Page:Interregional Highways.pdf/208

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Each lane loading shall consist of a uniform load per linear foot of traffic lane combined with a single concentrated load so placed on the span as to produce maximum stress. The concentrated load shall be considered as uniformly distributed across the lane on a line normal to the center line of the lane. For the computation of moments and shears, different concentrated loads shall be used as indicated in figures 2 and 4. The lighter concentrated loads shall be used when the stresses are primarily bending stresses and the heavier concentrated loads shall be used when the stresses are primarily shearing stresses.

Application of loadings.—In computing stresses, each 10-foot traffic lane loading or a single standard truck per lane shall be considered as a unit. The number and position of loaded lanes, and the type of loading—truck loading or lane loading—shall be such as to produce a maximum stress subject to reductions specified under the head “Reduction in load intensity.” Fractional lane widths are not to be considered. The H-S lane loading shall be used for loaded lengths over 40 feet, and the H-S truck loading for loaded lengths of 40 feet or less. For H loading, either the lane loading or the truck loading shall be used, depending upon which gives the larger stress.

On any series of continuous spans, discontinuous lengths of lane loading shall be used where necessary for maximum stress, but only one concentrated load shall be used.

Reduction in load intensity.—Where maximum stresses are produced in any member by loading any number of traffic lanes simultaneously, the following percentages of the resultant live load stresses shall be used in view of improbable coincident maximum loading:

The position and number of loaded lanes used shall be such as to produce maximum stresses in all cases.

The reduction in intensity of floor-beam loads shall be determined as in the case of main trusses or girders, using the width of roadway which must be loaded to produce maximum stresses in the floor beam.