Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/185

 a ae Marcu 1, 1872. only a clear and complete idea of the ingenious combinations of brick that were adopted. We must content ourselves here with indicating the principle of their con- struction, and pass on to a summary exami- nation of the second method employed by the Romans to support their vaults—a con- tinuous layer of flat tiles. This mode of carrying the solid vault was thus practised. On the convex surface of the centreing was lad a bed of the large square bricks, the lateral dimensions of which have been already given, and which were generally from lin. to 2in. thick. These large bricks cemented together with excellent plaster or quick- setting mortar, formed over the whole con- vexity of the centreing a thin bed with no apertures or cavities, which exactly followed the form of the intrados, and presented, as we have above said, the appearance of a hollow tile floor. This paving constituted in itself a complete shell of the vault; but usually a second ‘‘ floor” was superimposed in all respects similar to the first, but con- structed of bricks of smaller dimensions, and which formed on the curved planking of the centering a double envelope cemented to the first with plaster or mortar. As the result of this superposition, there was, over the whole extent of the centreing, like a protecting crust, a sort of light vault, from which, immediately after its completion, the centreing could not have been removed without running the risk of its breaking up under its own weight, but which gradually stiffened as the massive backings were filled in, and became ultimately capable of sustain- ing of itself the whole of the rubble work. In fact, the reason why the centreing could not be immediately struck was not so much the small thickness of the solid crust as in the semi-circular form of its section. A vault of flat bricks or tiles would be stable under the double condition of its section being a small are of a circle, and of being kept immovably between fixed abutments. If formed of a semi-circular section, it would acquire the rigidity it lacks by the haunches being solidly filled up, which would oppose any yielding to flexure, and prevent the thin shell of masonry sinking down upon itself. This last case is evidently that of the thin crust of tile ina Roman yault. The weight of the vault rested on the centreing only until the first courses of rubble had backed up the tile paving to a level greater or less as the case might be, and the part really employed in carrying the weight, z.e., the effective part of the ‘ floor,” being then a simple are of a circle, offered itself under the best conditions for equilibrium. The wooden centreing could at that moment have been struck and removed for use at some other point; in other words, the vault could be constructed in parts, and the same centre- ing used for different portions. This is, in fact, the course which the Romans more than once followed, and to convince oneself of this, it is enough to notice that the bricks of the shell, instead of being cut to shape and form- ing a floor with radiating joints, have, on the contrary, their edges left square, and simply range side by side like the squares of a draught-board. This circumstance agrees well with the idea of a construction in sections, for if we suppose the ‘‘ floor” laid with joints ranging to the summit, each of these sections (or lunes) would terminate in a toothing, and thus there would be certain troublesome con- ditions to attend to whenever it was required to join one of them to the next; the ancients, dispensing altogether with bonding the various ribs or sections together sideways, avoided thereby all difficulties in connecting them. As to the economy resulting in the centre- ing, it is evident that it was sufficient, as has been already remarked, for it to be stiff enough to carry the weight of one of the two ‘“ floors.” The first layer served as a centre upon which to bed the second, and the two together formed a rigid support upon which was carried the whole weight of the rough masonry. THE BUILDING NEWS. Let us go on to the detailed arrangements and yariations of the system. Sometimes were laid here and there amongst the flat bricks, bricks on edge, projecting into and giving a key tothe rough backing. Often, again, the second ‘ floor” was reduced to a series of ribs formed of small bricks laid as cover joints along the courses of the first layer. In time they were satisfied to place a small brick laid in cement on the points where a shock or a great pressure would have the most effect—that is, on the meeting point of four of the large bricks composing the mesh-work or ‘‘ floor.” These shells of flat bricks or tile were in very general use amongst the Romans: the Baths of Caracalla and the Villa of Hadrian are the most remarkable remaining examples. Finally, the use of flat bricks in vaults has not been entirely abandoned by [Italian builders. The vaulted cloisters which adorn the palaces of modern Rome are for the most part constructed of square tiles, the intrados is formed of a single layer of tiles jointed with cement, the rest is made up of very rough rubble work. Italian workmen call this sort of work volte alla volterrana, and sometimes give to it the expressive name of volte a foglio. SSS HOW TO BUILD SCIENTIFICALLY WITH THE AID OF MODERN IN- VENTIONS.—VI. WALLS. RICKS.