Recent trend on design and construction of steel and composite bridges in Japan

Transcription

1 IABSE-JSCE Joint Conference on Advances in Bridge Engineering-II, August 8-10, 2010, Dhaka, Bangladesh. ISBN: Amin, Okui, Bhuiyan (eds.) Recent trend on design and construction of steel and comosite bridges in Jaan M.Nagai Nagaoka University of Technology, Nagaoka, Niigata, Jaan E. Yamaguchi Kyushu Institute of Technology, Kitakyushu, Fukuoka, Jaan T. Yoda Waseda University, Tokyo, Jaan K. Nogami Tokyo Metroolitan University, Tokyo, Jaan ABSTRACT: This aer first introduces design codes for steel and steel-concrete comosite bridges in Jaan. Almost all roadway and railway bridges in Jaan have been designed according to Secifications for Highway Bridges and according to Standard Secifications for Steel and Steel-concrete Hybrid Railway Bridges, resectively. Standard Secifications for steel and comosite structures issued from Jaan Society of Civil Engineers is introduced in detail, since it is the first time erformance-based design in civil steel structural engineering field. The latter art of this aer deals with current construction trend on steel and steel-concrete comosite bridges in Jaan. Evaluating formulae of ultimate flexure, shear and couled strength of the comosite and double-comosite girders are roosed. It is for the establishment of the Limit State Design of comosite girder bridges. 1 INTRODUCTION Secifications for Highway Bridge and Standards Secifications 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 Jaan, the design of almost all highway and railway steel and steel-concrete comosite bridges has been carried out by emloying them. Committee on Steel Structures in Jaan Society of Civil Engineers (hereinafter the JSCE ) is now making Standard Secifications for Steel and Steel-concrete Comosite Structures. It consists of 6 volumes and, among them, five volumes have been ublished. The above JSCE code is based on erformance-based design. Since it is the first time design code in civil steel structural engineering in Jaan, the detailed exlanation is made in this aer. In Jaan, due to lack of the financial budget for ublic work, technological ideas or roosition for attaining the cost cut and higher durability are being strongly requested at the stage of new bridge construction. In this situation, the cometition between steel and concrete alternatives is now becoming severe. To coe with this subject, the develoment and roosition of long-life, steel-concrete comosite bridges, which utilized each merit from steel and concrete, is active. Furthermore, it is emhasized, for the design of comosite girder bridges, that the shift of design concet from ASD to LSD is imortant. Because, utilizing inelastic strength of the comosite girder contributes to enhance the cometitiveness. From this viewoint, the effort of LSD establishment for the design of comosite bridges carried out by our research grou is introduced. 2 DESIGN CODES FOR HIGHWAY AND RAILWAY BRIDGES Jaan Road Association is in charge of issuing Secifications for Highway Bridges (Jaan Road Association 2003). Photo 1 is the cover of it, which is 2003-version. The design of almost all highway bridges in Jaan follows it. The first version was issued in 1939, and modern style or format of it was established in

