[雙語翻譯]--橋梁外文翻譯--單跨預應力橋梁鋼結構設計與比較（原文）

1、Single-Span Prestressed Girder Bridge: LRFD Design and ComparisonRichard J. Nielsen, M.ASCE,1 and Edwin R. Schmeckpeper, M.ASCE2Abstract: This report summarizes the comparative design of a single-span AASHTO Type III gir

2、der bridge under the AASHTO Standard Specification for Highway Bridges, 16th Edition, and the AASHTO LRFD Bridge Design Specification. The writers address the differences in design philosophy, calculation procedures, and

3、 the resulting design. Foundation design and related geotechnical considerations are not considered. The LRFD design was similar in most respects to the Standard Specification design. The significant differences were: ?1

4、? increased shear reinforcement; ?2? increased reinforcement in the deck overhang; and ?3? increased reinforcement in the wing wall. The comparisons would likely change if the bridge were designed purely according to LRF

5、D Specifications rather than as a comparative design. Design procedures under the LRFD Specification tend to be more calculation-intensive. However, the added complexity of the LRFD Specification is counterbalanced by th

6、e consistency of the design philosophy and its ability to consider a variety of bridges.DOI: 10.1061/?ASCE?1084-0702?2002?7:1?22?CE Database keywords: Bridges, girder; Load and resistance factor design; Prestressing; Bri

7、dges, spans.IntroductionUntil the mid-1990s, the design of bridges in the United States was governed by the AASHTO Standard Specification for High- way Bridges, 16th Edition ?Standard Specification? ?AASHTO 1996?. The in

8、troduction of the AASHTO LRFD Bridge Design Specification ?LRFD Specification? in 1994 along with a second edition in 1998 provided a new standard for bridge design that addressed several of the perceived problems in the

9、 Standard Specification ?AASHTO 1994a, 1998?. As stated in the foreword of the LRFD Specification, the first area of concern was the ‘‘dis- cernable gaps, inconsistencies, and even some conflicts’’ that had existed in th

10、e Standard Specification as a result of its evolution over decades ?AASHTO 1994b?. The second concern was the desire to ‘‘incorporate the most recently developing design phi- losophy, load and resistance factor design’’

11、?AASHTO 1994b?. It is also evident that the writers of the LRFD Specification at- tempted to include more up-to-date research along with the LRFD design philosophy. The change in design philosophy and the incorporation o

12、f newer analytical methodologies resulted in a design procedure that is significantly different from the earlier procedure. However, the new code was intentionally calibrated to produce designs that are similar to those

13、produced by the Standard Specification, with some exceptions as suggested by more current research ?AASHTO 1994b?. Asward and Jacques ?1992? performed a para-metric study of the impacts of the change from Standard Specif

14、i- cation to LRFD Specification designs. The changes in design methodology are significant and repre- sent a significant challenge to engineers accustomed to working with the Standard Specification. In an effort to lead

15、a transition to the newer code, the Idaho Transportation Department ?ITD? had the first writer check the Standard Specification design of the single-span prestressed concrete girder bridge shown in Figs. 1 and 2 and then

16、 redesign that bridge using the LRFD Specification including the 1997 interim revisions ?AASHTO 1994b?. This paper summarizes the significant changes in the design procedures by the LRFD Specification and compares the re

17、sults with the Standard Specification. However, the conclusions given in this report should be considered in light of the scope of work. First, the design experience is limited to a single span AASHTO Type III girder bri

18、dge; these conclusions do not necessarily apply to multispan or steel girder bridges. Second, some design param- eters were selected to facilitate comparison between the Standard Specification and LRFD design. A design b

19、ased solely on LRFD considerations might be somewhat different. For example, the deck overhang and girder spacing were the same in the Standard Specification and LRFD designs. If direct comparisons were not needed, it mi

20、ght be advantageous to reduce the overhangs for the LRFD design and adjust the resulting girder spacings. The comparisons are presented in the order they were encoun- tered in the design: general design considerations, f

21、ollowed by flexural design of the girder, shear design of the girder, deck design, and abutment design. Foundation design and related geo- technical considerations are not included in this paper.General Design Considerat

22、ionsThe LRFD design philosophy provides a common framework for the design of structures made of steel, concrete, and other mate- rials. However, the flexibility of this approach also increases the complexity of the proce

23、ss.1Associate Professor, Dept. of Civil Engineering, Univ. of Idaho, Moscow, ID 83844-1022. 2Associate Professor, Dept. of Civil Engineering, Univ. of Idaho, Moscow, ID 83844-1022. Note. Discussion open until June 1, 200

24、2. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for rev

25、iew and possible publication on February 22, 2000; approved on February 22, 2001. This paper is part of the Journal of Bridge Engineering, Vol. 7, No. 1, Janu- ary 1, 2002. ©ASCE, ISSN 1084-0702/2002/1-22–30/$8.00?$

26、.50 per page.22 / JOURNAL OF BRIDGE ENGINEERING / JANUARY/FEBRUARY 2002J. Bridge Eng., 2002, 7(1): 22-30 Downloaded from ascelibrary.org by Jilin University on 08/25/16. Copyright ASCE. For personal use only; all rights

27、reserved.This approach avoids introducing inconsistencies in the LRFD philosophy.TerminologyAnalysis of the collision case described below led to an exami- nation of the terminology used in the LRFD Specification. The LR

28、FD Specification uses the word ‘‘extreme’’ to describe two different items. Article 3.4.1 refers to ‘‘Extreme Events,’’ i.e., extreme loading events ?AASHTO 1998?. For example, ‘‘Extreme Event II’’ is a loading event tha

29、t includes ‘‘collision by vehicles.’’ On the other hand, Article 3.6.1.3.1 refers to ‘‘extreme force effects.’’ A careful reading of this article indicates that the discus- sion of ‘‘extreme force effects’’ refers to the

30、 arrangement of loads to produce the maximum or minimum ?i.e., extreme? moment or shear ?AASHTO 1998?. Thus, the discussion of ‘‘the possibility that vehicles can mount the sidewalk’’ in the last paragraph of Article C3.

