COMPARATIVE COST OF CONCRETE BRIDGES The cost of concrete bridge construction is of especial interest when compared with the cost of bridge construction of wood, steel, stone, or other material, because it is the constant en deavor of engineers and contractors to find the cheapest form of construction which will meet the requirements. To answer its purpose, a bridge must not only satisfy present require ments but be of sufficient durability to keep maintenance and depreciation charges reason ably low. A paper read by Mr. E. P. Goodrich before the National Cement Users' Association, entitled "Comparative Construction and Main tenance Costs of Reinforced Concrete and Steel Bridges," bears directly on this question, and will be of great value to anyone working along the lines of concrete bridge building. In this paper Mr. Goodrich says: At the quarterly meeting of the Association of Amer ican Portland Cement Manufacturers, held in Philadel phia, April 10, 1907, Mr. George S. Webster discussed the subject of "Concrete Bridges." In it he described briefly the Walnut Lane Bridge in Philadelphia. In answer to an inquiry, he said: "The contract price for the bridge was $262,000. A steel bridge would probably cost less in this location; a stone bridge, approximately 50 per cent more. The addi tional cost of this bridge over one of steel is due to the cost of centering. As the bridge is located in Fairmount Park and over the picturesque Wissahickon creek, a steel bridge would be inappropriate with the surroundings." In this case it is to be observed that no real compe tition took place between those advocating concrete and those who exploit steel bridges. A decision was reached requiring the construction of concrete, and the first cost was of rather secondary consideration. And that has come to be the general attitude of those associated with the selection of types of bridges for given sites. At that time alternate bids were often asked for steel bridges and also for concrete arch construction. Among many such cases, the following may be cited, wherein the re inforced concrete design carried an estimated cheaper first cost : (a) A seven-span bridge of concrete at Waterloo, Iowa, cost $54,000, or $1.80 per sq. ft., while the lowest
bid for a plate-girder construction was higher.
(b) A seven-span bridge of concrete at Dayton, Ohio, cost $123,170. Eight bids were received for a steel plate girder design, and seven on the concrete-steel design. The latter were about $10,000 the lowest.
(c) A 120-foot span concrete bridge at Lansing, Mich., cost $31,000, while the lowest of the three steel bids was $35,000. . . .
(e) A cheap but substantial highway bridge in Wa bash county, Indiana, which was guaranteed flood-proof, cost $573 in competition with steel bridges and plain concrete culverts of same span and roadway, the lowest bid on steel being $665 and on plain concrete $943. . . .
(g) At Yorktown, Ind., was erected a 95-ft. span highway bridge for about $100 less than the lowest bid for a steel truss bridge of the same span.
On the other hand steel often is of less first cost than concrete: . . .
(b) At Stockbridge a small foot bridge over the Housatonic, if built of iron, was estimated to cost $1,475, while the concrete one actually erected cost more than that figure, because of bad foundations.
(c) The competitive plans prepared for the memorial bridge over the Potomac, for the Chief Engineer of the Army, included several different designs in concrete. It is said that a steel structure for the same site would have cost about 33 per cent less than that of the winning de sign in reinforced concrete.
(d) In the competition for a bridge at Plainwell, Mich., twenty-three proposals were submitted for dif ferent types of steel bridges, varying in price from $14, 000 to $26,000, all the leading builders in the country be ing represented. For concrete-steel construction six bids were received, ranging from $16,000 to $27,000. The board favored a concrete bridge, but the only bid within the appropriation ($20,000) was rejected on account of faulty design. At an adjourned letting, three bids were received for concrete-steel, varying from $19,900 to $20, 500.