DESIGN OF FIXED ENDED ARCHES BY THE ELASTIC THEORY 141 



and compressive stresses developed there. Circular-segmental arches 

 of low rise generally give considerable tension at the springing joints. 

 In this design the greatest tensions in the rib occur at these places. 

 Latticed girders, therefore, strengthen the concrete in the vicinity of 

 the springing points. The flanges are each composed of 2 — 6"x3^" 

 x|" angles, 1 — 13"x|" cover plate and 1 — 13"x|" side plate. The 

 stiffeners and web members are 3^"x3"x|" angles. 



The concrete of the ribs is composed of 1 — portland cement, 2 — 

 sand and 4— broken stone to pass a 2 -inch ring and be held on a 

 1-inch screen. 



The original design for this arch contemplated an asphalt road- 

 way supported on concrete floor arches, with the floor arches held by 

 I beam floor beams. The spandrel posts were I beams braced by 

 steel angles. Tn the revised design for which this article gives the 

 arch analysis the roadway and floor system remained unchanged, but 

 the steel spandrel work of the earlier plans was replaced by concrete 

 posts or pillars connected longitudinally and transveresly by concrete 

 walls and arches. The ribs of the revised design were therefore heav- 

 ier than in the original drawings. 



The calculations herewith are given for one foot width of rib. 

 The dead loads of the spandrel and rib are taken at 150 lbs. per cu. 

 ft., the dead load of the roadway and floor together at 170 fcs. per 

 sq. ft. The live load assumed is 200 fts. per sq. ft. of roadway plan, 

 comes on the bridge from left to right and covers about five-eighths 

 of the span, or sections V to 6. See Plate I. 



In Plate I the linear scale is 1 inch =60 ft.; the force scale 1 

 inch = 20,000 lbs.; and the scale for the deflection polygon, 60. 



The rib center line or neutral curve VrV is divided by trial 



n 

 into eighteen parts whose lengths n are such that -=;=- for each part 



is the same. Here I is the average moment of inertia of any part 

 and is obviously proportional to d^ where d is the average depth of 

 rib for that part. E is assumed constant and the same for tension 



n 

 and compression. Hence — is made a constant for each part. The 



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