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7-foot sidewalk, and was built to carry safely heavy loads. Soundings were made before work was commenced and it was supposed that rock would be reached from 40 to 60 feet below low water, the depth of water being from 20 to 28 feet. On reaching the depth at which it was supposed rock would be found, we were surprised to learn that there was no rock there within sounding distance, but we found a bed of small boulders mixed with sand and gravel instead. This kind of foundation was not considered safe to bear the load, consequently the difficulty was overcome by converting this bed of boulders and small material into concrete having a much larger area. The piers were put down by compressed air, and the following course was adopted. The pressure in the cylinder was relieved until about 4 feet of water came in. This body of water, the size of the cylinder and about 4 feet deep, was converted into a rich grout. The pressure was then put on, and this grout was sent down into the foundation, and the process repeated until it would take no more. It was found that this concrete spread out for considerable distance in all directions, for in grouting the second tube of any pier there was evidence that the grout used in the first tube had extended that far, so that the second tube would take less grout than the first.
“This course was followed for all the tubes, including those for the pivot pier, and I think without doubt that the foundation was converted into a mass of concrete, just as good as rock.
“This method can be followed very readily when compressed air is used, but not so readily when it is not used.”
This expedient of Mr. Thacher's was truly a novel one and well worthy not only of record but also of adoption under similar conditions. It would be well to use it for all pneumatic piers that are not carried to bed-rock and which rest on material into which grouting can be forced.
The late Horace E. Horton, Esq., C.E., who for many years was one of America's most prominent contractors, especially in highway bridgework, wrote as follows:
“I have in mind the doubling up, in fact even trebling up, of old spans as well as girders to fit the increased loading (a continuous performance of railroad demands). I have a case in mind of three 80' spans-3-truss, double-track, half-through bridges, which were re-erected as one single-track, 3-truss, 80' span deck bridge, and one 6-truss, single-track, 80' span deck bridge. This is as an extreme example and even with three times the material to do the work it seemed desirable to add rivets at certain points.
“I am disposed to question whether reminiscences of this class would have any particular value. They surely are interesting as showing the extreme of economy in using up old material.
“We have on repeated occasions reduced a double-track bridge to a single-track one, cutting off the beams and using four stringers for a single track. We have rearranged two single-track-span deck bridges into one span. We have made two single-track spans from three-single-track, deck-bridge spans. We have formed two single-track spans into a single-span through bridge, using equalizers for floor connections to the two spans, and have riveted one track stringer immediately on top of another.
“I am not speaking of the above as a matter of novelty or merit, merely facts that the business presented itself in these shapes, which I presume it has done to all other manufacturing concerns in our line.”
The eminent bridge engineer, Ralph Modjeski, Esq., wrote thus:
“Regarding expedients. At this time I can only mention a few which occur to me, as follows:
"In designing the Rock Island Bridge draw span, by certain requirements of the Commanding Officer under whose executive charge the bridge was being built, I was required to dispense with main pinions and gearing of the ordinary type. A sprocket chain gearing was therefore designed and has been operating very successfully, although I would not repeat this design on account of its expense and complication.
“During the construction of this draw span when the ice carried out one of the arms partly erected, both the railway and the river traffic had to be taken care of, and a lift span was improvised for that purpose. In this bridge there were also a few features of the erection which might be considered as expedients. All of these you will find in Appendix 5 of the Report to Chief of Ordnance, U. S. A., 1899.
“On the Thebes Bridge a number of expedients were employed both in designing and in construction. Those used in the foundations belong properly to the contractors, C. Macdonald & Co. of New York, who may be able to furnish you with some information.
“On the superstructure I would call your attention to an expedient at LSO for taking care of the expansion in the lateral system.* Also to the double pin arrangement at LOC, the object of the second pin being to relieve bending stresses in the bottom chord which would result from the simultaneous deflection of the two adjacent spans.f I send you the lithographs under separate cover.
“On the construction of the Willamette Bridge it was deemed advisable to lower the caissons from barges so that the barges could be placed and the caissons built at any convenient point. I am writing to Mr. Nickerson, Resident Engineer, to send you a photograph of this arrangement.I
“I would also refer you to the Transactions of the American Society of Civil Engineers for some details of rail locks and end lifts which may properly be considered as expedients. These were shown in connection with the discussion of Mr. Schneider's paper on Draw Bridges."
A. F. Robinson, Esq., the well-known bridge engineer of the Atchison, Topeka, and Sante Fe Railway System, wrote thus:
“We, of course, have to adopt a good many expedients in our practice which do not work out very successfully. Perhaps one of the items that has caused the writer the most trouble has been the expansion bearings under long girders and under short truss spans.
“Some years ago, Mr. Onward Bates, $ in discussing details of design, advised that for shoes under girders the sole plates be beveled, leaving the bearing of the sole plates about 8" in length, with sufficient width to distribute the loading into a cast base or a heavy wrought metal base. I adopted this scheme for our long girders from 70' spans up.
