

Gas Torch

: Reinforcing Steel Plate

Fig. 3 Reinforcing the Notched girder Specimen

reinforcing plates, and fatigue crack is prevented from propagating to the web by compressive

pre-stress.

3. Experimental results

3.1 Pre-stressing process

Fig. 4 shows changes of stress and temperature during the pre-stressing process. Tensile stress

is introduced into the reinforcing plate, and compressive stress is introduced into the web near

657

100

Fixing

-20

-40

-60

-80

0 10 20 30 40 50 60 70 80 90 100

Time minutes !

Cooling

Web (W 120 , South)

Web (W 120 , North)

Web (Mean)

Temperature change(South)

Reinforcing plate (South)

Reinforcing plate (North)

Reinforcing plate (Mean)

Temperature change(North)

Fig. 4 Change of stresses during pre-stressing

the notch during the cooling process. It takes about half an hour for the pre-stressing process to

be completed.

3.2 Static loading test results

Fig. 5 shows the change in horizontal stresses in the web (Test point W120d ) behind the cen-

ter of the reinforcing plate during the loading process. In the specimen without reinforcement,

the relations between horizontal stress and the magnitude of load ( ) are distributed linearly, and

horizontal stress is about 80MPa

when the load is maximum

(Pmax=300kN).

In the specimen with steel plate

reinforcement, the horizontal

stress in the web (D) can be re-

duced when P>60kN in compari-

son with the specimen without

reinforcement, because the speci-

men was reinforced when Pmin=

60kN which was assumed to be a

dead load. On the other hand, the

stress ( ) in the reinforcing steel

plate was increasing as decreasing

the stress in the web.

The stress under maximum load

(Pmax=300kN) is reduced 40%

from 75MPa to 45MPa compared

to the specimen without rein-

(Reinforcing Plate)

Meas. -No Reinforcement

-Steel Plate Reinforcement

-Steel Plate Pre-stressing method

R.P-Steel Plate Reinforcement

R.P-Steel Plate Pre-stressing method

W 8 v

W 120

150

W 12 d

W 4 d

/0))0-*%'1.2(

%&''()*+(',-(.)

100

"#$

10 9

W 4 h

-50

120

180

240

300

Load P (kN)

Fig. 5 Relation between horizontal stress and load

658

W 120

forcement. The stress in the reinforcing steel plate is about 25MPa.

In the specimen with steel plate pre-stressing reinforcement, the pre-stress was also introduced

into the web during dead loading (Pmin=60kN). Tensile stress 40MPa was introduced by the re-

inforcing steel plate and compressive stress -50MPa in the web plate. Although the gradients of

the stress change in web and reinforcing steel plate (, ) in the specimen with steel plate pre-

stressing reinforcement are almost same as those in the specimen with steel plate reinforcement

(D, ) when P>60kN, the web stress ( ) is compressive, and becomes about 0MPa when maxi-

mum loading. Consequently, the horizontal stress range in the web( ) during cyclic loading stays

in the compressive area. The stress( ) in the reinforcing steel plate with pre-stress is 40MP lar-

ger, which is exactly same as the magnitude of the pre-stress, than stress() in the reinforcement

steel plate without pre-stress.

Fig. 6 shows the principal stress distributions in the web near the notch during live loading. In

the specimen without reinforcement, the magnitude of measured maximum principal stress range

of 99MPa is almost horizontal at test point W40d. In the specimen with steel plate reinforcement,

the maximum principal stress range (test point W40d) near the center of the notched corner is

reduced to 65MPa. Thus, it is confirmed that the stress concentration of a notched corner is re-

C L

(Reinforcing Plate)

C L

(Reinforcing Plate)

Fatigue Crack

W 120

W 8 v

W 120

W 4 d

Fatigue crack

W 4 d

Bottom

Flange

Bottom

Flange

Bottom

Flange

101

Fillet

Weldment

Fillet

Weldment

Fillet

W eldment

W 4 h

-13.7

-9

-11

Meas.

P=240kN

Meas.

P=240kN

Meas.

P=240kN

No Reinforcement

Compression (-50MPa)

Tension (50MPa)

Reinforcing Plate

Steel Plate Reinforcement

Compression (-50MPa)

Tension (50MPa)

Reinforcing Plate

Steel Plate Pre-stressing Reinforcement

Compression (-50MPa)

Tension (50MPa)

Reinforcing Plate

(a) No Reinforcement

(b) Steel Plate Reinforcement

Reinforcement

Fig. 6 Maximum principal stress range distribution under the live loading (DP=240kN)

duced by steel plate reinforcement. In the specimen with steel plate pre-stressing reinforcement,

the magnitude and direction of the principal stress range distribution is almost the same as that in

the specimen with steel plate reinforcement under cyclic loading., as shown in Fig. 6 (b),(c).

Fig.7 shows the principal stress distribution in the web near the notch when maximum loading

(Pmax=300kN). The magnitude of the principal stress of both specimen without reinforcement

and specimen with steel plate reinforcement increase corresponding to increase in the magnitude

of load, in comparison with Fig. 6. In the steel plate pre-stressed specimen, the horizontal stress

of the web behind the reinforcing plate (test points W85V and W120d) changed to compression

659

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