2 version. Since then, even though small revision was made, essential change has not been made. It is based on ASD and secification-based design, and it has been announced that LRFD format will be emloyed in the next version under revision. Railway bridges have been designed using Standard Secifications for Steel and Hybrid Railway Bridges (Railway Technical Research Institute 2008). Photo 2 is the cover of it. In 1992, the design concet 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 u to solve secific roblems, and design codes are comlied and constantly udated based on the latest research outcomes. JSCE design codes are not mandatory. They are rather model codes, but much more advanced than codes of ractice which tend to be conservative. In 2000, Committee on Steel Structures formed a secial subcommittee on erformance-based design to study this new design aroach in the field of steel structures. In 2003, the subcommittee ublished a reort entitled For Construction of Performance-based Design for Steel Structures (JSCE 2003). Following this achievement, Subcommittee on Standard Secifications for Steel and Comosite Structures was set u in The subcommittee consists of six task forces, each of which deals with a secific hase of construction. The standard secifications thus would be of six volumes: General Provisions, Structural Planning, Design, Seismic Design, Construction and Maintenance. Three books have been already ublished 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 exected to come out in The covers of the reort (JSCE 2003) and the books (JSCE 2007, 2008, 2009) above exlained 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 u constantly, the rearation for the revision of the ublished volumes is always underway. 3.2 Outline of the first book of JSCE Standard Secifications Volume of General Provisions gives the basis of the standard secifications for steel and comosite structures. It describes the design aroach, 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 lanning hase of design. Volume of Design resents secific design requirements for the steel and comosite structure. This is the erformance-based tye of design code. Hence, the code does not have the secific design rocedures/verification equations that designers must follow. All that code matters is that the structure will erform satisfactorily; the way to ensure the satisfactory erformance of the structure in the design hase is no concern of the code. For the sake of design convenience, however, the code rovides the verification equations as well that designers may use to verify the erformance of the structure. These are often called deem-to-satisfy design equations. The erformance requirements that Volume of Design has recognized are safety, serviceability, restorability, durability, social and environmental comatibility and constructability. In general, the satisfaction of the erformance requirements is to be verified referring to the associated limit state. However, it is not ossible to set u the limit state for all the erformance requirements. Some erformance items in the social and environmental comatibility, for examle, need to be treated as an otimization roblem instead. 3.3 Style of JSCE Standard Secifications Committee on Steel Structures ublished 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 equations are secified. Volume of Design (JSCE 2007) is actually the udate of the above code (JSCE 1997). However, no equations are given, and the difference between two codes is obvious. This is because in the erformance-based design, a designer can use any method of his/her choice to verify that the designed structure would satisfy the erformance requirements. 13

3 Photo 1. Secifications for Highway Bridges Photo 2. Standard Secifications for Steel and Hybrid Railway Bridges Photo 3. For Construction of Performance-based design for steel structures Photo JSCE Standard Secifications (General rovisions, Basic Plan and Design) Photo JSCE Standard Secifications (Seismic design) Photo JSCE Standard Secifications (Construction) 14

4 Photo 7. English version of Photo 8. JSCE Design Code 2007 JSCE Standard Secifications for Steel Structures PART A issued in 1997 While the erformance-based design thus gives designers greater freedom, it could be burden in some case to establish verification rocedure from scratch. Hence, Volume of Design (JSCE 2007) rovides the information on the deemed-to-satisfy design equations in the commentary, the utilization of which can ensure the satisfaction of the corresonding erformance requirements. Thus, even by the erformance-based design code, it would be ossible to follow the same design rocedure as that by a conventional secification-based design code. 3.4 Format of verification equations Standard Secifications for Steel and Comosite Structures (JSCE 2007) have emloyed the artial factor method on the basis of the reliability theory for the erformance verification. Thus, in rincile, the verification equations in the deem-to-satisfy aroach in the standard secifications take one of the following forms. S d γ i 1.0, (1) R d Σγ as( γ f Fk ) γ i 1.0, (2) R( fk / γ m) γ b where, R d = the design resistance, f k =the characteristic value of material strength, γ m = the material factor, γ b = the structural-member factor, R = the function to calculate limit value of structure from material strength, S d = the design resonse, F k = the characteristic value of action, γ a = the structural-analysis factor, γ f = the action factor corresonding to each action (load factor), S = the function to calculate resonse value of structure from action and γ i =the structural factor. In general, the values of the artial factors should be determined by the theoretical consideration couled with aroriate data. But the structural factor that deals with the imortance 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 exlained in Introduction, the develoment and roosition of steel-concrete hybrid (comosite 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 simlified transverse stiffening system, which are alternatives roosed by bridge engineers belonging to three comanies, East-, Centraland West-Nion Exressway Comany Ltd., former Jaan Highway Public Cororation. Among these, comosite or non-comosite twin-i-girder bridge has been evaluated to be the most cometitive alternative for bridges with a san from 40 to 60 meters. Figure 3 shows the total construction number and owners of these tyes of bridge. From this figure, it is seen that increase of I-girder bridges is rominent. Figure 4 is PC box girder bridges with steel corrugated web or steel ie truss web. When the san length less than 40 meters, and exceeds 60 or 70 meters, PC bridges are evaluated to be very cometitive. 15

