Section 14: Curved Plate Girders

Materials

Use A 709 Grade 50W steel for unpainted bridges. Use A 709 Grade 50 steel for painted bridges. Use A 709 Grade HPS 70W steel for unpainted and 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.

Geometric Constraints

Minimum flange width is 0.25
D
, 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.
Satisfy the span-to-depth ratios in Article 2.5.2.6.3 as a minimum, unless vertical clearance constraints demand a shallower superstructure.

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-laneloaded 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.

Design Criteria

Girder designs must meet the following requirements :
  • Specify fit condition in the plans when necessary as recommended in Article 6.7.2, and specify steel dead load fit (SDLF) where possible.
  • 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 primary member criteria provided in Articles 6.8.4 and 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. When calculating stresses in structural steel for composite sections in negative bending for the Service II Limit state, only include the concrete deck in the section properties if tensile stress in the deck is less than 2fr per Article 6.10.4.2.1.
  • 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.
  • Investigate a possible erection sequence during design and verify possible locations of shore towers and cranes. Consider traffic phasing with underlying roadways when considering locations of shore towers and cranes. Do not include detailed erection plans in plan set.
  • Specify continuous placement of bridge deck where possible, and staged placement only if required. Do not disallow continuous placement solely based on whether a continuous pour may be unfeasible for a contractor. 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 staged placement if staged placement is the only placement option. If both staged and continuous placement are given as options, base dead load deflection and camber on continuous placement as long as there is no significant difference in final camber and deflection between the two methods. State in the plans which placement option is assumed for the dead load deflection and camber. Provide a staged placement diagram indicating the intended pour sequence in the design if staged placement is specified. In the plans state that for continuous placement, the minimum rate of placing and finishing shall not be less than that specified in Item 422. For stud connector designs, minimum longitudinal stud connector spacing is limited to 4
    d
    , where d is the stud connector diameter. Do not exceed a stud connector spacing of 24 in. regardless of girder depth.
  • For dapped girder ends, utilize Article D6.5.2 to avoid the use of additional stiffeners at dap bend points per Article 6.10.1.4.
  • In lieu of permanent bottom flange lateral bracing, increase bottom flange size if practical. If considering the use of bottom flange lateral bracing, contact TxDOT Bridge Design Section for approval.
Provide bolted field splices as the primary method of field splicing in the plans. Include the weight of the splice plates in the steel weight for payment. 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 6.13.6.1.4-1.