10(5 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[March, 



We liave next|clctailed seroral experiments upon brick and cement 

 beams, combined with hoop iron, laid horizontally between the joints. 

 I'roni the experience obtained in this investigation, the Colonel derives 

 tile following conclusions : — 



That cement bond, consisting of four or five courses of brickwork laid in 

 pure cement, if strengthened by longitudinal pieces of lioop iron in all the 

 joints, may be used to supersede not only the wooden bntels of doors and 

 windows, but all timber bond generally in the walls of buildings, as suggested 

 in Article 234, which was written before we had liied these last experiments. 

 In using hoop iron bond in w.alls, the irons should extend, if possible, the 

 whole length of each wall in one piece; but if a break be necessai'y, the ad- 

 joining ends need not be imited together by the blacksmith, Ijut turned down 

 at right angles into one of tlie vertical joints of the wall by the bricklayers 

 tiiemselves. Without hoop iron bond, on the contrary, the additional strength 

 communicated by cement alone would not suffice in difficult cases. 



It is to be observed, liowever, that a continued string of four oi five courses of 

 cement and hoop iron bond, in the walls of a building, would not be exposed by 

 any means to the same strain asour experimen^l brick beams ; for it would not 

 have to bear much more than its own weight in all the unsupported parts over 

 a door or a window, there being other windows above those, and in all the 

 intermediate portions of the wall corresponding with the ends of our experi- 

 mental brick beams, the courses of cement bond alluded to would not only be 

 supported from below, but their strength would be greatly increased by the 

 weight of the solid parts of the wall above, it being well known that all beams 

 have a much greater resistance, when firmly fixed, than when merely sup- 

 ported at their ends, which Mr. Barlow in his able and useful treatise on the 

 strength and stress of timber estimates from his own experiments, as l)eing 

 in proportion to the numbers of 3 and 2. Besides which, 10 feet between the 

 bearings is a much greater width than would be given in practice to the 

 windows, or even to the doors of the largest building, unless the latter were 

 carriage-gateways, which are more usually covered by semicircular or elliptical 

 arches, than by flat arches or straight lintels. 



It only remains further to remark, that the flattest and thinnest brick and 

 cement arch has sufficient power to resist great pressure, in openings of 10 or 

 even 15 feet, as was proved by one of our former experiments; though 

 a straight brick and cement beam is not to be recommended, over such open- 

 ings, unless consolidated by hoop iron bond. 



We have then some experiments on cements, tiles, and bricks, ap- 

 plied for steps or .staircases ; an investigation bearing upon a very useful 

 professional subject. 



In both of these artificial steps the fracture takes place near to the wall, but 

 that part of each, though entirely broken through, was suspended by the irons, 

 which did not break, but elongated or were drawn out from their original 

 position within the wall, just enough to admit of the far end of each step 

 striking the ground in falling. In reference to the consideration before stated, 

 the stone step may be considered to possess a resistance of about 5 times, the 

 plain tile step a resistance of about 3 times, and the paving tile step a resist- 

 ance fully double of the greatest weight, ever likely to press upon one step of 

 a geometrical staircase 4 feet wide ; tliat is, provided iis width, which was 

 only 12 inches, had been increased to 14 or lO inches, which is the more usual 

 width of the steps of such staircases, and which would of course increase its 

 resistance in proportion. I .shall observe also, that as the resistance of plain 

 tiles and of paving tiles without cement was proved to Ije very nearly equal 

 by our former experiments recorded in Table XVIII. (324), the marked 

 superiority of resistance of the plain tile and cement step over the 

 paving tile and cement step, though both formed of materials equally 

 or nearly equally strong, may probably be ascribed in this experi- 

 ment to the former being composed of a much greater number of tiles 

 and therefore having a much greater number of cement joints than the latter. 

 Notwithstanding, Ijowever, this inferiority of the paving tiles, 1 would recom. 

 mend their being used in preference to plain tiles, if the expedient of building 

 staircases with artificial steps composed of tiles, with cement and hoop iron 

 bond, should ever be adopted, because the paving tile step is quite strong 

 enough, and gives much less trouble in the workmanship than any very small 

 sort of tiles, such as plain tiles would do. But instead of using tiles 12 inches 

 square and 1^ inch thick, like the common paving tiles of this country, they 

 should be made 15 inches long, 12 inches wide, and about H or 1^ inch thick 

 only, so that 4 courses might be used for the steps of the principal staircase, 

 and .5 courses for those of a second rate staircase of the same house, the latter 

 of vt-hich are always made higher and also usually narrower than the former. 

 And in order to break joint properly, it would be better to make a proportion 

 of hall tiles of the same length, but only six inches wide, than to cut whole 

 tilesin two for this purpose 



Colonel Pasley strongly asserts the superiority of cement mortar over 

 hydraulic lime, in the coiistruction of wharf and river walls. Several 

 instances are given of the failure of liydranlic lime forthis purpose, and 

 particularly one remarkable instance— in the case of a wall wliich had 

 stood forty years without showing any symptoms of decay. The 

 Colonel observes, — 



Instead of plain tiles, long thin stones, such as schists, or coarse slates not 

 good enough for tiie roofs of buildings, might be used for the same purpose 

 of forming artificial steps, when united by cement and strengthened by hoop 

 iron bond ; but in all materials not before tried, it would be proper to make 

 ftn experimc.a step beforehand to asijertain Jhe most unitable dimeusieus of 



the parts, and the best mode of breaking bond in putting them together. 

