RECORD BRIDGES.

Putaruru Press, Volume VII, Issue 299, 1 August 1929, Page 3

RECORD BRIDGES.

MIGHTIEST’IN THE WORLD. Great Hudson River Span. Standing out prominently against a background of apartment houses on the east, against the Palisades on the west, and against a majestic sweep of river north and south, two massive steel towers are nearing completion J in the Hudson River opposite New | York City. Those towers, which are higher than the Washington Monu- 1 ment (says the Scientific American) | are to support the world’s greatest j . bridge, a bridge that is to solve to a j j great extent the problem of traffic i movement between New York and j New Jersey. Consequently it will t provide quicker access to Manhattan for countless thousands of motorists. Besides the towers, each of which will carry at the top a cable load of 112,500 tons, and which are later to be encased in concrete and granite { masonry, other works less visible to I the distant or casual observer are proceeding rapidly. The massive concrete and steel anchorage on the Manhattan side was completed in March, three months ahead of specified time. The extensive tunnel oper? 'lions necessary at Fort Lee for the New Jersey an- i chorage are likewise finished. ( During the past winter the exeavat- I ing for the New Jersey approach was • virtually completed, elevators were in-'j stalled in the towers, preparations I

were made for erecting the cables—scheduled to begin during the coming summer—and other incidental details . were taken care of. The tower elevators are for the use of the erectors at present, but when th*, bridge is completed new cages will be installed, so that the elevators may be used by the sight-seeing public. Progress of the Work. By the end of 1927 the two large cofferdams for the New Jersey tower I foundation had been completed and the placing of concrete within them started. Upon removal of the overburden of earth the rock was found to be throughout of solid of varying degrees of hardness, and of very rugged surface. This was fortu- ) nate because the natural steps formed an excellent bond with the concrete, so that little blasting was necessary. The concreting proceeded rapidly, i

About 9 feet below water level the granite facing was begun, amd thereafter kept pace with the concreting. This foundation work involved 75,500 . cubic yards of dredging, and placing of 35 480 cubic yards of concrete, 1400 . cubic yards of granite, and 300 tons of reinforcing steel. ' The New York tower rests upon a rocky point, and consists of two' piers or bases, one under each leg of the tower. Each base extends slightly beyond the water-line, so that only shallow, simple cofferdams were necessary jto exclude the water. Only 7300 cubic | yards of rock excavation and placing of 9700 cubic yards of concrete were | involved here. ! Immense Anchorage Tunnels. ] The roadway on the upper floor of the bridge will intersect the rock face of the Palisades about 50 feet below their summit, and the lower floor will 1 be about 35 feet below this level; 1 thus the New Jersey highway ap- 1 proach consists of an open cut through < the Palisades for a distance of 750 1 feet. When completed it will be 146 i feet wide at the roadway, and will 1 have involved the removal of 220,000 ’ cubic jzards of rock. j i The New Jersey anchorage tunnels, ] which are of such size that they could t accommodate four trolley tracks on each of the two levels, are below the j lower level and at the end of the inclined shafts. In these tunnels the 61 - ] strands of each of the cables will be i spread out, finger-like, and fastened i to eye-bars connecting to anchorage 1 1 girders set in concrete. Eye-bars, c chains, girders, and concrete will com-

pletely fill the tunnels. Perhaps the most interesting part of the work thus far is the construction of the large concrete blocks which wili serve for anchoring the cables on the New York side. Since each cable is to be made up if 26,474 double-gal-vanised, high-strength steel wires, each .192 of an inch in diameter—making a total diameter for the cable cf about 36 inches—the weight of the cable alone would make a huge an- ( chorage necessary. Add to this, howJ ever, the weight of the bridge structure, the estimated traffic load and a large safety factor, and it will be seen that only a miniature mountain of concrete would suffice as .an anchorage. Record Span of 3500 Feet. j The concreting of this anchorage I constitutes completion of only the first stage of the work. Later, certain con- |

- j Crete backing which was 'omitted, and | all granite facing, will be construct- j ed. The anchorage will represent, ! when fully completed, a gigantic mas- | onry block about 200 feet wide, 90 feet j long at its base, and 130 feet high, l resting on solid bedrock. It is a far cry from the day, a little l over 100 years ago, when Thomas Tel- | ford finished in Wales, what was then j the world’s greatest suspension bridge j which had a 503-foot span. The Hud- j son River bridge—over five-eighths of . a mile—will eclipse not only that famous structure, but also all succeeding ] ones, by a large margin. And while the new monster bridge is not likely ! | to be ranked throughout the ages as j j the eighth wonder of the world, as was ! I predicted for Telford’s, it wili surely | stand as the world’s greatest bridge 1 j for many years to come.