48 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[February 



The caps which cover the saddles and cables on the pyramids rise 3 

 feet aboTe the inside or trunk railing, and would obstruct the free pas- 

 sage of the tow-line ; but this is obviated by an iron rod which passes over 

 the top of the cap, and forms a gradual slope down to the railing on each 

 side of the pyramid. 



The wire cables, which are the main support of the structure, are sus- 

 pended next to the trunk, one on each side ; each of these two cables is 

 exactly 7 inches iu diameter, perfectly solid and compact, and constructed 

 in one piece from shore to shore, 1,175 feet long; it is composed of 1,900 

 ■wires of Jih inch thickness, which are laid parallel to each other. Great 

 care has been taken to insure an equal tension of the wires. Oxidation 

 is guarded against by a varnish applied to each wire separately, their 

 preservation, however, is insured for certain by a close, compact, and 

 continuous wrapping, made of annealed wire, and laid on by machinery 

 in the most perfect manner. A continuous wrapping is an important 

 improvement, which, in this case, has been for the first time successfully 

 applied. 



A well-constructed and well-wrapped cable presents the appearance of 

 a solid cylinder, which in strength greatly surpasses a chain, made of 

 bars of the same aggregate section or weight. It is not only the great 

 relative strength of wire which renders it superior to bar iron, but its 

 greater elasticity, which enables it to support strong and repeated Jtibra- 

 tions, add still more to its value as a material for bridge building. 



The extremities of the cables do not extend belou- ground, but connect 

 with anchor chains, which, in a curved line, pass through large masses of 

 masonry, the last links occupying a vertical position. The bars compos- 

 ing these chains average IJ X 4 inch, and are from 4 to 12 feet long; 

 tliey are manufactured of boiler scrap and forged in one piece without 

 a weld. The extreme links are anchored to heavy cast-iron plates of 6 

 feet square, which are held down by the foundations, upon which the 

 weight of 700 perches of masonry rests. The stability of this part of 

 tlie structure is fully insured, as the resistance of the anchorage is twice 

 as great as the greatest strain to which the chains can ever be sub- 

 jected. 



The plan of anchorage adopted on the aqueduct varies materially 

 from those methods usually applied to suspension bridges, where an open 

 channel is formed under ground for the passage of the chains. On the 

 aqueduct, the chains below ground are imbedded and completely sur- 

 rounded by cement. In the construction of the masonry, this material 

 and common lime mortar have beeu abundantly applied. The bars are 

 painted with red lead. Their preservation is rendered certain by the 

 known quality of calcareous cements to prevent oxidation. If moisture 

 should find its way to the chains, it will be saturated with lime, and 

 add another calcareous coating to the iron. This portion of the work 

 has been executed with scrupulous care, so as to render it unnecessary 

 on the part of those viho exercise a surveillance over the structure to 

 examine it. The re-painting of the cables every two or three years will 

 insure their duration for a long period. 



AVhere the cables rest on the saddles, their size is increased at two 

 points by introducing short wires, and thus forming swells, which fit 

 into corresponding recesses of the casting. Between these swells, the 

 cable is forcibly pressed down by three sets of strong iron wedges, driven 

 through openings which are cast in the side of the saddle. 



When the merits of the suspension liar were discussed previous to the 

 commencement of the structure, doubts were raised as to the stal)ility of 

 the pyramids and the masonry below, when unequal forces should hap- 

 pen to disturb the equilibrium of adjoining spans. It was then proved 

 by a statistical demonstration, that any of the arches with the water in 

 the trunk could support an extra weight of 120 tons, without disturbance 

 to any part of the work. In this examination, no allowance at all was 

 made for the great resistance of the wood-work, and the stiffness of the 

 trunk itself. During the raising of the frame-work, the several arches 

 were repeatedly subjected to very considerable unequal forces, which 

 never disturbed the balance, and proved the correctness of previous cal- 

 culations. 



The stiffness and rigidity of the structure is so great, that no doubt is 

 entertained that each of the several arches would sustain ilscl/ in case 

 the wood-work of the next one adjoining should be cousumed by fire. 



The wood-work in any of the arches separately may be removed and 

 substituted by new material, without affecting the equilibrium of the 

 next one. 



The original idea upon which the plan has been perfected, was to form 

 a u-uoden trunk, strong enough to support its own weight, and stiff 

 enough for an aqueduct or bridge, and to combine this structure with 

 wire cables of a suflicient strength to bear safely the great weight of 

 water. 



