iveted con Varren type hords up to span riveted Bridge and osts and the chords, hip The floor 3 are carried been commonly used for long span bridges, but the K-type of truss has the advantage of smaller secondary stresses and simplicity of design and ease of erection, and is rapidly coming into use. High truss pin-connected bridges should never be built with less than five panels. The Iowa Highway Commission uses high trusses for spans of 100 ft. and over, riveted with parallel chords to 140 ft. The Illinois Highway Commission uses high trusses for spans of 90 ft. and over, riveted with parallel chords to 160 ft. For spans longer than 160 ft. trusses may be riveted or pin-connected with parallel or inclined chords. The Massachusetts Public Service Commission uses high trusses for spans of 100 ft. and over, riveted to 125 ft., and riveted or pin-connected for spans over 125 ft. FIG. 4. DETAIL PLANS OF THROUGH TRUSS SPAN. WISCONSIN HIGHWAY COMMISSION. The Wisconsin Highway Commission uses high trusses of the Pratt type with riveted connections for spans of 80 to 150 ft. The American Bridge Company has prepared standards of high trusses of the Warren type with spans of 104 to 204 ft. with riveted connections. The bridges have parallel chords up to 150 ft. and inclined chords for longer spans. RIVETED HIGHWAY BRIDGES.-The detail shop plans of a III-ft. 6-in. span riveted Pratt truss highway bridge, as built for the U. S. Government by the Chicago Bridge and Iron Co., Chicago, Ill., are shown in Fig. 1 and Fig. 2. The top chords, the end-posts and the intermediate posts are made of two channels laced on both sides, while the bottom chords, hip verticals and diagonal ties are made of two angles fastened together with tie plates. The floorbeams are 18" @ 55 lb. I beams and are riveted below the lower chords. The joists are carried by connection angles riveted to the webs of the floorbeams. The portals and the sway struts are made of angles. The top and bottom laterals are made of adjustable rods. The expansion end of the bridge is carried on two nests of expansion rollers, each nest being composed of four 3 in. rollers. The floor covering is composed of a bottom layer of 2 in. × 8 in. pine plank laid transversely and spiked to 3 in. × 5 in. spiking strips that are bolted to the tops of the joists, and a top layer of 3 in. x 8 in. oak, laid diagonally. The 6 in. x 8 in. pine felloe (wheel) guard has its edge protected by an angle 3" X 3" X 1". The detailed estimate of the weight of this bridge is given in Table I. The per cent of details in this bridge is quite high, due to the fact that the end-posts and the top chords are made of two channels, laced. TABLE III. STANDARD STEEL THROUGH TRUSS SPANS GENERAL DATA AND ESTIMATED QUANTITIES, IOWA HIGHWAY COMMISSION. General design plans and data for a high truss steel highway bridge with a span of 112 ft. and an 18 ft. roadway, as designed by the Wisconsin Highway Commission are given in Fig.3. Detail drawings of a 120 ft. span high truss bridge are given in Fig. 4. Standard plans have been prepared for spans of from 90 to 150 ft., with 16 ft. and 18 ft. roadway. All spans have one end carried on rockers as shown. Data on these standard bridges are given in Table II. These designs have been worked out very economically by Mr. M. W. Torkelson, bridge engineer, and represent about the extreme economy in design that will conform to good practice. |