Arizona republican., 1912-04-14

pier columns. The tops of all these
 columns are connected crosswise of
 the bridge by large beams and length
 wise Of the bridge by small arches.
 Along the center line of the bridge
 the cross beams are connected bv smaller beams. On top of all these
 small arches and beams lies the floor slab. The floor is : inches
 thick at the curbs and is curved up to the middle of the roadway. where
 it is : inches thick A layer of bitu
 lithic paving will be placed on the floor and rolled This will give the
 roadway the sane sort of surface as has been used on the paved streets
 of Phoenix. At the curbs are screened drainLoles to carry off the
 water which runs from the roadway.
 The floor is about six feet wider
 across than the distance between the
 columns and posts on which it rests.
 so there is an overhang of about
 2 feet at each side of the bridge.
 This overhanging part of the floor
 IS supported by ornamental brackets which curve outward from the col
 umns near their tops. The tops of
 the curbs are about six inches high
 CT than the floor. On top of the
 curbs is an open balustrade or rail-
 ing about 31A feet high, such as is often seen along starways. The bal
 usters or posts are round and
 inches in diameter. and have inch
 spaces between them. Connecting the tops of the balusters is a hand
 rail inches wide and inches thick
 with rounded corners. At intervals
 of ten feet are larger posts s inches
 square which strengthen the railing. and break the monotony of the long line of small posts. These small posts will be nodded in forms on the is being built, the balusters will be set in place and the curb nodded around their lower ends and the handrail nodded around their tops. At points directly over each pier are still larger posts in the railing at each side of the roadway These posts are by 2i inches. On top of these will he placed cast-iron lamp posts. each Of which will carry single electric globe. Near the ends of the bridge there will be large or concrete columns. at the tops of which will be cluster of five electric light globes. somewhat l Ike those now used on the streets of 1 Phoenix. Insulated conduits under l the floor of the bridge will carry the | wires for these lights
 Excepting the lower portions of the l piers. all parts of the bridge are re- ! nforced with steel rods inside the 1 The strength of steel and concrete is well known. and each | part oc the bridge, piers. beams. arches posts. columns. brackets and floor, is made of such size that each Hill carry the probable load or weight Il which might come upon it. In fig II ring the strength of different parts II ,f d structure. a factor of safety of II hree or four is used. Factor of safe y is technical term and it Il means the ratio between the break ng strength of a material and the trength assigned to it in actual use Tor example. if a cube of certain concrete inches square would just upport q weight of 32OO lbs. with mt crushing. in figuring the strength Il f ths cube against crushing. we would use a factor of safety of four bus making the allowable load on he cube be only 5000 lbs. The factor f safety might be called a margin f safety
 At present eight of the twelve iers have been completed. includ- ng the south abutment, and work Fill soon begin on the arch-ribs. [ is a pleasant trip of nine miles rom Phoenix to the bridge site, and 7el worth while to see the con truction and get few interesting nd instructive points from the genial ridge engineer. Mir. J. c. Ryan.
 The Tempe bridge will be among hte very largest arch type of bridges n the world. The use of arches in
 bridge allows the building of much onger spans than in the beam or irder besides giving the bridge