VARIATION OF JOINT FORCES IN STEEL TRUSS BRIDGESUPERVISOR STUDENTDr. Kyaw Kyaw Ma Su Wit Yi MonDepartment of Civil Engineering Roll No. C-34 (M.E. Thesis)
Objectives of the Study To know the components of steel truss bridge. To know how to design a superstructure of steel truss bridge. To understand the concepts of the influence line analysis of steel truss bridge with the application of STAAD-Pro structural software. To study about the variation of joint forces in steel truss bridge. To safe the failures because of the effects such as seismic, wind, traffic loads, and so on.
Scope of the Study Only superstructure of steel truss bridge will be designed. In this study, American Association of State Highway and Transportation Officials (AASHTO) will be used. The live load is chosen HS 20-24 for six lanes. The structure will be analyzed by using STAAD-Pro structural software and study for joints design and preliminary design. Parallel Chord Warren truss will be designed. The bridge type is simple span truss bridge.
Implementation Programs Study on theoretical background for steel truss bridge. Study on configuration of proposed bridge. Study on preparation for analysis of bridge. Study on modeling analysis of bridge using STAAD-Pro structural software. Study on joints design of steel truss bridge. Discussions, conclusions and recommendation for the study of variation of joints forces for steel truss bridge.
Applicable span of Truss BridgeTruss brides are generally applied within the following range.1. Simple truss bridge is in the range of 55 meter to 85 meter span.2. Continuous truss bridge is in the range of 60 meter to 300 meter span.3. Cantilever truss bridge is in the range of 300 meter to 510 meter span (in Japan, only one bridge has longer span than 200 meter, and that is Minato Ohashi, with 510 meter span. Among the 3 types of bridges, the simple truss bridgeor the continuous truss bridge, either with approximate 60meter to 100 meter span is usually applied.
Characteristics of Truss Bridge1. Truss which is a frame structure composed of straight members is built by connecting the members with pins or by a member analytically regarded as connected with pins.2. As load is regarded to work on the panel point only, no bending moment and shear forces but only axial force works to the members composing the truss.3. Due to problems of wearing of pins and gathering rust, gusset plates are mostly used to connect the members by use of high-tension bolts.4. Bending moment occurs in the members and the secondary stress is expected to arise due to bending.5. However in case of ordinary truss bridge, influence of the secondary stress can be ignored.
Advantages of Truss BridgeMountain Region1. When the members are difficult to be transported to the site and when the conditions of construction is restricted.2. When a bridge in a curve alignment is required, a horizontal bent continuous bridge or a deck truss bridge with brackets can selected.Open Field Region1. Assurance of space below the bridge soffit due to adoption of through bridge2. Long span bridge over the mouth of a river or the coast.3. Double-deck bridge having upper and lower 2-layer road surface.
Disadvantages of Truss Bridge1. As it is composed by many members, maintenance requirements such as repainting is needed.2. The sight view from the driver in case of through bridges.
Over all height of trussand length between panels1. For simple truss, the truss height is 1/7-1/8 time the span length and the length between panels is 1/6-1/8 time the span length.2. For continuous truss, the truss height is 1/9- 1/10 time the span length and the length between panels is 1/8- 1/10 time the span length
Components of Superstructure of a Steel Truss Bridge 1. Upper Chord 2. Lower Chord 3. Upper Lateral Bracing 4. Lower Lateral Bracing 5. Portal Bracing 6. End Post 7. Bearing 8. Diagonal Member 9. Vertical Member 10. Floor Beams 11. Stringers 12. Sway Bracing 13. Upper Lateral Strut 14. Sway Strut 15. Gusset