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1 INTRODUCTION Specifications for Highway Bridge and Standards Specifications for Steel and Steel-concrete Hybrid Railway Bridges are introduced. The former is based on the Allowable Stress Design (hereinafter the “ASD”) and the latter is based on the Limit State Design (hereinafter the “LSD”), and both are legal codes. Hence, in Japan, the design of almost all highway and railway steel and steel-concrete composite bridges has been carried out by employing them.

Committee on Steel Structures in Japan Society of Civil Engineers (hereinafter the “JSCE”) is now making Standard Specifications for Steel and Steel-concrete Composite Structures. It consists of 6 volumes and, among them, five volumes have been published. The above JSCE code is based on performance-based design. Since it is the first time design code in civil steel structural engineering in Japan, the detailed explanation is made in this paper.

In Japan, due to lack of the financial budget for public work, technological ideas or proposition for attain-ing the cost cut and higher durability are being strongly requested at the stage of new bridge construction. In this situation, the competition between steel and concrete alternatives is now becoming severe. To cope with this subject, the development and proposition of long-life, steel-concrete composite bridges, which utilized each merit from steel and concrete, is active. Furthermore, it is emphasized, for the design of composite girder bridges, that the shift of design concept from ASD to LSD is important. Because, utilizing inelastic strength of the composite girder contributes to enhance the competitiveness. From this viewpoint, the effort of LSD establishment for the design of composite bridges carried out by our research group is introduced.

2 DESIGN CODES FOR HIGHWAY AND RAILWAY BRIDGES Japan Road Association is in charge of issuing Specifications for Highway Bridges (Japan Road Association 2003). Photo 1 is the cover of it, which is 2003-version. The design of almost all highway bridges in Japan follows it. The first version was issued in 1939, and modern style or format of it was established in 1972-

IABSE-JSCE Joint Conference on Advances in Bridge Engineering-II, August 8-10, 2010, Dhaka, Bangladesh. ISBN: 978-984-33-1893-0 Amin, Okui, Bhuiyan (eds.) www.iabse-bd.org

Recent trend on design and construction of steel and composite bridges in Japan M.Nagai Nagaoka University of Technology, Nagaoka, Niigata, Japan

E. Yamaguchi Kyushu Institute of Technology, Kitakyushu, Fukuoka, Japan

T. Yoda Waseda University, Tokyo, Japan

K. Nogami Tokyo Metropolitan University, Tokyo, Japan

ABSTRACT: This paper first introduces design codes for steel and steel-concrete composite bridges in Japan. Almost all roadway and railway bridges in Japan have been designed according to Specifications for Highway Bridges and according to Standard Specifications for Steel and Steel-concrete Hybrid Railway Bridges, re-spectively. Standard Specifications for steel and composite structures issued from Japan Society of Civil En-gineers is introduced in detail, since it is the first time performance-based design in civil steel structural engi-neering field. The latter part of this paper deals with current construction trend on steel and steel-concrete composite bridges in Japan. Evaluating formulae of ultimate flexure, shear and coupled strength of the com-posite and double-composite girders are proposed. It is for the establishment of the Limit State Design of composite girder bridges.

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version. Since then, even though small revision was made, essential change has not been made. It is based on ASD and specification-based design, and it has been announced that LRFD format will be employed in the next version under revision.

Railway bridges have been designed using Standard Specifications for Steel and Hybrid Railway Bridges (Railway Technical Research Institute 2008). Photo 2 is the cover of it. In 1992, the design concept was shifted from ASD to LSD.

3 JSCE STANDARD SPECIFICATIONS FOR STEEL AND COMPOSITE STRUCTURE

3.1 General Committee on Steel Structures of JSCE is making efforts for the advancement of technology in the field. The technical subcommittees are set up to solve specific problems, and design codes are complied and constantly updated based on the latest research outcomes. JSCE design codes are not mandatory. They are rather model codes, but much more advanced than codes of practice which tend to be conservative.

