Structural Analysis

Girder designs should meet the following requirements:
  • Base the self-weight of the girder on a minimum of 160 pcf.
  • For I-Sections: Distribute the weight of one railing to no more than three girders, applied to the composite cross section.
  • For U-Sections: Distribute 2/3 of the rail dead load to the exterior beam and 1/3 of the rail dead load to the adjacent interior beam applied to the composite cross section.
  • Haunch concrete placed on top of the girder may be considered when determining composite section properties.
  • Composite section properties can be calculated assuming either constant modulus of elasticity for the girders and slab, or transforming the sections based upon their respective modulus.
  • Live load distribution can be determined from one of the following methods:
    • Must conform to Article 4.6.2.2.2 for flexure moment and Article 4.6.2.2.3 for shear when used in conjunction with a line girder analysis;
    • As determined by use of the lever rule when the span/girder arrangement is out of the applicable range of Articles 4.6.2.2.2 and 4.6.2.2.3 when used in conjunction with a line girder analysis; or
    • As distributed by the model when used in conjunction with a grillage, finite element, or other refined model. The model must capture the effects of the complete unit and transfer loads in an acceptable fashion.
  • The live load used to design the exterior beam must never be less than the live load used to design an interior beam of comparable length.
  • Do not take the live load distribution factor for moment or shear as less than the number of lanes divided by the number of girders, including the multiple presence factor per Article 3.6.1.1.2.
  • Do not use the special analysis based on conventional approximation for loads on piles per Article C4.6.2.2.2d, unless the effectiveness of diaphragms on the lateral distribution of truck loads is investigated.
  • When prestressed concrete deck panels or stay-in-place metal forms are allowed, design the girder using the basic slab thickness.
Analysis must consider the effects of the following:
  • Staged construction
  • Addition and removal of temporary supports
  • Locked in forces
  • Staged post tensioning
  • Secondary forces due to post tensioning
  • Torsion due to horizontally curved alignments
  • Superstructure / Substructure interaction
  • Temperature variation