The plan of this work, therefore , is a combination which presents very 

 superior advantages, viz., great strength, stiffness, safety, durabilUy, and 

 econnmi/. 



This system, for the first time successfully carried out on the Pitts- 

 burgh aqueduct, may hereafter be applied, with the happiest results to 

 railroad bridges, which have to resist the powerful weight and "^reat 

 vibrations, which result from the passage of heavy locomotives and trams 

 of cars. 



Kemark. — The qaantities in the following table are calculated for a 

 depth of water of 4 feet, which has been in the aqueduct ever since the 

 opening. The depth contemplated was J J feet; a greater depth is at 

 present required ou account of the raising of the bottom of the canal by 

 bars and sediment, which have to be removed before the level can be 

 lowered. 



Table of Quanliliea of the Aqueduct. 



Length of Aqueduct without evtensioas 1,140 feet. 

 Length of cables, 1,175 feet. 

 Lengtli of cables and chains, 1,283 feet. 

 Diameter of cables, 7 inches. 

 Aggregate weight of botli cables, 110 tons. 

 Section of 4 feet of water in trunli. 59 sup* feet. 

 Total weight of water in aqueduct, 2,100 tons. 

 „ ,, one span, 295 torn. 



Weight of one span, including all, 4.0 tons. 

 Aggregate number of wires iu both cables, 3,800, 

 Aggregate solid section of both cables, 53 sup. inches. 



„ „ anchor chains, 72 sup. inches 



Deflection of cables. 14 feet G inches. 

 Elevation of pyramids above piers, 1(1 feet fi inches. 

 Weight of water in 1 span between piers, 275 tons. 

 Tension of cables resulting from this weight, 3112 tons. 

 Tension of one single wire, 2LitJlb. 

 Average ultimate strength of one wire, l,loO lb. 

 Ultimate strength of cables, 2,0'JO tons. 

 Tension resulting from weight of water upon one solid square inch of wire cable, 



ll.BOOlh. 

 Tension resulting from weight of water upou one square inch of anchor chains, 



11.000 lb. 

 Pressure resulting from weight of water upon one pyramid, l.?7^ tons, 



„ ,, „ „ one superficial foot, 18,400 lb. 



COLOGNE CATHEDRAL. 



It appears from the forty-ninth Report of the Committee of the Society 

 for the Restoration of Cologne Cathedral, that the advance made during 

 the period embraced in the present Report consists, on the south side, in 

 the additional height to which the pier of the transepts have been car- 

 ried. In the same part, the western entrance has been completely 

 vaulted in, and the eastern begun to be so. A great quantity of stone 

 is Iving ready cut for the work, and still more is expected from the 

 quarries, in order, if possible, to vault-in the middle space also before 

 the end of the year. 



Similarly, only somewhat further, advanced are the works in the 

 north transept. Here the three spaces are for the most part already 

 vaulted over, and they will at all events be quite completed in the 

 course of the present autumn. 



The works in the northern nave aisle were put in activity immedi- 

 ately after the illustrious visit of Queen Victoria, it being necessary 

 that the old roofing should be retained till up to that time. This has 

 now been removed, and scaffolding is in course of erection in order to 

 set to work upon the new vaulting. Seven bays of original vaulting- 

 as is well known, already existed on the north side; so that there 

 remained but five to construct. Dut on the removal of the old roofing 

 and woodwork, the south-eastesn pillar of the seventh bay was disco- 

 vered to be built of brick in the most slovenly and insufficient manner. 

 The groining bands and ribs of tuffstone springing from it were in the 

 same way most meanly put together, the lines broken so as to form 

 polygon*, and the joints very faulty. Still, supposing this defect could 

 have been partly discovered from below by the naked eye, and the con- 

 clusion thence arrived at that this vaulting was of later origin than the 

 other portions of the beautiful vaulting of the cathedral, with which it ad- 

 mitted of no comparison, this would not have prevented it from being 

 retained from antiquarian considerations, had the previously-concealed 

 pillar proved at all adequate to support the pressure of the mass rising 

 from it to the additional height of ninety feet and more. 



This not being the case, this pillar and the vault belonging to it had to 

 be given up to destruction. This is at present being accomplished, and 

 the construction of the remaining spaces of vaulting suffers some delay in 

 consequence. In general, the works will be carried on uninterruptedly 

 with about four hundred men. Meanwhile the supply of stone is by no 

 means kept up with the regularity to be desired, notwithstanding tha 



