ACI 342R-16 Report on Flexural Live Load Distribution Methods for Evaluating Exisiting Bridges.
3.5.1 Limitations—AASHTO (2014) is not applicable to every type and size of bridge. There are ranges of applica- bility in the specifcation to preserve the bridge’s integrity and calibrated reliability index. There are several general conditions for using the load distribution provisions that are applicable to all bridges: a) The bridge deck width cannot vary along its length. An example of the deck varying along the length would be if the bridge has two lanes in each direction with an exit lane at the end of the bridge. This bridge would be wider at the end and be designed using more refned methods such as fnite element or fnite strip grillage. The engineer can also use average beam spacing or maximum beam spacing for bridges with varying width. b) The bridge cross section, unless otherwise specifed, must have at least four beams or girders to support the bridge deck. Figure 3.5.1a shows an example bridge cross section. This cross section can have any type of girders: bulb-T, boxes, or I-beams. I-beams are shown as an example. There are a few exceptions to this where the minimum number is three, and these exceptions appear within the ranges of applicability for the relevant bridge types (refer to Table in AASHTO [2014]). c) The spacing between parallel bridge beams or girders must remain constant throughout the length of the span and have approximately the same stiffness EI.
3.6—Canadian Highway Bridge Design Code CAN/CSA-S6 specifes analysis requirements for many bridge superstructure types. For short- and medium-span concrete bridges, these superstructure types include slab and voided slab bridges, slab-on-girder bridges, arch bridges, rigid frames with integral abutments bridges, and box girder bridges. For each bridge type, CAN/CSA-S6 specifes the appro- priate structural response parameters to consider in design. These response parameters are longitudinal moment, trans- verse moment, longitudinal torsion, longitudinal vertical shear, transverse vertical shear, and in-plane forces. The clauses within CAN/CSA-S6 provide further guidance on additional factors such as cross bracing or variation of cross section, which can be incorporated in the modeling and analysis. CAN/CSA-S6 also permits refned methods and simplifed methods to determine the structural response to both dead and live loads. The refned methods of analysis include grillage analogy, orthotropic plate theory, fnite element, fnite strip, folded plate, and semi-continuum. CAN/CSA-S6 provides further guidance with respect to refned methods appropriate to particular superstructure types and formula for determining key geometric and material parameters for the various methods of analysis.ACI 342R pdf download.