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CICE 2010 - The 5th International Conference on FRP Composites in Civil EngineeringSeptember 27-29, 2010 Beijing, China

Trial Design of Cable-Stayed Bridges Using Hybrid Composite Girdersand Applicability to Free Passage over Railway

Hitoshi Nakamura (hnaha@tmu.ac.jp) & Ken-ichi MaedaDept. of Civil and Environmental Engineering, Tokyo Metropolitan University, Japan

Hiroshi MutsuyoshiDept. of Civil and Environmental Engineering, Tokyo Metropolitan University, Japan

Kenji YaginumaEast Japan Railway Company, Japan

Takahiro MatsuiToray Industries, Inc., Japan

ABSTRACT: A pultruted hybrid composite girder is being developed consisting of carbon and glass fibers.The innovative feature is the optimum use of CFRP and GFRP in the flanges to maximize structural perform-ance while reducing the overall cost by using glass fibers in the web section. In this paper, the cable-stayed

bridges were trially designed using the developed hybrid composite girders. In order to utilize the lightweightof FRP, the construction site was selected to the free passage over the busy railway as a case study. The ca-

ble-stayed bridges were two continuous-span bridges with the span lengths of 5.5 m and 24.0 m. As a result,the feasibility of the proposed structures and the reduction of total cost were confirmed.

1 INTRODUCTION

In the design of FRP footbridges, it is a subject that

the deflection limitation becomes dominant. It is de-sired that the development of the FRP compositegirders with high bending rigidity and the structuresystems which can control bending deflections ef-fectively.

In this study, in order to solve reasonably such aproblem, the applicability of the developed hybridcomposite girders to the free passage over railwaywas examined. The hybrid composite girder is beingdeveloped consisting of carbon and glass fibers. Theinnovative feature is the optimum use of CFRP and

GFRP in the flanges to maximize structural per-formance while reducing the overall cost by usingglass fibers in the web section and it can also bemanufactured by pultrusion. The hybrid compositegirders have been investigated experimentally by thematerial tests and bending tests of girders and theirconnections (Mutsuyoshi, H. et al. 2007, 2008, Na-kamura, H. et al. 2007, Manalo, A. C. et al. 2008).

As a case of the construction site under very se-vere restriction in erection, the free passage over twoor more rail tracks of an urban trunk railway was se-lected to demonstrate effective practical use of

lightweight FRP. Aiming at large shortening of con-struction period by weight saving and longer span,the cable-stayed bridges using hybrid compositegirders were proposed and trially designed.

2 APPLICABLE CONDITION AND TRIALDESIGN TO CABLE-STAYED SYSTEM

2.1

Set up of alternative modelThe general views of the free passages over an urbantrunk railway are shown in Figure 1. Figure 1 (a) isan example of the reference bridge, whose super-structure consists of three main steel girders of the I-shaped section, PC slab, walls, and sheds (slate ma-terial).

The case research has reported that the bridgepiers of P3 and P4 were in particular constructed inrail tracks, and the construction period became re-markably long, and also increased construction cost

considerably since construction work was limited tonighttime operation in the urban trunk railway.In such a situation, shortening drastically con-

struction period is predicted by minimizing the con-struction work in rail tracks, and the total cost reduc-tion of construction is expected, even if the materialcost increases considerably.

Therefore, it was investigated that the span lengthis longer by reducing a bridge pier, and the super-structure is made lightweight using the hybrid com-

posite girders for main girders in order to performeasily the large block erection of superstructure by a

crane.Since the bending rigidity of the main girder is

not enough against the vertical deflection when thespan length becomes longer, the cable-stayed systemis adopted. As a result of considering the arrange-

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The calculation of the cable tension including theprestress was based on the calculation technique as aconventional cable-stayed bridge. The cable pre-stresses were calculated so that the vertical deflec-tions under dead load become zero at the cable an-chor point. Main girders, cross beams and towerswere modeled with beam elements, and cables weremodeled with the axial elements.

In trial design, the required cross-sectional areasof cables were calculated so that the vertical deflec-tions of main girders become 1/500 or less of spanlength under the live load of 3.5 kN/m2(Japan RoadAssociation 1979).

3 RESULTS OF TRIAL DESIGN ANDDISCUSSIONS

3.1 Weight comparison of superstructure

As a part of trial design results, the weight compari-

son of constituent member is shown in Figure 4. Inthe cable-stayed bridge, the weight of towers, cablesand steel cross beams for the cable anchor increasescompared with the reference bridge. Because theweights of the other members were reduced drasti-cally, the total weight of the cable-stayed bridge was

below half of the reference bridge.

0 20 40 60 80 1

Cable-Stayed Bridge

(Case A)

Reference Bridge

Weight (ton)00

Pavement Slab Shed Main girder Lateral Tower Cable

92.3ton

42.2ton

Figure 4. Weight comparison of constituent member

3.2 Cross-sectional area and tensile stresses of staycables

The cross-sectional areas and the maximum tensilestress of cables vs. the elastic moduli of hybrid com-

posite girders are shown in Figure 5. Since the verti-cal deflections of main girders increases so that theelastic moduli is low, it was found that it is neces-sary to increase the cross-sectional areas of cables.

Moreover, the maximum stresses of cables be-came small with lowering the elastic moduli of gird-ers. And in the case D, where a cross-sectional areais the largest, the maximum stress was 247MPa.Generally, since the tensile strength of steel cables ishigh, and the tensile stress is small enough, it wasconfirmed that the required cross-sectional areas arealso governed by the deflection limitation.