In 2000, Committee on Steel Structures formed a special subcommittee on performance-based design to study this new design approach in the field of steel structures. In 2003, the subcommittee published a report entitled “For Construction of Performance-based Design for Steel Structures” (JSCE 2003). Following this achievement, Subcommittee on Standard Specifications for Steel and Composite Structures was set up in 2004. The subcommittee consists of six task forces, each of which deals with a specific phase of construction. The standard specifications thus would be of six volumes: General Provisions, Structural Planning, Design, Seismic Design, Construction and Maintenance. Three books have been already published from JSCE: the first book combines three volumes of General Provisions, Structural Planning and Design (JSCE 2007), while the second and third books are Volume of Seismic Design (JSCE 2008) and Volume of Construction (JSCE 2009). The last book on Maintenance is expected to come out in 2010. The covers of the report (JSCE 2003) and the books (JSCE 2007, 2008, 2009) above explained are shown in Photos 3 - 6. The first book (JSCE 2007) is already available in English (JSCE 2010), and Photo 7 shows the cover.

As technology advances continuously and new demands on structures come up constantly, the preparation for the revision of the published volumes is always underway.

3.2 Outline of the first book of JSCE Standard Specifications Volume of General Provisions gives the basis of the standard specifications for steel and composite struc-tures. It describes the design approach, the format for verification equations, terminology and so on, which all the volumes follow.

Volume of Structural Planning shows the issues that must be clarified at the planning phase of design. Volume of Design presents specific design requirements for the steel and composite structure. This is the

performance-based type of design code. Hence, the code does not have the specific design proce-dures/verification equations that designers must follow. All that code matters is that the structure will perform satisfactorily; the way to ensure the satisfactory performance of the structure in the design phase is no con-cern of the code. For the sake of design convenience, however, the code provides the verification equations as well that designers may use to verify the performance of the structure. These are often called deem-to-satisfy design equations.

The performance requirements that Volume of Design has recognized are safety, serviceability, restorabil-ity, durability, social and environmental compatibility and constructability. In general, the satisfaction of the performance requirements is to be verified referring to the associated limit state. However, it is not possible to set up the limit state for all the performance requirements. Some performance items in the social and envi-ronmental compatibility, for example, need to be treated as an optimization problem instead.

3.3 Style of JSCE Standard Specifications Committee on Steel Structures published Design Code for Steel Structures in 1997 (JSCE 1997). The cover is shown in Photo 8. The code is based on LSD. This is a conventional design code, and the verification equa-tions are specified. Volume of Design (JSCE 2007) is actually the update of the above code (JSCE 1997). However, no equations are given, and the difference between two codes is obvious. This is because in the per-formance-based design, a designer can use any method of his/her choice to verify that the designed structure would satisfy the performance requirements.

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Photo 1. Specifications for Highway Bridges Photo 2. Standard Specifications for Steel and Hybrid Railway Bridges

Photo 3. For Construction of Photo 4. 2007 JSCE Standard Specifications Performance-based design for steel structures (General provisions, Basic Plan and Design)

Photo 5. 2008 JSCE Standard Specifications Photo 6. 2009 JSCE Standard Specifications (Construction) (Seismic design)

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Photo 7. English version of Photo 8. JSCE Design Code 2007 JSCE Standard Specifications for Steel Structures PART A issued in 1997

While the performance-based design thus gives designers greater freedom, it could be burden in some case to establish verification procedure from scratch. Hence, Volume of Design (JSCE 2007) provides the infor-mation on the deemed-to-satisfy design equations in the commentary, the utilization of which can ensure the satisfaction of the corresponding performance requirements. Thus, even by the performance-based design code, it would be possible to follow the same design procedure as that by a conventional specification-based design code.

