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 APPENDIX VI

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. 174