5 In order to comete with long-san concrete bridges, steel bridge engineers are now roosing a doublecomosite girder bridge and cable-stayed comosite girder bridge shown in Figure 5, however, they have not been realized. In order to enhance the cometitiveness of steel-concrete hybrid bridges, not only inviting new structural system, such as double-comosite girder and so on but also it is strongly emhasized to emloy 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 imortance of shifting to LSD was emhasized in Chater 4. In order to establish LSD, the develoment or rearation of evaluating formulae of ultimate strength becomes very imortant. Herein, we introduce the exerimental research roject carried out in collaboration with Exressway Research Institute Ltd., Nagaoka University of Technology, Saitama University and Jaan Bridge Association. Figure 6 shows failure modes of comosite girders under ure flexure and shear, resectively. It is seen the crushing of the concrete slab and diagonal tension filed. Figure 7 also shows failure modes of doublecomosite girders under ure flexure and shear. In Chater 6, evaluating formulae are roosed. They are our original roosition and are derived based on nonlinear finite element analyses. The validity of them was confirmed through this extensive exerimental research results. Figure 1. Structural Innovation of I-girder bridges Figure 2. Structural Innovation of box girder bridges 16

6 (a) Construction number Figure 3. Newly develoed bridges (b) Owners (a) Steel corrugated web (b) Steel truss web Figure 4. PC box girder with steel corrugated web and ie truss web (a) Double comosite girder bridge Figure 5. Proosed long-san steel bridges (b) Cable-stayed comosite girder bridge (a) Under ure flexure Figure 6. Failure modes of comosite girders (b) Under shear 17

7 (a) Under ure flexure Figure 7. Failure modes of double-comosite girders (b) Under shear 6 EVALUATION OF ULTIMATE FLEXURE, SHEAR AND COUPLED STRENGTH OF COMPOSITE AND DOUBLE-COMPOSITE GIRDERS 6.1 Flexure strength of comosite girder under sagging bending moment The section is classified into comact when the web thickness (t w ) satisfies Equation 3 given below, and the strength is defined to be lastic moment (M ). 2Dc E 4.0 (3) t f ( or f ) w y yw At the actual design stage, ultimate flexure strength (M ult ) of comosite girder under the sagging bending moment is defined to be smaller value of βm or 1.3M y (AASHTO 2005). ult { M,1. M } M = min β 3 (4) Where, β is given by the following Equation 5. y β = 1.0 β = ( D / D t ) D / D 0.15 D t 0.5 / D t 0.4 (5a-b) β (=1.0) is given to take into account of ductility condition. If the distance (D ) from the concrete deck to to lastic neutral axis becomes relatively large comared to the total girder height (D t ), the concrete crushing is redicted to occur before reaching lastic moment. β is to take into account of this henomenon. Figure 8 shows the stress state at ultimate state, in which lastic neutral axis is calculated under the condition that the axial force of the section is zero, and M is the moment with resect to the neutral axis. The notations of D c, D t, D, f y and f yw are also indicated in the figure, and E is Young s modulus of elasticity. In case that the section at intermediate suorts is classified into slender (M ult = M y ), the maximum ultimate flexure strength is limited less than 1.3M y (AASHTO 2005) (0.9M is defined in Eurocode 4 (CEN 2004)). Hence, βm and 1.3M y are comared, and the smaller strength is selected as the ultimate flexure strength of the comosite section under the sagging bending moment. In a twin-i-girder bridge, almost all cases, the lastic neutral axis of the section is located within the concrete slab (D c =0). Hence, the section is classified into comact, and the ultimate flexure strength is lastic moment. Furthermore, D (=D c ) is small comared to the total height of the girder (D t ). It means that β can be left at

8 Figure 8. Stress in comosite cross section at ultimate state under sagging bending moment 6.2 Flexure strength of comosite girder under hogging bending moment At intermediate suorts, where the comosite 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. Normally, the dead load from steel and concrete slab is carried by steel girder only, and the suerimosed dead load and live load are carried by the comosite section consisted of steel section lus reinforcing bars. This means two different sections comrises the resisting ones. They are steel girder only and steel girder lus reinforcing 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 resisting section. In the figure, f cr,f is the strength of the lower flange under comression and f cr,w is the flexure strength of the web ( Fukumoto. Y. (ed.) 1997). f t 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 f R 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 19