"We used this plan for five or six years. Where the bridge pointed nearly North and South and where the pedestal stones were in one piece for the whole width of pier, or where they extended back through the parapet walls on abutments, we have had no trouble from the expansion. On the other hand, we have had several bridges which stood more nearly East and West in which the pedestal stones on the abutments or on the piers have pulled badly on account of the stress caused by the girders sliding on the bases. About three years ago we changed the detail for structures of this kind, using instead a heavy cast-iron base with a large lozenge-shaped rocker or disc. These rocker bearings have thus far worked very nicely.
“What I have been trying to avoid was the necessity for a lot of steel castings and
† See Fig. 456. # See Fig. 45c. § Past President of the American Society of Civil Engineers.
* See Fig. 45a.
either segmental or cylindrical rolling bearings for girders from 70' up and for short truss spans.
Details of this kind always cost much more relatively than the remainder of the structure. What I have been trying to obtain all the time is a design which shall work acceptably and which at the same time will not increase the average unit cost for our structures."
Mr. Robinson's pedestal detail is so clearly explained as to need no illustration. It appears to be an excellent one. For small expansions and contractions it ought to serve its purpose admirably.
Henry W. Hodge, Esq., C.E., in a late letter, wrote as follows:
“We note that you also ask that we send you any “expedients” in design, which we have made use of, and we would say that the main expedient which we indulge in is in varying the length of panels, as is exhibited in our fixed spans in the St. Louis Bridge, and in the cantilever and draw span designs which we send herewith. We send you a print of the general stress sheet of the St. Louis Bridge, which will give you the varying panels, and we would also call attention to the expedient which we have adopted of running the end lower laterals to the centre of the floor-beam and thus avoiding the complicated detail adjacent to the end shoes.
“We also send you the general drawing and detail of the cantilever arm of the Chico Cantilever in Mexico, and you will note on this that we used a varying panel and a varying depth of lower chord in each panel, and we inserted the lateral plates between the outside of one chord and the inside of the other chord, thus taking up almost all the variation in depth of chords between panels. We also here used a half pin-hole in the outer member of the lower chord and in the vertical posts to facilitate erection; and this drawing also shows an expedient of ours in making latticed laterals of an odd number of panels on one member, and an even number on the other, so that the lattice bars pass through each other at the central intersection and do away with the large and ugly looking batten plates so generally used on such laterals.
“We are also sending you drawings showing a vertical gate at the end of draw spans, which we have used for the State of Connecticut, owing to the fact that we wished something that would prevent trolley cars and automobiles moving at high speed from going into the opening. We have never seen anything exactly like this, hence we believe it to be new; and it certainly works most satisfactorily. Some photographs of this gate recently appeared in the Engineering Record.*
“We are also sending you a blue-print of the draw span which we are building at Troy, which shows a type of highway floor that we have adopted as standard, and which we find saves a great amount of metal. We place the floor-beams at regular intervals (in the neighborhood of 10') regardless of the panel points; in fact, we try to make this arrangement so as to avoid the panel points and thus do away with complications in connections. By this means we get all floor-beams exactly alike. The stringers are in such short lengths that they can be made extremely light and of rolled sections, and we find that the amount added to make a stiff lower chord still leaves the total weight of the floor very much below that of a floor composed of long stringers with short cross beams to hold the flooring. We generally use a reinforced concrete slab floor, but on this draw span we have used 5' plank to save weight. While, of course, on a draw span we would require a stiff chord in any event, we use this same type of chord for fixed spans with a very considerable saving.
"You will also note that in the top laterals of this span we make a considerable saving in weight by running a central longitudinal strut and using single anchor diagonals, thus avoiding the deep latticed laterals which would otherwise be required for rigidity.”
* See the issue of September 19, 1914.
Mr. Hodge's expedient of varying the panel length with the depth of truss is a good one, as it adds to the appearance of the structure.
SECTION 0-8 Fig. 45a. Details of Expansion Joint in the Lateral System at the End of the Suspended
Span of the Thebes Bridge. would have been adopted by the author long ago had it not been for the opposition of the bridge shops. In the opinion of almost everybody connected in any way with the manufacture of structural steel, it has been rank heresy for anyone to think for an instant of varying the panel length, excepting only at the ends of skew spans, the objection being the lack of duplication involved; and the shops have had such influence on the bridge engineers as to keep them in line on this question until Mr.
Fig. 456. Details of the Bottom Chord Joint at the Piers of the Thebes Bridge.
Hodge had the courage to break away from the established precedent. The practically parallel diagonals of the trusses in the long spans of the St. Louis Free Bridge certainly add greatly to the appearance of the structure.
Mr. Hodge's detail for connection of end lower laterals is a good one. When hearing about it for the first time, one might be inclined to think that it involves weakness by putting bending moment on the end floorbeams; but such is not the case, for the bringing together of the two end laterals gives them the function of end chord members of the horizontal lateral truss, thus cutting out the end panels of the bottom chords from aiding to form the said truss. The great advantage of this detail, as