—In dealing with this subject, less difficulty presents itself than with the preceding materials, because the use of brick is more general, and we have consequently greater experience. Another reason is that the material has been in general use since the days of Richard IT., when its manufacture became common. Leland mentions this latter fact in his ‘‘ Itinerary.” Although I have nothing to do with the great antiquity, yet I cannot help reminding my reader that bricks are often mentioned in Holy Writ, they being alluded to as early as the Book of Genesis. It is not supposed that these bricks, or that bricks for some time thereafter, were burnt in furnaces or kilns, but it is certain that the ancient Greeks and Romans did so burn their bricks. Definition —A brick is a factitious stone, manufactured from argillaceous or clayey earth, well tempered, and squeezed into a mould. When so formed, it is stacked to dry in the sun, and finally burnt to a proper degree of hardness in a clamp, or kiln. Ordinary Brick Walls.—One of the sins of the present day is that bricks are not now manufactured so good as in olden times. In a paper read at the Architectural Association, it is advanced that a great falling off in the manufacture of stock bricks has taken place since the commencement of this century, and this was followed by a statement that the only difficulty was to know how bad they might be made, and yet pass. No doubt, as I have pre- viously pointed out with regard to other ma- terials, there should be some absolute test applicable to the brick; and I cannot but think the Royal Institute of British Architects would be doing good service if they defined what those tests should be. They have just issued to us a most useful paper relating to builders’ contracts, and perhaps may, there- fore, have time to attend to this suggestion. Varieties —The number of different kinds of bricks is very large ; the leading kinds I will only mention—malms, or marl stocks, stocks, place bricks, Advantages.—Durability ; cheapness ; not so liable to osmus ; fire-resisting qualities. I do not think I need at length confirm the first advantage--namely, durability. The remains of brick buildings from the earliest periods attest it. The old Roman walls in this country and in France might be mentioned as instances. For an example of the endurance of decorative brickwork, perhaps none I could 169 name is better known than the house in §. Martin’s Lane. As to cheapness, it seems now likely it will find a rival in concrete. The cost of ordinary brickwork in mortar is about £12 10s. per rod. I mention this because I propose taking this price in dealing with the comparative cheapness between it and other materials. Its non-liability to osmus is a great advantage. Where I am building in Worcestershire, with the local stone, I am putting a lining of bricks (as is customary) to prevent the osmatic action. I may mention brick, though as absorbent as limestone, is not as liable to osmus, for the reason that oneisof a heating nature under the influence of moisture, while the other is cooling, and the absorbent action of the sun quickly draws outagain the damp from the brick, while with the limestone the in- ternal heat attracts it through the wall, and the sun’s influence only makes it more ab- sorbent and prepares it more effectually for the next supply of rain. As to its fireproof qualities, [need only quote Professor Lewis, who says: ‘‘ In fact, the result really seems to me that the only secure protection from fire isastructure of brick arches on brick supports. Nothing else that I can call to mind will stand the effects of great heat and the action of flames; stone and granite fly to pieces, but good brickwork never does.” Disadvantages.— Uniformity, inferiority of crushing weight, difficulty of grandness of effect with such small parts, colour. As to the first I would quote the Rev. Thomas Hugo, because he appears devoted to brick buildings, and regrets the demolition of those old ones that remain. He says: ‘‘ I admit to the full, however, that there is a kind of uniformity, and therefore, monotony, in all brick buildings, and that by the use of other materials greater variety of effect may be obtained.” I amaware I shall be answered that this motonony is broken by introducing varied coloured bricks, yet I think the fact that this style of work is falling into disuse is sufficient to show that unless done by a master hand, such treatment is unsuccessful, and the fact of its having obtained a vulgar cognomen is proof thereof. Pillars —When built of brick these should not be more in height than twelve times the thickness at the base ; when more than this there is a considerable falling off in strength. A height of 24 times the thickness reduces the strength from 10 to 7; when increased to 30 times, the strength is reduced to one-half; and when increased to 40 times, the strength is reduced to one-third. In practice the safe load should seldom exceed one-tenth to pro- duce fracture. The weight to produce fracture per super- ficial foot :— tons WBTiCks (Ord ALY)) Movasseestuvaccaeescsrneceseeseces 40 do. strong well burnt ee nO) osmprirel int cette ants 100 Brickwork in cement. 30 do. in mortar. es 20 Concrete (made with 1 n found 24. 80 130 Magnesian limestone (Roa 100 Cragleith sandstone 200 Yorkshire do. - we. 300 Aberdeen granite .........ccscccscceseesssescsrees 500 Ido not think the artistic mind usually sufficiently realises the third objection. Yet how effective it is on the popular mind. A monolith of the most outrageous proportions, if it only weighed a few tons more than any other stone, or was a few feet lorger, and was placed in position, would obtain more opinions in praise than the most correctly proportioned erection of similar size. Take an article [ remember reading in the Zimes, advocating a monolith as a monument to the Prince Consort. It was to be, they ad- vised, the largest block ever sent from a quarry. ‘The length of time to produce it was not to be considered, and if no vessel could bring it to London a special one was to be built for the purpose—and all for what ?