The Montgomery advertiser., 1904-04-10
NEW BRIDGE.
Land Spans Show Greater Tremors
 Than River Spans.

4Ahh 1slV0T OpduS.
 Many observant pedestrians who take their daily constitutional across the new and recently opened Brooklyn bridge have noticed, an unusual amount of vi- oration in certain parts of the new struc- ture Truck drivers who have had occas- ion to cross 1t with heavy loads have ob- served the same thing, and have re- marked it to their fellows. In short, there has grown up a considerable amount of talk in the Eastern district regarding this "shakiness," as it is called, of the big bridge, and several of the observers of inquiring mind have written letters to the Eagle asking whether or not this is as it should be or if 1t is not a symptom Of weakness and danger.
 Before beginning a discussion of the reasons for this vibration in the two land spans, 1t should be stated as briefly and as emphatically as possible that the Wal liamsburg bridge is just as it was in- tended to be from the beginning, vibra- ton and all, and that 1t is perfectly safe; in fact. much safer than 1t would bo if 1t didn't shake when the heavy trucks pass over 1t.
 The fact of the matter is that the bridge vibrates noticeably in two sec- tions only, the land spans. which extend from the towers on either side to the great stone anchorages. This is true, not in theory only but by actual observations made by an Eagle reported with instru- ments designed to measure the vibra- ticrs.
 Of course, the only basis upon which to frame conclusions in regard to the structure is A comparison with Brooklyn bridge. As the Brooklyn bridge is be- ing constantly crossed and recrossed by endless lines of bridge and trolley cars, heavily freighted with passengers, it is unfair to the older structure to make ob- servations on the Williamsburg bridge, which has no car lines, and draw con- clusions detrimental to the older bridge. There can be little question. however. that so far as the towers are concerned, thc massive pillars of granite which sus- tain Brooklyn bridge are much more rigid and unyielding than are the steel towers of the newer bridge.
 In testing the vibration of the Will liamsburg bridge on the occasion of the passage of heavy trucks, which fur nish the greatest strain which the struc- ture has yet been called upon to bear. the Eagle reporter obtained these results: The vibrations are greatest about 200 feet Inside the towers on the land spans which connect the great river span, or bridge proper, with the supported roadways which have been built for approaches. The bridge in its entirety, from the plaza in Williamsburg to the terminal in Manhattan. really consists of five sepa- rate and independent structures, the two roadways built upon Iron and stone piers; the two land spans, which are nothing more nor less than two independent can tilever bridges, and the suspension bridge, which is the main span supported by the four big cables hanging over the towers. It should be noted at this point that the land spans of Brooklyn bridge are sup ported in the same way as the central span, by the cables and are consequently part and parcel of the bridge proper.
 Comparing the vibration of the differ ens parts of the Williamsburg bridge. one with the other, the Eagle man learned that the roadways Wbrate none at all. or so imperceptibly as to give only the very slightest indication by the instrument used The central span vibrates to a perceptible extent, but not to a notice able one. The cantilever land spans vi- brate at least three or four times as much.
 Compared with the Brooklyn bridge, the central span of the new bridge vi- brates, under present conditions, about one-half as much The land spans of the Williamsburg bridge, under much smaller strain, vibrate nearly twice as much as does any part of Brooklyn bridge.
 With these observations and facts the Eagle reporter went to see Chief Engin- eer Nichols. MT. Nichols not being at the office, he was referred to Engineer Robinson, who was in charge of the con- struction of the Williamsburg bridge for several months during the last fall and winter MT. Robinson said:
 70 one need feel the slightest alarm at the safety of the new bridge I can say from personal observation that the structure Is exactly as it was intended to be in every particular. There is a mo- ticeable vibration in the two cantilever spans. They would not be safe if this vibration were absent. It is the rule of all cantilever structures that they show a tendency to vibrate. They arc built in that way. The very fact that they are constructed on counterbalance princi- pie, without being rigidly fixed, con- tributes to their vibration. This is as 1t should be. The land spans of the Will ton to the bridge proper.
 'In the central span a different system oi stiffening the truss is used from that employed on the Brooklyn bridge. feel n" hesitation in saying 1t Is a better one. Of course, the bridge has not yet been put to the test of having the cars run over 1t, but can see no possible reason to doubt that such test. when 1t does come, will show that 1t Is more rigid