3.4 Format of verification equations Standard Specifications for Steel and Composite Structures (JSCE 2007) have employed the partial factor method on the basis of the reliability theory for the performance verification. Thus, in principle, the verifica-tion equations in the deem-to-satisfy approach in the standard specifications take one of the following forms.

0.1≤d

di R

Sγ , (1)

0.1)/(

)(≤

Σ

bmk

kfai fR

FSγγ

γγγ , (2)

where, Rd = the design resistance, fk =the characteristic value of material strength, γm = the material factor, γb = the structural-member factor, R = the function to calculate limit value of structure from material strength, Sd = the design response, Fk = the characteristic value of action, γa = the structural-analysis factor, γf = the action factor corresponding to each action (load factor), S = the function to calculate response value of structure from action and γi =the structural factor.

In general, the values of the partial factors should be determined by the theoretical consideration coupled with appropriate data. But the structural factor that deals with the importance of the structure and/or its social influence when it reaches a limit state is somewhat different: it is usually decided by the owner.

4 COMPETITIVE STEEL ALTERNATIVES

As explained in Introduction, the development and proposition of steel-concrete hybrid (composite or mixed) bridges in both steel and concrete sides is active.

Figure 1 and Figure 2 show steel I-girder and box girder bridges with a very simplified transverse stiffen-ing system, which are alternatives proposed by bridge engineers belonging to three companies, East-, Central- and West-Nippon Expressway Company Ltd., former Japan Highway Public Corporation. Among these, composite or non-composite twin-I-girder bridge has been evaluated to be the most competitive alternative for bridges with a span from 40 to 60 meters. Figure 3 shows the total construction number and owners of these types of bridge. From this figure, it is seen that increase of I-girder bridges is prominent. Figure 4 is PC box girder bridges with steel corrugated web or steel pipe truss web. When the span length less than 40 me-ters, and exceeds 60 or 70 meters, PC bridges are evaluated to be very competitive.

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In order to compete with long-span concrete bridges, steel bridge engineers are now proposing a double-composite girder bridge and cable-stayed composite girder bridge shown in Figure 5, however, they have not been realized. In order to enhance the competitiveness of steel-concrete hybrid bridges, not only inviting new structural system, such as double-composite girder and so on but also it is strongly emphasized to employ the Limit State Design (LSD) or to shift from ASD to LSD

5 EXPERIMENTAL STUDY ON ULTIMATE STRENGTH OF COMPOSITE GIRDERS

On designing steel-concrete hybrid bridges, the importance of shifting to LSD was emphasized in Chapter 4. In order to establish LSD, the development or preparation of evaluating formulae of ultimate strength be-comes very important.

Herein, we introduce the experimental research project carried out in collaboration with Expressway Re-search Institute Ltd., Nagaoka University of Technology, Saitama University and Japan Bridge Association.

Figure 6 shows failure modes of composite girders under pure flexure and shear, respectively. It is seen the crushing of the concrete slab and diagonal tension filed. Figure 7 also shows failure modes of double-composite girders under pure flexure and shear.

In Chapter 6, evaluating formulae are proposed. They are our original proposition and are derived based on nonlinear finite element analyses. The validity of them was confirmed through this extensive experimental re-search results.

Figure 1. Structural Innovation of I-girder bridges

Figure 2. Structural Innovation of box girder bridges

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(a) Construction number (b) Owners

Figure 3. Newly developed bridges

(a) Steel corrugated web (b) Steel truss web

Figure 4. PC box girder with steel corrugated web and pipe truss web

(a) Double composite girder bridge (b) Cable-stayed composite girder bridge

Figure 5. Proposed long-span steel bridges

(a) Under pure flexure (b) Under shear

Figure 6. Failure modes of composite girders

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(a) Under pure flexure (b) Under shear

Figure 7. Failure modes of double-composite girders

6 EVALUATION OF ULTIMATE FLEXURE, SHEAR AND COUPLED STRENGTH OF COMPOSITE AND DOUBLE-COMPOSITE GIRDERS

6.1 Flexure strength of composite girder under sagging bending moment The section is classified into “compact” when the web thickness (tw) satisfies Equation 3 given below, and the strength is defined to be plastic moment (Mp).