31、6.1.3.1 refers to the positioning of the load to obtain the maximum force effect. It does not necessarily imply that the placement of the vehicle on the curb or sidewalk is an extreme loading event per Article 3.4.1 ?AAS

32、HTO 1998?. Thus, it is up to the engineer’s judgment to decide whether the placement of the load on the curb or sidewalk should be included in Extreme Event II ?Article 3.4.1? or whether it should be in- cluded in the se

33、rvice and strength limit states ?e.g., Service I, Service III, or Strength I?. Inclusion in Extreme Event II is ap- propriate if the recurrence interval associated with the event ‘‘is thought to exceed the design life’’

34、?Article C3.4.1; AASHTO 1998?. Inclusion in Service I, Service III, or Strength I is appro- priate if the load event occurs more frequently; i.e., it has a re- currence interval less than the service life of the structur

35、e.Girder DesignCompared with the Standard Specification, the LRFD Specifica- tion makes several significant changes in the way the dead and live loads are distributed to the bridge girders.Permanent Deck LoadsLRFD Specif

36、ication Article 4.6.2.2.1 states that ‘‘where bridges meet the conditions specified herein, permanent loads of and on the deck may be distributed uniformly among the beams and/orstringers’’ ?AASHTO 1998; emphasis added?.

37、 This is a substantial change from the Standard Specification design practice in con- junction with ITD standard design practice, both of which dictate that railings, parapets, and sidewalk dead loads are applied only to

38、 the exterior girders, and deck self-weight is distributed in pro- portion to the tributary width ?ITD 1994?. The LRFD approach is reasonable for railings and sidewalks that are installed after the deck is in place and c

39、an distribute loads from the exterior to the interior girders. Although permitted, this approach may not be reasonable for the diaphragms and the deck itself. Before the deck concrete is set, the concrete is in the plast

40、ic state and it cannot distribute these loads to the interior girders. For this reason, these loads were not distributed between the in- terior and exterior girders in the LRFD design of the example bridge. A comparison

41、on the dead loads for the Standard Specification design and the LRFD design is shown in Table 1. The values in this table assume that the diaphragm weight is replaced by a uniform load, and that the stay-in-place forms a

42、re metallic, having an equivalent load of 960 Pa ?20 psf?. These results indicate that, compared with the Standard Specification design, the LRFD de- sign increases the noncomposite dead load on the exterior girder by 9%

43、, and decreases the noncomposite dead load on the interior girder by 4%. Also, the LRFD design decreases the composite dead load on the exterior girder by 50% and increases the com- posite dead load on the interior girde

44、r by 97%. Although some of these individual changes are significant, they represent a small portion of the total load, and they do not change the final design.Vehicular Live LoadFor the Standard Specification design, the

45、 bridge was to carry an HS-25 loading, which is 125% of the AASHTO HS-20 truck con- sisting of a 440.5 kN ?45-ton? design truck or a design lane load comprised of a 11.7 kN/m ?800 lb/ft? distributed load plus a 100 kN ?2

46、2.5 kip? or 145 kN ?32.5 kip? point load for the flexure or shear design cases, respectively ?Fig. 3?. For the LRFD Specifi- cation design, the bridge was to carry an HL-93 load, which con- sists of a 325 kN ?36 ton? des

47、ign truck or design tandem and a 9.3 kN/m ?640 lb/ft? design lane load ?Fig. 4?. Furthermore, the HL-93 design lane load is not interrupted for the design truck or design tandem. Interruption is needed only where pattern

48、 loadings are used to produce maximum load effects. For bridges of thisTable 1. Dead Load ComparisonLoad type SectionExterior girder Interior girderStandard Specification LRFD Standard Specification LRFDNoncomposite dead

49、 load, kN/m ?kip/ft? Deck 13.5a ?0.925a? 14.0 ?0.958? 14.2a ?0.975a? 14.0 ?0.958?Camber strip 0.12a ?0.008a? 0.12 ?0.008? 0.12a ?0.008a? 0.12 ?0.008?Diaphragm 0.19a ?0.013a? 0.19a ?0.013a? 0.38a ?0.026a? 0.38a ?0.026a?St

50、ay-in-placeforms1.2a ?0.084a? 2.0 ?0.140? 2.45a?0.168a? 2.0 ?0.140?Total 15.0 ?1.030? 16.33 ?1.119? 17.18 ?1.177? 16.52 ?1.132?Composite dead load kN/m ?kip/ft? Sidewalk 7.39a ?0.506a? 2.47 ?0.169? 0.000a 2.47 ?0.169?Rai

51、l 3.93a ?0.269a? 1.31 ?0.090? 0.000a 1.31 ?0.090?Futurewearingsurface1.12a ?0.077a? 2.38 ?0.163? 3.12a ?0.214a? 2.38 ?0.163?Total 12.4 ?0.852? 6.16 ?0.422? 3.12 ?0.214? 6.16 ?0.422?aItems not distributed uniformly betwee

52、n girders.24 / JOURNAL OF BRIDGE ENGINEERING / JANUARY/FEBRUARY 2002J. Bridge Eng., 2002, 7(1): 22-30 Downloaded from ascelibrary.org by Jilin University on 08/25/16. Copyright ASCE. For personal use only; all rights res