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Structure Steel Design's Handbook 2009 part 15

Tham khảo tài liệu 'structure steel design's handbook 2009 part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | SECTION 12_ BEAM AND GIRDER BRIDGES Alfred Hedefine P.E. Former President Parsons Brinckerhoff Quade Douglas Inc. New York NY John Swindlehurst P.E. Former Senior Professional Associate Parsons Brinckerhoff Quade Douglas Inc. Newark N.J. Mahir Sen P.E. Professional Associate Parsons Brinckerhoff-FG Inc. Princeton N.J. Steel beam and girder bridges are often the most economical type of framing. Contemporary capabilities for extending beam construction to longer and longer spans safely and economically can be traced to the introduction of steel and the availability in the early part of the twentieth century of standardized rolled beams. By the late thirties after wide-flange shapes became generally available highway stringer bridges were erected with simply supported wide-flange beams on spans up to about 110 ft. Riveted plate girders were used for highwaybridge spans up to about 150 ft. In the fifties girder spans were extended to 300 ft by taking advantage of welding continuity and composite construction. And in the sixties spans two and three times as long became economically feasible with the use of high-strength steels and box girders or orthotropic-plate construction or stayed girders. Thus now engineers as a matter of common practice design girder bridges for medium and long spans as well as for short spans. 12.1 CHARACTERISTICS OF BEAM BRIDGES Rolled wide-flange shapes generally are the most economical type of construction for shortspan bridges. The beams usually are used as stringers set at regular intervals parallel to the direction of traffic between piers or abutments Fig. 12.1 . A concrete deck cast on the top flange provides lateral support against buckling. Diaphragms between the beams offer additional bracing and also distribute loads laterally to the beams before the concrete deck has cured. 12.1 12.2 SECTION TWELVE FIGURE 12.1 Two-lane highway bridge with rolled-beam stringers. a Framing plan. b Typical cross section. Spacing. For