0

500

1000

1500

2000

2500

25 30 35 40 45 50 55 60 65

Elastic modulus of hybrid composite girder E(GPa)

Sectinalarea(mm2/cable)

0

50

100

150

200

250

300

350

Maximumstress(MPa)

Sectional area

Maximum stress (D)Maximum stress (D+L)

Figure 5. Cross-sectional areas and maximum tensile stress of cables

vs. elastic moduli of hybrid composite girders

3.3 Flexural characteristics of girders

The vertical deflections of main girders under deadload are shown in Figure 6. Because the cable

prestress were determined in the design condition,where the deflections at those points are zero underdead load, the deflections hardly occurred at the ca-

ble anchor points. However, except the cable anchorpoints and the supported points, it was also foundthat the deflections increase with lowering the elas-tic moduli of main girders.

Figure 7 shows deflection distribution under liveload. It was found that the deflection limitation(L/500) is satisfied in all cases.

-2

-1

0

1

2

3

4

5

6

Verticaldeflection(mm)

Case A

Case BCase C

Case D

P1 P2 P3

Figure 6. Vertical deflection distribution of girder under dead load

-10

0

10

20

30

40

50

Verticaldeflection(mm)

Case A

Case B

Case C

Case D

Deflection limitation: L/500

P1 P2 P3

Figure 7. Vertical deflection distribution of girder under live load

3.4 Stress checks of girders

The results of the stress check are shown in Figure8. This figure shows the stress distribution of the

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main girder in Case A, where the stresses becomethe highest under dead and live load. The stress un-der dead load was small enough, and the stress underdead and live load were also from -50 to 30 MPa.

Therefore, it was confirmed that the stresses aresufficiently small compared with the materialstrength of the hybrid composite coupon specimen(Manalo, A. C. et al. 2008).

-50

-30

-10

10

30

50

Normalstress(MPa)

D (U.Flg.)D (L.Flg.)D+L (U.Flg.)D+L (L.Flg.)

Case A

P1 P2 P3

Figure 8. Normal stress distribution of girders under dead and live

loads

3.5 Natural frequency and vibration serviceability

The relationships between the elastic moduli of hy-brid composite girders and natural frequencies areshown in Figure 9. Although the frequencies of thesymmetrical deflection modes were the smallest, thevibration serviceability in the Japanese standard for

pedestrian bridges (Japan Road Association 1979)was satisfied. The frequencies lower modes werealmost constant regardless of the elastic moduli of

main girders. The cable tensile rigidity designed dueto the deflection limitation has contributed the fre-quencies of deflection modes.

On the other hand, the frequencies were higher inproportion to the elastic moduli of main girders asthe higher order mode. In addition, it was also con-firmed that the frequencies of the torsional modesand out-of-plane deflection modes were compara-tively high.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

25 30 35 40 45 50 55 60 65

Elastic modulus of hybrid composite girder E(GPa)

Naturalfrequencyf(Hz)

Asymmetrical in-plane deflection modeOut-of-plane deflection and torsional modeSymmetrical torsional modeSymmetrical In-plane deflection mode

Figure 9. Relationships between elastic moduli of hybrid composite

girders and natural frequencies

3.6 Selection of laminated constitution

Although the deflection limitation became dominantin the design, it was confirmed that the cable-stayed

bridge with any laminated constitution is feasible byusing the cables of the required sectional area.

In the selection of laminated constitution, whenthe elastic modulus is adopted more than 45 GPa(equivalent to Case C), there is no problem for prac-tical use, because the deflection of the main girder ofCase D, which is the lowest elastic modulus, is par-tially large under dead load.

4 CONCLUSION

The cable-stayed bridges were trially designed usingthe developed hybrid composite girders. In order toutilize the lightweight of FRP, the construction sitewas selected to the free passage over the busy rail-way as a case study.

Consequently, the deflection limitation becamedominant in the structural design. However, thenormal stresses under design loads were very small

and the vibration serviceability due to the Japanesestandard for pedestrian bridges was also satisfied.Moreover, It was found that the weight saving con-tributes to large shortening of the construction pe-riod. Therefore, the feasibility of the proposed struc-tures and the reduction of total cost were confirmedcompared with a typical steel girder bridge.

ACKNOWLEDGEMENT

This research is financially supported by MLIT(Ministry of Land, Infrastructure and Transport inJapan) grant-in-aid for scientific research of con-struction technology, which is greatly acknowl-edged.

PREFERENCES

Mutsuyoshi, H. et al. 2007. Development of New HybridComposite Girders Consisting of Carbon and Glass Fibers.COBRAE conference 2007 Benefits of composites in civil

engineering, 2, University of Stuttgart.Nakamura, H. et al. 2007. Shear Deformation Characteristics

and Web-Crippling of New Hybrid Composite Girders.Proc. of Asia-Pacific Conference on FRP in Structures,

APFIS 2007, Hong Kong, 12-14 December 2007: 459-464.Manalo, A. C. et al. 2008. Mechanical behavior of hybrid FRP

composites with bolted joints, Proc. of 20th AustralasianConference on the Mechanics of Structures and Materials,

ACMSM20, Toowoomba, Queensland, Australia, 2-5 De-cember 2008. London: Taylor & Francis Group, 47-53.

Mutsuyoshi, H. et al. 2008. Composite Behavior of HybridCFRP-GFRP Bridge Girders, Proc. of 20th AustralasianConference on the Mechanics of Structures and Materials,

ACMSM20, Toowoomba, Queensland, Australia, 2-5 De-cember 2008. London: Taylor & Francis Group, 61-67.

Japan Road Association. 1979. Japanese standard for pedes-trian bridges and underpasses, Tokyo: Maruzen. (in Japa-nese)