)(0.4

2

ywyw

cp

forfE

t

D≤ (3)

At the actual design stage, ultimate flexure strength (Mult) of composite girder under the sagging bending moment is defined to be smaller value of βMp or 1.3My (AASHTO 2005).

{ }ypult MMM 3.1,min β= (4)

Where, β is given by the following Equation 5.

4.0/15.0)/(33.005.1

5.0/0.1

≤≤−=

≤=

tptp

tp

DDDD

DD

β

β (5a-b)

β (=1.0) is given to take into account of ductility condition. If the distance (Dp) from the concrete deck top to plastic neutral axis becomes relatively large compared to the total girder height (Dt), the concrete crushing is predicted to occur before reaching plastic moment. β is to take into account of this phenomenon.

Figure 8 shows the stress state at ultimate state, in which plastic neutral axis is calculated under the condi-tion that the axial force of the section is zero, and Mp is the moment with respect to the neutral axis. The nota-tions of Dcp, Dt, Dp, fy and fyw are also indicated in the figure, and E is Young’s modulus of elasticity.

In case that the section at intermediate supports is classified into “slender (Mult = My)”, the maximum ulti-mate flexure strength is limited less than 1.3My (AASHTO 2005) (0.9Mp is defined in Eurocode 4 (CEN 2004)). Hence, βMp and 1.3My are compared, and the smaller strength is selected as the ultimate flexure strength of the composite section under the sagging bending moment.

In a twin-I-girder bridge, almost all cases, the plastic neutral axis of the section is located within the con-crete slab (Dcp=0). Hence, the section is classified into “compact”, and the ultimate flexure strength is plastic moment. Furthermore, Dp (=Dcp) is small compared to the total height of the girder (Dt). It means that β can be left at 1.0.

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Figure 8. Stress in composite cross section at ultimate state under sagging bending moment

6.2 Flexure strength of composite girder under hogging bending moment At intermediate supports, where the composite girder is subjected to the hogging bending moment, cracking in the concrete slab occurs. Hence, the resistant section consists of steel girder and reinforcing bars. Nor-mally, the dead load from steel and concrete slab is carried by steel girder only, and the superimposed dead load and live load are carried by the composite section consisted of steel section plus reinforcing bars. This means two different sections comprises the resisting ones. They are steel girder only and steel girder plus re-inforcing bars. Hence, there are certain difficulties in assessing the strength.

Here, as shown in Figure 9, the strength is calculated by using steel girder and reinforcing bars as the re-sisting section. In the figure, fcr,f is the strength of the lower flange under compression and fcr,w is the flexure strength of the web ( Fukumoto. Y. (ed.) 1997). ft is the tensile stress in the flange, which is given under the condition that axial force of the girder is zero. Since the stress in reinforcing bar fR is set to be larger than that of actual situation, flexure strength calculated using this stress state overestimates the strength. Hence, 90% of the strength thus obtained is set as the design strength.

Figure 9. Stress in [steel + reinforcement] cross section at ultimate state under hogging bending moment

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6.3 Flexure strength of double-composite girder under hogging bending moment The flexure strength is given by

ptpult MDDM )/(β= (6)

Since the concrete is attached to the web through lying studs as shown in Figure 10, the section is expected to be classified into “compact”. In the actual case, the concrete slab has to be arranged that the ratio of (Dcp /tw) satisfies Equation 3.

6.4 Flexure strength of steel girders under construction From Figure 9, flexure strength of steel girder is calculated. fcr,f and fcr,w in the figure are the same as those de-fined in 6-2. ft is also given from the condition that the axial force in the girder is zero.

