Load Distribution in Highway Bridge Decks

A general method is presented for computing the distribution of longitudinal moments, deflections, and similar quantities in bridge decks. This method is based on the assumption that the discrete girders of the transverse system can be replaced by a uniformly spread material having the same total flexural rigidity as the original structure. Distribution coefficients are derived for each harmonic of the total bending moment or deflection curve for the span. The derivation of these coefficients is illustrated for the general case of beams with arbitrary torsional rigidity. In design work, however, it is sufficiently accurate to interpolate between zero torsional rigidity and infinite torsional rigidity by the use of a suitable interpolation function. It is shown that a bridge having a large number of longitudinals can be replaced by an equivalent five-girder structure for the purpose of deter mining its deflected cross section and, thence, distribution coefficients for its longitudinals. Graphs of the distribution coefficients for a five-girder bridge are included herein.

The application of this method to slabs is considered. In this case it is necessary to derive coefficients for a system in which the ends of the longitudinals remain upright. Again, the general solution for arbitrary torsional rigidity is demonstrated. but, as in the previous case, it is possible in design computations to interpolate between zero torsion al rigidity and infinite torsional rigidity. Numerical examples showing the method of computation are included, and comparisons between theoretical and experimental results are made for a steel-and-concrete T-beam, a steel beam and jack arch, a beam and slab, a filler joist bridge deck, and a reinforced concrete slab.