DESIGNS OF FLOORBEAMS AND STRINGERS. 



115 



For a bridge 17 ft. center of trusses and 18 ft. panels, from Fig. 9 the required floorbeam 

 is a 24 ; n. I @ 80 lb., while from Fig. 10 the required floorbeam is a 20 in. I @ 70 Ib. 



The sizes of steel I-beams required for floorbeams for panel lengths of 10 ft. to 24 ft., and 

 widths center to center of trusses or girders of 15 ft. to 26 ft. to carry a dead load of 100 lb. per sq. 

 ft. and a 15-ton auto truck without impact, or a uniform live load of 100 lb. per sq. ft. without im- 

 pact are given in Fig. II. These are practically the floorbeams required by the specifications of 

 thr Illinois, Iowa, and Wisconsin Highway Commissions. Steel stringers for the same loading 

 are given in Fig. n. 



The bending moments for the design of built-up floorbeams may be obtained from Fig. 9, 

 Fig. 10, or Fig. 1 1. 



24'hSO* 



UVCLOAD:l5-Tonavtotruck(noimpad),orMlt>. 

 persq.Ft.(noimpact).DEADLQAD:IOO/hpfrsa.Ft. 



10 12 14 16 18 20 22 

 Panel Length in Feet. ' 



2345 

 Spacing in feet. 



FIG. ii. BENDING MOMENTS IN FLOORBEAMS AND STRINGERS FOR IS-TON AUTO TRUCK. 

 (No IMPACT.) CONCRETE FLOOR. 



CALCULATION OF STRESSES. For the calculation of the stresses in highway bridges, 

 see the author's "The Design of Highway Bridges," also see Chapter XVI. 



ALLOWABLE STRESSES. For allowable stresses to be used in the design of steel highway 

 bridges, see "General Specifications for Steel Highway Bridges," printed in the last part of this 

 chapter. 



SHORT-SPAN STEEL HIGHWAY BRIDGES. The term short-span highway bridges 

 will be assumed to include beam, low truss and plate girder bridges. 