 About tluee months should be allowed for the cement to set, before such steps 

 are let into the walls of a building. • * 



I h."ive seen an official drawing, of 1789, evidently in reference to a project 

 for the completion of this wharf, a section contained in which very nearly 

 agrees with the present profile of the wall, which is known to have been 

 finished more than 40 years,»andl have ascertained by inquiry that no appear- 

 ance of failure was ever noticed until the year 1K25, when part of it was 

 observed to have bulged a little forward, but no materiid change took place 

 until soiue yers afterwards, when a substantial granite cojiing was laid in front 

 of the wall, as a substitute for the timber capping and laud ties, which had 

 become rotten. The weight of this coping, which could have done no harm, 

 had the mortar of the brickwork been good, has undoubtedly accelerated the 

 sep.aration of the front of the wall from the counterforts, which action has been 

 gradually in progress, but exerted itself more powerfully, as soon as the bond 

 timber and lower row of bond ties became rotten. f . . 



The circumstance of this wall having remained perfect for at least 27 years 

 after it was finished, and of some parts of it still remaining so, may be con. 

 sidered a proof, that the profile was sufficient, if belter mortar had been used, 

 for the wall, which was about 24 feet high and had olfsets or footings at 

 bottom, had an exterior slope of one tenth of its height, and would have been 

 fj^ feet thick at top, if the back of it had been carried up vertically, instead 

 of which its thickness was reduced to 4 feet at top, by a step iir rear, about 

 7i feet below the level of the ground. It had very substantial counterforts 

 measuring rather more than 6 feet square in plan, at central intervals of 

 18 feet, and terminating about 4 feet below the same level, that is .several feet 

 higher than the step at the back of the wall, the lower part of which by being 

 thicker was in itself a sort of counterfort to the upper part of it, in consequence 

 of which the front part of the wall being the thinnest and less capable of re- 

 sisting the pressure of earth in rear, separated from the b.ack part in rear 

 of the said step, whereas had the whole back of the wall being carried up ver- 

 tically, the separation, resisted by a greater mass of brickwork, would have 

 been less considerable, and would have taken place farther back, entirely be- 

 hind the back of the wall, and in front of the counterfort. 



In the following judicious observations the Colonel points out the 

 cases, in which hydraulic lime may be used, and those in which it ought 

 to be avoided. 



For the general purposes of Civil Architecture, concrete should therefore, 

 I again repeal, be chiefly confined to foundations ; but I conceive that the 

 failure of the new concrete foundation of the .Storehouse in Chatham Dock- 

 yard has proved, th,it it is generally, or at least when formed as Mr. Ranger 

 has usually done, with rather a greater proportion of lime than was originally 

 adopted by Sir Robert Smirke, liable to settlements like lime mortar, whicii 

 in fact forms the principal part of it. Hence care must be taken, in com- 

 mencing the brick footings of a building over a concrete foundation, not only 

 to use cement mortar and hoop iron bond, in order to do away the necessity 

 of the more expensive expedients of Yorkshire landing stouts and chain tim- 

 bers, but also to coniitruct inverted arches under all the proposed openings 

 for doors and windows, in order to equalize the pressure. 



In using- concrete for the backing of wharf walls or other retaining 

 walls, care must be taken to connect it well with the stone or brick facing of 

 the wall, but I apprehend, that the wall and its backing .ahoidd be constructed 

 of a sufficiently substantial profile to dispense with coimterforts, because a 

 substance having so little resistance and adhesiveness, as concrete, would 

 admit of the wall in front being forced away from the counterforts, by the 

 pressure of earth acting upon the^back of it ; as has often occurred to retaining 

 walls and their counterforts, even when built of brickwork. 



In works of Fortification, whilst 1 have already reprobated the use of con- 

 crete for casemates or vaults, yet as the severest frosts seem to destroy those 

 surfaces of concrete only, which are alternately saturated with water and then 

 exposed to the atmosphere, as in the facing of the wharf w.alls of tide rivers, 

 I see no reason to withdraw the opinion fornred by me, previtiusly to the re- 

 cent failures in her Majesty's Dock-yards at Woolwich and Chalham, that it 

 may be used for retaining walls not exposed to the action of water, as in the 

 sea wall at Brighton improperly so termed, and also for the revetments of 

 fortresses in the peculiar situations before mentioned, in which it is possible 

 that it might be so much cheaper than regular masonry or brickwork, that 

 although greatly inferior in resistance and consequently liable to be much 

 sooner and more easily breached, whether by battering guns or by mining, this 

 disadvantage would not be a sufficient argument against the use of it in those 

 situations. 



We omitted to mention in its projier place that the Colonel has dis- 

 covered a cement, wliich appears from the trials to which it has been 

 subjected, stronger than Roman cement, and very useful as an hydraulic 

 mortar. It is composed of 4 parts of pure chalk, and ."jj parts of fresh 

 blue alluvial clay ; and the method of preparing, mixing and calcining 

 is fully described. 



At the end of the work is an appendix, giving a description and the 



* From thia drawin;; one would inter, that a briuk wall with counterforts, either 

 tinislied or perhaps only in in-ogress, existed in 1789, which it was proposed to face 

 with stuni'. But lliis is conjecture, as 1 have never seen any docuiueut cxidanatorj of 

 the drawint? alluded to. 



t To guard against thii evil, chain cables or strong iron bolti or bars have recently 

 been used by the engiueers of the present dav as land ties, for wharf walls. These are 

 parlicularh'necessarv in wharfs iaeed with iron, which lm« very little stability in 

 itieir, and must there'lore be aided by long land lies running through the backing ut 

 the wharf, and well secured to some immoveable objests in rear. 



