SHORING is the scientific placing of supports to parts of a building which are liable to distortion or collapse either because the fabric of the building is unsound—which may be evidenced by failure or settlement—or to guard against the disturbance of adjacent parts of a structure and adjoining premises where altera tions to the fabric are being made. The word "shore" means a prop or support and is applied to the work under description because every member employed is virtually a prop or a strut, opposing movement by its own resistance to compression. The craft of shoring lies in so placing the shoring members and forming the joints and connections, that the shores as a whole may function perfectly; this condition requires that all parts shall fit closely and squarely at their ends and to be brought into close contact without "shock" to the structure which is being operated upon. Wedging requires the use of the hammer, causes shocks and vibration and should be used as little as possible ; though it cannot be dispensed with entirely. Where wedges are adopted they should be placed at the ends of members distant from the defective portions of the structure and great care must be exer cised in using the wedges, which should be slowly and cautiously driven by gentle blows.
In all shoring it is imperative to maintain the condition of the structure to which it is applied, not to disturb it, or to attempt to restore it to an original position. There are several different forms of shoring, each adapted to suit particular circumstances. Much ordinary shoring is done with heavy, roughly sawn timbers strongly braced together, but for heavy work steel members may be introduced with advantage. Generally, steel is only employed for short heavy beams called "needles" (see below Dead Shoring), but in some special cases, as in the restoration of the piers sup porting the dome of St. Paul's cathedral, shoring and scaffolding must necessarily be of steel to support the immense loads during repair operations.
The form of shore in most general use is that known as the raking shore. It consists of one or more timbers sloping from the face of the structure to be supported and bedded upon the ground. When the ground is of a yielding nature, a stout timber plate termed a sole-piece, is placed to receive the base of the raking timber or timbers. A wall-plate, to increase the area of
support, is fixed to the face of the wall by hooks driven into the joints. Where space is available, a slope of 6o° is found con venient for the main shore, the auxiliary members ranging in their slope from to In many cases, especially in towns, the angle of slope is governed by outside influences such as the width of the footway or by local regulations. Raking shores are erected singly or in "systems" in planes at right angles to the face of the wall. The members rise fanwise from the sole-plate to support the wall at different points. The spacing between systems depends on the condition of the building to be supported, and also upon the spacing of its window and other openings. The usual spacing is so ft. to i 5 ft. apart, but depends upon the openings in the wall.
The application of the shores needs care, support being given only where there is a correspond ing thrust from a floor or roof. A clear idea of the construction of a system of raking shores can be obtained from a study of the illustration (fig. ). The names and functions of the different timbers are indicated here.
Raking Shore or Raker.—A piece of timber sloping up from the sole-plate to the wall-piece and joined as in fig. 2. The top and longest shore may necessarily be formed in two pieces. The up per one is the riding shore or rider, and the lower, which sup ports it, is the back shore. At their junction folding wedges are introduced to give the head of the rider a firm bearing against the needle and wall-plate above. The sole-piece (fig. 2) usually con sists of a piece of I I by 3 plank, but may have to be bedded on a platform of timber to spread the weight over a large area. The sole should be placed at an angle (say 80°) with the inside of the shore to enable the latter to be gradually levered to a firm bearing with the aid of a crowbar. Wedging should not be resorted to or the building may sustain injury through vibration. When in posi tion the foot of the shore is fixed by dog-irons to the sole-piece, and for additional security against slip, a cleat is spiked very firmly on the sole plate.