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Section 15: Curved Plate Girders

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Materials

Use A 709 Grade 50W or HPS 70W steel for unpainted bridges. Use A 709 Grade 50 steel for painted bridges. Use A 709 Grade HPS 70W steel for painted bridges if it is economical or otherwise beneficial to do so.

Use 0.875-in. or 1-in. diameter bolts for bolted connections.

For bridges in the Amarillo District only, specify tension components to meet Zone 2 tension component impact test requirements.

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Geometric Constraints

Minimum flange width is 0.25D, where D=web depth, but not less than 15 in.

Minimum flange thickness is 1 in.

Minimum web thickness is 0.50 in.

Minimum stiffener thickness used to connect cross frames or diaphragms to girder is 0.50 in.

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Structural Analysis

Girder designs must meet the following requirements:

  • Distribute the weight of one railing to no more than three girders, applied to the composite cross section.
  • Assume no slab haunch when determining composite section properties.
  • A grid analysis or other refined analysis is required for curved girders. Curved girders satisfying Article 4.6.1.2.4b are excluded from this requirement. Use a single-lane-loaded multiple presence factor of 1.0.
  • Use only one lane of live load in the structure model when checking the Fatigue and Fracture Limit State.
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Design Criteria

Girder designs must meet the following requirements:

  • Regarding Article 6.7.2, do not specify girders to be out-of-plumb in the steel-dead-load-only or theoretical-no-load condition if field-welded diaphragm/cross-frame connections are used. Diaphragms and cross-frames have traditionally been field-welded to plumb girders without problems to date. If diaphragms/cross-frames are to be field-bolted to the girder, consult with a steel bridge girder fabricator on an appropriate load condition for detailing cross-frame/diaphragm fit. If analysis indicates that girders will be significantly beyond plumb after slab concrete is placed, contact the Director of the Bridge Division for guidance.
  • Diaphragm and cross-frame designs must meet the following requirements:
    • The maximum spacing is 20 ft. with curved girders if all limit states requirements are met.
    • Provide diaphragms/cross-frames at all end bearings.
    • Place interior diaphragms/cross-frames radial to girders. Do not use staggered placement of diaphragms/cross frames.
  • Check the limiting slenderness ratio of cross-frame members using main compression member criteria provided in Article 6.9.3.
  • Diaphragm and cross-frame members are primary members. Verify their adequacy for the Strength Limit State and other applicable limit states.

Girder designs must meet the following requirements:

  • Use composite design and place shear connectors the full girder length.
  • Do not use longitudinal stiffeners unless web depth exceeds 120 in.
  • Use short-term modular ratio equal to 8 and long-term modular ratio equal to 24.
  • Provide longitudinal slab reinforcement in accordance with Article 6.10.1.7.
  • Assume the composite slab is effective in negative bending regions for Deflection check, Fatigue and Fracture Limit State, and Service Limit State.
  • At flange splices, extend thicker flanges beyond the theoretical flange splice location by a length equal to the flange width but not more than 2 ft.
  • Include an assumed stay-in-place formwork weight of 15 psf in design.
  • Specify continuous placement of bridge deck where possible, and staged placement only if required. If staged placement is specified, base girder design on the worst case effect of staged and continuous placement. Base dead load deflection and camber on an analysis for continuous placement, even if staged placement is specified in the plans.
  • For stud connector designs, minimum longitudinal stud connector spacing is limited to 4d, where d is the stud connector diameter.

Bolted field splices must meet the following requirements:

  • Use ASTM F3125 Grade A325 bolts. Use galvanized Grade A325 bolts for painted structures. Use Grade A490 bolts only if the connection cannot be designed with A325 bolts. Do not specify galvanized Grade A490 bolts for any structure.
  • Assume Class A surface conditions. Class B surface conditions may be used only when slip controls the number of required bolts. Always note the surface condition assumed for design in the plans.
  • Add at least 0.125 in., and preferably 0.25 in., to minimum edge distances shown in Table 6.13.2.6.6-1.
  • Do not extend and develop fill plates equal to or thicker than 0.25 in. Instead, reduce bolt shear strength with Equation 6.13.6.1.5-1.

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