Interregional Highways/Appendix 6
APPENDIX VI
Standard Design Loadings for Highway Bridges
As Specified by the American Association of State Highway Officials, 1941
Highway loadings.—The highway live loadings on the roadway of bridges or incidental structures shall consist of standard trucks or of lane loads which are equivalent to truck trains. Two systems of loading are provided, the H loadings and the H-S loadings, the corresponding H-S loadings being heavier than the H loadings.
The H loadings are illustrated in figures 1 and 2 of this appendix. They consist of a four-wheel truck or the corresponding lane loading. The H loadings are designated H followed by a number indicating the gross weight in tons of the standard truck.
The H-S loadings are illustrated in figures 3 and 4 of this appendix. They consist of a tractor-truck with semitrailer or the corresponding lane loading. The H-S loadings are designated by the letter H followed by a number indicating the oss weight in tons of the tractor-truck and the letter S followed by the gross weight in tons of the single axle of the semitrailer. The H-S lane loading shall be used for loaded lengths greater than 40 feet. The H-S truck loading shall be used for loaded lengths of 40 feet or less.
The H-S loading is optional under these specifications and shall not be construed as a requirement thereof.
Highway loadings shall be of five classes: H20, H15, H10, H20-S16, and H15-S12. Loadings H15 and H10 are 75 percent and 50 percent, respectively, of loading H20. Loading H15-S12 is 75 percent of loading H20-S16. If loadings of weights other than those designated are desired, they shall be obtained by proportionately changing the weights shown for both the standard truck and the corresponding lane loads and maintaining the axle spacing constant. Truck loads for one classification and lane loads for another classification shall not be used in combination.
Traffic lanes.—The lane loadings or standard trucks shall be assumed to occupy traffic lanes, each having a width of 10 feet corresponding to the standard truck clearance width. Within the curb-to-curb width of the roadway, the traffic lanes shall be assumed to occupuy position which will produce the maximum stress, but which will not involve overlapping of adjacent lanes, nor place the center of the lane less than 5 feet from the roadway face of the curb.
Standard trucks and lane loads.—The wheel spacing, weight distribution, and clearance of the standard H and H-S trucks shall be as shown in figures 1 and 3 and corresponding lane loads shall be as shown in figures 2 and 4. 
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:
| Percent | |
1 or 2 lanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
3 lanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
90 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
4 lanes or more . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
75 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . |
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.