9 6.3 Flexure strength of double-comosite girder under hogging bending moment The flexure strength is given by M = β ( D / D ) M (6) ult t Since the concrete is attached to the web through lying studs as shown in Figure 10, the section is exected to be classified into comact. In the actual case, the concrete slab has to be arranged that the ratio of (D c /t w ) satisfies Equation Flexure strength of steel girders under construction From Figure 9, flexure strength of steel girder is calculated. f cr,f and f cr,w in the figure are the same as those defined in 6-2. f t is also given from the condition that the axial force in the girder is zero. 6.5 Shear strength of comosite girders The shear strength Q ult is assessed using formula roosed by Basler (Basler, K. 1961). It is derived for the steel girder only and is the sum of elastic buckling strength and ost buckling strength. In case of comosite girders, due to the contribution obtained from concrete slab, the strength is exected to increase. However, an exact identification of contribution of the slab to strength is difficult. Hence, from a conservative viewoint, its effect is neglected. Figure 10. Double-comosite section for flexure strength under hogging bending moment 6.6 Shear strength of double-comosite girders As shown in Figure 11, the web height is divided into h w1 and h w2 in order to evaluate the shear strength of the double-comosite girder. The shear strength of the steel art with the deth of h w1 is assessed by Basler s formula and the strength of the steel art with the deth of h w2 is assessed as τ y h w2 t w. Where, τ y is the shear yield stress. The sum of the both strength is the shear strength of the double-comosite girders. 6.7 Couled flexure and shear strength of steel and comosite girders Because the couling effect of flexure and shear is comaratively small, it is neglected in case of comosite girders. However, in case of steel girder, the following formula is used. M M 4 + Q ult Q ult (7) 20

10 where, M and Q are actions under factored load. M ult and Q ult are flexure strength and shear strength defined above, resectively. Figure 11. Double-comosite section for shear strength 7 CONCLUDING REMARKS The design code of Standard Secifications for Highway Bridges issued from Jaan Road Association and Standard Secifications for Steel and Hybrid Railway Bridges are introduced. Most of highway and railway steel and comosite bridges in Jaan have been designed according to them, secification-based design. The overview of some efforts of JSCE in the field of steel and comosite structures is resented, laying emhasis on the design codes, which is the first time erformance-based design in civil steel structural engineering. The current trend on steel and comosite bridge construction is introduced. In order to enhance the cometitiveness of comosite bridges, the shift of design from current ASD to LSD is emhasized. In this connection, cometitive formulae for evaluating ultimate flexure, shear and couled strength of comosite and double-comosite girders are roosed. They are based on finite element analyses, and the validity of them is examined through exerimental research roject carried out in collaboration of 4 organizations. REFERENCE AASHTO LRFD bridge design secifications interim revisions -. Washington, D.C.: AASHTO. Basler, K Strength of late girders in shear. Journal of Structural Division, ASCE, Vol.86 No.ST7: CEN, Euroean committee for standardization Eurocode 4, design of comosite steel and concrete structures, Part2, General rules and rules for bridges. Brussels: CEN. Fukumoto. Y. (ed.) Structural stability design - Steel and Comosite Structures -. Elsevier Science. JSCE, Committee on Steel Structures Design code for steel structures Part A; structures in general. Tokyo: JSCE. Jaan Road Association Secifications for Highway Bridges, Part-2 Steel Bridges (in Jaanese). Tokyo: Maruzen Publication. JSCE, Committee on Steel Structures For construction of erformance-based design for steel structures. Tokyo: JSCE. JSCE, Committee on Steel Structures Standard Secifications for Steel and Comosite Structures - I General rinciles, II Structural lanning, III Design -. Tokyo: JSCE. JSCE, Committee on Steel Structures Standard Secifications for Steel and Comosite Structures IV Seismic design -. Tokyo: JSCE. JSCE, Committee on Steel Structures Standard Secifications for Steel and Comosite Structures V Construction -. Tokyo: JSCE. JSCE, Committee on Steel Structures Standard Secifications for Steel and Comosite Structures (English version). Tokyo: JSCE. Railway Technical Research Institute Design Standards for Railway Structures and Commentary (Steel-Concrete Hybrid Structures). Tokyo: Maruzen Publication. 21