6.5 Shear strength of composite girders The shear strength Qult is assessed using formula proposed by Basler (Basler, K. 1961). It is derived for the steel girder only and is the sum of elastic buckling strength and post buckling strength. In case of composite girders, due to the contribution obtained from concrete slab, the strength is expected to increase. However, an exact identification of contribution of the slab to strength is difficult. Hence, from a conservative viewpoint, its effect is neglected.

Figure 10. Double-composite section for flexure strength under hogging bending moment

6.6 Shear strength of double-composite girders As shown in Figure 11, the web height is divided into hw1 and hw2 in order to evaluate the shear strength of the double-composite girder. The shear strength of the steel part with the depth of hw1 is assessed by Basler’s for-mula and the strength of the steel part with the depth of hw2 is assessed as τyhw2tw. Where, τy is the shear yield stress. The sum of the both strength is the shear strength of the double-composite girders.

6.7 Coupled flexure and shear strength of steel and composite girders Because the coupling effect of flexure and shear is comparatively small, it is neglected in case of composite girders. However, in case of steel girder, the following formula is used.

0.144

≤⎟⎟⎠

⎞⎜⎜⎝

⎛+⎟⎟

⎠

⎞⎜⎜⎝

⎛

ultult QQ

MM

(7)

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where, M and Q are actions under factored load. Mult and Qult are flexure strength and shear strength defined above, respectively.

Figure 11. Double-composite section for shear strength

7 CONCLUDING REMARKS

The design code of Standard Specifications for Highway Bridges issued from Japan Road Association and Standard Specifications for Steel and Hybrid Railway Bridges are introduced. Most of highway and railway steel and composite bridges in Japan have been designed according to them, specification-based design.

The overview of some efforts of JSCE in the field of steel and composite structures is presented, laying emphasis on the design codes, which is the first time performance-based design in civil steel structural engi-neering.

The current trend on steel and composite bridge construction is introduced. In order to enhance the com-petitiveness of composite bridges, the shift of design from current ASD to LSD is emphasized. In this connec-tion, competitive formulae for evaluating ultimate flexure, shear and coupled strength of composite and dou-ble-composite girders are proposed. They are based on finite element analyses, and the validity of them is examined through experimental research project carried out in collaboration of 4 organizations.

REFERENCE

AASHTO 2005. LRFD bridge design specifications - 2005 interim revisions -. Washington, D.C.: AASHTO. Basler, K. 1961. Strength of plate girders in shear. Journal of Structural Division, ASCE, Vol.86 No.ST7:151-180. CEN, European committee for standardization 2004. Eurocode 4, design of composite steel and concrete structures, Part2, General rules and rules for bridges. Brussels: CEN. Fukumoto. Y. (ed.) 1997. Structural stability design - Steel and Composite Structures -. Elsevier Science. JSCE, Committee on Steel Structures 1997. Design code for steel structures Part A; structures in general. Tokyo: JSCE. Japan Road Association 2003. Specifications for Highway Bridges, Part-2 Steel Bridges (in Japanese). Tokyo: Maruzen Publica-tion. JSCE, Committee on Steel Structures 2003. For construction of performance-based design for steel structures. Tokyo: JSCE. JSCE, Committee on Steel Structures 2007. 2007 Standard Specifications for Steel and Composite Structures - I General princi-ples, II Structural planning, III Design -. Tokyo: JSCE. JSCE, Committee on Steel Structures 2008. 2008 Standard Specifications for Steel and Composite Structures 2008 - IV Seismic de-sign -. Tokyo: JSCE. JSCE, Committee on Steel Structures 2009. 2009 Standard Specifications for Steel and Composite Structures 2009 - V Construc-tion -. Tokyo: JSCE. JSCE, Committee on Steel Structures 2010. 2007 Standard Specifications for Steel and Composite Structures (English version). Tokyo: JSCE. Railway Technical Research Institute 2008. Design Standards for Railway Structures and Commentary (Steel-Concrete Hybrid Structures). Tokyo: Maruzen Publication.