[...]
Surface Finish.
Various methods have been adopted for procuring satisfactory surface finish on concrete structures. Among these methods may be mentioned cement washing, tooling, sand blasting, rough casting or slap dashing, scrubbing, cold-water painting, and acid treating. The Connecticut Avenue Bridge at Washington has corners and moldings made of concrete blocks and to remove form marks the body and flat face work were bush hammered.
The Walnut Lane Bridge at Philadelphia has a rough surface finish similar to pebble dash, but of coarser grain. The surface shows stone chips not larger than three-eights of an inch in diameter, formed by washing the concrete face before the cement had hardened. [...]
Henry Hudson Memorial Bridge.
[...] The next longest masonry arches of the world are as follows:
| Feet, span. | |
| Stone arch bridge over Adda River............ | 230 |
| Stone arch bridge at Luxemburg, Germany..... | 278 |
| Stone arch bridge at Plauen, Germany......... | 295 |
| Concrete arch bridge at Gruenwald............ | 230 |
| Concrete arch bridge at Walnut Lane, Philadelphia ...................................... | 233 |
| Stein-Teufen bridge, Switzerland.............. | 259 |
| Concrete arch bridge at Rocky River, Cleveland. | 280 |
| Aukland, New Zealand....................... | 320 |
Walnut Lane Bridge, Philadelphia.
Walnut Lane crosses the Wissahickon valley on a new concrete bridge at a height of 147 feet above the river bed. At the time of completion it was the longest concrete masonry bridge, having a clear span of 233 feet. It consists of two separate arch rings, 18 feet wide at the crown, increasing to 21 feet 6 inches at the springs. At the crown the two rings are separated by a space of 16 feet. The double rib construction is similar to that used in the stone arch bridge at Luxemburg, Germany, having a span of 275 feet. The main arch is an approximate ellipse, has a rise of 73 feet, and carries 10 cross walls which support the floor system. There are also five semicircular approach arches with clear spans of 53 feet. The bridge connects Germantown and Roxborough, two residential suburbs of Philadelphia. It has a 40-foot roadway, and two 10-foot sidewalks. The entire structure is solid concrete, not reinforced, excepting in certain minor details. The surface finish is rough, somewhat similar to pebble dash, but of coarser grain. The exposed surface shows stone clips of not over three-eighths inch in size, formed by washing before the cement had hardened. The total length of bridge over all is 585 feet, and the cost $259,000. George S. Webster, Chief Engineer, Bureau of Surveys. H. H. Quimby, Bridge Engineer. Reilly & Riddle, Contractors. [...]
Ribbed Arches.
[...]The Walnut Lane bridge at Philadelphia, and the Rocky River and Piney Creek bridges now under construction, illustrate to some extent the saving which may be accomplished by the use of ribbed in place of slab arches, and yet all of these three bridges are only partially ribbed. They each consistent of a pair of twin arch rings separated by a distance of from 10 to 20 feet, which space between the rings is spanned by simple floor construction. The saving in the arch ring by this expedient is from 25% to 30% of the cost of the ring, which saving would be still further increased by using entire ribbed designs. The Luxemburg stone arch bridge in Germany with a span of 275 feet, and completed in the year 1903, is of the same type. An unusual example of ribbed arch design prepared by Mr. Turner of Minneapolis, is shown in Figure 27. It is one of several designs submitted for the Grand Avenue viaduct in Milwaukee. The main compression members are octagonal and are hooped.