This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
(By The Editor)
Shores are temporary supports to walls and buildings, and are usually employed when these are in dangerous condition and likely to fall over. They are almost invariably constructed of timber, and are of two principal types, known as "Raking shores" and "Flying shores" respectively.
Raking Shores are such as rest upon the ground and support the wall or building by being inclined against it. A simple form is shown in Fig. 242. It consists of a "raker" A, resting upon a "sole piece" B, to which it is placed nearly at right angles, although not quite so, being levered into position by means of a crowbar; it is thus tightened up against the short "needle" C, which passes through the "wall piece " D, and a short distance into the wall. E, E are small " cleats " which are spiked to the sole piece and wall piece respectively to secure stability. The foot or bottom of the shore A is further secured to the sole piece by means of dog irons; while the strut F is commonly but not necessarily inserted to give rigidity to the system.
A more elaborate and more usual system of raking shore is that shown in Fig. 243, A, B, and C being known as the bottom, middle, and top rakers respectively. These are bound together with hoop iron at the foot, and are also connected both to one another and to the wall piece by planks. The sole piece in this instance is shown resting upon a platform of boards, this being necessary for all other than very solid ground in order to distribute the thrust.
Another and even more elaborate system is shown in Fig. 244, consisting of the previous system with what is known as a "Ride or Riding shore" springing from the back of the top raker. This system is employed for tall houses only, where a timber long enough for a fourth or outer raker is not obtainable in a single piece. The method of attaching these various members to one another is shown in the details which comprise Fig- 245.
When erecting raking shores of either of these descriptions, care should be taken to place the tops of the rakers at the level of the various floors of the building, so that when levered into place they may resist any thrust from the floors, and not themselves exert an undue inward pressure upon unsupported wall, and so cause failure in the opposite direction to any bulge that there may be in the brickwork or masonry. Alternatively to this, the shores may be placed against the ends of internal walls. Frequently this is essential, it being these walls which are tending to cause failure; but no definite rules can be laid down, as shoring is at best a rough - and - ready means of meeting temporary difficulties. It is, for instance, impossible to calculate what sizes the timbers ought to be, as the thrusts to which they are to be exposed are almost always unascertainable. It may, however, be taken as a general rule that if the distance from the top needle to the sole piece in feet be divided by five this will give the size of the timber to be used in inches. Thus if the distance be 35 feet, the rakers should all consist of 7 by 7-inch timbers. Frequently, however, shoring- has to be done at short notice, and whatever timbers are available are used.
Sometimes for supporting garden or retaining walls of small size a small, strongly constructed double shore of the type shown in Fig. 246 is used. The heads of these are shown to be bearing upon the under side of stone slabs inserted in holes made in the wall; and this method of support is frequently employed instead of wall pieces, when using the ordinary raking shores against stone buildings.
Flying Shores are such as are used to support one building from another across an intervening space; they are frequently employed during building operations, when one house of a row has been pulled down for rebuilding. The ordinary form is shown in Fig. 247, though it is varied occasionally by the use of steel joists in place of the long horizontal timber when this is not obtainable of sufficient length. This, it will be noticed, is supported upon a small needle and cleat, as are the heads of raking shores, but it is further pinned up tightly against the wall piece by means of oak wedges. Upon the upper and under sides of this, straining pieces are nailed from which struts spring upwards and downwards, and these are wedged up, from the straining piece, against other cleats spiked to the wall piece.
A variation of the Flying Shore is that shown in Fig. 248. This is usually employed for comparatively narrow spans, and for supporting a higher building from a lower one. It is open to considerable variation, according to the circumstances of each individual case.
When it is intended to remove the lower portion of a building, as, for example, for the insertion of a bay window or a shop front, the upper part has to be temporarily supported. This process is known as "Needling." Before this is done, however, it is usual and proper to take the precaution of erecting raking shores against the upper walls, so as to resist any tendency to bulge during the process, placing these at the corner of the building and opposite any cross walls. All windows over the projected opening should also be cross strutted, both internally and externally, the window frames being temporarily removed.
The operation of needling is by no means one to be lightly undertaken, and has to be done with the greatest care. Large timbers (see Fig. 249), either 12 by 21 inches or 9 by 9 inches, are commonly employed.
A long sole piece of this size is first laid on solid ground parallel to the wall, both within and without the building. It is not sufficient, it may be noticed, for this to rest upon a floor. It must be carried on the solid, and, if the soil be at all doubtful, should rest upon a broad platform of planks. Upon this a series of vertical timbers known as "Dead Shores" are erected with oak wedges underneath their bases, but all of equal height in each range - external or internal. All these must be opposite to one another on the internal and external sole pieces, and, directly in line between them and at the level of their heads, a hole is made in the wall through which a strong bearing timber known as a "Needle" is passed, so as to rest on the heads of the "Dead Shores," to which they are attached by dog irons. These needles are brought up tightly against the brickwork above by driving up the oak wedges. The dead shores are now dogged to the sole piece, and if for any reason they are more than some 2 feet from the wall a strut is inserted, as shown in the illustration. If any floor rests on the wall which is being dealt with, the joists are supported by a piece of timber running transversely underneath them, and about 2 feet from their bearing on the wall. This timber is carried at 5 or 6-feet intervals by posts, which in turn have their feet resting on another timber lying on a floor below or on the ground, wedges being driven in to make them firm. An alternative method is shown in Fig. 249, sometimes employed for extremely heavy work, the fir needles being replaced by steel joists or built-up girdles, which are brought up to their work by screw-jacks instead of wedges. These, however, must be used with some caution, as it is quite possible to screw them up too far.
Systems of needles thus constructed on the same internal and external sole pieces are placed not more than 5 feet apart, and when all have been wedged up, the brickwork or masonwork between them may be safely removed, as the wall above will now be carried by them even though there be no longitudinal bearer from one to another. As soon as possible, however, the piers should be made good, and built up in cement, and a girder inserted beneath the level of the needles, within the thickness of the wall and resting upon the piers. The new wall can now be built on the top of this girder until the old work is met, cement mortar being used, and the work carefully pinned up. As soon as this has set the wedges may be gently released, and another day allowed to elapse to enable the old wall to take its bearing upon the new work and the girder before they are entirely removed. Finally, the holes through which the needles had passed are made good, and if the work has been carefully done there ought to be no sign of settlement.
When a building has given signs of settlement due to a bad foundation, or when it is desired to extend it downwards by excavating a cellar, resort has to be had to the process known as underpinning. This in some respects is similar to needling, save that no needles or timber struts are required. An excavation is made along one side of the foundations to the necessary depth, and for a length of not more than 5 feet, and the old foundations are undermined, as shown in Fig. 249A, for a length of about 4 feet and to a width equal to the calculated width of the new foundation. The superincumbent wall is carried by the adhesion of its mortar across the gap, and the new wall, to a length of 4 feet, is built up in the trench upon a new foundation until it meets the old wall. All this is done in cement mortar, and the new work is pinned to the old, if necessary, with slate wedges in cement, care being taken that these are driven very gently. Sometimes the work is done continuously, 4 feet at a time, but more often piers are carried down in this way, each 4 feet apart from its neighbour; and when all these have been built and pinned up they act the part of Needle Shores, and the intervening earth can then be removed and the gaps made good one by one.